论文部分内容阅读
Abstract Potted seedlings of Hedera nepalensis and H. helix were exposed to formaldehyde and low light alone or in combination for four months， before the morphological and nutritive indices of the plants were measured to assess the effects of formaldehyde and low??light stress on the growth and nutrient accumulation of Hedera species. The results showed that treatment with either formaldehyde or low??light stress reduced leaf length， leaf width， stem length， stem diameter， root length and biomass， but increased leaf shape index of the two Hedera species. Treatment with formaldehyde alone increased root??shoot ratio， while treatment with formaldehyde + low light or low light alone decreased root??shoot ratio of the two Hedera species. Under the stress of formaldehyde， soluble sugar content decreased， while starch content increased in roots， stems and leaves of the two Hedera species； total carbon content， proline content and carbon??to??nitrogen （C/N） ratio increased， while protein content and phosphorus content decreased in roots of the two Hedera species； the contents of total carbon， protein and total nitrogen in leaves of the two Hedera species； C/N ratio in roots of H. nepalensis increased； the C/N ratio in roots of H. nepalensis and that in leaves of the two Hedera species significantly increased. Under formaldehyde + low light stress， the soluble sugar content decreased， while starch content increased in stems and leaves of the two Hedera species； starch content in roots of the two Hedera species decreased； the contents of protein and total nitrogen decreased， while C/N ratio increased in leaves of H. nepalensis； proline content in roots and stems of the two Hedera species significantly increased.
Key words Hedera spp.； Formaldehyde； Weak light； Growth； Nutrition
Formaldehyde （HCHO） is widely used in the manufacture of plastics， rubbers， resins， plywood， and adhesives[1]. It is also well known as a preservative in medical laboratories[2]. Cigarette smoke， decorative materials， textiles and formaldehyde??containing biocides are the main sources of formaldehyde in indoor air[3]. At present， the concentration of formaldehyde in indoor air in 80% to 90% of houses in China exceeds the maximum allowable level proposed by Hygienic Standard for Formaldehyde in Indoor Air of House by 3 to 4 times， or even hundreds of times， posing a serious threat to public health[4-5]. Formaldehyde has now become one of the main pollutants in indoor air. Exposure to low levels of formaldehyde can cause headaches， dizziness， upper respiratory tract irritation， eye irritation， allergic dermatitis and other symptoms. High??concentration formaldehyde is potentially teratogenic and carcinogenic. It usually takes 3 to 15 years for formaldehyde??containing materials to release all formaldehyde. Many physical and chemical agents cannot completely remove formaldehyde， and likely cause secondary pollution. Therefore， planting ornamental plants is a feasible solution to absorb and metabolize indoor formaldehyde. However， the intensity of light indoors is much lower than outside， which greatly affects the growth and development of indoor plants. As an important environmental factor， light plays an extremely important role in the growth and development of plants， and affects plant morphology and physiological functions[6]. Long??term exposure to low light influences plant morphogenesis and physiological and biochemical processes[7]. Existing studies are mostly focused on the effects of single factors such as formaldehyde[8-9] or low light[10-11] on plant growth and development， and the effects of the interactions between formaldehyde and low light on plant growth and nutrition has been rarely reported. Hedera， commonly called ivy， is a genus of 12-15 species of evergreen climbing or ground??creeping woody plants in the family Araliaceae. They are highly adaptable， easy to reproduce， with beautiful and fragrant leaves， can be planted both indoors and outdoors， and have high ability to remove formaldehyde. At present， the ability of ivies to remove formaldehyde has been extensively studied， but their growth and nutrition under formaldehyde and low light stresses have not been reported. Therefore， in this experiment， 0.5??year old seedlings of Hedera nepalensis and H. helix were exposed to formaldehyde and low light to clarify their adaptability to formaldehyde and low light， and to provide a theoretical basis for indoor cultivation of ivies.
Materials and Methods
Materials
H. nepalensis （hereafter abbreviated as HN） and H. helix plants （hereafter abbreviated as HH） grown in the campus of Kunming University were used as the experimental materials. Their 0.5??year old seedlings with a vigorous root system and luxuriant foliage were selected and transplanted into 20 cm ?? 20 cm pots containing a mixture of peat and vermiculite （1?? 1， v?? v）， with one seedling in each pot. Then， the pots were transferred to glass containers of 100 cm??60 cm??100 cm， with 20 pots （10 pots of HH and 10 pots of HN） in each container. And 200 ml of Hoagland??s nutrient solution （pH 5.5） was added to each pot once a week.
Experimental design
After two weeks of culture in glass containers， the seedlings were assigned into each of the four treatments： T1=formaldehyde （T1??HH for H. helix， and T1??HN for H. nepalensis）， T2=low light （T2??HH for H. helix， and T2??HN for H. nepalensis）， T3=formaldehyde plus low light （T3??HH for H. helix， and T3??HN for H. nepalensis） and control （CK）. Three replicates were prepared for each treatment. To simulate formaldehyde stress in treatments T1 and T3， 1.0 ml of 40% formaldehyde solution was dropped onto an absorbent cotton ball that was hung in the center of each glass container， and then the container was covered with a glass plate， and sealed with a seal ring to prevent formaldehyde from leaking out. The air and formaldehyde in each glass container were refreshed once a week. To simulate low light stress in treatments T2 and T3， the glass containers were covered with a shading net to reduce the light intensity to 1/10. The amount of formaldehyde and the intensity of low light had been determined by preliminary experiments. After four months of stress treatment， samples were collected to determine the morphological， physiological and biochemical parameters of roots， stems and leaves. Measurement items and methods
Leaf length， leaf width， stem length and root length were measured using a ruler marked in mm. Leaf shape index was calculated according to the formula： Leaf shape index = Leaf length/Leaf width. Stem diameter was measured using a vernier caliper. To measure biomass seedlings were washed， fixed in an oven at 60 ?? for 30 min， dried at 100 ?? till a constant weight； the aboveground and the underground parts of each seedling were separately weighed using an analytical balance with an accuracy of 0. 000 1 g， and the sum of the weights of the two parts was the biomass of a seedling. The root??to??shoot ratio of each seedling was calculated using the formula as follows： Root??to??shoot ratio= Dry weight of underground part/Dry weight of aboveground part ?? 100%. Ten plants of each treatment were measured for above indices.
After biomass was measured， the roots， stems and leaves of the samples were separated， ground into a powder with a mortar and pestle and passed through 200 mesh. Soluble sugar content was quantified by phenol??sulfuric acid assay， soluble protein content was determined using Coomassie Brilliant Blue G250， the content of free proline was determined spectrophotometrically after extraction with toluene[11]. Total nitrogen was quantified by Kjeldahl method， and phosphorus content was determined by molybdenum blue method. There were three repetitions for each measurement， and the average value was used in the final computation.
