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Abstract To investigate plant biomass and nutrient distribution and accumulation in organs of Alnus cremastogyne at different ages from 1 to 4 years， the biomass， N， P， K， Ca， Mg， Fe and Zn were tested. The results showed that the average biomass of the whole tree and the biomass of leaf， branch， stem， and root were in positive correlation with tree age， but the growth rate of biomass had a decreasing trend with the tree age increasing， and only the biomass proportion of the trunk in the whole individual plant showed an increasing trend with age. The contents of nutrient elements in organs showed an order of N>Ca>K>Mg>P>Fe>Zn； and the contents of N， P and K were higher in the leaf than in other organs， and the contents of Ca， Mg and Fe in the root were higher than in other organs. The accumulations of N， P， K， Ca， Mg and Zn were the highest in the trunk， and that of Fe was the highest in the root. The annual net accumulations of N， P， K， Ca and Mg in the average trees from 1 to 4 years old were 17.07， 40.79， 95.82 and 106.71 g， respectively， and the annual net accumulations of microelements （Fe and Zn） were 335.04， 577.26， 1267 and 1525.27 mg， respectively.
Key words Alnus cremastogyne； Forest stands at different ages； Demands for nutrient elements； Biomass； Nutrient elements
Received： August 23， 2017 Accepted： December 8， 2017
Supported by Project of Science and Technology Department in Sichuan Province（2016NZ0043）.
Anmin MIN （1963-）， male， P. R. China， researcher， devoted to soil fertility， plant nutrition and fertilizer application.
*Corresponding author. Email： [email protected]
Alnus cremastogyne is a plant in Alnus of Betuleae in Betulaceae family， also known as Shuidonggua tree， which is a kind of lofty deciduous leaf arbor， native to Sichuan Basin. It is only grow in China， and is one of the important fastgrowing indigenous tree species in Sichuan Province. A. cremastogyne grows fast， and propagates easily， with developed root system attached with root nodules. The tree is tolerant to water， with short leaf fall period， and has a high nitrogen content in leaves. It is thus a fastgrowing commercial tree species in the southwest region of China， a good tree species for dyke strengthening， conservation of water and soil， soil improvement and forestation， as well as an ideal associated species for China fir， pine and cypress. The tree could be used as fuel wood and industrial raw material， and could be used for soil fertility. A. cremastogyne has good texture in color of reddish brown， without remarkable difference between heartwood and sapwood. The timber has proper hardness and straight texture from top to bottom， and could serve as a material for the artificial board， papermaking， musical instrument and furniture. After a long term of development， A. cremastogyne has become a main tree species for fastgrowing and highyield plantation in South China， as well as an important tree species for pulpwood and fiber timber.
Directive breeding of A. cremastogyne as a smalldiameter and shortcycle industrial raw material could effectively alleviate the pressure of increasing demand for raw material in artificial board and wood pulp industries. Fertilization on young A. cremastogyne stand is one of the key measures for improving yield and realizing anticipated breeding targets. Therefore， the research about the biomass and distribution and accumulation of nutrient elements in organs of young A. cremastogyne plants could guide rational fertilization on young stand of A. cremastogyne in production.
At present， there have been reports about the biomass and nutrient distribution and accumulation of A. cremastogyne at certain ages[1-5]， but there were very few studies about the biomass， nutrient distribution and accumulation and demand for nutrients in young trees of A. cremastogyne at different ages. In this study， the biomass and nutrients in young A. cremastogyne plants at the age of 1-4 years were determined， and the distribution and accumulation characteristics of nutrients in A. cremastogyne organs were analyzed， so as to quantify the demands of young A. cremastogyne plants for nutrients. This study will provide a scientific basis for the fertilization management of young stands of A. cremastogyne， so as to realize the purpose of sustainable utilization of forest land through the improvement of yield， shortening of the cycle of rotation felling and prevention of land fertility declining[6].
Materials and Methods
Experimental materials
The young stands of A. cremastogyne at the age of 1-4 years were selected. The investigated forest is located in Xuzhou Town， Shuangban Township and Xianfeng Township in Zitong County， Mianyang City， Sichuan Province （104°57′-105°28′ east longitude， 31°25′-31°52′ North latitude）， with an altitude of 520-650 m， and Fubao State Forest Farm located in Hejiang County， Luzhou City， Sichuan Province （105°32′-106°28′ east longitude， 28°27′-29°01′ North latitude）， with an altitude of 920-1 100 m. Methods
Selection of investigation field： The young stands of A. cremastogyne at the age of 1-4 years with the same site conditions （soil type， thickness， slope， exposure and altitude） and operating management were selected as the investigation objects. The forestation was carried out according to a spacing of 2 m × 2 m at a density of 166 plants/667 m2.
Investigation method： For each age， three sample plots （20 m × 20 m） were selected， and according to conventional method， field individual measurement （tree height or diameter at breast height （DBH）） was performed， for the calculation of average tree height and average DBH. In each sample plot， 1 plant with a tree height or DBH within 95%-105% of the average data was selected as average tree[7]， and 12 average trees were selected in total.
After the actual measurement of DBH or tree height and crown breadth， the average trees growing normally were hewed down and cut， for the determination of the fresh weights of various organs （leaf， branch and trunk） of the aboveground part and the root as the underground part， and mean values were obtained according to tree age and organs.
