陆地生态系统在调节大气CO₂浓度方面扮演重要的角色，定量研究区域尺度生态系统碳汇量需要同时确定生态系统碳周转时间的空间分布格局以及NPP变化的空间分布格局。地表过程与资源生态国家重点实验室周涛等人，以北美生态系统为案例，采用反演分析方法确定了生态系统碳周转时间的空间分布格局，并结合遥感监测的NPP变化趋势，定量评价了其生态系统的碳汇量及其空间分布。

 

反演得到的美国生态系统的碳周转时间具有很强的空间异质性，其中大部分地区的周转时间介于15～65年，其平均周转时间为46年。当反演估算的碳周转时间的空间格局与NPP变化的空间格局相结合时，模型模拟的生态系统总碳汇量为每年0.15PgC。在这些碳汇中，农田与草地生态系统中土壤碳汇所占比例较大（47～70%)，而森林生态系统中土壤碳汇所占比例较小（18～27%）。尽管碳汇绝对量的空间分布同时取决于碳周转时间与NPP变化率，但土壤碳汇所占的比例主要由生态系统碳周转时间决定，与NPP变化速率的大小关系不大。

 

 

 

 

 

 

 

Spatial patterns of ecosystem carbon residence time and NPP-driven carbon uptake in the conterminous United States

Tao Zhou and Yiqi Luo

 

Terrestrial ecosystems play an important role in regulating atmospheric CO₂ concentration. Quantification of net ecosystem carbon (C) uptake from the atmosphere at a regional scale requires identification of spatial patterns of both C residence times and NPP changes. In this study, an inverse modeling method was applied to estimate spatial patterns of C residence times in the conterminous United States. Then the spatial patterns of estimated residence times were combined with a NPP change trend to assess the spatial patterns of regional C uptake in the United States. The estimated residence times are highly heterogeneous over the conterminous United States, with most of the regions having values between 15 and 65 years. The averaged C residence time for the whole conterminous United States is 46 years. When the estimated residence times and the spatially heterogeneous NPP increases were incorporated into the forward modeling, the estimated total C uptake of the whole conterminous United States is 0.15 PgC a^-1, about one third of which were stored in soil. The cropland and grassland have a higher proportion of C uptaked in soil (47–70%) than do forests and woodlands (18–27%). Although the spatial pattern of net C uptake is controlled by both C residence times and rate of NPP change, we found that the proportion of soil C uptake is determined only by ecosystem C residence times and they are independent of the rate of NPP increase. Therefore the spatial patterns of C residence times are valuable for the evaluation of terrestrial ecosystem C sink.

 

Figure. Ecosystem carbon uptakes driven by NPP increases. (A1, A2) Ecosystem carbon uptake and proportions of soil carbon uptake, respectively, driven by an assumed uniform NPP increase. (B1, B2) Ecosystem carbon uptake and proportions of soil carbon uptake, respectively, driven by the actual spatially heterogeneous NPP increases.

 

 

Global Biogeochemical Cycles, 2008

http://www.agu.org/pubs/crossref/2008/2007GB002939.shtml