摘要：
Aims Terrestrial net primary production (NPP), the balance of gross primary production (GPP) and autotrophic respiration (AR), is a critical measure of carbon sequestration capacity for the Earth's land surface. The aim of this study was to understand the spatio-temporal variability of NPP associated with GPP and AR in the Yangtze River Basin (YRB), China, from 2000 to 2009 during which the basin warmed significantly.
Methods We first derived AR and carbon-use efficiency (CUE) from the improved Moderate Resolution Imaging Spectroradiometer GPP/NPP products (MOD17) and then conducted spatial analysis to quantify how NPP relates to GPP, AR and their relationship with key observed climate variables (temperature, precipitation and sunshine percentage) in the YRB during 2000–2009.
Important findings The spatial pattern of NPP in the YRB was predominantly determined by GPP and further modified by AR. Higher GPP and relatively low AR made the southern Jinshajiang sub-basin the most productive area in NPP in the YRB. A large portion of the YRB experienced a warmer and drier climate trend in the growing season during 2000–2009. In the upper reaches of the basin, possessing a relatively low temperature base, increases in temperature led to greater increases in GPP than those in AR, resulting in greater increased NPP. However, in the middle and lower reaches of the basin where the base temperature is relatively high, increases in temperature led to greater increases in AR than those in GPP, leading to decreases in NPP. Overall, 86.7% of the vegetated area showed a consistent GPP and NPP trend through time with 71.3% of the vegetated area having a positive trend both in GPP and NPP, and the remaining 13.3% of vegetated areas showed an opposite trend in GPP and NPP, with positive GPP and negative NPP trajectories dominating (10.1% of vegetated area) the trend. Although climate warming generally had positive effects on vegetation growth in most areas of the basin, areas with increased NPP (74.5%) were less extensive than those with increased GPP (81.4%) due to the wider increase in AR (82.2%). During the study period, increases in AR offset 62% of the total increased GPP, leading to a substantial decline of CUE, particularly in the warmer lower altitude regions in the southeast. Our work reveals the diverse responses of NPP associated with GPP and AR as the climate warms and generally suggests that NPP in the middle and lower sub-basins in the YRB is more sensitive to future climate warming. These findings enhance our understanding of terrestrial ecosystem carbon dynamics in response to global warming and provide a scientific basis for managing ecosystem productivity in the YRB, China.
