CO2浓度升高和氮沉降对树木光合碳向SOM关键组分转化的影响

Photosynthetic carbon is the main source of soil organic matter in forest ecosystems. Ascertaining the belowground input of tree photosynthetic carbon and its influence on the composition, function and gain-loss balance of soil organic matter is the key issue of assessing the source or sink of soil carbon pool in forest ecosystems. However, dynamical transformation and allocation of photosynthetic carbon to soil organic matter and its key fractions (e.g., amino acid, amino sugar, neutral sugars, and lignin) is still not clear. Furthermore, how CO2 elevation and nitrogen deposition affect the transformation and allocation of photosynthetic carbon is need to be explored. Thus, the project will address this key issue using 13C labeled method and Gas chromatography-combustion -isotope ratio mass spectrometry technique (GC-IRMS). In this experiment, seedlings of Chinese fir will be planted in the soils collected from long-term nitrogen deposition plots and grow under different 13CO2 concentrations. GC-IRMS technology is often used to distinguish the sources of new and old soil organic matter and its fractions. We will examine the allocation and enrichment of tree photosynthetic carbon to light and heavy fractions of soil organic matter and its key fractions through root deposition and their dynamics under 13CO2 concentrations and nitrogen deposition. This will elucidate the transformation characteristics of photosynthetic carbon to soil organic matter and its response to CO2 elevation and nitrogen deposition. We also examine the effect of CO2 elevation and nitrogen deposition on the allocation of soil organic carbon and its key fraction to light and heavy of soil organic matter. In the context of global change, findings from the project will reveal the process of soil organic matter transformation and cycle and the control mechanism, and also can provide basic data for assessing the carbon source/ sink of forest soils and predicting the future change.

植物光合碳是土壤有机质（SOM）的主要来源。在全球变化背景下，明确树木光合碳向地下部分的输入及其对SOM组成、功能及产-失平衡的影响是评价土壤碳库源汇功能的关键。然而，光合碳向SOM及关键组分（氨基酸、氨基糖、中性糖、木质素）的转化动态和分配特征仍不清楚，如何受CO2浓度升高和氮沉降的影响也亟待探讨。因此，本项目以杉木-土壤生态系统为研究对象，利用不同氮沉降处理的土壤和不同浓度的13CO2供给杉木生长，采用13C示踪和GC-IRMS技术区分SOM新老化合物，通过研究树木光合13C向土壤及其关键分子组分中的转化和富集动态，阐明光合碳向土壤有机碳库的转化特征及其对CO2浓度升高和氮沉降的响应；通过研究不同CO2浓度和氮沉降对SOM及其关键组分在轻组和重组有机质间分配动态的影响，揭示全球变化背景下森林SOM转化循环过程及调控机制，为科学评价森林土壤碳库的源汇功能、预测其未来变化奠定坚实的基础。

在氮沉降增加、CO2浓度持续升高等全球变化背景下，明确树木光合碳向地下部分的输入及其对土壤有机质的影响是评价土壤碳库源汇功能的关键。基于此，该项目利用开顶箱系统，结合13C技术，分析了氮沉降和CO2浓度升高背景下光合碳在杉木不同器官中的分配、植物和土壤有机质库中13C的变化，阐明了CO2浓度升高和氮沉降对光合碳在杉木-土壤系统中分配的影响；分析氨基糖、中性糖和木质素在土壤有机质库、轻组与重组有机质、不同团聚体中的分配与周转，阐明了光合碳向土壤有机质及关键分子组分的转化和分配特征，及其对CO2浓度升高和氮沉降的响应。.CO2浓度升高和N沉降均促进了杉木对大气CO2的吸收与固定。CO2浓度升高显著降低了杉木各器官中碳的δ13C值，而氮沉降改变了CO2浓度升高对光合产物分配的影响。植物光合固定的13C主要分配在植物体中，尤其是树干中，而分配到土壤有机质的相对较少，不足1.0%。氮沉降和CO2浓度升高显著增加了植物各器官新光合碳的含量。氮沉降显著增加土壤颗粒有机碳和矿物复合体有机碳中的13C含量。在CO2浓度升高和氮沉降背景下，杉木光合碳在土壤团聚体中的分配发生了变化。.植物光合碳主要分配在氨基葡萄糖和氨基半乳糖组分中。在土壤轻组有机质库中胞壁酸、氨基葡萄糖和氨基半乳糖所占的比例仅为5-15%，主要分布在重组有机质库。CO2浓度升高及其与氮沉降的耦合处理提高了氨基半乳糖在土壤轻组有机质库中的比例。氮沉降、CO2浓度升高在一定程度上影响了氨基糖在土壤不同粒径团聚体中的分配。在土壤中性糖组分中葡萄糖含量最高，占到了总量的37.0-41.8%，而核糖所占的比例最低，不足1.0%。氮沉降和CO2浓度升高对中性糖不同组分的影响存在差异。光合碳主要分配在细根木质素的肉桂基中，而在香草基型和丁香基型中的分配比例差异较小；氮沉降和CO2浓度升高对其影响不显著。.该项目在实施期间共发表论文9篇，其中SCI 论文8篇；申请专利授权2项。共参加国内外学术会议8人次，专题报告6人次；培养研究生4名。