中亚热带马尾松人工林土壤呼吸δ13C变异特征及其影响机制

The subtropical forest ecosystems in the east Asian monsoon region has a high carbon dioxide uptake similar to North America and Europe temperate forests. The difference of soil respiration components in response to environment variability has a significant influence on the soil and ecosystem carbon balance. Compared with the direct measurements of soil CO2 efflux, high time resolution and continuous observation of carbon isotopic composition of soil respiration and its components will help us to gain a better understanding of the soil respiration process and its underlying mechanism. In this study, we will carry on two factor interaction experiment with root trench/not trench and litter removal/not removal treatments (four treatments and three repetitions), and carry on an in situ continuous observation experiment in a mid-subtropical Pinus massoniana plantation. During the three years of observation period, there is no processing in the first year. The treatment will be done in the second year, and then we are about to observe the changes of treatment. After the changes of treatment achieve a steady state, we will carry on continuous observation in the third year. We will also measure the chemical composition, microbial population structure and δ13C of root, rhizosphere soil, soil organic matter and litter. Based on the dataset above, we will elucidate the variability and the underlying environment and biological mechanisms of the δ13C in soil respiration and its components on different time scales including diurnal cycle, precipitation and seasonal drought. We will also elucidate the time lag effects of soil CO2 efflux and the δ13C in response to the diurnal cycle, precipitation and seasonal drought, and its underlying environment and biological mechanisms.

东亚季风区亚热带森林碳吸收强度与“北美和欧洲温带森林”相当，该区域土壤呼吸及其组分对环境变化响应的差异，将深刻影响土壤和生态系统碳平衡。高时间分辨率的土壤呼吸CO2δ13C数据比仅土壤呼吸CO2数据更有助于土壤呼吸过程及其影响机制的理解。拟以中亚热带马尾松人工林为研究对象，设置切根/不切根和凋落物移除/不移除(4个处理*3个重复)的双因素交互试验，开展土壤呼吸CO2δ13C原位连续观测研究。三年观测期间，第一年不做任何处理，第二年进行处理并观测处理导致的变化，第三年处理稳定后继续连续观测。综合测定根系、根际土壤、土壤有机质和凋落物等的化学组分、微生物种群结构以及相应的δ13C。综合揭示土壤呼吸及其组分δ13C在不同时间尺度上(包括昼夜循环、降水和季节性干旱等)的变异特征及其生物和环境控制机制，阐明土壤呼吸CO2及其δ13C对昼夜循环、降水和季节性干旱等响应的时滞效应及其生物与环境控制机制。

东亚季风区亚热带森林碳吸收强度与“北美和欧洲温带森林”相当，该区域土壤呼吸及其组分对环境变化响应的差异，将深刻影响土壤和生态系统碳平衡。高时间分辨率的土壤呼吸CO2 δ13C数据更有助于土壤呼吸过程及其影响机制的理解。.(1) 基于Picarro G2131-i CO2 δ13C分析仪，构建了12通道土壤呼吸CO2及其δ13C全自动箱式观测系统与土壤CO2释放量(Fs)及其δ13C(δRs)C的模拟通量验证系统(FSS)各一套。零通量测试表明12个气室Fs范围为-0.1306~0.0901 μmol m-2 s-1，平均值为0.0135±0.0453 μmol m-2 s-1，气密性良好。三次模拟通量测试的观测值与理论值的结果对比表明，Fs及其δRs模拟通量不存在明显的系统误差，Fs 随机误差或分析精度随着Fs的减小而减小，δRs随着Fs的减小而离散且其随机误差也增加，其分析精度和准确度满足野外观测的需求。.(2) 以中亚热带马尾松人工林为研究对象，开展了土壤呼吸CO2 δ13C原位连续观测，结合非稳态CO2同位素扩散模型(NSS)，解析非稳态扩散分馏对δRs的昼夜变异特征以非稳态扩散分馏和观测误差中亚热带人工针叶林土壤Fs和δRs的昼夜变异特征的影响。结果表明，低Fs(4 μmol m-2 s-1)时，δRs观测误差可达2‰，且无昼夜变异。NSS模型模拟表明δRs昼夜变异幅度受土壤CO2生产速率和呼吸深度的影响，表现出上午富集而午后贫化的昼夜变异特征；低Fs下非稳态扩散分馏对δRs昼夜变异的影响更为显著。低Fs下δRs观测误差的增大导致不足以捕捉本研究δRs的昼夜变异特征。.(3) 系统梳理了现有箱式通量观测技术的理论、假设与应用，概述了箱式通量观测系统的组成、分类和基本原理，阐述了系统设计的理论要求与假设，综述了从野外到室内土壤、植物叶-茎-根以及生态系统尺度箱式通量观测研究的应用进展及存在问题。.(4) 系统评价了现有的理论模型(KP、MT和FR模型)、曲线拟合方法(OLS、GMR、LSB和ODR回归方法)以及相关的数据处理与分析方法。从P值分析和异常值检验、[CO2]跨度和d13CO2/dz效应、[CO2]跨度和d13CO2/dz阈值的确定等方面展开论述，分析了三种模型和四种回归方法差异性存在的原因以及观测误差对分析结果的影响。