温带森林溶解性有机质通量与稳定性及其对环境变化响应机制

There is tremendously limited knowledge about the fluxes and stabilization of dissolved organic matter (DOM) in Chinese temperatue forests and their responses to increasing atmospheric nitrogen (N) deposition and climate change. This is indeed not extremely beneficial for our understanding of carbon (C) and N processes in forest soils of China. In this program, temperate forest stands at different succession stages, which locate at the foot of Changbai Mountains in northeastern China, can be selected to carry out in situ measurements of DOM input and leaching, and a series of field experiments involving increased N deposition and changes in throughfall as well as the exclusion of roots or litter. Together with a series of laboratory simulation experiments, spectral analysis of DOM and stable isotope studies, we try to systematically find out the seasonal and annual changes in both concentrations and fluxes of carbon and nitrogen in DOM and biodegradable dissolved organic matter (BDOM) in temperate forest stands along a forest sucession and their responses to increased atmospheric N deposition and changes in throughfall as well as disturbances of roots and litter. An effective measurement method for BDOM in forest stands can be established, and it can be illustrated key biological and non-biological factors affecting the fluxes and stabilization of DOM. In the light of the above-mentioned observations and soil properties, especially microbial population structure and microbial activities under these forest floors, we will try to reveal the mechanisms involving the responses of DOM stabilization to the changes in soil moisture and temperature as well as the addition of C and N coupling, and the effects of DOM flux on organic matter sequestration and N availabilty in forest mineral soil layers. The obtained results can improve one to understand the fluxes and stabilization of DOM under the Chinese temperate forests and their respective responses to increasing atmospheric N deposition and precipitation change. Some theories and methods will be provided for future researches in the fields of fluxes of carbon and nitrogen and their stabilization in forest soils of China.

基于我国温带森林溶解性有机质(DOM)通量与稳定性机理，尤其是气候变化与大气氮沉降增加的响应研究十分缺乏，极不利于阐述森林地表碳氮过程及其影响机制。本项目以林地DOM通量与稳定性及其对环境变化响应为核心，通过长白山温带森林氮沉降模拟、降水变化和凋落物/根系控制实验，以及大气降水DOM通量观测，并整合实验室过程研究、DOM光谱分析和稳定性同位素研究，建立林地环境中生物可降解有机质(BDOM)含量的定量预测方法，阐明林地不同来源的DOM和BDOM中碳和氮浓度及其通量特征和各自关联性，以及不同生物和非生物因子的影响，剖析其内在驱动机制和关键控制因素；阐明森林土壤DOM稳定性对水热条件与碳氮耦合的响应机制，分析林地DOM通量对矿质层土壤有机质蓄积和氮素有效性的影响。研究结果增进认识温带森林DOM通量和稳定性及其对氮沉降增加和降水变化的响应机制，为森林土壤碳氮排放与蓄积过程研究提供理论与方法借鉴。

当前我国仍缺乏研究温带森林土壤溶解性有机质通量与稳定性机理，尤其是气候变化与大气氮沉降增加的响应特征。本项目以森林演替阶段不同林分溶解性有机质通量与稳定性及其对环境变化的响应为核心，依托我们在长白山温带阔叶红松混交成熟林及其演替初级阶段的次生白桦林构建的野外控制实验观测，并结合实验室模拟实验以及不同来源的溶解性有机质生物可降解量测定和三维荧光光谱-平行因子分析方法，分析了氮沉降量增加、森林根系/凋落物及其与施氮交互作用对不同季节内上述两种林分森林表层土壤渗漏液中溶解性有机质含量和组分及其稳定性的影响；建立了温带森林土壤渗漏液溶解性有机质的生物可降解量与溶解性有机质的荧光组分及其相关光谱参数之间的定量化关系；阐述了外源碳和氮添加及其耦合作用、水热条件变化对上述两种林分温带森林土壤溶解性有机质含量和组分及其稳定性的影响。基于野外控制实验多年观测结果，显示阔叶红松混交成熟林和次生白桦林土壤溶解性有机碳年淋溶通量分别为15.3-41.8(均值28.2)和31.0-61.7(均值51.3)kg C ha-1 yr-1，两种林分土壤溶解性有机氮年淋溶通量分别为1.1-2.6(平均值1.5)和2.8-2.9(平均值2.9)kg N ha-1 yr-1。与保留凋落物实验样地相比，阔叶红松混交成熟林去凋落物微区土壤溶解性有机碳和溶解性有机氮年淋溶通量平均降低32%和20%，次生白桦林去凋落物微区土壤分别降低61%和36%。初步结果显示模拟施氮对温带森林土壤溶解性有机质年淋溶通量的影响因不同林分、不同氮素形态及其剂量而发生变化。依据长白山温带森林穿透雨增加/减少控制实验6年野外观测，构建了阔叶红松混交成熟林土壤溶解性有机质年淋溶通量与年降雨量的定量化关系，指出该地区生长季年降雨量增加100mm时，该林分土壤溶解性有机碳和溶解性有机氮年淋溶量分别增加5.28±0.44 kg C ha-1 yr-1和0.39±0.05 kg N ha-1 yr-1。项目获得的研究结果为认识我国东北温带森林土壤溶解性有机质通量和稳定性及其对气候变化和大气氮沉降增加的响应提供重要支撑，为拓展我国不同区域森林土壤溶解性有机质动态及稳定性研究提供基础理论与方法借鉴。