Effects Of Simulated Precipitation On Water Use Efficiency Of Main Plants In Desert Steppe

Global warming is bound to change the global precipitation pattern,and extreme drought and precipitation events will occur frequently,which will have a significant impact on grassland ecosystems.Precipitation is the main water source for the growth and development of desert steppe plants.In-depth study of the effects of precipitation changes on the water use efficiency（WUE）of desert steppe plants will help to understand the adaptation strategies of desert steppe plants to cope with future precipitation changes from the individual level and community level,and provide a theoretical basis for the effective utilization of water resources in desert steppe.This experiment was based on the simulated precipitation test platform in the Stipa breviflora desert steppe of Siziwang Banner,Inner Mongolia,since 2016.The completely randomized block design was used to set up four different precipitation treatments by means of rain-shielding rack and artificial irrigation,which were 50%natural precipitation reduction treatment,natural precipitation treatment,50%natural precipitation increase treatment and 100%natural precipitation increase treatment.In this experiment,seven main species,Stipa breviflora,Cleistogenes songorica,Artemisia frigida,Kochia prostrata,Heteropappus altaicus,Convolvulus ammannii and Chenopodium aristatum were studied.The photosynthetic characteristics,water use efficiency,carbon（C）and nitrogen（N）content,stable carbon isotope content(δ¹³C),aboveground biomass,soil water content,soil temperature and soil nutrients were measured.The response strategies of instantaneous water use efficiency（WUE_t）andδ¹³C value representing long-term water use efficiency of seven plants and their different functional groups to precipitation changes were compared and analyzed.The main results are as follows:（1）Under the four different precipitation treatments,The water content of soil surface layer was significantly higher than that of deep layer（P<0.05）,and the water content decreased gradually with the deepening of soil layer.Soil temperature was the highest under 50%water reduction treatment and the lowest under 100%water increase treatment（P<0.05）.With the deepening of soil depth,soil temperature decreased linearly.（2）Different precipitation treatments had different effects on the aboveground biomass of different plants.The water addition treatment significantly increased the aboveground biomass of grassland community,and the water reduction treatment significantly reduced the aboveground biomass of grassland community（P<0.05）.The50%water addition treatment significantly increased the aboveground biomass of Stipa breviflora（P<0.05）.The 100%water addition treatment significantly increased the aboveground biomass of Cleistogenes songorica grassland（P<0.05）.There was a significant positive correlation between precipitation and aboveground biomass of Stipa breviflora,Cleistogenes songorica and Kochia prostrata（P<0.05）.（3）The net photosynthetic rate of Stipa breviflora,Cleistogenes songorica,Kochia prostrata,Heteropappus altaicus and Convolvulus ammannii showed a bimodal curve in a day,with a more obvious lunch break phenomenon;the midday depression of Chenopodium aristatum was not obvious.The net photosynthetic rate of Chenopodium aristatum was delayed by 50%and 100%water increase.（4）The 50%water reduction treatment significantly increased the WUE_tof perennial forbs and annual herbs（P<0.05）,and the 50%and 100%water increase treatments significantly reduced the WUE_tof perennial herbs and semi-shrubs（P<0.05）.The 50%water reduction treatment significantly increased the WUE_tof C₃and C₄plants（P<0.05）.The 50%water increase only significantly decreased the WUE_tof C₃plants（P<0.05）.The 100%water increase significantly decreased the WUE_tof C₃and C₄plants（P<0.05）.（5）50%water reduction significantly increased theδ¹³C values of Kochia prostrata and Chenopodium aristatum（P<0.05）,and 100%water increase significantly decreased theδ¹³C values of Cleistogenes songorica,Kochia prostrata and Convolvulus ammannii（P<0.05）.100%water addition significantly reduced theδ¹³C value of perennial herbs（P<0.05）.Under different precipitation gradients,theδ¹³C value of C₄plants was significantly higher than that of C₃plants.（6）The net photosynthetic rate and transpiration rate of the main plants were significantly positively correlated with precipitation（P<0.05）;There was a significant positive correlation with stomatal conductance of six plants except Artemisia frigida（P<0.05）.There was a significant negative correlation between WUE_tand precipitation,except for Cleistogenes songorica（P<0.05）.There was a significant negative correlation between precipitation andδ¹³C values of Cleistogenes songorica and Kochia prostrata（P<0.05）.According to the above research results,plants can adapt to precipitation changes by adjusting their own water use efficiency.