不同林木凋落物诱导土壤微生物调控激发效应机制的研究

Litter is the main source of organic carbon and nutrient in forest soil. Litter input could induce priming effect, which will affect organic carbon stocks and nutrient cycling of soil. The priming effect is strongly related to the nutrient content of litter inputted. However, the influence of litter nutrient on priming effect is currently under debate. Furthermore, the mechanism of priming effect regulated by soil microorganisms has not been clarified yet. Hence, the four litters of Hippophae rhamnoides, Robinia pseucdoacacia, Pinus tabulaeformis , and Platycladus orientalis characterized by different nutrient contents will be used as the experiment materials for this project. The direction and magnitude of priming effect will be determined via combination the stable-isotope probing (SIP) with high-throughput sequencing (HTS) and phospholipid fatty acid (PLFA) analysis. The different soil microorganism species and their contribution to priming effect will be also detected. Moreover, the effect of carbon and nitrogen content, and C:N stoichiometric ratio in litter on soil microbial community and function will be measured to clarify the coupling relationships between litter, soil microorganisms, and soil carbon pool during the turnover process of organic matter in soil. The experimental results might provide a valuable insight into the regulatory mechanism of priming effect by soil microorganism. The influence of litter nutrient on priming effect could be further clarified based on the results. The research findings are also expected to be advisable to understand the soil carbon cycling, forest soil utilization, and afforestation.

凋落物输入是森林生态系统有机碳和养分的主要来源，并能诱导激发效应，影响土壤有机碳的储存和养分循环。凋落物的养分含量与激发效应密切相关。目前，凋落物养分对激发效应的影响仍存在争议，土壤微生物在激发效应过程中的调控机制尚不清楚。本项目拟以4种养分含量不同的林木凋落物为试材，采用稳定性13C同位素示踪、磷脂脂肪酸和高通量测序技术，研究不同凋落物对激发效应方向和强度的影响，在分子水平上确定参与激发效应的具体微生物种属，并量化其贡献大小。同时研究凋落物碳氮含量及其化学计量比对激发效应中土壤碳库、微生物种群结构和功能的影响，探索土壤有机质周转过程中凋落物-土壤微生物-土壤碳库之间的耦合关系。该研究将有助于揭示森林凋落物激发效应的微生物调控机制，进一步阐明凋落物碳氮养分对激发效应的影响，以提高对森林生态系统土壤碳循环的认识，为可持续性利用森林土壤、合理营造森林植被等提供一定的理论和实践依据。

凋落物输入是森林生态系统有机碳和养分的主要来源，并能诱导激发效应，影响土壤有机碳的储存和养分循环。凋落物的养分含量与激发效应密切相关。目前，凋落物养分对激发效应的影响仍存在争议，土壤微生物在激发效应过程中的调控机制尚不清楚。本项目以油松叶凋落物（低质量）、刺槐叶凋落物（高质量）、油松与刺槐叶混合凋落物（1:1）为试材，采用稳定性13C同位素示踪、磷脂脂肪酸和高通量测序技术，研究不同养分含量凋落物对不同土层土壤激发效应方向和强度的影响，确定参与激发效应的具体微生物种属，并量化其贡献大小。研究结果表明：（1）凋落物添加能显著影响激发效应的方向和强度。在表层（0-20cm）土壤，添加油松和刺槐凋落物引起负激发效应，减缓土壤有机质的分解速率，有利于土壤碳的固存。而在深层（60-80cm）土壤，添加油松凋落物促进了土壤有机质的分解，造成正激发效应。添加混合凋落物所产生的激发效应均为正激发。深层土壤激发效应的强度均大于表层土壤。（2）添加凋落物显著增加了总PLFA、细菌、真菌、革兰氏阴性菌含量及F:B值，降低了G+:G-值，对革兰氏阳性菌、菌根真菌无影响。土壤全氮、总有机碳和pH值是引起微生物群落结构变异的主要因素。参与土壤激发效应的微生物种群主要有细菌（16:0）、真菌（18:1ω9c）、革兰氏阴性菌（18:1ω7c）。三种微生物分别吸收了凋落物碳的66.70%–86.63%，68.04%–91.38和53.39%–64.67%。（3）从分子水平来看，添加凋落物显著增加了放线菌门的相对丰度。绿弯菌门、芽单胞菌门、己科河菌门的相对丰度均有显著降低。真菌群落以子囊菌门、担子菌门和球囊菌门为主。添加凋落物对子囊菌门和担子菌门无明显影响。添加刺槐凋落物显著增加球囊菌门的相对丰度。绿弯菌门对调控激发效应的方向和强度有关键作用。研究结果能为进一步阐明森林生态系统中土壤碳循环的微生物过程，指导混交林营造和土壤管理提供科学依据。