羊草叶片气体交换参数对温度和土壤水分的响应

 采用生长箱控制的方法研究了羊草(Leymus chinensis)幼苗叶片光合参数对5个温度和5个水分梯度的响应和适应。结果表明：轻度、中度土壤干旱并没有限制羊草叶片的生长，对气体交换参数亦无显著影响，反映了羊草幼苗对土壤水分胁迫的较高耐性。叶片生物量以26 ℃时最大，其它依次为23 ℃、20 ℃、29 ℃和32 ℃。温度升高使气孔导度和蒸腾速率增加, 却使光合速率和水分利用效率降低。水分和温度对叶片生物量、光合速率、气孔导度和蒸腾速率存在显著的交互作用，表明高温加强了干旱对叶片生长和气体交换的影响, 降低了羊草对土壤干旱的适应能力。高温和干旱的交互作用将显著减少我国半干旱地区草原的羊草生产力。

RESPONSES OF GAS EXCHANGE CHARACTERISTICS IN LEAVES OF LEYMUS CHINENSIS TO CHANGES IN TEMPERATURE AND SOIL MOISTURE

Drought and high temperature often occur simultaneously in arid and semiarid regions, but few investigators have studied the interactions between these two stresses. Our objective was to compare the effects of soil moisture, temperature and their interactions on the photosynthesis and growth of Leymus chinensis. Plants were subjected to different soil moisture regimes (relative soil water content ranged from 25% to 80%) at temperatures of 20, 23, 26, 29 and 32 ℃ in a controlled environment. Under sufficient soil moisture conditions, both net photosynthetic rates and water use efficiency decreased with increasing temperature whereas both stomatal conductance and transpiration rates increased. There were no significant effects of soil moisture alone on net photosynthetic rates but significant soil moisture-temperature interactive effects were observed; net photosynthetic rates increased under conditions of moderate soil drought at 20-26 ℃ but were significantly reduced under drought conditions at extremely high temperature (32 ℃). Water use efficiency showed a similar response to changes in temperature and soil moisture as net photosynthetic rates. Soil moisture did not significantly affect leaf stomatal conductance or transpiration rates indicating that higher adaptive ability to soil drought may be exhibited under these experimental conditions. However, under all soil moisture conditions, both net photosynthetic rates and water use efficiency always decreased with increasing temperature whereas both stomatal conductance and transpiration rates always increased with increasing temperature. Leaf biomass also responded to changes in soil moisture and temperature. The leaf biomass was greatest under conditions of light to moderate soil drought at temperatures from 20-26 ℃ but decreased with decreasing soil moisture at higher temperatures of 29 ℃ and 32 ℃. Leaf biomass of plants grown at 26 ℃ was greatest under sufficient soil moisture and light drought conditions, but the leaf biomass at 23 ℃ was greatest under moderate to high drought conditions. These results suggest that the optimal growing temperature might be lowered under droughty conditions. Leaf biomass was reduced in plants grown at higher temperatures (29 ℃ and 32 ℃) under all soil moisture regimes. Interactions between water stress and temperature were highly significant for several physiological processes examined. Leaf gas exchange characteristics and growth were more impacted by drought conditions at high temperatures than at low temperatures. Similarly, the productivity of L. chinensis was reduced more by the combined stresses of drought and high temperature than by either stress alone and much of the effect was on photosynthetic processes. Our research suggests that the decreased precipitation and increased temperatures forecasted for this semi-arid region due to global climate change could adversely affect the distribution and abundance of L. chinensis. To conserve this species, future research should focus on ways to enhance the drought tolerance of L. chinensis at high temperatures.