Water Utilization Characteristics Of Dominant Plants In Typical Steppe Under Different Degradation Degrees

Water is the most important limited factor of the species diversity and primary productivity in semi-arid grassland.Grassland degradation caused by grazing has limitation on the ecological function and increasing productivity in China.Revealing the water utilization of the dominant plants in the typical grassland under different grazing degradation degree is conducive to understand the degradation mechanism of grassland ecosystem in individual level.In this study,the water sources of Stipa grandis,Leymus chinenesis and Cleistogenes squarrosa in the typical steppe of Inner Mongolia under different degradation degrees was measured and analyzed at the individual level with the stable isotope technology,and the water holding capacity,water use efficiency,water loss changes and their response to precipitation events were also measured and analyzed.The main results are as follows:1.The water sources of Stipa grandis had significant changes under different degradation degrees.Compared with light degradation,the water sources of Stipa grandis under moderate degradation moved to the deep soil layer,Stipa grandis under the light degradation only use the water in 0-10 cm soil layer.However,Stipa grandis under moderate degradation utilized the water from both 0-10 cm and 10-50 cm soil layers.Leymus chinensis under diffenent degradation degrees showed the subtle variations of water source.Leymus chinensis used under both degradation conditions utilize the soil water in both 0-10 cm and 10-50 cm,soil layers,but it inclined to use more water in 0-10 cm soil layer under lightly degradation condition and 10-50 cm under moderate degradation condition.There was no significant change of water source for Cleistogenes squarrosa with the change of the degradation degree.2.After the medium rainfall event,the three plants all used soil water in 0-10 cm in the light degradation condition.Compared with light degradation,Leymus chinensis gradually absorbed soil water from the soil surface layer in moderate degradation,while Stipa grandis slightly inclined to absorb the water in the deep soil layer and the water source of Cleistogenes squarrosa did not change obviously.After the heavy rain,the three plants under the two degradation conditions all utilized the water from 0-10 cm soil layer.The water sources of plant responded differently to the different rainfall intensity.With the increase of rainfall intensity,the proportion of plant using surface soil water increased.3.Compared with the light degradation,both the water absorbing capacity of the three plants and the water holding capacity of Leymus chinensis and Cleistogenes squarrosa significantly increased under the medium degradation condition,but decreased for Stipa grandis.4.Compared with the light degradation,the water use efficiency of Stipa grandis and Leymus chinensis significantly increased under the moderate degradation,but no significant change was found for Cleistogenes squarrosa.The plant water loss was the highest in July.In conclusion,the plants under the medium degradation condition can adapt to the environmental changes by the strategies of changing water sources,increasing water use efficiency and water absorption and retention,and reducing water loss.