气候过渡带森林生态系统根系-土壤-微生物互作机制及其对氮沉降的响应

Atmospheric nitrogen deposition has an important impact on the structure and function of forest below-ground ecosystems, and as a result of soil acidification and plant diversity reduction. N deposition also affected the decomposition process of forest litter and the storage of soil organic matter. Soil microbes played an important role in the underground ecosystem, and which were the drivers of soil nutrient transformation and directly participated in the process of nutrient transformation, absorption and transportation. There was obvious interaction feedback between forest roots and soil microbes. There were facilitative interaction and competitive interaction between plant roots and soil microbes, which would respond to soil environmental changes. The coupling point between above-ground and below-ground organisms was the interaction area between roots, soil and microorganism, which was rich in matter and information communication. The climate transition zone forest ecosystem was more sensitive to the external environment stimulation, and would make a clear response to the nitrogen deposition process. N deposition would obviously change the response strategy of root system, and lead to the change of root exudates, and influence the N transformation of forest soil and the release of C. The interaction feedback between plant roots and soil microbes was an important ecological process in below-ground ecosystems. The results could reflect the stabilization of forest soil ecosystem under the background of N deposition, and promoted the cognition of forest soil carbon storage and release mechanism.

氮沉降对森林生态系统结构和功能造成重要影响，导致森林土壤酸化以及植物多样性降低，并影响林下凋落物的降解过程以及土壤有机质的储存。根际微生物在地下生态系统中扮演重要角色，是土壤养分转化的驱动者，直接参与养分的转化、吸收和运输等过程。林木根系与根际微生物之间存在明显的互作关系，二者之间既有互助关系，也存在竞争关系，会依据土壤环境变化做出响应。气候过渡带森林生态系统对外界环境刺激较为敏感，将对氮沉降过程做出明显应答。氮沉降将明显改变林木根系的应对策略，导致根系分泌物发生变化，并影响森林土壤氮转化及有机碳的释放。通过对气候过渡带优势乔木树种根系-微生物互作关系的研究，揭示此区域森林生态系统优势树种栓皮栎、麻栎和枫香树地下生态过程对大气氮沉降的响应及应对策略。结果能够反映氮沉降背景下森林土壤生态系统的稳定状态，并增加对林木根系-根际微生物互作机理的认知。

由于人为活动的不断影响，全球大气氮沉降浓度不断增加，其对森林生态系统群落结构和功能特征产生明显的影响。亚热带与暖温带气候过渡期森林植被对大气环境变化的影响更为敏感，对此区域森林生态系统优势树木如何响应大气氮沉降开展深入研究尤为迫切和必要。该试验从以下两个科学问题切入：(1) 林冠模拟不同浓度氮沉降对优势树种生理生态特征的影响是否具有明显差异性，差异性如何；(2) 氮沉降影响气候过渡区森林生态系统优势树种根系与根际微生物相互作用强度吗？本试验选择了北亚热带和暖温带气候过渡区两个优势树种栓皮栎(Quercus variabilis Bl. )和枫香树(Liquidambar formosana Hance)作为研究对象，开展两种优势树种对林冠模拟氮沉降的生理生态响应和地下根系及根际土壤响应状况。研究结果显示北亚热带-暖温带气候过渡区森林生态系统优势树种生理生态特征（如叶绿素、酶活性、淀粉、总糖、酚类物质、木质素、氨基酸、养分特征等）对不同浓度大气氮沉降反映敏感，优势树种根际土壤化学性质（有机碳、全氮、全磷、pH值、速效氮、速效磷、脲酶活性、转化酶活性等）和微生物群落结构（微生物生物量、细菌群落、真菌群落、放线菌群落等）也呈现出相应的特征，林冠模拟不同浓度大气氮沉降对优势树种栓皮栎和枫香树的影响具有明显差异，这也体现出他们各自对环境的适应能力，能够及时调整自身特征以适应外界环境变化的物种更容易生存下来，在竞争过程中占据优势。研究会持续关注两种优势树种栓皮栎和枫香树生理生态特征变化的阈值情况，发现阈值范围，从中发现植物生理特征对外界氮沉降浓度变化的非线性响应特征以及地下-地上的相互反馈规律。还会关注两种优势树种栓皮栎和枫香树根际土壤理化性质和微生物群落变化，从中发现连接根际土壤与植物生理变化特征的纽带指标，进而更加系统地研究氮沉降处理下森林生态系统树木的变化特征及响应特点。