亚热带人工针叶林生态系统碳同位素比值和通量的原位连续观测与过程解析

High temporal resolution and continuous isotope ratio and flux ratio of δ13C of CO2 in soil-plant-atmosphere continumum provide us a foundation for elucidating the response and feedback mechanisms of ecosystem carbon cycling process to climate change. Isotope ratio infrared spectroscopy (IRIS) is an emerging technology for making in-situ, continuous δ13C observation in ambient conditions. With proper calibration, it can achieve precision similar to that of isotope ratio mass spectrometry (IRMS). In this research, we will carry on in-situ and continuous observation and process analyses of the isotope ratio and flux ratio of δ13C in soil-plant-atmosphere continuum in a subtropical coniferous plantation in southeast China, which is Qianyanzhou station in CERN/ChinaFLUX network. The carbon and water fluxes have been measured since 2003 based on the eddy covariance technique. Based on the isotope ratio infrared spectroscopy (IRIS) technology, we will develop a gradient system of the isotope ratio and flux ratio of δ13C in atmosphere CO2, and an automatic chamber system of the isotope ratio and flux raio of δ13C in leaves (tigs), stems and soil CO2. We focus on the variation characteristic of isotope ratio and flux ratio of δ13C in soil, plant and atmosphere CO2 and their underlying environment and biological mechanism at different time scales. Combining with the eddy covariance technique, we will solve the underestimate of GEP and RE by the conventional partitioning methods based on eddy covariance methods at moist, drought, and diurnal variation. Finnaly, we will elucidate that how the interaction between RE and GEP determine the carbon budget, and reveal the response mechanism to the short-term environment variation.

高时间分辨率和连续的土壤-植被-大气连续体CO2δ13C比值和通量数据是深入开展陆地碳循环过程的稳定同位素示踪研究的基础和保障。稳定同位素红外光谱技术已经替代传统大气CO2气瓶采样-同位素质谱仪技术，将促进生态系统生态学的发展。拟以CERN/ChinaFLUX亚热带人工针叶林生态系统为研究对象，在2003年至今的长期碳水通量观测的基础上，构建大气CO2δ13C比值和通量连续观测的廓线分析系统、植物叶片(或小枝)、茎杆和土壤CO2δ13C比值和通量的全自动箱式观测系统，开展原位连续观测研究。重点解析土壤、植物和大气CO2δ13C比值和通量不同时间尺度上(小时、日和季节尺度，包括昼夜循环、降水和季节性干旱等)的变异特征及其环境和生物控制机制；与涡度相关技术相结合，解决湿润、干旱和昼夜变化下传统涡度相关技术间接统计拆分NEP组分GEP与RE的低估问题，阐明GEP和RE的相互关系如何决定碳收支。

高时间分辨率和连续的土壤-植被-大气连续体CO2 δ13C比值和通量数据是深入开展陆地碳循环过程的稳定同位素示踪研究的基础和保障。稳定同位素红外光谱技术已经替代传统大气CO2气瓶采样-同位素质谱仪技术，将促进生态系统生态学的发展。本项目以亚热带人工针叶林生态系统为研究对象，主要取得以下成果：.(1)构建并成功运行了具有7层采样高度的大气CO2和δ13C比值和通量连续观测的廓线分析系统，以及3层采样高度的植物叶片(或小枝)、茎杆和土壤CO2 δ13C比值和通量的全自动箱式观测系统，获得了CO2和δ13C比值和通量及配套的常规气象和生物要素的观测数据(201501-201812)。.(2)基于浓度依赖性和时间漂移校正以及数据溯源，建立了稳定的CO2同位素校正方法，保证δ13C测量的最优精度和准度均优于0.15‰。从仪器的最优测量精度、δ13C浓度依赖性、时间漂移和准确性等方面对G1101-i和G2201-i CO2 δ13C分析仪性能与数据可比性进行了系统分析。.(3)系统评价了不同模型(KP、MT和FR)和回归方法(OLS、GMR、LSB和ODR)对生态系统呼吸同位素组成(δ13CRs)计算的影响。仅OLS回归方法下三种模型不存在显著差异，其它三种回归方法下MT和FR模型结果均比KP模型结果偏正。随着[CO2]跨度和d13CO2/dz的降低三模型下四种回归方法的估算偏差和不确定性均增大。添加高斯噪声模拟结果表明，不同模型和回归方法组合估算结果的不确定主要来源于δ13C观测误差。.(4)系统评价了现有的植物光合碳同位素判别模型及其对白天NEE拆分的影响。其中，Δclassical与Δdiffusion估算的Δcanopy偏差较小，而Δclassical与Δsimple估算的偏差均值可达2.16±2.18~2.88±2.34‰。采用∆classical和Δdiffusion计算的通量组分差异较小，而采用∆simple计算的FA被高估2.17~2.02倍。采用∆classical和Δdiffusion模型在Period I中午时段估算的FNR低于统计拆分方法获得的Reco，这种白天呼吸通量的降低可能与Kok效应和季节性干旱有关。采用isoflux-based IFP理论实现了2015-2017年白天NEE组分FA和FNR拆分，并与统计拆分方法获得的GEE和Reco对比分析。