Results and Analysis
Effects of different stress treatments on plant morphology
Both formaldehyde and low light had a certain influence on the morphology of the two Hedera species. As can be seen in Table 1， treatments with formaldehyde and low light alone and in combination decreased both leaf length and leaf width of the two Hedera species， most significantly in treatment T3??HN， and most slightly in treatment T2??HH. Among them， only Treatment T3??HN showed significant difference from CK??HN in leaf length， and the leaf width of treatments T1??HN， T2??HN and T3??HN was significantly smaller than that of CK??HN. Under the stresses of formaldehyde and low light alone and in combination， the leaf shape index of the two Hedera species increased， and the effect in HN was more significant than in HH. In detail， the leaf shape index of HN under all three stress treatments was significantly higher than that of CK??HN， while the leaf shape index of HH in only treatments T2??HH and T3??HH was significantly higher than that of CK??HH. Under the stresses of formaldehyde and low light alone and in combination， the stem length， stem diameter and root length of the two species also declined. The stem length of treatments T1??HN and T3??HN was significantly smaller than that of CK??HN， and the stem length of Treatment T2??HH was significantly smaller than that of CK??HH. Among all the treatments， the decrease in stem length of Treatment T3??HN was the largest， and that of Treatment T1??HH was the smallest. The stem diameter of the two Hedera species was little affected by stress treatments. Among them， the decrease in stem diameter of Treatment T2??HH was the largest， and that of Treatment T1??HH was the smallest. The root length of only Treatment T3??HN was significantly smaller than that of CK??HN. The decrease in root length of Treatment T3??HN was the largest， and that of Treatment T1??HN was the smallest. The biomass of treatments T1??HN， T2??HN and T3??HN was significantly lower than that of CK??HN， and the biomass of treatments T2??HH and T3??HH was significantly lower than that of CK??HH. According to the reduction in biomass， the treatments were T1??HN > T3??HN> T2??HH> T2??HN> T3??HH> T1??HH， suggesting that the effect of formaldehyde on biomass accumulation was more significant in HN than in HH， while the effect of low light on biomass accumulation was more significant in HH than in HN. In addition， treatment with formaldehyde in combination with low light had more significant influence on biomass accumulation than treatment with either formaldehyde or low light. Moreover， the root??to??shoot ratio of treatments T1??HN and T1??HH was significantly higher than that of all other treatments except CK??HH， and the root??to??shoot ratio of treatments T2??HN and T2??HH was significantly lower than that of other treatments. Formaldehyde treatment increased the root??to??shoot ratio of the two species， and the effect was more significant in HN than in HH. On the contrary， low light alone or together with formaldehyde decreased the root??to??shoot ratio of the two species， and according to the reduction in root??to??shoot ratio， the treatments were T2??HH> T2??HN> T3??HH> T3??HN （Fig. 1）.
Agricultural Biotechnology 2018Effects of different stress treatments on the contents of soluble sugar and starch
Soluble sugar and starch are important non??structural carbon sources in plants. As can be seen in Fig. 2， the soluble sugar content in roots of the two Hedera species was little affected by formaldehyde and low light. Among all the treatments， the increment in soluble sugar content in roots of Treatment T3??HH was the largest， up to 34.59%， and that of Treatment T2??HH was the smallest， only -19.69%. However， the soluble sugar content in stems of the two Hedera species significantly decreased in all the stress treatments， compared with CK. And the decrease of Treatment T3 was the largest， and that of Treatment T1 was the smallest， and the effect was more significant in HH than in HN. In addition， for each Hedera species， there was significant difference in soluble sugar content in stems between these treatments， which were CK>T1>T2>T3 in deceasing order of soluble sugar content in stems. Treatments 1， T2， and T3 had no significant difference in soluble sugar content in leaves， and were all significantly lower than CK. The reduction in soluble sugar content in leaves of was the greatest （32.46%） in Treatment T3??HN， and the smallest （18.5%） in Treatment T2??HN. The root starch content of Treatment T1??HN was significantly higher than that of other treatments， while the root starch content Treatment T3??HH was lower than that of all other treatments except T3??HN. Both T2 and T3 treatments reduced root starch content， and they were T3??HH > T3??HN> T2??HH> T2??HN in decreasing order of the reduction in root starch content. For either species， the treatments were T1> CK> T2> T3 according to root starch content， showing significant difference in root starch content between them. The stem starch content of Treatment T1??HN was significantly higher than that of other treatments， while the stem starch content of treatment CK??HH was significantly lower than that of other treatments. Compared with CK， T1， T2， and T3 all increased stem starch content， and they were T1??HH> T2??HH> T3??HH> T1??HN> T3??HN> T2??HN according to the increment. Compared with CK??HN， the leaf starch content of treatments T1??HN and T2??HN changed little， but that of Treatment T3??HN significantly decreased. The leaf starch content of treatments T2??HH and T3??HH was significantly higher than that of Treatment CK??HH.
Effects of different stress treatments on protein and proline contents
As can be seen from Fig. 3， there was no significant difference in root protein content for either species between these stress treatments. Compared with CK， the root protein content of HN increased under all three stress treatments， most significantly in Treatment T1??HN and most slightly in Treatment T2??HN； the root protein content of HH increased in Treatment T1??HH， but decreased in both treatments T2??HH and T3??HH. There was no significant difference in stem protein content of HN between these stress treatments. Compared with CK， the stem protein content in treatments T1??HN and T3??HH slightly increased， and that in all other treatments decreased， and the increase of Treatment T3??HH was greater than that of Treatment T3??HH. The leaf protein content for either species significantly decreased under all stress treatments except T2??HH. Among them， the leaf protein content of treatments T1??HN， T2??HN and T3??HN was 22.56%， 40.26% and 30.73% lower than that of CK??HN， and the leaf protein content of treatments T1??HH， T2??HH and T3??HH was 32.45%， 6.54% and 14.59% lower than that of CK??HH. The results suggested that treatment with either formaldehyde or low light alone decreased the leaf protein content of both Hedera species， and the effect of formaldehyde was more significant in HH than in HN， while the effect of low light was more significant in HN than in HH. Proline is an important osmotic regulator in plants. Compared with CK， all stress treatments significantly increased the root proline content of both Hedera species. Among them， the root proline content of treatments T1??HN， T2??HN and T3??HN was 65.67%， 11.75% and 61.65% higher than that of CK??HN， while the root proline content of treatments T1??HH， T2??HH and T3??HH was 20.29%， 102.74% and 51.35% higher than that of CK??HH. Compared with CK， the stem proline content of treatments T1??HN， T3??HN and T3??HH significantly increased， and that of treatments T2??HN and T2??HH changed little， while that of Treatment T1??HH significantly decreased. The leaf proline content of treatments T1??HN， T2??HH， T3??HN and T3??HH was significantly higher， and that of Treatment T1??HH was significantly lower than that of CK.
