Abstract: Based on the measurement of soil heat flux of Kobresia humilis and Potentilla fruticosa meadows at Haibei station,Qilian Mountains,the results indicated that the diurnal change of soil heat flux for both types of meadows in clear days was lower at night and higher in the afternoon,representing a single-peak distribution.And it was complex in rainy days,with drastic fluctuation caused by rain and cloud.Whether it was sunny or not,the diurnal change of soil heat flux for Potentilla fruticosa meadow was more stable and its extent was smaller for high canopy height and much soil water content in Potentilla fruticosa meadow,with respecting to Koresia humilis.The monthly change of soil heat flux which was lowest in December(Kobresia humilis and Potentilla fruticosa meadows were-40.27MJ/m2,-16.85MJ/m2 respectively)and highest in June(Kobresia humilis and Potentilla fruticosa meadows were 20.47MJ/m2,18.98MJ/m2 respectively),appearing a single-peak distribution.The annual total soil heat flux for Kobresia humilis and Potentilla fruticosa meadows was significantly different and was-24.72MJ/m2 and 48.10MJ/m2 respectively.Both of the annual change of soil heat flux was relevant to the variations of plant growth,soil water,seasonal frozen soil,especially net radiation.Due to the difference of vegetation types and environment factors,Potentilla fruticosa meadows' soil heat flux was a smaller consumer of net radiation than that of Kobresia humili.However,the synchronicity between soil heat flux and net radiation was worse for Potentilla fruticosa,whose delay feedback was 2.5 hours,longer than that of Kobresia humilis.

Key words: Potentilla fruticosa meadows, Potentilla fruticosa meadows, Kobresia humili meadows, Soil heat flux, Net radiation