地膜覆盖与施肥条件下光合碳固定的土壤微生物学机制

Fertilization has been considered as an important measure to improve soil fertility under plastic film mulching. The previous researches put emphasizes on the effect of plastic film mulching combined with fertilization on the dynamics of soil organic carbon and nutrient elements, while there were few researches on the mechanism of photosynthesized-carbon (C) sequestration in soil. This proposal will investigate the microbial community structure during the process of the sequestration of photosynthesized-C by using the in-situ 13C pulse-labeling method combined with phospholipid fatty acid (PLFA) — stable isotope probing (SIP) technique at the long-term experimental station. The objectives are to: (1) determine the active microbial community structure assimilating photosynthesized-C, and explore their dynamics characteristics by analyzing the total PLFA and mono PLFA and their 13C contents and comparing their relative contribution of different C sources under plastic film mulching combined with fertilization; (2) analyze the availability of soil nutrient elements and C sources for microorganism, discuss the relationship between them and active microbial community structure by using the multivariate statistics analysis method, determine the main factors driving the dynamics of microbial community structure, and (3) further explore the microbial mechanism of the photosynthesized-C sequestration in soil under plastic film mulching and fertilization. The results would provide bases for the sequestration of soil organic carbon, improvement of soil fertility and the function of microbial community.

施肥是地膜覆盖条件下土壤肥力提升的重要措施。以往研究集中在地膜覆盖结合施肥对土壤有机碳和养分动态的影响，然而关于光合碳在土壤中固定的微生物学机制尚不清楚。本项目以棕壤长期定位试验站为平台，通过采取13CO2田间原位脉冲标记方法，结合磷脂脂肪酸（PLFA）—稳定同位素探测（SIP）技术，对固定光合碳的土壤微生物群落结构进行研究。研究目的：（1）通过测定土壤PLFA总量和单体PLFA含量及其13C含量，对比不同碳源的相对贡献，确定地膜覆盖与施肥条件下固定光合碳的活性微生物群落结构，揭示其动态变化特征；（2）分析土壤养分有效性和碳源有效性，并通过多元统计分析方法探讨其与微生物群落结构间的关系，明确地膜覆盖与施肥条件下影响土壤微生物群落结构变化的主要驱动因子；（3）进一步揭示光合碳在土壤中固定的微生物学机制。研究结果将为土壤有机碳固定、肥力提升和土壤微生物作用提供依据。

植物通过光合作用固定大气CO2，然后将光合碳以根际沉积物或植物残体等形式输入土壤。光合碳在植物-土壤-微生物系统的分配与固定对于认识土壤有机碳（SOC）循环、周转和固定机制具有重要意义。本项目基于棕壤长期定位试验站，采用13CO2田间原位脉冲标记的方法，研究了地膜覆盖与施肥条件下光合碳在地下部的动态分配及其微生物的固定；分析了土壤微生物群落结构动态变化特征；探讨了不同秸秆添加量对秸秆碳在土壤团聚体中的分配与固定的影响。主要研究结果如下：（1）裸地施氮肥（N4）处理增加了光合碳在地下部分配比例和土壤可溶性有机碳中13C（13C-DOC）含量。标记结束时土壤固定13C（13C-SOC）中13C-DOC比例最高，尤其是N4处理，这说明衰老根系分解对SOC的贡献。标记初期覆膜土壤微生物量碳中13C（13C-MBC）含量及其占13C-SOC比例高于裸地，说明覆膜提高了微生物活性，促进了微生物对根际沉积物的同化利用。标记结束裸地施有机肥处理土壤微生物仍保持较高活性；（2）标记第7 d与第1 d相比，除不施肥处理外根际和非根际土壤总磷脂脂肪酸（TPLFA）含量增加了8.65%~46%和24%~57%。覆膜和施肥条件下土壤微生物以细菌为主，其PLFAs占TPLFA的80%。长期覆膜改变了土壤水热条件，有利于真菌和革兰氏阳性菌（G+）的生长，氮肥的施用促进了细菌和G+的生长却降低了真菌和革兰氏阴性菌的数量；（3）秸秆碳分配到大团聚体（>250 μm）的比例为13%~23%，微团聚体（53-250 μm）平均为5%，仅有2%的秸秆碳分配到粘粉粒组分（<53 μm）。随着秸秆添加量的增加大团聚体和微团聚体组分有机碳含量增加，而粘粉粒组分先于大团聚体和微团聚体组分达到碳饱和水平。