Effects of different stress treatments on phosphorus and total nitrogen contents
Formaldehyde and low??light stress caused a decrease in phosphorus content in roots， stems， and leaves of two Hedera species （Fig. 4）. The root phosphorus content of treatments T2??HN and T3??HN was significantly lower than that of CK??HN， while the root phosphorus content of treatments T1??HH， T2??HH and T3??HH was significantly lower than that of CK??HH. And the effect in HH was more significant than in HN. For either species， the treatments were CK> T3> T1> T2 according to stem phosphorus content. In order of reduction in stem phosphorus content， the treatments were T2??HH> T1??HH> T2??HN> T3??HN> T1??HN> T3??HH. The leaf phosphorus content of Treatment CK??HN was significantly higher than that of other treatments， while the leaf phosphorus content of treatments T2??HH and T3??HH was significantly lower than that of other treatments. Compared with CK??HN， the leaf phosphorus content of treatments T1??HN， T2??HN， and T3??HN decreased by 15.11%， 32.5%， and 32.91%， respectively. Compared with CK??HH， the leaf phosphorus content of treatments T1??HH， T2??HH and T3??HH decreased by 9.81%， 46.11% and 54.28%， respectively.
The total nitrogen content in roots of HN significantly decreased under all stress treatments， while for HH， the total nitrogen content in roots of Treatment T1??HH was significantly higher than that of Treatment CK??HH， but there was no significant difference between treatments T2??HH， T3??HH and CK??HH in total nitrogen content in roots. The total nitrogen content in stems of treatments T2??HN and T3??HN were significantly lower than that of treatments T1??HN and CK??HN. The total nitrogen content in stems of Treatment T1??HH was significantly lower than that of CK??HH， while there was no significant difference between treatments T2??HN， T3??HN and CK??HN in stem total nitrogen content. Among all the stress treatments， the total nitrogen content in stems of Treatment T3??HN decreased most significantly， while that of treatment T3??HH slightly increased compared with CK. The total nitrogen content in leaves of all stress treatments decreased， and the decrease was larger in HN than in HH in each treatment. Effects of different stress treatments on total carbon content and carbon??to??nitrogen （C/N） ratio
Formaldehyde and low??light stress had a certain influence on the total carbon content and carbon??to??nitrogen （C/N） ratio of the two Hedera species， as shown in Fig. 5. Compared with CK， the total carbon content in roots of both Hedera species in treatment T1 slightly increased， and the increase in HN was larger than in HH； the total carbon content in roots of both Hedera species of treatments T2 and T3 decreased， and they were T2??HH >T3??HN> T3??HH> T2??HN according to the decrease. The total carbon content in stems of treatments T2??HN and T3??HN decreased by 24.28% and 32.82%， compared with CK??HN， and that of treatments T2??HH and T3??HH decreased by 23.48% and 60.11%， compared with CK??HH. However， there was no significant difference in total carbon content in stems between treatments T1 and CK. Formaldehyde in combination with low??light stress caused a decrease in total carbon content in leaves of the two Hedera species. Among them， the total carbon content in leaves of treatments T1??HN， T2??HN and T3??HN decreased by 15.87%， 11.74% and 29.58%， compared with CK??HN， and that of treatments T1??HH， T2??HH and T3??HH decreased by 24.22%， 12.5%， and 15.4%， compared with CK??HH.
Among all the stress treatments， only T1??HN and T2??HN increased root C/N ratio， and other treatments decreased root C/N ratio to varying extents. The largest decrease was observed in Treatment T2??HH， and the smallest was in Treatment T1??HH. Both treatments T2 and T3 significantly decreased the stem C/N ratio of the two Hedera species， and the effect was more significant in HH than in HN. There was no significant difference in stem C/N ratio between T1 and CK. The leaf C/N ratio of treatments T1??HN， T2??HN， and T3??HN increased by 28.0%， 52.44%， and 18.29%， compared with CK??HN， and that of treatments T1??HH and T3??HH increased by 15.34% and 2.12%， compared with CK??HH. The results prove that formaldehyde treatment can increase the C/N ratio of the two Hedera species.
Conclusions and Discussion
It has been widely accepted that ornamental plants can remove indoor formaldehyde. Plant growth and development is usually influenced by low light indoors. Low light delays the growth rate of Zea mays by thinning leaves， increasing plant height， decreasing dry matter accumulation and grain yield[12]. Shading reduces root length， increases leaf length， leaf number and aboveground biomass of Vallisneria natans[13]. Studies on the effects of formaldehyde on plant growth have mostly focused on damage to the leaves. Liu et al.[14] reported that formaldehyde stress resulted in withered leaf margin of plants. However， the effect of formaldehyde on growth indices of plants has not yet been reported. Our data showed that treatment with either formaldehyde or low light reduced leaf length， leaf width， stem length， stem diameter， root length and biomass， and significantly increased leaf shape index of H. nepalensis and H. helix. However， root??to shoot ratio was increased by treatment with formaldehyde， but was significantly decreased by treatment with low light alone or in combination with formaldehyde， and the decrease was greater in treatment with low light alone. The reason might be that low light promotes the growth of aboveground parts and inhibits the growth of underground parts of plants， and formaldehyde inhibits the growth of aboveground parts and promote the growth of underground parts of plants. Osmoregulation is defined as a lowering of osmotic potential due to net intracellular solute accumulation in response to water stress. Plants exposed to stresses can regulate osmotic pressure by changing the concentration of organic osmoregulators， such as soluble sugar， to increase the osmotic potential of the cells and adapt to the changes in the external environment. Liu et al.[14] reported that formaldehyde increased the soluble sugar content and decreased the protein content of Salvia splendens， Zebrina pendula and Chlorophytum comosum. And similar results were observed in H. helix[8]. Our data showed that under the stress of formaldehyde， soluble sugar content and phosphorus content decreased， while starch content increased in roots， stems and leaves of the two Hedera species； total carbon content increased， while protein content decreased in roots of the two Hedera species； total carbon content significantly declined， while protein content increased in leaves of the two Hedera species； total nitrogen content decreased， while C/N ratio increased in roots of H. nepalensis； total nitrogen content in roots of H. helix increased， while total nitrogen content in its stems significantly decreased； total nitrogen content significantly decreased， while C/N ratio increased in leaves of the two Hedera species. The increased C/N ratio indicates increased total carbon content or decreased total nitrogen content. The increase in total carbon content may be conducive to the removal of toxic substances in the leaves under formaldehyde stress. The decrease in total nitrogen content is probably due to that the expression of some genes is down??regulated， or some proteins are degraded under stress， and this may be the physiological responses of plants to environmental stress.