Sample collection： On the basis of the biomass investigation of young stands of A. cremastogyne， leaf， trunk， branch and root samples were collected from sample trees. The samples of the same organ from the trees at the same age were mixed well， and 100-200 g of the mixed sample of each organ of the trees at each age were sampled for the determination of moisture. The samples of the same organ from the trees at different ages were mixed well， and 400-500 g of the mixed sample of each organ of the trees at the age of 1-4 years were sampled， for the determination of nutrient contents in organs. The collected samples should be transported to laboratory for treatment and determination.
Determination items of samples： The determined items included moisture， N， P， K， Ca， Fe and Zn.
Sample determination methods： Moisture was determined by drying method； N was determined by Kjeldahl method； for P， the samples were digested with HNO3HClO4 and determined by MoSb antispectrophotography method； and for K、Ca， Mg， Fe and Zn， the samples were digested with HNO3HClO4 and determined by atomic absorption spectrometry （LY/T 12701999）. The determination was designed with two parallel samples， and the absolute deviation and relative error should satisfy the requirements stipulated by industrial standard[8]. Data analysis
Statistic analysis of data adopted analysis of variance [9].
Results and Analysis
Tree height， DBH and biomass of A. cremastogyne
Tree height， DBH and tree age
For young stands of A. cremastogyne at the age of 1-4 years， tree height and DBH increased year by year （Table 1）. The trees at the age of 2 years showed a tree height increased by 77.78% compared with those at the age of 1 year； the trees at the age of 3 years had a tree height increased by 59.38% compared with those at the age of 2 years； and the trees at the age of 4 years exhibited a tree height increased by 21.57% compared with those at the age of 3 years. As to DBH， the trees at the age of 2 years exhibited a DBH increased by 136.36% compared with those at the age of 1 year； the trees at the age of 3 years had a DBH increased by 80.77% compared with those at the age of 2 years； and the trees at the age of 4 years exhibited a DBH increased by 36.17% compared with those at the age of 3 years. The growth rates of the two parameters decreased year by year. Variance analysis showed that there were very significant differences in tree height and DBH between trees at the various ages.
Table 1 Height， DBH and biomass composition and their differences of A. cremastogyne young average tree
Tree age∥aDBH∥cmTree height∥m
Biomass composition∥g
LeafBranchTrunkRootSum∥g
11.1±0.131.80±0.20101.3±11.4285.8±9.68247.6±27.96131.1±14.76565.8
22.6**±0.213.2**±0.26282.7**±22.62417.9**±33.47822.7*±65.89334.5**±26.781 857.8
34.7**±0.455.1**±0.48632.9**±60.13811.8**±77.153 270.8**±310.71736.0**±69.925 451.5
46.4**±0.526.2**±0.501 075.9**±87.111 380.1**±111.815 560**±450.281 251.1**±101.319 267.1
* indicates significant difference at 5% level； and ** indicates very significant difference at 1% level.
Biomass and tree age
At the age of 1-4 years， the average biomass of A. cremastogyne was in positive correlation with its age （Table 1）. The biomass at the second year was 2.28 times higher than that at the first year； the biomass at the third year was 1.93 times higher than that at the second year； and the biomass at the fourth year was 0.7 time higher than that at the third year. The relationship between biomass and tree age was the same as those of tree height and DBH， and the growth rate decreased year by year.
Organ biomass and tree age
For young stands of A. cremastogyne， the relationship between biomass of each of leaf， branch， trunk and root organs and tree age and the changing trends of the various organs accorded with the biomass of whole plant （Table 1）. The analysis of differences in the biomass of leaf， branch， trunk and root organs between various ages showed that except the significant difference in the trunk biomass between the twoyearold and oneyearold trees， the differences in the biomass of the various organs were very significant between trees at other ages. At this growth stage， there were also great differences between the biomass of the various organs. The absolute increases of the biomass of leaf， branch and root organs by years showed no big differences. For the three organs， the biomass at the second year increased by 180-330 g compared with that at the first year； the biomass at the third year increased by 350-400 g compared with that at the second year； and the biomass at the fourth year increased by 370-520 g than that at the third year. However， as to the trunk， the biomass at the second year increased by about 400 g compared with the first year； the biomass at the third year increased over 2 400 g compared with the second year； and the biomass at the fourth year increased over 3 200 g compared with the third year. The increase of the trunk biomass was far higher than those of the leaf， branch and root organs， which is beneficial to the purpose of operation. Organ biomass and total biomass
At the age of 1 year， the biomass of leaf， branch， trunk and root organs accounted for 17.90%， 15.16%， 47.36% and 23.17% of the total biomass， respectively； at the age of 2 years， the biomass of the various organs accounted for 15. 22%， 22.49%， 44.28% and 18.01% of the total biomass， respectively； at the age of 3 years， the biomass of the various organs accounted for 11.61%， 14.89%， 60.00% and 13.50% of the total biomass， respectively； and at the age of 4 years， the biomass of the various organs accounted for 11.61%， 14.89%， 60.00% and 15.50% of the total biomass， respectively （Table 1）. The proportions of the leaf， branch and root biomass exhibited a decreasing trend overall with the age increasing， while the proportion of the trunk biomass showed an increasing trend with the age increasing[1-5]， which is in line with the purpose of operation.
