Abstract

We assembled homogenized long-term time series, up to 19 years, of measurements of net ecosystem exchange of CO₂ (NEE) and its partitioning between gross primary production (GPP) and respiration (R_eco) for five different ecosystems representing the main plant functional types (PFTs) in France. Part of these data was analyzed to determine the influence of the main environmental variables on carbon fluxes between temperate ecosystems and the atmosphere, and to investigate the temporal patterns of their variations. A multi-temporal statistical analysis of the time series was conducted using random forest (RF) and wavelet coherence approaches. The RF analysis showed that, in all ecosystems, the incident solar radiation was highly correlated with GPP and that GPP was better correlated with the temporal variations of NEE than R_eco. The air temperature was the second most important driver in ecosystems with seasonal foliage, i.e., deciduous forest, cropland and grassland; whereas variables related to air or soil drought were prominent in evergreen forest sites. The environmental control on CO₂ fluxes was tighter at high frequency suggesting an increased resilience to environmental variations at longer time spans. The spectral analysis performed on three of the five sites selected revealed contrasting temporal patterns of the cross-coherence between CO₂ fluxes and climate variables among ecosystems; these were related to the respective PFT, management and soil conditions. In all PFTs, the power spectrum of GPP was well correlated with NEE and clearly different from R_eco. The spectral correlation analysis showed that the canopy phenology and disturbance regime condition the spectral correlation patterns of GPP and R_eco with the soil moisture and atmospheric vapour deficit.

摘要

我们收集了长达19年的均质化长期时间序列，用于测量CO ₂（NEE）的净生态系统交换及其在总初级生产力（GPP）和呼吸作用（R _eco）代表法国的主要植物功能类型（PFT）的五个不同的生态系统。对这些数据的一部分进行了分析，以确定主要环境变量对温带生态系统与大气之间的碳通量的影响，并调查其变化的时间模式。使用随机森林（RF）和小波相干方法对时间序列进行了多时间统计分析。射频分析表明，在所有生态系统中，入射太阳辐射均与GPP高度相关，并且与R _eco相比，GPP与NEE的时间变化具有更好的相关性。在具有季节性叶子的生态系统中，即落叶森林，农田和草地，气温是第二重要的驱动因素。而与空气或土壤干旱有关的变量在常绿林地中尤为突出。在高频下，对CO ₂通量的环境控制更加严格，这表明在较长的时间跨度内，对环境变化的适应力增强。在所选择的五个地点中的三个地点进行的光谱分析揭示了生态系统之间CO ₂通量与气候变量之间的交叉一致性的对比时间模式；这些都与各自的PFT，管理和土壤条件有关。在所有PFT中，GPP的功率谱与NEE相关性很好，并且明显不同于R _eco。光谱相关分析表明，冠层的物候和扰动状态决定了GPP和R _eco的光谱相关模式与土壤水分和大气水汽亏缺的关系。