杉木林植物源和微生物源土壤有机质对氮磷添加的响应

The effects of nitrogen deposition on soil organic carbon source-sink processes and carbon stability are related to the extent of nitrogen limitation. In phosphorus-limited area, a large uncertainty occurs about the ecological effects of nitrogen deposition. An important way to understand the response of soil carbon stability to global change is to study the ecological effect of phosphorus in company with nitrogen on soil carbon. Moreover, it is not clear of the responses of carbon stability to nitrogen and phosphorus additions due to the complex composition of soil organic matter. Therefore, the forms and pathways of plant- and microbial-derived soil organic matter transformed into stable soil carbon pool are the key processes to understand the regulating mechanism of soil carbon stability and the effects of nitrogen and phosphorus additions. The Chinese fir plantation, which is widely distributed in the subtropical zone and is affected by nitrogen deposition and phosphorus limitation, will be chose in the project. Based on the long-term nitrogen and phosphorus addition research platform, the wet chemical combined with gas chromatography-mass spectrometry method and amino sugar analysis method will be used to determine the content and composition of plant- and microbial-derived organic matter. Meanwhile, the dynamic of soil organic carbon will be estimated by indoor incubation and monitoring in suit. We will reveal the influencing mechanism of nitrogen and phosphorus on organic carbon stability in subtropical forest soils and elucidate the contribution of plant- and microbial-derived organic matter to soil carbon stability, as well as explore the ecological effects of nitrogen deposition on soil organic carbon under phosphorus-limited environment. Our results will deepen the understanding of the carbon cycling under the background of global change and provide scientific basis for promoting soil carbon storage of plantations in Southern China.

氮沉降对土壤有机碳“源-汇”过程及稳定性的影响与氮限制程度有关。在磷限制区，氮沉降效应存在很大不确定性，开展磷氮协同作用研究是理解土壤碳稳定性对全球变化响应的关键。土壤有机质成分的复杂性导致其对氮磷添加的响应特征还不明确，研究不同来源（植物和微生物）有机质进入稳定土壤碳库的形式和途径是剖析土壤碳稳定机制和理解氮磷协同调控机理的重要环节。选取亚热带区广泛分布且受氮沉降和磷限制双重作用的杉木林为对象，基于氮磷添加长期野外平台，采用湿化学结合气相色谱-质谱联用仪法和氨基糖分析法测定植物源/微生物源土壤有机质含量及组成，原位监测和室内培养评估土壤有机碳动态特征，揭示氮磷添加对亚热带森林土壤有机碳稳定性的影响机制，阐明植物源/微生物源有机质动态对土壤碳稳定性的贡献，探究亚热带区磷限制下氮沉降对土壤有机碳的生态效应，研究结果有助于加深对全球变化背景下碳循环的理解，为提升南方人工林固碳增汇功能提供依据。

土壤有机碳库的大小与其稳定性密切相关，而有机碳组成是影响其稳定性的首要因素。氮（N）沉降是影响森林土壤有机碳稳定性重要因子，同时亚热带森林常常受到磷（P）限制。当前，N、P协同对亚热带森林土壤有机碳组成及其稳定性的影响还未受到广泛关注。本项目以亚热带杉木（Cunninghamia lanceolata）林为对象，布设长期野外N、P添加试验，采集土壤进行密度和粒径分组，通过室内微宇宙培养和生物标志物方法，分析代表微生物源碳的氨基糖和表征植物源碳的木质素，及表征微生物和植物源碳的脂肪酸含量和组成变化，计算有机质降解程度，结合有机碳矿化、δ13C丰度、红外光谱和微生物群落分析等，重点从植物源和微生物源有机质角度，阐明N、P添加对土壤有机碳稳定性的调控机制。结果表明，仅N添加促进土壤有机碳矿化，而P添加抑制有机碳矿化，且抑制作用随N添加量增加而增强。P添加而不是N添加降低全土及颗粒组分（>53μm）木质素含量及其占有机碳的比值；同时，P添加增加了木质素香草基和丁香基的酸醛比，表明木质素降解程度增加，利于有机碳稳定，分析显示真菌担子菌门丰度增加是土壤木质素变化的驱动因子。N添加降低了全土δ13C值，P添加后轻组有机碳占比下降和δ13C值升高，表征N添加降低而P添加增加了土壤中稳定性碳组分。N、P添加增加了全土及重组总氨基糖含量，而P添加增加了其占有机碳的比值。N添加降低，而P添加增加基于脂肪酸分析的有机质降解程度。综合来看，N添加增加了土壤中新鲜有机质的输入，而P添加促进了有机质的降解，增加了土壤中微生物源有机碳的积累。在亚热带N沉降区，土壤P有效性增加有利于增强森林土壤有机碳稳定性。本研究阐明了N、P添加影响森林土壤有机碳稳定性的有机质质量驱动机制，为理解全球变化背景下森林土壤有机碳动态提供了理论依据。

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