亚热带森林土壤矿物结合态氮动态变化及影响因素研究

Litter input by the quality and quantity plays an important role in forest soil nitrogen formation, stability and transformation. However, the soil organic nitrogen is not uniform nitrogen pool, the relation between mineral-associated nitrogen and large differences in mineralization of them was found. Therefore, it is of great significance to study the dynamics of mineral-associated nitrogen to understand the nitrogen cycle deeply. In order to investigate the dynamics of mineral-associated nitrogen and the mechanism in the process of litter decomposition and soil organic nitrogen mineralization in forest ecosystem. The project was carried out in natural broad-leaved forest and coniferous forest, using the method of field experiments and indoor cultivation, physical and chemical fractionation, analyzing litter and soil nitrogen characteristics, mineral elements, biological metabolites and microbial community structure. Therefore, the effects of litter decomposition on soil mineral-associated content, transformation and mineralization was investigated. The deep information of the mechanism in the effect of litter decomposition in different stages on soil mineral-associated nitrogen, the difference in organic nitrogen mineralization and relationship among different mineral-associated nitrogen pools were explored. In addition, the effects of the moisture, carbon and nutrients on mineral-associated nitrogen was paid close attention, which could explained by the role of microbial in utilize the carbon and nitrogen, and metabolic matter. The implementation of this project will strengthen the study of soil organic nitrogen in forest soil, and provide a theoretical basis for understanding the process and mechanism of soil nitrogen cycle, improve nitrogen saturation and retention theoretical research.

凋落物的不断输入对森林土壤氮的形成、稳定和转化发挥着重要的作用，为了探究森林生态系统凋落物分解和土壤有机氮矿化过程中，矿物结合态氮的动态变化及影响机理。本项目选择天然林阔叶和人工针叶林，采用野外试验和室内培养的方法，利用物理化学分组、分析土壤和凋落物氮特性、矿物元素组成、生物代谢产物和群落结构。研究凋落物分解对土壤矿物结合态氮含量、相互转化、矿化的影响。揭示凋落物分解不同阶段对土壤矿物结合态氮的影响，矿物结合态有机氮矿化的差异和相互关系，从水分、碳和养分的角度探究影响机理，从微生物的选择利用和代谢的角度深入探究其原因。本项目的实施将加强森林土壤有机氮研究，为深入理解土壤氮循环过程和机理，完善氮饱和、保持理论研究提供理论依据。

凋落物的不断输入对森林土壤氮的形成、稳定和转化发挥着重要的作用，我们对森林生态系统凋落物分解阶段性差异、矿物结合态氮的动态变化、以及凋落物的影响进行了研究。研究发现，去除凋落物确实降低了土壤碳氮含量，且主要表现在>250 μm土壤组分；在去除凋落物情况下，与对照比较，低氮和高氮沉降分别降低杉木林土壤全碳氮，主要表现在活性碳氮组分，且降低幅度与氮沉降水平有关。杉木林的响应比阔叶林大，不同土壤组分水解碳氮和矿化碳氮的响应存在差异。培养实验显示，针叶林凋落物释放的可溶性碳比阔叶林更容易淋失，主要发生凋落物分解的早期，而氮添加影响早期的DOC，而影响后期的NO3--N。葡萄糖对阔叶林全土和250-2000 μm组分DON矿化的促进作用大于针叶林，有机氮添加促进全土净氨化、全土和大颗粒组分净硝化。无机氮促进20-53 μm和<2 μm组分惰性氮的矿化，DOC在小粒径中矿化得较多，DON在大颗粒组分中矿化得较多。全土净氨化速率的变化主要源自20-53 μm和<2 μm组分的增加，及250-2000 μm组分的降低，而净硝化速率相反。结果表明土壤组分差异确实可以反映全土变化。生物因素对不同粒径土壤组分碳氮矿化的影响作用较大，酶活性与微生物群落结构的差异反映了这些组分中碳氮含量及循环的差异。影响< 2μm组分、2-20μm和20-53μm组分、< 53μm组分、53-250μm组分、250-2000μm组分、>2000μm组分、及全土壤碳氮矿化的关键因素分别是βG、真菌、MBC、AMF、MBC、LAP、MBN。同时，本研究虽然观察到了不同组分混合培养后碳氮矿化结果与单独培养的差异，显示了它们之间存在相互作用，表明了土壤响应外在环境变化波动或不确定性是与内在组分响应差异有关的，而分析土壤部分与整体的关系还存在极大的挑战。本项目为加强森林土壤有机碳氮研究，剖析土壤碳氮循环过程和机理，揭示土壤组分间关系和环境条件变化影响，提供理论依据。

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