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利用氮同位素自然丰度(δ15N)法研究了重庆青木关岩溶区不同植被类型下的土壤氮同位素分异特征及其影响因素。研究结果表明区内土壤1δ5N受不同的植被、地质和土地利用等影响而具有明显的横向和垂向分异特征,具体表现为:0—20 cm层土壤1δ5N与植物体1δ5N具有显著相关性,该层土壤1δ5N大小为草地土(4.79‰)>退耕还林土(4.77‰)>稻田土(4.28‰)>旱地土(4.25‰)>灌丛土(3.82‰)>针叶林土(3.81‰)>砂岩区针叶林土(3.40‰);20—40 cm层土壤δ15N大小为砂岩区针叶林土(5.21‰)>退耕还林土(5.10‰)>草地土(5.01‰)>稻田土(4.88‰)>灌丛土(4.70‰)>旱地土(4.55‰)>针叶林土(4.26‰);40 cm以下土壤1δ5N差异较小,灌丛最高,旱地最低。总体上,砂岩区林地土壤除表层贫化15N外,其余各层均富集15N,且分异较小。而岩溶区土壤δ15N具有明显的垂直变异特征,特别是灌丛林,表现为40 cm以上的土壤贫化15N,且变化较大,其中0—10 cm土壤δ15N受植物凋落物影响而较低,10—20 cm土壤δ15N受微生物作用影响稍显偏高,20—30 cm土壤δ15N随微生物活动减弱而有所降低;40 cm以下土壤矿化程度较大而富集15N,且变化较小。除受植被类型影响外,岩溶区土壤1δ5N还受其偏碱、富钙、高粘粒含量的物理化学特性以及农业施肥活动等因素共同影响。
The natural nitrogen isotope abundance (δ15N) method was used to study the variation of soil nitrogen isotope variability and its influencing factors under different vegetation types in Qingmuguan karst area of Chongqing. The results showed that 1δ5N in the soil had obvious lateral and vertical differentiation under the influence of different vegetation, geology and land use. The results showed that there was a significant correlation between 1δ5N in the 0-20 cm layer and 1δ5N in plant, The soil δ5N in this layer was 4.79 ‰> 4.77 ‰> paddy soil 4.28 ‰> dry soil 4.25 ‰> irrigated soil 3.82 ‰> coniferous forest soil 3.81 ‰)> coniferous forest soil (3.40 ‰) in sandstone area; δ15N in 20-40 cm layer was 5.21 ‰ in sandstone area> 5.10 ‰ soil grassland> 5.01 ‰> Paddy soil (4.88 ‰)> Irrigated soil (4.70 ‰)> Upland soil (4.55 ‰)> Coniferous forest soil (4.26 ‰); The difference of 1δ5N was less in the soil under 40 cm, highest in shrub and lowest in dry land. In general, all the soil layers in the woodland soil in sandstone area were enriched 15N except for the 15N surface depletion, with little difference. However, δ15N in the karst area had obvious vertical variation, especially in the shrubbery. The soil with 40 cm or more showed 15N, which varied greatly. Among them, δ15N in 0-10 cm soil layer was affected by plant litter, while 10 Δ15N in -20 cm soil layer was slightly higher than that in soil layer. Δ15N in 20-30 cm soil layer decreased with the decrease of microbial activity. Soil mineralization below 40 cm depth was larger and enriched in 15 N, with little change. In addition to the vegetation type, 1δ5N in karst soil is also affected by factors such as partial alkali, physicochemical characteristics of calcium-rich and high-clay content, and agricultural fertilization activities.