Content， distribution and accumulation of nutrient elements in organs of young A. cremastogyne trees
Content of nutrient elements
The nutrient contents in organs of A. cremastogyne ranked as N>Ca>K>Mg>P>Fe>Zn （Table 2）. In the various organs， the N contents were in order of leaf>branch>trunk>root； and the K and P contents ranked as leaf>branch>root>trunk； the Ca and Mg contents ranked as root>leaf>branch>trunk[3，5]； the contents of microelement Fe were in order of root>leaf>trunk>branch； and the contents of microelement Zn showed an order of branch>leaf>trunk>root. The overall trends were as follows： the elements N， P and K had higher contents in the leaf， the elements Ca， Mg and Fe showed higher contents in the root， and the contents of elements N， P， K， Ca， Mg， Fe and Zn were lower in the trunk.
Agricultural Biotechnology2018
Table 2 Nutrient element contents of organ of A. cremastogyne young stand forest
SampleN∥g/kgP∥g/kgK∥g/kgCa∥g/kgMg∥g/kgFe∥mg/kgZn∥mg/kg
Leaf25.241.498.2710.572.25205.9058.89
Branch12.240.804.219.591.5867.0668.56
Trunk10.410.453.808.301.2079.0146.76
Root10.180.644.4810.962.721 983.0041.81
Distribution of nutrient elements
At the tree age of 1 year， the average accumulations of nutrient elements N， P， K， Ca and Mg in plant organs ranked as trunk>leaf>root>branch （Table 3）； and at the tree ages of 2， 3 and 4 years， the average accumulations of nutrient elements were in order of trunk>leaf>branch>root. The accumulations of nutrient elements were the highest in the trunk， indicating that nutrient elements mainly concentrate in the trunk and leaf parts. At the age of 1 year， the accumulations of microelement Fe in the various organs of A. cremastogyne ranked as root>leaf>trunk>branch； and at the ages of 2， 3 and 4 years， the accumulations of microelement Fe in the various organs were in order of root>trunk>leaf>branch， indicating that Fe is mainly accumulated in the root. At the age of 1 year， the accumulations of Zn in the various organs ranked as trunk>leaf>branch>root； and at the ages of 2， 3 and 4 years， the accumulations of Zn in the various organs were in order of trunk>branch>leaf>root， indicating that Zn is mainly accumulated in the trunk. Table 3 Nutrient element distributions and accumulations in organ of average tree
Accumulations of nutrient elements
Accumulation of N element： At the age of 1-4 years， in the average tree of A. cremastogyne， the N accumulation accounted for 44.05%， 40.38%， 43.89% and 44.03% of the total accumulation of N， P， K， Ca and Mg， respectively， indicating that the growth of young A. cremastogyne trees requires N the most.
Accumulation of P element： At the age of 1-4 years， the P accumulation in average tree accounted for 2.4%， 2.26%， 2.3% and 1.98% of the total accumulation of the various elements， respectively， indicating that the growth of young A. cremastogyne trees requires little P.
Accumulation of K element： At the age of 1-4 years， in the average tree of A. cremastogyne， the K accumulation accounted for 15.99%， 21.29%， 15.86% and 16.08% of the total accumulation of the various elements， respectively， indicating that young A. cremastogyne trees have a higher demand for K.
Accumulation of Ca： At the age of 1-4 years， in the average tree of A. cremastogyne， the Ca accumulation accounted for 31.52%， 29.78%， 32.33% and 32.44% of the total accumulation of macroelements， indicating that the growth of young A. cremastogyne trees requires more Ca， only second to N.
Accumulation of Mg element： At the age of 1-4 years， in the average tree of A. cremastogyne， the Mg accumulation accounted for 6.03%， 5.44% ， 5.61% and 5.63% of the total accumulation of macroelements， indicating that young A. cremastogyne trees have little demand for Mg， slightly higher than P.
Accumulation of microelement Fe： At the age of 1-4 years， in the average tree of A. cremastogyne， the Fe accumulation accounted for 91.37%， 89.28 %， 87.31 % and 88.30 % of the total accumulation of Fe and Zn， respectively， indicating the demand for Fe element is high.
Accumulation of microelement Zn： At the age of 1-4 years， in the average tree of A. cremastogyne， the Zn accumulation accounted for 8.62%， 10.71%， 12.69% and 12.69% of the total accumulation of Fe and Zn， respectively， indicating that the demand for Zn is lower.
To sum up， in the average tree， the order of the accumulations of different nutrient elements was not affected by tree age， and was N>Ca>K>Mg>P>Fe>Zn.
In the average tree of A. cremastogyne at the age of 1-4 years， the total accumulation of nutrient elements N， P， K， Ca and Mg increased in multiples with the tree age increasing. The nutrient accumulations in the average trees at the ages of 2， 3 and 4 years were 3.4， 9 and 15.2 times of that in the average tree at the age of 1 year. The total accumulations of microelements Fe and Zn in the average trees at the ages of 2， 3 and 4 years were 2.7， 6.5 and 11 times of that in the average tree at the age of 1 year. It could be seen that with the tree age increasing， the tree biomass increased， and the forest stand absorbed more nutrients from forest land. In practice production， necessary nutritive fertilizer should be supplied to the land， to ensure the normal growth of plants and prevent land fertility declining. The specific fertilizing rate could be determined according to the demands of A. cremastogyne at various ages for nutrients and soil fertility. Net accumulations of nutrient elements
For the trees at the age of 1 year， the annual net accumulation of nutrients was the same as the accumulation， i.e.， 17.07 g， and the annual net accumulations of N， P， K， Ca and Mg were 7.52， 0.41， 2.73， 5.38 and 1.03 g， respectively. The annual net accumulation of microelements （Fe and Zn） in the very year was 335.04 mg， and the annual net accumulations of Fe and Zn were 306.14 and 28.9 mg， respectively （Fig. 1）.
