气候变暖下根系分泌物有机酸对峨眉冷杉与麦吊云杉的根际调控机理

Soil nutrient deficiency is an important factor that restricts the constant growth of plants under warming. Previous studies found that root exudates of low-molecular-weight organic acids are closely related to soil nutrient availability. The study of root exudates on rhizosphere ecological processes can undoubtedly provide a new idea for the forest productivity maintaining in the context of climate warming. However, few studies have attempted to examine the rates of organic acids and associated microbial processes under climate warming. Gongga Mountain is representative of the typical mountain ecological system in the region of the eastern Tibet Plateau. Owing to its high altitude and complex ecological dynamics，this region is very sensitive to climate change. Abies fabri and Picea brachytyla are two dominant species of coniferous forest in the Gongga Mountain. In this project, A. fabri and P. brachytyla saplings are selected for our study. Our primary objectives are to quantify the rhizosphere effects of the two species under experimental warming, and to evaluate the effect of root exudates organic acids on root growth, soil N content, microbial community structure and enzymes activity. With a combined approach of field investigation, greenhouse pot-experiments and indoor physical and chemical analysis, we investigate the effects of experimental warming on the characteristics and the amounts of organic acids as well as the variation law of the root exudates composition. Also, we explore the relationship between the root exudates composition and root growth and metabolism. By simulating organic acids concentrations with adding exogenous organic acids to the soil, the effects of organic acids on the root architecture and physiological traits, rhizosphere soil nutrient activation under elevated temperature are to be studied. We also investigate the effects of exogenous organic acids under warming on soil enzyme activities, N mineralization and nitrification rates, soil N transformation and related microbial community structure. In order to reveal the mechanism of soil nutrient balance under warming, the relationships between the change of soil nutrient availability and the evolution of soil microbial community are to be established. The research results not only provide scientific and technical guidance for the sustainable management of subalpine coniferous forest under climate change, but also promote the improvement and development of plant-soil feedback mechanism theory.

土壤养分不足是制约增温下植物生产力持续增长的重要因素。前期实验发现根系分泌物有机酸与土壤养分有效性密切相关，探究根系分泌物对根际生态过程的调控作用无疑可为气候变暖背景下维持森林生产力研究提供新思路，但有关气候变暖下有机酸根际调控机理研究甚少。本课题拟采用原位试验与控制试验相结合的方法，以贡嘎山针叶林主要树种峨眉冷杉与麦吊云杉幼苗为试验材料，结合GC-MS技术检测增温下不同树种根系分泌物有机酸种类和含量的异同及其变化规律，探究根系生长状况和代谢与根系分泌物组成演变的动态关系；通过外源添加根系分泌物有机酸方法研究其对增温下根系生长与生理代谢的影响，探讨增温下有机酸对土壤氮磷转化相关微生物群落结构的影响，阐明土壤养分有效性变化与土壤微生物群落演变的关联性，破解增温下土壤养分平衡维持机制。研究成果为气候变化背景下亚高山针叶林可持续管理提供科学指导，同时促进植物-土壤反馈机制理论的完善与发展。

根系分泌物所介导的根际微生物过程对驱动森林生态系统土壤养分循环具有重要意义。本项目采用原位试验与控制试验相结合的方法，以贡嘎山针叶林主要树种峨眉冷杉与麦吊云杉为试验材料，开展了气候变暖背景下贡嘎山针叶林主要树种根系分泌物分异规律的研究，开展了增温与模拟根系分泌物有机酸添加联合作用对峨眉冷杉与麦吊云杉根系生理生态的影响，开展了增温与有机酸添加联合作用对土壤养分有效性和土壤微生物群落结构影响的研究。主要结果如下：与对照相比，增温条件下草酸、富马酸、丁酸、乳酸含量均增高。增温处理显著提高了有机碳分泌速率。相反，根系氮分泌率在增温条件下有下降趋势，因而增温提高了根系分泌物碳氮比。根系总有机碳分泌率与土壤无机氮呈负相关，与比根长、根系活力、根系侵染力成正比。根系氮分泌率与根系呼吸、光合速率显著正相关。增温对土壤净氮转化速率的影响结果依赖于处理时间。增温与增温+有机酸添加处理显著提高了磷矿化能力。三年增温使土壤微生物量磷的含量降低，增温处理使土壤微生物量碳磷比增加。土壤微生物碳利用效率（CUE）随温度的升高而减小。增温处理后，土壤微生物碳磷比、氮磷比化学计量不平衡性升高，有机酸添加缓解了增温下微生物化学计量不平衡性。增温对土壤细菌群落Simpson 指数、Shannon 指数、Chao 指数和 Coverage 指数）均无显著影响。增温和有机酸添加对树种影响效应取决于处理时间和测定指标。已发表相关论文5篇（全部为标注基金号），其中4篇为SCI 论文。培养硕士研究生1人，在读博士生2人。