高寒森林冬季雪被对微生物源土壤有机质积累的影响

Microbial residues are a significant source for accumulation of soil organic matter (SOM), but how the microbial-derived SOM accumulates in soils is largely unknown. In cold biomes, different depths and durations of snow cover may alter soil microbial activity and further modulate microbial-derived SOM accumulation, but our current understanding is very limited. Here, we hypothesize that winter snow cover modulates soil temperature and moisture, changes soil microbial biomass and community composition and further controls fungal and bacterial residues contributing to SOM accumulation. This project will be developed based on our previous findings that were conducted at the Long-term Research Station of Alpine Forest Ecosystems in an alpine forest on the eastern Tibetan Plateau with significant shifts in winter snow cover. Organic and mineral soils will be incubated in control, snow reduction and snow removal plots and will be sampled during snow formation, snow covering and snowmelt in wintertime as well as at early, middle and late periods during the subsequent growing season. Accumulation of fungi- and bacterial-derived amino sugars, fungi and bacterial community composition, microbial biomass and microbial respiration in organic and mineral soils will be measured with the methods of biomarker and phospholipid fatty acid by using gas chromatography-mass spectrometry. Environmental factors, such as soil temperature, moisture and freeze-thaw cycles will be also continually monitored. The objectives of this project are to tease out how microbial-derived SOM accumulates in soils and its links with soil microbial community composition and to shed light on the potential effect of winter snow cover on microbial-derived SOM and its links with the SOM accumulation during the subsequent growing season in this alpine forest. This experiment is designed to provide more strong evidence in enriching our current empirical understanding in SOM formation and its potential response to the changing climate.

微生物残体是土壤有机质积累的重要来源，然而不同雪被厚度和持续时间均可能改变微生物活性并影响微生物源土壤有机质积累过程。基于“冬季雪被调控土壤水热条件，改变土壤微生物生物量和微生物群落组成，进而影响真菌、细菌残体对土壤有机质积累的贡献”的科学假设，在前期工作基础上，以具有明显季节性雪被的高寒森林为研究平台，拟通过原位培养实验，采用生物标识物和PLFA技术研究雪被减少和雪被去除处理下冬季(雪被形成期、覆盖期和融化期)和生长季节(初期、中期和末期)不同关键时期有机层和矿质层土壤真菌/细菌来源的氨基糖积累速率、真菌/细菌群落组成及微生物生物量、微生物呼吸速率。结合土壤温湿度动态，阐明微生物来源的土壤有机质积累过程及其与微生物群落组成的联系，揭示高寒森林季节性雪被影响微生物源土壤有机质积累的作用机制及其与生长季节土壤有机质积累的联系，深入认识土壤有机质形成过程及其对气候变化的响应。

微生物周转是土壤有机质形成的重要途径，其死亡残体可能贡献森林土壤有机质的30%以上。高寒森林冬季雪被可能调控土壤微生物生物量、群落和活性，影响微生物周转过程及其残体对土壤有机质的贡献，但相关机理仍不清晰。本项目聚焦森林土壤有机质形成过程，运用生物标志物等生物地球化学方法，以具有明显季节性雪被的川西高寒森林为研究对象，建立了凋落物输入微宇宙实验（LIME），通过野外土柱原位培养，研究雪被减少和雪被去除后冬季（雪被形成期、覆盖期和融化期）和生长季节（初期、中期和末期）等不同关键时期建群种岷江冷杉凋落叶分解和易分解碳释放，有机层和矿质层土壤溶解性碳和养分周转，微生物生物量、微生物呼吸和酶活性，不同土层真菌、细菌残体来源的土壤有机质分布格局和调控机制，主要取得了以下成果：1）雪被减少后凋落叶中溶解性有机碳、热水溶性有机碳、非结构性碳等易分解碳释放的减缓是导致有机碳分解减慢的主要原因；2）雪被减少诱导土壤冻融作用的增强是土壤微生物生物量、微生物呼吸和酶活性降低的重要因素；3）雪被对土壤溶解性有机碳、硝态氮等易分解组分的淋溶作用是调控土壤微生物生物量周转的重要驱动；4）微生物残体碳占森林土壤有机碳的30-62%，且随土层增加而显著增加；5）森林表层土壤中微生物残体碳主要受微生物生物量和土壤C/N调控，而在深层土壤中主要受粘粒物理保护。以上结果为厘清气候变化情景下寒冷生物区雪被减少对微生物源土壤有机质形成过程提供了理论支持，为深入认识森林土壤有机质形成过程提供了理论依据。在项目支持下，在Soil Biology and Biochemistry、Global Ecology and Biogeography、植物生态学报等国内国际主流期刊上发表论文24篇；主编/副主编专著2部。