Fig. 1 Annual net accumulations of nutrient elements in average tree
As to the trees at the age of 2 years， the annual net accumulation of nutrients in the very year was 41.20 g， which was 70.95% of the accumulation， and the annual net accumulations of N， P， K， Ca and Mg were， respectively， 16.21， 0.92， 9.78， 12.12 and 2.17 g， which were 39.34%， 2.23%， 23.74%， 29.42% and 5.27% of the annual net accumulation of nutrients in the very year， respectively. The annual net accumulation of microelements （Fe and Zn） was 577.26 mg， and the annual net accumulations of Fe and Zn were， respectively， 508.41 and 68.85 mg， which were 88.07% and 11.93% of annual net accumulation of microelements in the very year， respectively.
At the tree age of 3 years， the annual net accumulation of nutrients in the very year was 95.41 g， which was 61.76% of their accumulation， and the annual net accumulations of N， P， K， Ca and Mg were， respectively， 43.72， 2.21， 11.87， 32.19 and 5.42 g， which were 45.82%， 2.32%， 12.44%， 33.74% and 5.68% of the annual net accumulation of nutrients in the very year， respectively. The annual net accumulation of microelements （Fe and Zn） was 1 267 mg， and the annual net accumulations of Fe and Zn were， respectively， 1 088.11 and 178.89 mg， which were 85.88% and 14.12% of annual net accumulation of microelements in the very year， respectively.
For the trees at the age of 4 years， the annual net accumulation of nutrients in the very year was 107.13 g， which was 40.98% of the accumulation of nutrients， and the annual net accumulations of N， P， K， Ca and Mg were， respectively， 47.21， 1.62， 17.48， 34.77 and 6.05 g， which were 44.07%， 1.51%， 16.32%， 32.46% and 5.65% of the annual net accumulation of nutrients in the very year， respectively. The annual net accumulation of microelements （Fe and Zn） was 1 525.27 mg， and the annual net accumulations of Fe and Zn were， respectively， 1 331.64 and 193.63 mg， which were 87.31% and 12.69% of annual net accumulation of microelements in the very year， respectively. In the young stand of A. cremastogyne at the age of 1-4 years， the annual net accumulation of N was the highest， followed by Ca and K， Mg element had a lower value， and P showed the lowest annual net accumulation； and the annual net accumulation of microelement Fe was 6-10 times higher than that of Zn. This is in line with the law of the accumulations of nutrient elements in average tree， indicating that A. cremastogyne at the age of 1-4 years has higher demands for N， Ca and K elements， which increase the most at the age of 2 years. In practice production， combining with soil nutrient supply， the matched application of N， P and K nutrient fertilizers is a key consideration， and Ca and Mg elements could be supplemented through the application of P fertilizer （such as superphosphate， containing abundant Ca and Mg）.
Conclusions
For A. cremastogyne at the age of 1-4 years， the biomass of average tree and the biomass of leaf， branch， trunk and root organs were in positive correlation with age， and the growth rate of biomass exhibited a decreasing trend with the age increasing. Among the biomass composition of various organs， only the proportion of the biomass of trunk was on the increase with the age increasing. In the organs of A. cremastogyne， the contents of nutrients ranked as N>Ca>K>Mg>P>Fe>Zn； and N， P and K elements had higher contents in the leaf， and Ca， Mg and Fe elements showed higher contents in the root. The accumulations of N， P， K， Ca， Mg and Zn elements were the highest in the trunk， and the accumulation of Fe was the highest in the root. The A. cremastogyne trees at the ages from 1 to 4 years showed the annual net accumulations of nutrients （ N， P， K， Ca and Mg） in the very year were 17.07， 40.79， 95.82 and 106.71 g/plant， respectively， and the annual net accumulations of microelements of （Fe and Zn） were 335.04， 577.26， 1 267 and 1 525.27 mg/plant， respectively.
References
[1] LIU XC， WEN SZ， FENG HH， et al. Study on biomass of artificial forest of Alnus cremastogyne at different ages in Sichuan Province[J]. Journal of Central South University of Forestry & Technology， 2007， 27（2）： 83-86.
[2] FU H， CHEN AG. Accumulation of aboveground biomass and nutrients in swidden fallows： A comparison between planted alder fallows and unmanaged grassy fallows in Yunnan[J]. Acta Ecologica Sinica， 2004， 24（2）：209-214.
[3] GUO TF， FENG HH， XU QH. The accumulation and distribution of nutrients of artificial Alnus cremastogyne forests[J]. Journal of Sichuan Forestry Science and Technology， 2009， 30（4）： 89-91. [4] WANG YH， LONG LM， ZHANG HC， et al. Mineral nutrient characteristics of red alder[J]. Jiangsu Agricultural Sciences， 2013， 41（10）： 137-138， 142.
[5] ZHU WZ， XUE JH， WANG JX， et al. Studies on the stand biomass and the distribution of nutrients of Alnus formosana plantation[J]. Journal of Nanjing Forestry University： Natural Science Edition， 2002， 26（2）： 15-20.
[6] XIE XJ， ZHANG J， FENG MS. Accumulation and distribution of major nutrient elements in Eucalyptus grandis stand[J]. Journal of Sichuan Forestry Science and Technology， 2005， 26（2）： 1-6.
