冻融干扰下温带森林土壤碳素排放与稳定性变化及驱动机制

There is tremendously limited knowledge about the key proceses of soil carbon (C) cycling in Chinese temperatue forests during freeze-thaw periods and their driving mechanisms. In this program, temperate forest stands at different succession stages, which locate at the foot of Changbai mountains in northeastern China, are selected to mainly study soil C flux and C stabilization during freeze-thaw periods and their influencing factors. Measurements of in situ soil-core translocation experiment and a series of long-term field experiments involving increased nitrogen (N) deposition and the exclusion of forest roots or litters will be carried out, to study the changes in fluxes of carbon dioxide (CO2) and methane (CH4) as well as leaching and stabilization of dissolved organic carbon (DOC) under the selected temperate forests during freeze-thaw and non-freeze-thaw periods, and their respective responses to the changes in field freeze-thaw conditions, the exclusion of forest roots or litters and long-term simulated N deposition. The relationships between fluxes of CO2 and CH4 and DOC leaching against soil properties and meteorologic parameters can be analyzed under freeze-thaw periods. Together with a series of laboratory simulated freeze-thaw experiments, a parallel factor analysis to decompose the fluorescence excitation–emission matrices, soil biological technologies and incubation experiments using labeled 13carbon sources, we try to study the changes in priming mineralization of forest soil native organic C under different freeze-thaw disturbances and the responses of the priming mineralization to soil moisture and the addition of nutrients and forest litters and the driving mechanisms. Together with the changes in biomass of fine roots and microbial biomass, amount and bioavailability of DOC, the potential mineralization of organic C in soil aggregates at thaw, and the soil C cycling–associated microbes population and activities, the mechanisms involving the fluxes and stabilization of C in temperate forest soils will be eventually analyzed. The results can provide basic theories and methods for future researches in the field of temperate forest soil C cycling under freeze-thaw disturbances.

基于当前我国温带森林冻融期土壤碳循环过程及其驱动机制研究十分缺乏，本项目拟通过温带森林长期控制实验和不同林分土柱野外置换实验冻融期和非冻融期观测，结合室内冻融模拟实验、荧光光谱分析、土壤生物学和13C标记物实验，研究冻融期温带林地土壤二氧化碳和甲烷净通量及溶解性有机碳淋溶及其稳定性特征，分析凋落物和根系以及模拟氮沉降增加的影响及其作用机制；建立冻融期林地二氧化碳和甲烷净通量及溶解性有机碳淋溶通量分别跟土壤属性和气象因素的定量化关系；阐述冻融干扰下温带森林土壤有机碳分解的激发效应变化规律，以及土壤湿度、营养源添加和凋落物输入的影响。结合冻融期林地细根量、微生物量、溶解性有机碳含量及其有效性、团聚体碳含量及其可矿化性、碳循环相关微生物群落和活性变化，分析冻融干扰对温带森林土壤碳素排放和稳定性的影响机制。研究结果为人们有效认识冻融期温带森林土壤碳循环过程及其驱动机制提供基础理论和方法体系。

当前我国仍缺乏研究冻融干扰下温带森林土壤碳素循环关键过程及作用机制，尤其是野外冻融期水热条件变化的协同影响。本项目以长白山温带阔叶红松混交成熟林(BKPF)及其演替初级阶段的次生白桦林(WBF)土壤碳素循环关键过程对冻融干扰响应为核心，通过两种林分样地和原状土柱野外置换实验全年期间定期观测，实验室冻融模拟实验、以及溶解性有机质三维荧光分析与平行因子分析方法，并结合土壤微生物量、氮素净矿化量以及土壤酶活性等有关环境要素测定，分析了不同冻融干扰下两种林分温带森林土壤二氧化碳和甲烷净通量变化特征、土壤渗漏液溶解性有机质含量和组分及其生物可降解性变化规律以及湿度变化和林分类型的影响效应；揭示了不同冻融干扰下温带森林土壤有机碳分解的激发效应及湿度变化的影响，以及森林土壤二氧化碳排放和溶解性有机质生物可降解量分别与溶解性有机质的荧光组分及其相关光谱参数之间的关联性。基于两种林分样地控制实验多年野外观测结果，显示在非生长季(每年11月至次年4月末)，BKPF和WBF土壤二氧化碳(CO2)和甲烷(CH4)净通量分别为0.06~1.32和0.06~1.55(平均值为0.49和0.56)μmolCO2/m2/s，及-2.54~0.04和-2.74~0.05(平均值为-0.74和-0.76)nmolCH4/m2/s，分别约占全年净通量16.4%和19.4%，及35.9%和38.2%。两种林分郁闭度和生境差异，使得冬春期间WBF表层土壤冻融状况有别于BKPF林地，BKPF原状土柱置换于WBF时，非生长季和生长季土壤二氧化碳排放量均呈现增加，而WBF土柱置换于BKPF时两时期内土壤二氧化碳排放量呈现降低。研究结果增进人们认识冻融干扰下我国北方温带森林土壤溶解性有机质动态及其稳定性以及二氧化碳和甲烷净通量特征，为拓展极端气候变化下我国高寒区森林土壤碳循环关键过程及其作用机制研究提供基础理论与方法体系。