北半球陆地生态系统碳交换通量的空间格局及其区域特征

陆地生态系统通过植被的光合作用吸收大气中的CO2，深入了解陆地生态系统碳吸收强度的空间变异及其区域特征对于准确地预测和评估全球碳收支以及制定高效的区域性生态系统管理政策具有重要的指导性意义。本文以China FLUX的长期联网观测数据为基础，整合了北半球区域已发表的涡度相关文献数据，对北半球区域碳交换通量，即总初级生产力（GPP）、生态系统呼吸（RE）和净生态系统生产力（NEP）的空间格局及其区域特征进行综合分析。我们获取了233个通量站点，732条站点年数据。观测站点分布于亚洲、欧洲和北美洲，纵跨纬度2.97°N到74.47°N，横跨经度148.88°W到161.34°E。气候类型涵盖了热带、亚热带、温带、北方林、极地与亚极地以及高山气候类型。生态系统类型包涵了森林（107个站点）、草地（65个站点）、农田（33个站点）和湿地（28个站点）四大生态系统。研究结果得出：北半球陆地生态系统GPP和RE呈现出显著的随着纬度升高而线性降低的趋势，纬度每升高1°N，GPP和RE在空间格局上约减少22.9gC/m2/a，而NEP的纬向变化规律不明显。森林和农田生态系统的GPP和NEP显著高于草地和湿地生态系统。RE则在森林生态系统最高，平均约为1185±641gC/m2/a，而在其余生态系统间无显著差异。在亚洲、欧洲和北美洲3个区域之间，森林、农田和湿地生态系统的GPP，RE和NEP均无显著差异。仅在草地生态系统中，欧洲草地生态系统的GPP和RE分别为1472±473gC/m2/a和1236±452gC/m2/a，显著高于亚洲和北美洲。GPP，RE和NEP呈现出从温暖性气候区向寒冷性气候区逐渐降低的趋势，同时受到水分状况的调节，表现出在相同的温度带里，相对湿润的气候区具有更高的NEP。这些结果表明北半球陆地生态系统碳交换通量存在着空间变异性，但没有显著的区域差异，然而在不同气候区和生态系统类型间差异显著，这意味着北半球陆地生态系统碳交换通量主要受到温度和水分环境条件以及人类活动的共同影响。

SPATIAL PATTERN AND REGIONAL CHARACTERISTICS OF TERRESTRIAL ECOSYSTEM CARBON FLUXES IN THE NORTHERN HEMISPHERE

Terrestrial vegetation fixes CO2 from atmosphere via photosynthesis. Understanding the spatial pattern and regional characteristics of the terrestrial ecosystem carbon uptake is of great significance for accurately predicting and assessing the global carbon budget and developing efficient regional ecosystem management policy. In this study, we analyzed the spatial pattern and regional characteristics of terrestrial ecosystem carbon fluxes (Gross Primary Productivity(GPP), Ecosystem Respiration (RE), and Net Ecosystem Productivity (NEP)) based on long-term observational data from ChinaFLUX and literature on studies in the Northern Hemisphere. A total of 732 site-years out of 233 flux sites were included in the analysis. These sites were distributed across the Asian, European and North American regions, spanning from 2.97°N to 74.47°N in latitude, and from 148.88°W to 161.34°E in longitude. These sites covered six climate zones: tropical, subtropical, temperate, boreal, arctic and subarctic, and alpine, and were grouped into four ecosystem types:forests (107 sites), grasslands (65 sites), croplands (33 sites) and wetlands (28 sites). The results showed that GPP and RE linearly decreased with an increase in latitude, with one degree increase in latitude, GPP and RE declined by 22.9g C/m2/a, while there was no apparent latitudinal trend in NEP. GPP and NEP were higher in cropland and forest ecosystems than in grassland and wetland ecosystems. RE was highest in forest ecosystems (1185±641g C/m2/a on average)but did not differ among other ecosystems. There were no differences among the Asian, European and North-American regions in GPP, RE and NEP of forest, cropland, and wetland. Only GPP and RE in the European grasslands was averaged at 1472±473g C/m2/a and 1236±452g C/m2/a respectively, which were notably higher than those in Asia and North-America. GPP, RE and NEP tended to decrease from warm environments to cold environments, and exhibited higher values in humid areas under the regulation of water condition. Our findings demonstrate that there are spatial variations but no regional differences in terrestrial ecosystem carbon fluxes in the Northern Hemisphere the differences are significant among biomes and ecosystems types. It shows that environmental conditions (temperature and water) and human activities are important factors commonly regulating the terrestrial ecosystem carbon fluxes in the Northern Hemisphere.