Abstract: Water use efficiency (WUE) is an important parameter for investigating the responses of terrestrial ecosystems to global change. It is of great significance to analyze the variation of WUE and its response to meteorological factors for research of carbon water cycling and regional scientific management of water resources. Based on MODIS GPP and ET remote sensing data, meteorological data and land cover data in 2000 and 2014, we analyzed the spatialtemporal change of vegetation WUE and the relationship between vegetation WUE and key meteorological factors in Sanjiang Plain. We further examined the change characteristics of WUE for each vegetation type in terms of land cover change. Annual mean variation of WUE in Sanjiang Plain showed a fluctuated decreasing trend. The mean annual vegetation WUE was 1.44 g C·kg^-1 H₂O. Monthly variation of WUE roughly showed a mono-peak curve. While WUE was lower from January to March and from November to December, it was higher in growing season (May to September). The seasonal WUE was highest in summer, followed by autumn, spring and winter. The intraannual change of WUE for each vegetation type showed a double peak curve, with the peak being mainly distributed in April-June and September. The averaged WUE values of different vegetation types ranked as mixed forest>coniferous forest>broadleaf forest>grassland>Cultivated land>permanent wetland. Vegetation WUE in Sanjiang Plain was positively correlated with precipitation, relative humidity and vapor pressure, but negatively correlated with temperature and sunshine hours. With the reduction of cultivated land area, the WUE of cultivated land increased by 11.1%. With the increased area of deciduous broadleaved forest and grassland, vegetation WUE increased by 12.8% and 15.9%, respectively.

Key words: light-temperature potential productivity, sowing date., CERES-Maize, maize