Biomass Distribution of Natural Grasslands and It Response to Climate Change in North China

Aboveground and belowground biomasses and their distribution are the important parameters of carbon cycle.Many achievements about the distribution pattern of aboveground biomass have been achieved,but the studies about belowground biomass are very limited.In this paper,the root-shoot ratios and fBNPP(defined as the fraction of belowground net primary productivity(BNPP) in total NPP) as well as their relationships with climatic variables are lucubrated by synthesizing the references about biomass of grasslands in north China.The results show that the root-shoot ratios and fBNPP are obviously different from different grasslands types,and they vary in ranges of 1.66~15.21 and 0.29~0.98 respectively.In general,the root-shoot ratio and fBNPP of desert steppe are high,but their change extent is low;the root-shoot ratio and fBNPP of forest grasslands are low,but their change extent is high.There is a negative correlation between the root-shoot ratio and fBNPP and the climatic factors,that is the rootshoot ratio and fBNPP are significantly decreased with the increase of annual precipitation,but their decrease trend with the increase of annual temperature is not so significant.The study results also reveal that the values of root-shoot ratio and fBNPP might be overestimated if the maximum biomass in the growth season of grasslands is used.It is necessary to research the effects of different study methods on estimating the NPP of grasslands and veraciously evaluate the importance of grasslands in regional and global carbon circle using the long-term measured biomass data,especially the data of belowground biomass.