Light intensity has a great influence on the soluble sugar and protein contents of plants. Qin et al.[15] reported that the contents of soluble sugar and protein in leaves of Scaevola aemula were decreased under low??light stress. Our results showed that the treatments with low light alone and in combination with formaldehyde significantly reduced the soluble sugar content in roots of H. helix， in leaves and stems of both Hedera species， and the effect of low light in combination with formaldehyde was more significant than low light alone. The starch content in roots of the two Hedera species was reduced by low light alone， and significantly reduced by low light and formaldehyde in combination. Under the stress of low light alone and in combination with formaldehyde， the starch content in stems of the two Hedera species was significantly increased； the starch content in leaves of H. nepalensis was reduced， while that of H. helix was increased； the phosphorus content in roots， stems and leaves was decreased. There were insignificant differences in protein content in roots and stems of the two Hedera species between the treatment with low light in combination with formaldehyde and the control. The protein content in leaves of H. helix was little changed， while that of H. nepalensis was significantly decreased by low light， compared with the control. Under the stress of low light alone and in combination with formaldehyde， the total nitrogen content in roots， stems and leaves of H. nepalensis dropped significantly， while that of H. helix varied slightly； the total carbon content in roots， stems and leaves of the two Hedera species dramatically declined， and the effect of low light and formaldehyde in combination was more significant. Under low??light stress， the C/N ratio in roots of H. nepalensis rose， that of H. helix significantly declined， and the C/N ratio in stems of both species reduced， suggesting that H. nepalensis can accumulate more carbohydrates， and thus has better adaptability to low light than H. helix. The massive accumulation of proline is a protective mechanism for plants to adapt to adverse stresses， but the physiological functions of proline accumulation are still controversial. Some studies indicated that as one of the non??enzymatic scavengers of reactive oxygen species in plants， the accumulation of proline was related to stress resistance[16-17]. However， some other studies suggested that proline accumulation could be used as an indicator for stress sensitivity， as less proline was accumulated in plants with higher resistance to stress[9， 18]. We found that formaldehyde stress caused a significant increase in proline content in roots of the two Hedera species， and the increase was greater in H. helix than in H. nepalensis； the content of proline rose significantly in stems and leaves of H. nepalensis， decreased significantly in stems and leaves of H. helix under low??light stress. In addition， the content of proline in roots of the two Hedera species increased at varying degree under the stress of low light alone and in combination with formaldehyde； the content of proline in leaves of H. nepalensis significantly increased under the stress of low light alone； the content of proline in stems and leaves of the two species significantly increased under the stress of low light and formaldehyde in combination. Similar results have been reported by in Luffa cylindrica by Jiang et al.[19].
References
[1] KIM CW， SONG JS. Occupational asthma due to formaldehyde[J]. Yonsei Med J， 2001， 42（2）： 439-445.
[2] LEMUS R， ABDELGHANI AA， AKERS TG， et al. Pot entail health risks from exposure to indoor formaldehyde[J]. Rev Environ Health， 1998， 13（12）： 91-98.
[3] ZHU TJ， GUAN LX. Influence of indoor air pollution caused by decorative materials on human immune system[J]. Shanxi Preventive Medicine， 2001， 10 （2）： 134-135.
[4] DUNCAN GF， NIGEL B， STEPHEN BG. Indoor air pollution from biomass fuel smoke is a major health concern in the developing world[J]. Transactions of the Royal Society of Tropical Medicine and Hygiene， 2008， 102： 843-851.
[5] BILKIS AB， SAMIR KP， DILDAR H， et al. Indoor air pollution from particulate matter emissions in different households in rural areas of Bangladesh[J]. Building and Environment， 2009， 44（5）： 898-903.
[6] BAZZAZ FA. Plants in changing environments： linking physiological， population， and community ecology[M]. Cambridge： Cambridge University Press， 1996.
[7] CALLAHAN HS， PIGLIUCCI M. Shade induced plasticity and its ecological significance in wild populations of Arabidopsis thaliana[J]. Ecology， 2002， 83（7）： 1965-1980. [8] XUAN XX， XIAO SL， YOU L， et al. The analysis of the intermediates for formaldehyde metabolism and physiological changes under gaseous formaldehyde stress in Hedera helix[J]. Life Science Research， 2013， 17（2）： 125-135.
[9] LINGHU YW， LI B， LI SF， et al. Monitoring， purification and response of three indoor ornamental plants on formaldehyde pollution[J]. Acta Botanica Boreali??Occidentalia Sinica， 2011， 31（4）： 776-782.
[10] CAO YH， ZHOU BZ， CHEN SL. Effects of water stress on physiological characteristics of different Illicium lanceolatum ecotypes under low light intensity[J]. Acta Ecologica Sinica， 2014， 34（4）： 814-822.
[11] MENG YN， YAN LB， FAN YQ. Research on changes of three enzymes activities of sweet （hot） pepper under low temperature and poor light and the tolerance[J]. Journal of Hebei Agricultural Sciences， 2014， 18（6）： 21-24， 85.
[12] LI CH， LUAN LM， YIN F， et al. Effects of light stress at different stages on the growth and yield of different maize genotypes （Zea mays L.）[J]. Acta Ecologica Sinica， 2005， 25（4）： 824-830.
[13] LI HJ， NI LY， CAO T， et al. Responses of Vallisneria natans to reduced light availability and nutrient enrichment[J]. Acta Hydrobiologica Sinica， 2008， 32（2）： 225-230.
[14] LIU D， SHI BS， WEI WX. Effect of formaldehyde gas stress on morphology and partial physiological indexes of three ornamental plants[J]. Journal of Agricultural University of Hebei， 2011， 34（2）： 66-70.
[15] QIN HJ， HE BH， CAI XH， et al. Effect of low light stress on features and physiological characteristics of Scaevola aemula cutting seedlings[J]. Journal of Henan Agricultural Sciences， 2013， 42（9）： 103-107.
[16] LI HL， ZHAO QF， WANG XC. Effects of air pollution on plant physiology in Lanzhou City[J]. Journal of Northwest Normal University （Natural Science）， 2005， 41（1）： 55-57.