[7] DONG ZY. Laboratory technical manual engineer[M]. Beijing： China Forestry Publishing House， 1995.
[8] ZHANG WR， YANG GY， TU XN， et al. LY/T 12701999 Determination of total nitrogen， phosphorus， potassium， sodium， calcium， magnesium， iron， zinc， manganese， copper and sulphur in forest plant and forest floor[S]. Beijing： China Standards Press， 1999.
[9] LI CW， LIAN ZH. Agrochemical study method[M]. Beijing： Agriculture Press， 1980： 5-12， 179-184.
Key words Alnus cremastogyne； Forest stands at different ages； Demands for nutrient elements； Biomass； Nutrient elements
Received： August 23， 2017 Accepted： December 8， 2017
Supported by Project of Science and Technology Department in Sichuan Province（2016NZ0043）.
Anmin MIN （1963-）， male， P. R. China， researcher， devoted to soil fertility， plant nutrition and fertilizer application.
*Corresponding author. Email： [email protected]
Alnus cremastogyne is a plant in Alnus of Betuleae in Betulaceae family， also known as Shuidonggua tree， which is a kind of lofty deciduous leaf arbor， native to Sichuan Basin. It is only grow in China， and is one of the important fastgrowing indigenous tree species in Sichuan Province. A. cremastogyne grows fast， and propagates easily， with developed root system attached with root nodules. The tree is tolerant to water， with short leaf fall period， and has a high nitrogen content in leaves. It is thus a fastgrowing commercial tree species in the southwest region of China， a good tree species for dyke strengthening， conservation of water and soil， soil improvement and forestation， as well as an ideal associated species for China fir， pine and cypress. The tree could be used as fuel wood and industrial raw material， and could be used for soil fertility. A. cremastogyne has good texture in color of reddish brown， without remarkable difference between heartwood and sapwood. The timber has proper hardness and straight texture from top to bottom， and could serve as a material for the artificial board， papermaking， musical instrument and furniture. After a long term of development， A. cremastogyne has become a main tree species for fastgrowing and highyield plantation in South China， as well as an important tree species for pulpwood and fiber timber.
Directive breeding of A. cremastogyne as a smalldiameter and shortcycle industrial raw material could effectively alleviate the pressure of increasing demand for raw material in artificial board and wood pulp industries. Fertilization on young A. cremastogyne stand is one of the key measures for improving yield and realizing anticipated breeding targets. Therefore， the research about the biomass and distribution and accumulation of nutrient elements in organs of young A. cremastogyne plants could guide rational fertilization on young stand of A. cremastogyne in production.
At present， there have been reports about the biomass and nutrient distribution and accumulation of A. cremastogyne at certain ages[1-5]， but there were very few studies about the biomass， nutrient distribution and accumulation and demand for nutrients in young trees of A. cremastogyne at different ages. In this study， the biomass and nutrients in young A. cremastogyne plants at the age of 1-4 years were determined， and the distribution and accumulation characteristics of nutrients in A. cremastogyne organs were analyzed， so as to quantify the demands of young A. cremastogyne plants for nutrients. This study will provide a scientific basis for the fertilization management of young stands of A. cremastogyne， so as to realize the purpose of sustainable utilization of forest land through the improvement of yield， shortening of the cycle of rotation felling and prevention of land fertility declining[6].
Materials and Methods
Experimental materials
The young stands of A. cremastogyne at the age of 1-4 years were selected. The investigated forest is located in Xuzhou Town， Shuangban Township and Xianfeng Township in Zitong County， Mianyang City， Sichuan Province （104°57′-105°28′ east longitude， 31°25′-31°52′ North latitude）， with an altitude of 520-650 m， and Fubao State Forest Farm located in Hejiang County， Luzhou City， Sichuan Province （105°32′-106°28′ east longitude， 28°27′-29°01′ North latitude）， with an altitude of 920-1 100 m. Methods
Selection of investigation field： The young stands of A. cremastogyne at the age of 1-4 years with the same site conditions （soil type， thickness， slope， exposure and altitude） and operating management were selected as the investigation objects. The forestation was carried out according to a spacing of 2 m × 2 m at a density of 166 plants/667 m2.
Investigation method： For each age， three sample plots （20 m × 20 m） were selected， and according to conventional method， field individual measurement （tree height or diameter at breast height （DBH）） was performed， for the calculation of average tree height and average DBH. In each sample plot， 1 plant with a tree height or DBH within 95%-105% of the average data was selected as average tree[7]， and 12 average trees were selected in total.
After the actual measurement of DBH or tree height and crown breadth， the average trees growing normally were hewed down and cut， for the determination of the fresh weights of various organs （leaf， branch and trunk） of the aboveground part and the root as the underground part， and mean values were obtained according to tree age and organs.
Sample collection： On the basis of the biomass investigation of young stands of A. cremastogyne， leaf， trunk， branch and root samples were collected from sample trees. The samples of the same organ from the trees at the same age were mixed well， and 100-200 g of the mixed sample of each organ of the trees at each age were sampled for the determination of moisture. The samples of the same organ from the trees at different ages were mixed well， and 400-500 g of the mixed sample of each organ of the trees at the age of 1-4 years were sampled， for the determination of nutrient contents in organs. The collected samples should be transported to laboratory for treatment and determination.
Determination items of samples： The determined items included moisture， N， P， K， Ca， Fe and Zn.
