Spatial and temporal relationships between precipitation and ANPP of four types of grasslands in northern China.

Precipitation is considered to be the primary resource limiting terrestrial biological activity in water-limited regions. Its overriding effect on the production of grassland is complex. In this paper, field data of 48 sites (including temperate meadow steppe, temperate steppe, temperate desert steppe and alpine meadow) were gathered from 31 published papers and monographs to analyze the relationship between above-ground net primary productivity (ANPP) and precipitation by the method of regression analysis. The results indicated that there was a great difference between spatial pattern and temporal pattern by which precipitation influenced grassland ANPP. Mean annual precipitation (MAP) was the main factor determining spatial distribution of grassland ANPP (r(2) = 0.61, P < 0.01); while temporally, no significant relationship was found between the variance of ANPP and inter-annual precipitation for the four types of grassland. However, after dividing annual precipitation into monthly value and taking time lag effect into account, the study found significant relationships between ANPP and precipitation. For the temperate meadow stcppe, the key variable determining inter-annual change of ANPP was last August May precipitation (r(2) 0.47, P= 0.01); for the temperate steppe, the key variable was July precipitation (r(2)= 0.36, P= 0.02); for the temperate desert steppe, the key variable was April-June precipitation (r(2)=0.51, P< 0.01); for the alpine meadow, the key variable was last September-May precipitation (r(2)= 0.29, P < 0.05). In comparison with analogous research, the study demonstrated that the key factor determining inter-annual changes of grassland ANPP was the cumulative precipitation in certain periods of that year or the previous year.