[17] TAO L， REN J， DU Z. Studies on effects of sulfur dioxide on physiological indexes changes in plants[J]. Journal of Shanxi Agricultural Sciences， 2007， 26（5）： 710-711.
[18] JIE JM， YU JH， JIE MH， et al. Changes of three osmotic regulatory metabolites in leaves of pepper under low temperature and poor light stress and their relations with plant stress tolerance[J]. Acta Botanica Boreali??Occidentalia Sinica， 2009， 29（1）： 105-110.
[19] JIANG XT， LIN BY， LIN YZ. Effect of low light stress on growth and physiological and biochemistry characteristics of loofah seedlings[J]. Northern Horticulture， 2015， （9）： 14-18.
Key words Hedera spp.； Formaldehyde； Weak light； Growth； Nutrition
Formaldehyde （HCHO） is widely used in the manufacture of plastics， rubbers， resins， plywood， and adhesives[1]. It is also well known as a preservative in medical laboratories[2]. Cigarette smoke， decorative materials， textiles and formaldehyde??containing biocides are the main sources of formaldehyde in indoor air[3]. At present， the concentration of formaldehyde in indoor air in 80% to 90% of houses in China exceeds the maximum allowable level proposed by Hygienic Standard for Formaldehyde in Indoor Air of House by 3 to 4 times， or even hundreds of times， posing a serious threat to public health[4-5]. Formaldehyde has now become one of the main pollutants in indoor air. Exposure to low levels of formaldehyde can cause headaches， dizziness， upper respiratory tract irritation， eye irritation， allergic dermatitis and other symptoms. High??concentration formaldehyde is potentially teratogenic and carcinogenic. It usually takes 3 to 15 years for formaldehyde??containing materials to release all formaldehyde. Many physical and chemical agents cannot completely remove formaldehyde， and likely cause secondary pollution. Therefore， planting ornamental plants is a feasible solution to absorb and metabolize indoor formaldehyde. However， the intensity of light indoors is much lower than outside， which greatly affects the growth and development of indoor plants. As an important environmental factor， light plays an extremely important role in the growth and development of plants， and affects plant morphology and physiological functions[6]. Long??term exposure to low light influences plant morphogenesis and physiological and biochemical processes[7]. Existing studies are mostly focused on the effects of single factors such as formaldehyde[8-9] or low light[10-11] on plant growth and development， and the effects of the interactions between formaldehyde and low light on plant growth and nutrition has been rarely reported. Hedera， commonly called ivy， is a genus of 12-15 species of evergreen climbing or ground??creeping woody plants in the family Araliaceae. They are highly adaptable， easy to reproduce， with beautiful and fragrant leaves， can be planted both indoors and outdoors， and have high ability to remove formaldehyde. At present， the ability of ivies to remove formaldehyde has been extensively studied， but their growth and nutrition under formaldehyde and low light stresses have not been reported. Therefore， in this experiment， 0.5??year old seedlings of Hedera nepalensis and H. helix were exposed to formaldehyde and low light to clarify their adaptability to formaldehyde and low light， and to provide a theoretical basis for indoor cultivation of ivies.
Materials and Methods
Materials
H. nepalensis （hereafter abbreviated as HN） and H. helix plants （hereafter abbreviated as HH） grown in the campus of Kunming University were used as the experimental materials. Their 0.5??year old seedlings with a vigorous root system and luxuriant foliage were selected and transplanted into 20 cm ?? 20 cm pots containing a mixture of peat and vermiculite （1?? 1， v?? v）， with one seedling in each pot. Then， the pots were transferred to glass containers of 100 cm??60 cm??100 cm， with 20 pots （10 pots of HH and 10 pots of HN） in each container. And 200 ml of Hoagland??s nutrient solution （pH 5.5） was added to each pot once a week.
Experimental design
After two weeks of culture in glass containers， the seedlings were assigned into each of the four treatments： T1=formaldehyde （T1??HH for H. helix， and T1??HN for H. nepalensis）， T2=low light （T2??HH for H. helix， and T2??HN for H. nepalensis）， T3=formaldehyde plus low light （T3??HH for H. helix， and T3??HN for H. nepalensis） and control （CK）. Three replicates were prepared for each treatment. To simulate formaldehyde stress in treatments T1 and T3， 1.0 ml of 40% formaldehyde solution was dropped onto an absorbent cotton ball that was hung in the center of each glass container， and then the container was covered with a glass plate， and sealed with a seal ring to prevent formaldehyde from leaking out. The air and formaldehyde in each glass container were refreshed once a week. To simulate low light stress in treatments T2 and T3， the glass containers were covered with a shading net to reduce the light intensity to 1/10. The amount of formaldehyde and the intensity of low light had been determined by preliminary experiments. After four months of stress treatment， samples were collected to determine the morphological， physiological and biochemical parameters of roots， stems and leaves. Measurement items and methods
Leaf length， leaf width， stem length and root length were measured using a ruler marked in mm. Leaf shape index was calculated according to the formula： Leaf shape index = Leaf length/Leaf width. Stem diameter was measured using a vernier caliper. To measure biomass seedlings were washed， fixed in an oven at 60 ?? for 30 min， dried at 100 ?? till a constant weight； the aboveground and the underground parts of each seedling were separately weighed using an analytical balance with an accuracy of 0. 000 1 g， and the sum of the weights of the two parts was the biomass of a seedling. The root??to??shoot ratio of each seedling was calculated using the formula as follows： Root??to??shoot ratio= Dry weight of underground part/Dry weight of aboveground part ?? 100%. Ten plants of each treatment were measured for above indices.
After biomass was measured， the roots， stems and leaves of the samples were separated， ground into a powder with a mortar and pestle and passed through 200 mesh. Soluble sugar content was quantified by phenol??sulfuric acid assay， soluble protein content was determined using Coomassie Brilliant Blue G250， the content of free proline was determined spectrophotometrically after extraction with toluene[11]. Total nitrogen was quantified by Kjeldahl method， and phosphorus content was determined by molybdenum blue method. There were three repetitions for each measurement， and the average value was used in the final computation.