Sample determination methods： Moisture was determined by drying method； N was determined by Kjeldahl method； for P， the samples were digested with HNO3HClO4 and determined by MoSb antispectrophotography method； and for K、Ca， Mg， Fe and Zn， the samples were digested with HNO3HClO4 and determined by atomic absorption spectrometry （LY/T 12701999）. The determination was designed with two parallel samples， and the absolute deviation and relative error should satisfy the requirements stipulated by industrial standard[8]. Data analysis
Statistic analysis of data adopted analysis of variance [9].
Results and Analysis
Tree height， DBH and biomass of A. cremastogyne
Tree height， DBH and tree age
For young stands of A. cremastogyne at the age of 1-4 years， tree height and DBH increased year by year （Table 1）. The trees at the age of 2 years showed a tree height increased by 77.78% compared with those at the age of 1 year； the trees at the age of 3 years had a tree height increased by 59.38% compared with those at the age of 2 years； and the trees at the age of 4 years exhibited a tree height increased by 21.57% compared with those at the age of 3 years. As to DBH， the trees at the age of 2 years exhibited a DBH increased by 136.36% compared with those at the age of 1 year； the trees at the age of 3 years had a DBH increased by 80.77% compared with those at the age of 2 years； and the trees at the age of 4 years exhibited a DBH increased by 36.17% compared with those at the age of 3 years. The growth rates of the two parameters decreased year by year. Variance analysis showed that there were very significant differences in tree height and DBH between trees at the various ages.
Table 1 Height， DBH and biomass composition and their differences of A. cremastogyne young average tree
Tree age∥aDBH∥cmTree height∥m
Biomass composition∥g
LeafBranchTrunkRootSum∥g
11.1±0.131.80±0.20101.3±11.4285.8±9.68247.6±27.96131.1±14.76565.8
22.6**±0.213.2**±0.26282.7**±22.62417.9**±33.47822.7*±65.89334.5**±26.781 857.8
34.7**±0.455.1**±0.48632.9**±60.13811.8**±77.153 270.8**±310.71736.0**±69.925 451.5
46.4**±0.526.2**±0.501 075.9**±87.111 380.1**±111.815 560**±450.281 251.1**±101.319 267.1
* indicates significant difference at 5% level； and ** indicates very significant difference at 1% level.
Biomass and tree age
At the age of 1-4 years， the average biomass of A. cremastogyne was in positive correlation with its age （Table 1）. The biomass at the second year was 2.28 times higher than that at the first year； the biomass at the third year was 1.93 times higher than that at the second year； and the biomass at the fourth year was 0.7 time higher than that at the third year. The relationship between biomass and tree age was the same as those of tree height and DBH， and the growth rate decreased year by year.
Organ biomass and tree age
For young stands of A. cremastogyne， the relationship between biomass of each of leaf， branch， trunk and root organs and tree age and the changing trends of the various organs accorded with the biomass of whole plant （Table 1）. The analysis of differences in the biomass of leaf， branch， trunk and root organs between various ages showed that except the significant difference in the trunk biomass between the twoyearold and oneyearold trees， the differences in the biomass of the various organs were very significant between trees at other ages. At this growth stage， there were also great differences between the biomass of the various organs. The absolute increases of the biomass of leaf， branch and root organs by years showed no big differences. For the three organs， the biomass at the second year increased by 180-330 g compared with that at the first year； the biomass at the third year increased by 350-400 g compared with that at the second year； and the biomass at the fourth year increased by 370-520 g than that at the third year. However， as to the trunk， the biomass at the second year increased by about 400 g compared with the first year； the biomass at the third year increased over 2 400 g compared with the second year； and the biomass at the fourth year increased over 3 200 g compared with the third year. The increase of the trunk biomass was far higher than those of the leaf， branch and root organs， which is beneficial to the purpose of operation. Organ biomass and total biomass
At the age of 1 year， the biomass of leaf， branch， trunk and root organs accounted for 17.90%， 15.16%， 47.36% and 23.17% of the total biomass， respectively； at the age of 2 years， the biomass of the various organs accounted for 15. 22%， 22.49%， 44.28% and 18.01% of the total biomass， respectively； at the age of 3 years， the biomass of the various organs accounted for 11.61%， 14.89%， 60.00% and 13.50% of the total biomass， respectively； and at the age of 4 years， the biomass of the various organs accounted for 11.61%， 14.89%， 60.00% and 15.50% of the total biomass， respectively （Table 1）. The proportions of the leaf， branch and root biomass exhibited a decreasing trend overall with the age increasing， while the proportion of the trunk biomass showed an increasing trend with the age increasing[1-5]， which is in line with the purpose of operation.
Content， distribution and accumulation of nutrient elements in organs of young A. cremastogyne trees
Content of nutrient elements
The nutrient contents in organs of A. cremastogyne ranked as N>Ca>K>Mg>P>Fe>Zn （Table 2）. In the various organs， the N contents were in order of leaf>branch>trunk>root； and the K and P contents ranked as leaf>branch>root>trunk； the Ca and Mg contents ranked as root>leaf>branch>trunk[3，5]； the contents of microelement Fe were in order of root>leaf>trunk>branch； and the contents of microelement Zn showed an order of branch>leaf>trunk>root. The overall trends were as follows： the elements N， P and K had higher contents in the leaf， the elements Ca， Mg and Fe showed higher contents in the root， and the contents of elements N， P， K， Ca， Mg， Fe and Zn were lower in the trunk.
