温带森林土壤有机碳矿化温度敏感性的微生物生态学机制研究

Temperate forests are presumed to be more vulnerable to climate warming compared to other terrestrial ecosystems, due to the higher soil organic carbon accumulation and lower turnover rate. And thus, temperate forests became the hot-spot for the topic of feedback between terrestrial carbon cycle and global warming. It was widely accepted that soil microbial community is one of the major factors influencing the temperature sensitivity of SOC decomposition. However, the relationship between temperature sensitivity of SOC decomposition and microbial community were not well documented, lacking the intensive analysis of microbial community structure and function genes based on the molecular genetic marker. To date, to what degree the soil microbial community can influence the temperature sensitivity of SOC decomposition and its presumed mechanism were still not known. In the present study, natural Broad-leaved Korean pine mixed forests along a latitudinal gradient from Northeast China were selected. The latitudinal patterns and seasonal variation of temperature sensitivity of SOC decomposition in these typical temperate forests would be investigated, and the environmental factors driving these patterns are expected to be revealed. Soil microbial community structure and functional gene composition would be analyzed by Illumina MiSeq sequencing platform and GeoChip method, respectively, and their linkages with temperature response of SOC decomposition would be evaluated. The in-depth understanding of the factors that control the temperature sensitivity of SOC decomposition in temperate forests, specifically, the exploring of microbial ecological mechanisms on temperature response of SOC decomposition, will provide the sound scientific support for evaluating the SOC mineralization potential in temperate forest ecosystem and elucidating its regulatory mechanism under the projected global warming.

温带森林生态系统土壤有机碳（SOC）累积量大，周转缓慢，而使SOC分解具有高度的温度敏感性，因此成为全球变暖-碳循环反馈问题关注的热点区域。土壤微生物一直被认为是影响SOC矿化温度敏感性的重要因素之一，但相关研究尚不够深入，缺乏基于分子遗传标记对微生物群落结构和功能的精细解析，迄今尚不明确微生物群落能够在多大程度上影响SOC矿化温度敏感性及其潜在机制。本项目拟选取东北天然阔叶红松林为研究对象，分析典型温带森林生态系统SOC矿化温度敏感性的纬度梯度格局、季节变异及其驱动因素，重点采用高通量测序 (MiSeq) 和基因芯片 (GeoChip) 技术探讨微生物群落结构和功能基因与SOC矿化过程及其温度敏感性的关系。对温带森林SOC矿化温度敏感性及其影响因素的深入研究，特别是目前研究较为薄弱的微生物生态学机制的探讨，将为评估全球变暖背景下温带森林SOC的矿化潜势并阐明其调控机制提供重要的科学依据。

土壤有机碳（SOC）矿化温度敏感性（Q10）在很大程度上决定着全球气候变化与碳循环之间的反馈关系，但SOC矿化温度敏感性对升温的响应趋势及其驱动机制尚不明确，特别是缺乏微生物学机制方面的研究。本研究选取分布在不同纬度的东北天然阔叶红松林为研究对象，分析了SOC矿化温度敏感性与年均温的关系及其季节动态，同时探讨了影响土壤SOC矿化温度敏感性的生物和非生物影响因素，包括土壤理化性质、微生物群落结构和功能基因等。结果表明，分布在东北的阔叶红松林土壤Q10随年均温的增加而增加，其主要机制为年均温较高地区样地土壤碳有效性较低，微生物趋于采取K-策略，其特征为寡营养微生物/富营养微生物比值较高，细菌群落核糖体rRNA拷贝数低，菌根真菌/腐生真菌比值较高，利用难降解碳基因丰度/易降解碳基因丰度比值较高，符合“碳质量温度”假说。土壤Q10与年均温的关系受采样季节影响，夏季土壤Q10与年均温增加无明显相关关系，春秋两季随年均温增加而增加。其原因为主要是在不同季节土壤Q10的驱动因素不同，在夏季，土壤有机碳矿化Q10主要受土壤可溶性有机碳（DOC）调控；而春秋两季，除了土壤DOC含量，还受土壤碳有效性和土壤微生物群落组成和功能基因的影响。基于实验室365天长期培养实验数据的二库模型拟合表明，中部和南部样地土壤Q10主要由土壤惰性有机碳降解贡献，而高纬度样地土壤Q10主要由土壤易降解有机碳降解贡献。我们推测增温将导致我国典型温带针阔混交林土壤碳有效性降低，微生物群落向K-策略转变，从而导致土壤有机碳矿化对增温更加敏感，加剧对气候变暖的反馈作用。研究结果对于评估未来气候变暖条件下温带森林SOC的矿化潜势及其调控机制具有重要意义。