Results and Analysis
Effects of different stress treatments on plant morphology
Both formaldehyde and low light had a certain influence on the morphology of the two Hedera species. As can be seen in Table 1， treatments with formaldehyde and low light alone and in combination decreased both leaf length and leaf width of the two Hedera species， most significantly in treatment T3??HN， and most slightly in treatment T2??HH. Among them， only Treatment T3??HN showed significant difference from CK??HN in leaf length， and the leaf width of treatments T1??HN， T2??HN and T3??HN was significantly smaller than that of CK??HN. Under the stresses of formaldehyde and low light alone and in combination， the leaf shape index of the two Hedera species increased， and the effect in HN was more significant than in HH. In detail， the leaf shape index of HN under all three stress treatments was significantly higher than that of CK??HN， while the leaf shape index of HH in only treatments T2??HH and T3??HH was significantly higher than that of CK??HH. Under the stresses of formaldehyde and low light alone and in combination， the stem length， stem diameter and root length of the two species also declined. The stem length of treatments T1??HN and T3??HN was significantly smaller than that of CK??HN， and the stem length of Treatment T2??HH was significantly smaller than that of CK??HH. Among all the treatments， the decrease in stem length of Treatment T3??HN was the largest， and that of Treatment T1??HH was the smallest. The stem diameter of the two Hedera species was little affected by stress treatments. Among them， the decrease in stem diameter of Treatment T2??HH was the largest， and that of Treatment T1??HH was the smallest. The root length of only Treatment T3??HN was significantly smaller than that of CK??HN. The decrease in root length of Treatment T3??HN was the largest， and that of Treatment T1??HN was the smallest. The biomass of treatments T1??HN， T2??HN and T3??HN was significantly lower than that of CK??HN， and the biomass of treatments T2??HH and T3??HH was significantly lower than that of CK??HH. According to the reduction in biomass， the treatments were T1??HN > T3??HN> T2??HH> T2??HN> T3??HH> T1??HH， suggesting that the effect of formaldehyde on biomass accumulation was more significant in HN than in HH， while the effect of low light on biomass accumulation was more significant in HH than in HN. In addition， treatment with formaldehyde in combination with low light had more significant influence on biomass accumulation than treatment with either formaldehyde or low light. Moreover， the root??to??shoot ratio of treatments T1??HN and T1??HH was significantly higher than that of all other treatments except CK??HH， and the root??to??shoot ratio of treatments T2??HN and T2??HH was significantly lower than that of other treatments. Formaldehyde treatment increased the root??to??shoot ratio of the two species， and the effect was more significant in HN than in HH. On the contrary， low light alone or together with formaldehyde decreased the root??to??shoot ratio of the two species， and according to the reduction in root??to??shoot ratio， the treatments were T2??HH> T2??HN> T3??HH> T3??HN （Fig. 1）.
Agricultural Biotechnology 2018Effects of different stress treatments on the contents of soluble sugar and starch
Soluble sugar and starch are important non??structural carbon sources in plants. As can be seen in Fig. 2， the soluble sugar content in roots of the two Hedera species was little affected by formaldehyde and low light. Among all the treatments， the increment in soluble sugar content in roots of Treatment T3??HH was the largest， up to 34.59%， and that of Treatment T2??HH was the smallest， only -19.69%. However， the soluble sugar content in stems of the two Hedera species significantly decreased in all the stress treatments， compared with CK. And the decrease of Treatment T3 was the largest， and that of Treatment T1 was the smallest， and the effect was more significant in HH than in HN. In addition， for each Hedera species， there was significant difference in soluble sugar content in stems between these treatments， which were CK>T1>T2>T3 in deceasing order of soluble sugar content in stems. Treatments 1， T2， and T3 had no significant difference in soluble sugar content in leaves， and were all significantly lower than CK. The reduction in soluble sugar content in leaves of was the greatest （32.46%） in Treatment T3??HN， and the smallest （18.5%） in Treatment T2??HN. The root starch content of Treatment T1??HN was significantly higher than that of other treatments， while the root starch content Treatment T3??HH was lower than that of all other treatments except T3??HN. Both T2 and T3 treatments reduced root starch content， and they were T3??HH > T3??HN> T2??HH> T2??HN in decreasing order of the reduction in root starch content. For either species， the treatments were T1> CK> T2> T3 according to root starch content， showing significant difference in root starch content between them. The stem starch content of Treatment T1??HN was significantly higher than that of other treatments， while the stem starch content of treatment CK??HH was significantly lower than that of other treatments. Compared with CK， T1， T2， and T3 all increased stem starch content， and they were T1??HH> T2??HH> T3??HH> T1??HN> T3??HN> T2??HN according to the increment. Compared with CK??HN， the leaf starch content of treatments T1??HN and T2??HN changed little， but that of Treatment T3??HN significantly decreased. The leaf starch content of treatments T2??HH and T3??HH was significantly higher than that of Treatment CK??HH.
Effects of different stress treatments on protein and proline contents
As can be seen from Fig. 3， there was no significant difference in root protein content for either species between these stress treatments. Compared with CK， the root protein content of HN increased under all three stress treatments， most significantly in Treatment T1??HN and most slightly in Treatment T2??HN； the root protein content of HH increased in Treatment T1??HH， but decreased in both treatments T2??HH and T3??HH. There was no significant difference in stem protein content of HN between these stress treatments. Compared with CK， the stem protein content in treatments T1??HN and T3??HH slightly increased， and that in all other treatments decreased， and the increase of Treatment T3??HH was greater than that of Treatment T3??HH. The leaf protein content for either species significantly decreased under all stress treatments except T2??HH. Among them， the leaf protein content of treatments T1??HN， T2??HN and T3??HN was 22.56%， 40.26% and 30.73% lower than that of CK??HN， and the leaf protein content of treatments T1??HH， T2??HH and T3??HH was 32.45%， 6.54% and 14.59% lower than that of CK??HH. The results suggested that treatment with either formaldehyde or low light alone decreased the leaf protein content of both Hedera species， and the effect of formaldehyde was more significant in HH than in HN， while the effect of low light was more significant in HN than in HH. Proline is an important osmotic regulator in plants. Compared with CK， all stress treatments significantly increased the root proline content of both Hedera species. Among them， the root proline content of treatments T1??HN， T2??HN and T3??HN was 65.67%， 11.75% and 61.65% higher than that of CK??HN， while the root proline content of treatments T1??HH， T2??HH and T3??HH was 20.29%， 102.74% and 51.35% higher than that of CK??HH. Compared with CK， the stem proline content of treatments T1??HN， T3??HN and T3??HH significantly increased， and that of treatments T2??HN and T2??HH changed little， while that of Treatment T1??HH significantly decreased. The leaf proline content of treatments T1??HN， T2??HH， T3??HN and T3??HH was significantly higher， and that of Treatment T1??HH was significantly lower than that of CK.