Agricultural Biotechnology2018
Table 2 Nutrient element contents of organ of A. cremastogyne young stand forest
SampleN∥g/kgP∥g/kgK∥g/kgCa∥g/kgMg∥g/kgFe∥mg/kgZn∥mg/kg
Leaf25.241.498.2710.572.25205.9058.89
Branch12.240.804.219.591.5867.0668.56
Trunk10.410.453.808.301.2079.0146.76
Root10.180.644.4810.962.721 983.0041.81
Distribution of nutrient elements
At the tree age of 1 year， the average accumulations of nutrient elements N， P， K， Ca and Mg in plant organs ranked as trunk>leaf>root>branch （Table 3）； and at the tree ages of 2， 3 and 4 years， the average accumulations of nutrient elements were in order of trunk>leaf>branch>root. The accumulations of nutrient elements were the highest in the trunk， indicating that nutrient elements mainly concentrate in the trunk and leaf parts. At the age of 1 year， the accumulations of microelement Fe in the various organs of A. cremastogyne ranked as root>leaf>trunk>branch； and at the ages of 2， 3 and 4 years， the accumulations of microelement Fe in the various organs were in order of root>trunk>leaf>branch， indicating that Fe is mainly accumulated in the root. At the age of 1 year， the accumulations of Zn in the various organs ranked as trunk>leaf>branch>root； and at the ages of 2， 3 and 4 years， the accumulations of Zn in the various organs were in order of trunk>branch>leaf>root， indicating that Zn is mainly accumulated in the trunk. Table 3 Nutrient element distributions and accumulations in organ of average tree
Accumulations of nutrient elements
Accumulation of N element： At the age of 1-4 years， in the average tree of A. cremastogyne， the N accumulation accounted for 44.05%， 40.38%， 43.89% and 44.03% of the total accumulation of N， P， K， Ca and Mg， respectively， indicating that the growth of young A. cremastogyne trees requires N the most.
Accumulation of P element： At the age of 1-4 years， the P accumulation in average tree accounted for 2.4%， 2.26%， 2.3% and 1.98% of the total accumulation of the various elements， respectively， indicating that the growth of young A. cremastogyne trees requires little P.
Accumulation of K element： At the age of 1-4 years， in the average tree of A. cremastogyne， the K accumulation accounted for 15.99%， 21.29%， 15.86% and 16.08% of the total accumulation of the various elements， respectively， indicating that young A. cremastogyne trees have a higher demand for K.
Accumulation of Ca： At the age of 1-4 years， in the average tree of A. cremastogyne， the Ca accumulation accounted for 31.52%， 29.78%， 32.33% and 32.44% of the total accumulation of macroelements， indicating that the growth of young A. cremastogyne trees requires more Ca， only second to N.
Accumulation of Mg element： At the age of 1-4 years， in the average tree of A. cremastogyne， the Mg accumulation accounted for 6.03%， 5.44% ， 5.61% and 5.63% of the total accumulation of macroelements， indicating that young A. cremastogyne trees have little demand for Mg， slightly higher than P.
Accumulation of microelement Fe： At the age of 1-4 years， in the average tree of A. cremastogyne， the Fe accumulation accounted for 91.37%， 89.28 %， 87.31 % and 88.30 % of the total accumulation of Fe and Zn， respectively， indicating the demand for Fe element is high.
Accumulation of microelement Zn： At the age of 1-4 years， in the average tree of A. cremastogyne， the Zn accumulation accounted for 8.62%， 10.71%， 12.69% and 12.69% of the total accumulation of Fe and Zn， respectively， indicating that the demand for Zn is lower.
To sum up， in the average tree， the order of the accumulations of different nutrient elements was not affected by tree age， and was N>Ca>K>Mg>P>Fe>Zn.
In the average tree of A. cremastogyne at the age of 1-4 years， the total accumulation of nutrient elements N， P， K， Ca and Mg increased in multiples with the tree age increasing. The nutrient accumulations in the average trees at the ages of 2， 3 and 4 years were 3.4， 9 and 15.2 times of that in the average tree at the age of 1 year. The total accumulations of microelements Fe and Zn in the average trees at the ages of 2， 3 and 4 years were 2.7， 6.5 and 11 times of that in the average tree at the age of 1 year. It could be seen that with the tree age increasing， the tree biomass increased， and the forest stand absorbed more nutrients from forest land. In practice production， necessary nutritive fertilizer should be supplied to the land， to ensure the normal growth of plants and prevent land fertility declining. The specific fertilizing rate could be determined according to the demands of A. cremastogyne at various ages for nutrients and soil fertility. Net accumulations of nutrient elements
For the trees at the age of 1 year， the annual net accumulation of nutrients was the same as the accumulation， i.e.， 17.07 g， and the annual net accumulations of N， P， K， Ca and Mg were 7.52， 0.41， 2.73， 5.38 and 1.03 g， respectively. The annual net accumulation of microelements （Fe and Zn） in the very year was 335.04 mg， and the annual net accumulations of Fe and Zn were 306.14 and 28.9 mg， respectively （Fig. 1）.
Fig. 1 Annual net accumulations of nutrient elements in average tree
As to the trees at the age of 2 years， the annual net accumulation of nutrients in the very year was 41.20 g， which was 70.95% of the accumulation， and the annual net accumulations of N， P， K， Ca and Mg were， respectively， 16.21， 0.92， 9.78， 12.12 and 2.17 g， which were 39.34%， 2.23%， 23.74%， 29.42% and 5.27% of the annual net accumulation of nutrients in the very year， respectively. The annual net accumulation of microelements （Fe and Zn） was 577.26 mg， and the annual net accumulations of Fe and Zn were， respectively， 508.41 and 68.85 mg， which were 88.07% and 11.93% of annual net accumulation of microelements in the very year， respectively.
