Simulation and evaluation of terrestrial ecosystem NPP with M-SDGVM over continental China

Using the regional terrestrial Net Primary Production (NPP) from different observations and models over China, we validated the NPP simulations and explored the relationship between NPP and climate variation at interannual and decadal scales in the Modified Sheffield Dynamic Global Vegetation Model (M-SDGVM) during 1981-2000. M-SDGVM shows agreement with the NPP data from 743 sites under the Global Primary Production Data Initiative (GPPDI). The spatial and the zonal averaged NPP of M-SDGVM agree well with different historic datasets and are closest to the IGBP NPP. Compared to the 1980s, NPP in the 1990s increases in most of China with a high degree of spatial heterogeneity. The multi-year mean NPP of forest types is reasonably modeled (above 500 g C m(-2) yr(-1)) while that of C-3 path of photosynthesis (C-3) grasslands is underestimated. The NPP of 7 M-SDGVM main plant functional types (PFTs) increases and the increment of the broad-leaved deciduous forest is the most obvious (5.05 g C m(-2) yr(-1)). During the studied period, the annual NPP of M-SDGVM over China increases, with significant fluctuations, at an average rate of 0.0164 Gt C yr(-1). Regulated by annual temperature and precipitation, the interannual variation of the total NPP shows more significant correlation with temperature (relativity and probability are R= 0.61, P = 0.00403) than precipitation (R = 0.40, P = 0.08352). CO2 fertilization may play a key role in the increase of terrestrial ecosystem NPP over continental China, and CO2 stimulation increases with CO2 concentrations, and also with the climate variability of the 1980s and 1990s.