Effects of different stress treatments on phosphorus and total nitrogen contents
Formaldehyde and low??light stress caused a decrease in phosphorus content in roots， stems， and leaves of two Hedera species （Fig. 4）. The root phosphorus content of treatments T2??HN and T3??HN was significantly lower than that of CK??HN， while the root phosphorus content of treatments T1??HH， T2??HH and T3??HH was significantly lower than that of CK??HH. And the effect in HH was more significant than in HN. For either species， the treatments were CK> T3> T1> T2 according to stem phosphorus content. In order of reduction in stem phosphorus content， the treatments were T2??HH> T1??HH> T2??HN> T3??HN> T1??HN> T3??HH. The leaf phosphorus content of Treatment CK??HN was significantly higher than that of other treatments， while the leaf phosphorus content of treatments T2??HH and T3??HH was significantly lower than that of other treatments. Compared with CK??HN， the leaf phosphorus content of treatments T1??HN， T2??HN， and T3??HN decreased by 15.11%， 32.5%， and 32.91%， respectively. Compared with CK??HH， the leaf phosphorus content of treatments T1??HH， T2??HH and T3??HH decreased by 9.81%， 46.11% and 54.28%， respectively.
The total nitrogen content in roots of HN significantly decreased under all stress treatments， while for HH， the total nitrogen content in roots of Treatment T1??HH was significantly higher than that of Treatment CK??HH， but there was no significant difference between treatments T2??HH， T3??HH and CK??HH in total nitrogen content in roots. The total nitrogen content in stems of treatments T2??HN and T3??HN were significantly lower than that of treatments T1??HN and CK??HN. The total nitrogen content in stems of Treatment T1??HH was significantly lower than that of CK??HH， while there was no significant difference between treatments T2??HN， T3??HN and CK??HN in stem total nitrogen content. Among all the stress treatments， the total nitrogen content in stems of Treatment T3??HN decreased most significantly， while that of treatment T3??HH slightly increased compared with CK. The total nitrogen content in leaves of all stress treatments decreased， and the decrease was larger in HN than in HH in each treatment. Effects of different stress treatments on total carbon content and carbon??to??nitrogen （C/N） ratio
Formaldehyde and low??light stress had a certain influence on the total carbon content and carbon??to??nitrogen （C/N） ratio of the two Hedera species， as shown in Fig. 5. Compared with CK， the total carbon content in roots of both Hedera species in treatment T1 slightly increased， and the increase in HN was larger than in HH； the total carbon content in roots of both Hedera species of treatments T2 and T3 decreased， and they were T2??HH >T3??HN> T3??HH> T2??HN according to the decrease. The total carbon content in stems of treatments T2??HN and T3??HN decreased by 24.28% and 32.82%， compared with CK??HN， and that of treatments T2??HH and T3??HH decreased by 23.48% and 60.11%， compared with CK??HH. However， there was no significant difference in total carbon content in stems between treatments T1 and CK. Formaldehyde in combination with low??light stress caused a decrease in total carbon content in leaves of the two Hedera species. Among them， the total carbon content in leaves of treatments T1??HN， T2??HN and T3??HN decreased by 15.87%， 11.74% and 29.58%， compared with CK??HN， and that of treatments T1??HH， T2??HH and T3??HH decreased by 24.22%， 12.5%， and 15.4%， compared with CK??HH.
Among all the stress treatments， only T1??HN and T2??HN increased root C/N ratio， and other treatments decreased root C/N ratio to varying extents. The largest decrease was observed in Treatment T2??HH， and the smallest was in Treatment T1??HH. Both treatments T2 and T3 significantly decreased the stem C/N ratio of the two Hedera species， and the effect was more significant in HH than in HN. There was no significant difference in stem C/N ratio between T1 and CK. The leaf C/N ratio of treatments T1??HN， T2??HN， and T3??HN increased by 28.0%， 52.44%， and 18.29%， compared with CK??HN， and that of treatments T1??HH and T3??HH increased by 15.34% and 2.12%， compared with CK??HH. The results prove that formaldehyde treatment can increase the C/N ratio of the two Hedera species.
Conclusions and Discussion
It has been widely accepted that ornamental plants can remove indoor formaldehyde. Plant growth and development is usually influenced by low light indoors. Low light delays the growth rate of Zea mays by thinning leaves， increasing plant height， decreasing dry matter accumulation and grain yield[12]. Shading reduces root length， increases leaf length， leaf number and aboveground biomass of Vallisneria natans[13]. Studies on the effects of formaldehyde on plant growth have mostly focused on damage to the leaves. Liu et al.[14] reported that formaldehyde stress resulted in withered leaf margin of plants. However， the effect of formaldehyde on growth indices of plants has not yet been reported. Our data showed that treatment with either formaldehyde or low light reduced leaf length， leaf width， stem length， stem diameter， root length and biomass， and significantly increased leaf shape index of H. nepalensis and H. helix. However， root??to shoot ratio was increased by treatment with formaldehyde， but was significantly decreased by treatment with low light alone or in combination with formaldehyde， and the decrease was greater in treatment with low light alone. The reason might be that low light promotes the growth of aboveground parts and inhibits the growth of underground parts of plants， and formaldehyde inhibits the growth of aboveground parts and promote the growth of underground parts of plants. Osmoregulation is defined as a lowering of osmotic potential due to net intracellular solute accumulation in response to water stress. Plants exposed to stresses can regulate osmotic pressure by changing the concentration of organic osmoregulators， such as soluble sugar， to increase the osmotic potential of the cells and adapt to the changes in the external environment. Liu et al.[14] reported that formaldehyde increased the soluble sugar content and decreased the protein content of Salvia splendens， Zebrina pendula and Chlorophytum comosum. And similar results were observed in H. helix[8]. Our data showed that under the stress of formaldehyde， soluble sugar content and phosphorus content decreased， while starch content increased in roots， stems and leaves of the two Hedera species； total carbon content increased， while protein content decreased in roots of the two Hedera species； total carbon content significantly declined， while protein content increased in leaves of the two Hedera species； total nitrogen content decreased， while C/N ratio increased in roots of H. nepalensis； total nitrogen content in roots of H. helix increased， while total nitrogen content in its stems significantly decreased； total nitrogen content significantly decreased， while C/N ratio increased in leaves of the two Hedera species. The increased C/N ratio indicates increased total carbon content or decreased total nitrogen content. The increase in total carbon content may be conducive to the removal of toxic substances in the leaves under formaldehyde stress. The decrease in total nitrogen content is probably due to that the expression of some genes is down??regulated， or some proteins are degraded under stress， and this may be the physiological responses of plants to environmental stress.