At the tree age of 3 years， the annual net accumulation of nutrients in the very year was 95.41 g， which was 61.76% of their accumulation， and the annual net accumulations of N， P， K， Ca and Mg were， respectively， 43.72， 2.21， 11.87， 32.19 and 5.42 g， which were 45.82%， 2.32%， 12.44%， 33.74% and 5.68% of the annual net accumulation of nutrients in the very year， respectively. The annual net accumulation of microelements （Fe and Zn） was 1 267 mg， and the annual net accumulations of Fe and Zn were， respectively， 1 088.11 and 178.89 mg， which were 85.88% and 14.12% of annual net accumulation of microelements in the very year， respectively.
For the trees at the age of 4 years， the annual net accumulation of nutrients in the very year was 107.13 g， which was 40.98% of the accumulation of nutrients， and the annual net accumulations of N， P， K， Ca and Mg were， respectively， 47.21， 1.62， 17.48， 34.77 and 6.05 g， which were 44.07%， 1.51%， 16.32%， 32.46% and 5.65% of the annual net accumulation of nutrients in the very year， respectively. The annual net accumulation of microelements （Fe and Zn） was 1 525.27 mg， and the annual net accumulations of Fe and Zn were， respectively， 1 331.64 and 193.63 mg， which were 87.31% and 12.69% of annual net accumulation of microelements in the very year， respectively. In the young stand of A. cremastogyne at the age of 1-4 years， the annual net accumulation of N was the highest， followed by Ca and K， Mg element had a lower value， and P showed the lowest annual net accumulation； and the annual net accumulation of microelement Fe was 6-10 times higher than that of Zn. This is in line with the law of the accumulations of nutrient elements in average tree， indicating that A. cremastogyne at the age of 1-4 years has higher demands for N， Ca and K elements， which increase the most at the age of 2 years. In practice production， combining with soil nutrient supply， the matched application of N， P and K nutrient fertilizers is a key consideration， and Ca and Mg elements could be supplemented through the application of P fertilizer （such as superphosphate， containing abundant Ca and Mg）.
Conclusions
For A. cremastogyne at the age of 1-4 years， the biomass of average tree and the biomass of leaf， branch， trunk and root organs were in positive correlation with age， and the growth rate of biomass exhibited a decreasing trend with the age increasing. Among the biomass composition of various organs， only the proportion of the biomass of trunk was on the increase with the age increasing. In the organs of A. cremastogyne， the contents of nutrients ranked as N>Ca>K>Mg>P>Fe>Zn； and N， P and K elements had higher contents in the leaf， and Ca， Mg and Fe elements showed higher contents in the root. The accumulations of N， P， K， Ca， Mg and Zn elements were the highest in the trunk， and the accumulation of Fe was the highest in the root. The A. cremastogyne trees at the ages from 1 to 4 years showed the annual net accumulations of nutrients （ N， P， K， Ca and Mg） in the very year were 17.07， 40.79， 95.82 and 106.71 g/plant， respectively， and the annual net accumulations of microelements of （Fe and Zn） were 335.04， 577.26， 1 267 and 1 525.27 mg/plant， respectively.
References
[1] LIU XC， WEN SZ， FENG HH， et al. Study on biomass of artificial forest of Alnus cremastogyne at different ages in Sichuan Province[J]. Journal of Central South University of Forestry & Technology， 2007， 27（2）： 83-86.
[2] FU H， CHEN AG. Accumulation of aboveground biomass and nutrients in swidden fallows： A comparison between planted alder fallows and unmanaged grassy fallows in Yunnan[J]. Acta Ecologica Sinica， 2004， 24（2）：209-214.
[3] GUO TF， FENG HH， XU QH. The accumulation and distribution of nutrients of artificial Alnus cremastogyne forests[J]. Journal of Sichuan Forestry Science and Technology， 2009， 30（4）： 89-91. [4] WANG YH， LONG LM， ZHANG HC， et al. Mineral nutrient characteristics of red alder[J]. Jiangsu Agricultural Sciences， 2013， 41（10）： 137-138， 142.
[5] ZHU WZ， XUE JH， WANG JX， et al. Studies on the stand biomass and the distribution of nutrients of Alnus formosana plantation[J]. Journal of Nanjing Forestry University： Natural Science Edition， 2002， 26（2）： 15-20.
[6] XIE XJ， ZHANG J， FENG MS. Accumulation and distribution of major nutrient elements in Eucalyptus grandis stand[J]. Journal of Sichuan Forestry Science and Technology， 2005， 26（2）： 1-6.
[7] DONG ZY. Laboratory technical manual engineer[M]. Beijing： China Forestry Publishing House， 1995.
[8] ZHANG WR， YANG GY， TU XN， et al. LY/T 12701999 Determination of total nitrogen， phosphorus， potassium， sodium， calcium， magnesium， iron， zinc， manganese， copper and sulphur in forest plant and forest floor[S]. Beijing： China Standards Press， 1999.
[9] LI CW， LIAN ZH. Agrochemical study method[M]. Beijing： Agriculture Press， 1980： 5-12， 179-184.