|Other Abstract||Net primary productivity of terrestrial vegetation was the major part of carbon cycling in ecosystem and reflects the utilization of vegetation to natural and environmental resource. With the changes of climate and the over exploitation of water and soil resource, productivity of ecosystem changed largely. Hence, study on NPP of terrestrial vegetation had an important scientific significance to achieve agricultural sustainable development and enhanced ecosystem sustainability in an arid region. Manas River Watershed, which had various vegetation types, was part of mountain ecosystems of arid regions and its landscape was special and distinctive. Therefore, based on experimental observations and model simulation, the study estimates NPP of terrestrial ecosystem and analyzed the temporal and spatial pattern of NPP and scale effect. Conclusions showed that:
(1) On the whole, the dynamic of NEE, ecosystem respiration (Reco) or GPP showed a single-peak curve in the entire growth period of cotton. The study showed that accumulative net carbon flux (NEE), accumulative ecosystem respiration (Reco) and accumulative gross primary production were -304.8 g C m-2, 706.18 g C m-2 and 1011.00 g C m-2 over the whole cotton growing season. Moreover, with time scaling up, the correlations of GPP to net solar radiation (Rn), air temperature (Tair), and soil water content (SWC) became stronger gradually due to resistance and resilience of ecosystem and the protection of plastic film mulching. The GPP was more strongly correlated with Rn than Tair at time scales from minutes to days, while it reversed at time scales from days to weeks. This was largely determined by the biochemical characteristics of photosynthesis. Moreover, there were the responses of NPP to environmental factors, which was the same responses as GPP because relationships between GPP and factors were similar to relationships between NPP and factors.
(2) Based on SEBAL and light utility efficiency model, the study estimated vegetation NPP of 2013 of Manas River Watershed located in the northern slope of Tianshan Mountain in arid regions. The parameters in the study were only adjusted for the characteristics of arid regions, and the innovation was the calculation of the water stress index(Wε). Estimated result of NPP in Manas River Watershed by coupling model was reasonable and it could actually reflect the NPP of vegetation. It not only would improve the model quality, but would reduce the difficulty of model manipulation. It was an efficient way of estimating vegetation NPP of arid regions.
(3) The total annual NPP of vegetation and the mean annual NPP in Manas River Watershed in 2013 were 7066.72 Mt C·a-1 and 278.06 g C·m-2·a-1 respectively. With the variation of geomorphic type and land cover, the spatial changes of NPP were remarkable: from south to north, NPP increased firstly, and decreased secondly, and then increased, finally decreased. The temporal variations of NPP were also obvious, and the NPP in two months of July and August was account for 52.2% of total annual NPP. With the increasing of the elevation and slope, the mean annual NPP decreased as a whole with fluctuations induced by different land covers and environmental factors. With scaling up, NPP of crop increased, but NPP of forest, grassland and bare land almost remained unchanged. Average stimulated NPP of 30m resolution was 5.36% higher than of 990m resolution. Scaling up induced the change of mean estimated NPP in Mans River Watershed and scale effect, and the main reason was the change of land cover. The optimum scale of estimating NPP of unused land was 30m but the optimum scale of estimating NPP of cropland ranges from 330m to 400m.|