增温是否导致中亚热带森林土壤“微生物碳泵”失效？

The microbial plays a very important role in controlling soil carbon reserve, but the carbon fixation function of microorganism is neglected. It is now found that soil microbial debris carbon makes greater contribution to the accumulation of organic carbon in the soil than what we previously thought, and it is estimated to account for 80% of the soil organic carbon. Obviously, compared with heterotrophic respiration, microorganism contributes more to soil’s carbon sink function. However, studies have shown that global warming may nullify this function (Microbial Carbon Pump) of microorganism, which may lead to serious consequences for the stabilized carbon pool in soil. Based on the in-situ soil warming platform at Fujian Sanming Global Change and Forest Ecosystem Observation Station, this study makes integrated researches by increasing the outdoor in-situ soil temperature by 5°C (buried heating cable) and conducting indoor simulation experiments. With the amino sugar in the soil as Biology marker, which explores the warming’s impact on the accumulation and decomposition of microbial residue/necromass carbon in the soil, makes comparative analysis on its accumulation and decomposition by replacing amino sugar with chitosan, and reveals the microbial residue/necromass carbon’s response mechanism towards warming in mid-subtropical forests. Revealing the effect of global warming on soil carbon pool from a new perspective is of great significance to correctly and objectively understand the soil carbon pool’s response and adaptation mechanism to global warming.

微生物在土壤碳循环中扮演重要角色，但是关于其残体的碳汇功能却长期受到忽视，当前研究表明微生物残体碳占土壤总有机碳的比例高达80%，其动态消长直接关乎土壤碳库稳定性，增温通过改变土壤水分和温度影响微生物残体碳的累积和分解，然而当前关于增温对土壤微生物残体碳的影响则鲜见报道，相关作用机制尚不明确。本研究以福建三明全球变化与森林生态系统观测研究站的原位土壤增温平台为依托，通过野外原位土壤增温5℃（埋加热电缆）和室内模拟实验相结合，采用氨基糖分子标志物技术测定土壤微生物残体碳组成及含量，探讨增温对土壤微生物残体碳的影响.通过室内添加凋落物淋溶液和微生物残体碳类似物（壳聚糖）的方式，探讨增温对微生物残体碳累积及分解的影响，揭示中亚热带森林土壤微生物残体碳对增温的响应机制。项目从一个较新的视角研究全球变暖对土壤碳库的影响，对准确、客观的认识土壤碳库对全球变暖的响应和适应机制有重要意义。

项目以湿润亚热带杉木人工林为研究对象，借助野外原位土壤增温平台和长期氮沉降观测样地，探讨土壤增温和氮沉降对亚热带森林土壤微生物残体碳的影响。结果发现：1）增温显著降低了0-10 cm土层的氨基糖葡萄糖(GluN)、氨基半乳糖（GalaN）、胞壁酸（MurA）、氨基甘露糖含量和GluN/MurN，但未显著影响氨基糖占土壤有机碳的比例。相关分析发现氨基糖含量与土壤微生物（GP、GN、ACT、AMF、Fungi和Total PLFAs）和FeO、AlO、SOC显著正相关。以上结果表明增温降低了杉木人工林表层土壤的微生物残体碳含量，但并未改变残体碳对土壤总碳的贡献，土壤微生物和铁铝氧化物的变化可能是增温后微生物残体碳降低的重要因素。2）与表层土相反，增温和隔离降雨显著增加了20-60 cm土层氨基葡萄糖和总氨基糖的含量。表明增温和隔离降雨改变了土壤微生物残体碳的分布，导致底层土壤微生物残体碳含量增加。3）氮沉降显著增加了米槠天然林表层土壤的氨基糖含量，冗余分析结果发现真菌和土壤磷有效性是土壤微生物残体碳增加的主要因素。4）天然林转换为次生林、马尾松和杉木人工林后，两个土层（0-10 cm和10-20 cm）的氨基糖（GluN、GalN，MurN和总氨基糖）含量均显著降低，但是氨基糖占土壤有机碳的比例显著增加。且土壤有机碳、细根生物量和土壤有效磷与氨基糖含量显著相关。表明森林转换降低了土壤微生物残体碳的含量，却增加了残体碳对土壤总碳的相对贡献，而土壤有机碳和细根生物量等环境因子可能是这一变化的主要原因。