Effects of water and temperature stresses on radiation use efficiency in a semi-arid grassland

Accurate estimation of radiation use efficiency (RUE) is essential in modeling plant productivity, but little information on RUE is available for dry grassland. To quantify the RUE, aboveground biomass (AGB) and photosynthetically active radiation intercepted by plants (IPAR) were measured under different conditions of soil water and air temperature in a Mongolian field for 2 years. A wide range of RUE (0.23-1.06 g AGB/MJ IPAR) was found in negative association with variations in soil water and low temperature stresses. Compared with the temperature stress, the water stress was a strong down-regulator on RUE, verifying that drought is the major concern on radiation utilization in the study area. The maximum RUE was then found to be 2.34 +/- 0.16 g AGB/MJ IPAR by excluding the effects of water and temperature stresses. This study is one of the few assessments on RUE for natural grasslands under various levels of seasonally varying water and temperature conditions.