Abstract: To accurately examine the water budget of degraded meadow ecosystems in the Three-River Source Region, eddy covariance system (EC) and lysimeter were used to continuously measure the evapotranspiration (ET) of a degraded meadow. Our results showed that ET mea-sured by two methods had the same trend of annual variation. The annual cumulative ET measured by EC was 481 mm (accounting for 86% of annual precipitation), which was lower than that measured by lysimeter (558 mm). The annual energy balance ratio (EBR) of turbulent fluxes measured by eddy covariance against the independently available energy was about 0.78. TheEBR in the growing season was higher than that in the non-growth season. When the friction-velocity (u^*) was less than 0.25 m·s^-1, the EBR increased with the increasing u^*. There was no significant change in EBR when u^*>0.25 m·s^-1. The changes in soil heat flux relatively lagging behind the net radiation might be one of the causes of energy imbalance. The value of ET measured by EC was getting close to that by lysimeter with the increases of net radiation, temperature and wind speed. Soil water content had no obvious effect on ET measured by both methods. The results suggested that there was a good relationship of the ET obtained with both methods, but ET may be underestimated by EC in this meadow ecosystem.

Key words: Panonychus citri, fenpropathrin, avermectin, life-table parameters., sublethal effect