Light intensity has a great influence on the soluble sugar and protein contents of plants. Qin et al.[15] reported that the contents of soluble sugar and protein in leaves of Scaevola aemula were decreased under low??light stress. Our results showed that the treatments with low light alone and in combination with formaldehyde significantly reduced the soluble sugar content in roots of H. helix， in leaves and stems of both Hedera species， and the effect of low light in combination with formaldehyde was more significant than low light alone. The starch content in roots of the two Hedera species was reduced by low light alone， and significantly reduced by low light and formaldehyde in combination. Under the stress of low light alone and in combination with formaldehyde， the starch content in stems of the two Hedera species was significantly increased； the starch content in leaves of H. nepalensis was reduced， while that of H. helix was increased； the phosphorus content in roots， stems and leaves was decreased. There were insignificant differences in protein content in roots and stems of the two Hedera species between the treatment with low light in combination with formaldehyde and the control. The protein content in leaves of H. helix was little changed， while that of H. nepalensis was significantly decreased by low light， compared with the control. Under the stress of low light alone and in combination with formaldehyde， the total nitrogen content in roots， stems and leaves of H. nepalensis dropped significantly， while that of H. helix varied slightly； the total carbon content in roots， stems and leaves of the two Hedera species dramatically declined， and the effect of low light and formaldehyde in combination was more significant. Under low??light stress， the C/N ratio in roots of H. nepalensis rose， that of H. helix significantly declined， and the C/N ratio in stems of both species reduced， suggesting that H. nepalensis can accumulate more carbohydrates， and thus has better adaptability to low light than H. helix. The massive accumulation of proline is a protective mechanism for plants to adapt to adverse stresses， but the physiological functions of proline accumulation are still controversial. Some studies indicated that as one of the non??enzymatic scavengers of reactive oxygen species in plants， the accumulation of proline was related to stress resistance[16-17]. However， some other studies suggested that proline accumulation could be used as an indicator for stress sensitivity， as less proline was accumulated in plants with higher resistance to stress[9， 18]. We found that formaldehyde stress caused a significant increase in proline content in roots of the two Hedera species， and the increase was greater in H. helix than in H. nepalensis； the content of proline rose significantly in stems and leaves of H. nepalensis， decreased significantly in stems and leaves of H. helix under low??light stress. In addition， the content of proline in roots of the two Hedera species increased at varying degree under the stress of low light alone and in combination with formaldehyde； the content of proline in leaves of H. nepalensis significantly increased under the stress of low light alone； the content of proline in stems and leaves of the two species significantly increased under the stress of low light and formaldehyde in combination. Similar results have been reported by in Luffa cylindrica by Jiang et al.[19].
References
[1] KIM CW， SONG JS. Occupational asthma due to formaldehyde[J]. Yonsei Med J， 2001， 42（2）： 439-445.
[2] LEMUS R， ABDELGHANI AA， AKERS TG， et al. Pot entail health risks from exposure to indoor formaldehyde[J]. Rev Environ Health， 1998， 13（12）： 91-98.
[3] ZHU TJ， GUAN LX. Influence of indoor air pollution caused by decorative materials on human immune system[J]. Shanxi Preventive Medicine， 2001， 10 （2）： 134-135.
[4] DUNCAN GF， NIGEL B， STEPHEN BG. Indoor air pollution from biomass fuel smoke is a major health concern in the developing world[J]. Transactions of the Royal Society of Tropical Medicine and Hygiene， 2008， 102： 843-851.
[5] BILKIS AB， SAMIR KP， DILDAR H， et al. Indoor air pollution from particulate matter emissions in different households in rural areas of Bangladesh[J]. Building and Environment， 2009， 44（5）： 898-903.
[6] BAZZAZ FA. Plants in changing environments： linking physiological， population， and community ecology[M]. Cambridge： Cambridge University Press， 1996.
[7] CALLAHAN HS， PIGLIUCCI M. Shade induced plasticity and its ecological significance in wild populations of Arabidopsis thaliana[J]. Ecology， 2002， 83（7）： 1965-1980. [8] XUAN XX， XIAO SL， YOU L， et al. The analysis of the intermediates for formaldehyde metabolism and physiological changes under gaseous formaldehyde stress in Hedera helix[J]. Life Science Research， 2013， 17（2）： 125-135.
[9] LINGHU YW， LI B， LI SF， et al. Monitoring， purification and response of three indoor ornamental plants on formaldehyde pollution[J]. Acta Botanica Boreali??Occidentalia Sinica， 2011， 31（4）： 776-782.
[10] CAO YH， ZHOU BZ， CHEN SL. Effects of water stress on physiological characteristics of different Illicium lanceolatum ecotypes under low light intensity[J]. Acta Ecologica Sinica， 2014， 34（4）： 814-822.
[11] MENG YN， YAN LB， FAN YQ. Research on changes of three enzymes activities of sweet （hot） pepper under low temperature and poor light and the tolerance[J]. Journal of Hebei Agricultural Sciences， 2014， 18（6）： 21-24， 85.
[12] LI CH， LUAN LM， YIN F， et al. Effects of light stress at different stages on the growth and yield of different maize genotypes （Zea mays L.）[J]. Acta Ecologica Sinica， 2005， 25（4）： 824-830.
[13] LI HJ， NI LY， CAO T， et al. Responses of Vallisneria natans to reduced light availability and nutrient enrichment[J]. Acta Hydrobiologica Sinica， 2008， 32（2）： 225-230.
[14] LIU D， SHI BS， WEI WX. Effect of formaldehyde gas stress on morphology and partial physiological indexes of three ornamental plants[J]. Journal of Agricultural University of Hebei， 2011， 34（2）： 66-70.
[15] QIN HJ， HE BH， CAI XH， et al. Effect of low light stress on features and physiological characteristics of Scaevola aemula cutting seedlings[J]. Journal of Henan Agricultural Sciences， 2013， 42（9）： 103-107.
[16] LI HL， ZHAO QF， WANG XC. Effects of air pollution on plant physiology in Lanzhou City[J]. Journal of Northwest Normal University （Natural Science）， 2005， 41（1）： 55-57.
[17] TAO L， REN J， DU Z. Studies on effects of sulfur dioxide on physiological indexes changes in plants[J]. Journal of Shanxi Agricultural Sciences， 2007， 26（5）： 710-711.
[18] JIE JM， YU JH， JIE MH， et al. Changes of three osmotic regulatory metabolites in leaves of pepper under low temperature and poor light stress and their relations with plant stress tolerance[J]. Acta Botanica Boreali??Occidentalia Sinica， 2009， 29（1）： 105-110.
[19] JIANG XT， LIN BY， LIN YZ. Effect of low light stress on growth and physiological and biochemistry characteristics of loofah seedlings[J]. Northern Horticulture， 2015， （9）： 14-18.