Abstract: In this paper, the relationships between the rootshoot ratios and meteorological factors were analyzed using the data of aboveground and underground biomasses of five types of natural grasslands and the synchronous meteorological data in northern slope of the Qilian Mountains. The results indicated that the biomass of five types of natural grasslands was in an order of mountain meadow > mountain steppe > mountain meadow steppe > alpine steppe > mountaindesert grasslands; difference of the biomass among the five types of natural grasslands was significantly except that among alpine steppe, mountain meadow steppe and mountain steppe (P＜0.05); rootshoot ratios of alpine steppe, mountain meadow, mountain meadow steppe, mountain steppe and mountaindesert grasslands were 9.3, 8.7, 5.1, 7.0 and 7.1 respectively; there was a reverseparabolashaped seasonal variation in curves of rootshoot ratios of the five types of natural grasslands, but the seasonal variation of their rootshoot ratios was different; rootshoot ratio of alpine steppe was significantly decreased with the increase of soil moisture content in previous month, the rootshoot ratios of mountain meadow steppe and mountain steppe were significantly decreased with the increase of potential evapotranspiration in previous month, but there was no significant correlation between the rootshoot ratios of mountain meadow and mountaindesert grasslands and the hydrological and sunshine factors in previous month.

Key words: natural grassland, biomass, root-shoot ratio, climatic factor, the Qilian Mountains