中亚热带典型森林倒木分解碳释放驱动机制

Fallen trees caused by chronic mortality and various forest disturbances is an important component for carbon budget in terrestrial forest ecosystems. There is an important research need to understand the mechanisms or factors responsible for CO2 release during long-term decay of fallen trees, particularly in mid-subtropic forests. In this proposed study, I will select major typical forests including evergree broadleaved forests, Chinese fir forests and massonia forests located in Jiangxi Province to study how CO2 is released from fallen trees. The study methods include down wood decay experiments in different temperature zones, controlling experiements using various simulated light intensities and types, and field experiments using reciprocal fallen trees transplanting. During these experiments, data on biomass loss, CO2 release, microbial communities, structural components and physical structures of fallen trees will be carefully monitored and collected. Our objectives are to understand how CO2 is released over fallen trees decay course and what factors (temperature, light, substrates and microbial communities) are driving mechanisums for C releases, and to explore fallen trees decay under the conditions of "Home-field Advantage" and photodegradation. Our ultimate goal is to quantify the contribution of fallen trees to forest ecosystem C budget and to support designing of suitable fallen trees management strategies.

树木自然死亡和各种干扰产生的倒木是森林生态系统碳库的重要组成部分，其分解释放的CO2是生态系统碳收支中不容忽视的一个组分。但目前对倒木分解碳释放的机制尚不明确，特别是对中亚热带水分条件下倒木分解的驱动机制研究较为缺乏。本项目选择江西为中亚热带代表区域，开展典型森林类型（常绿阔叶林、杉木林、马尾松林）倒木在不同温度区的原位分解、光强以及光质模拟调控试验、倒木交互置换野外控制试验，通过监测倒木分解质量损失及其CO2释放、微生物群落特征、结构性组成与物理结构的变化，以阐明中亚热带湿润气候区倒木分解碳释放规律，揭示中亚热带区倒木分解碳释放的温度、光照等环境因子、基质、微生物驱动机制，探讨倒木分解"主场效应"及光降解效应及其机制。为进一步量化倒木分解碳释放对森林生态系统碳平衡的影响提供理论依据，对科学、准确估算中亚热带森林碳源/汇和林地倒木科学管理有重要意义。

倒木（Coarse woody debris：CWD）是森林生态系统碳库的重要组成部分，其分解呼吸释放出CO2是森林生态系统向大气排放CO2的重要来源。本项目以庐山国家级自然保护区为试验点，研究倒木分解碳释放特征及其影响因素。结果表明：.不同树种倒木分解碳释放为化香（Platycarya strobilacea）（3.92μmol/m2/s）>石栎（Lithocarpus glaber）（3.84μmol/m2/s）>日本柳杉（Cryptomeria japonica）（2.18μmol/m2/s），针叶树种与阔叶树种间存在显著差异。不同树种倒木温度解释了碳释放总变异的42.9-59.2%；倒木湿度的变化解释了不同树种倒木分解碳释放总变异的11.7-16.6%。.阔叶树种化香（3.92 μmol/m2/s）和青榨槭（4.24 μmol/m2/s）倒木在“主场”分解碳释放要显著高于“客场”的2.40和2.58 μmol/m2/s。而日本柳杉倒木则表现为在“客场”（2.96 μmol/m2/s）要显著高于“主场”（2.18 μmol/m2/s）。“主场”和“客场”土壤微生物群落的差异可以解释本研究中观察到的倒木分解“主场”效应。 .光强和光质对倒木分解有显著影响，和对照CK处理相比，遮阴30%、遮阴60%、遮阴100%处理下木荷倒木分别降低了20.74%、32.72%、48.85%，杉木倒木分别降低了24.10%、36.41%、51.79%，而樟树倒木则分别降低了20.40%、32.40%和49.60%。各遮阴处理条件下，樟树和木荷倒木的年平均分解碳释放量要显著大于杉木倒木。.紫外辐射（UV-B）增强和氮沉降都会增加倒木分解碳释放，和对照CK处理相比，在N、UV-B、UV-B & N处理条件下，杉木分别增加67%、149%、273%；而樟树则分别增加了58%、152%和259% 。.随海拔梯度增加黄山松和樟树倒木分解碳释放都呈现了显著降低的变化趋势。和海拔215m相比，随着海拔梯度的增加，黄山松和樟树倒木分别降低了18.40%-127.06%和12.33%-84.78%。.综上研究结果表明：全球环境变化中的重要驱动因素（UV-B增加、光强变化、氮沉降增加和温度升高）将协同作用促进亚热带森林生态系统中倒木分解碳释放。