Response Of Three Plant Functional Character And Water Physiological Ecology To Degradation Degree Of Desert Grassland

Grassland ecosystem is an important part of terrestrial ecosystem in China.Grassland degradation caused by grazing has attracted much attention.Overgrazing strongly affects the pattern and process of grassland ecosystem,and causes the continuous decline of grassland productivity and ecosystem services.The change of plant functional traits is a comprehensive manifestation of plants adapting to environmental changes.Analyzing the changes of plant functional traits in grasslands with different degraded degrees helps to clarify the mechanism of grazing on grassland productivity and ecosystem functions,and has guiding significance for scientific management of grasslands and ecological restoration of degraded grasslands.Sheramoren desert grassland is seriously degraded due to overgrazing.Its productivity and biodiversity decrease,and its ecosystem service function decreases.Taking three common plant species S.breviflora,C.squarrosa and C.ammannii in grassland with different degraded degrees as research objects,the changes of functional traits,photosynthetic physiology and plant interception characteristics of three plants under different degraded degrees were studied by means of field investigation and indoor research.The responses of three plant functional traits to the degraded degree of grassland were clarified,and the photosynthesis and interception characteristics of three plants under different degraded degrees were revealed.The effects of grassland degradation degree and plant morphology on water use efficiency and plant interception were clarified in order to provide theoretical basis for rational utilization of grassland resources and scientific grazing.The main research results show that:(1)Indicators of individual plant functional traits of the three plants decreased with the aggravation of grassland degradation.Grassland degradation had a greater impact on plant height of S.breviflora and C.ammannii,with 49.1% and 48.8% decrease in plant height and 32.2% decrease in C.squarrosa,respectively.The biomass of S.breviflora changed greatly with the increase of grassland degradation,and decreased by 42.3%.The biomass of C.ammannii changed significantly in moderate and severe degraded plots.Grassland degradation changed the distribution of aboveground substances,and the ratio of stem to leaf decreased.The effect of grassland degradation on the ratio of stem to leaf of three plants was not very different.The decrease of the ratio of stem to leaf varied between 28% and 35%.With the aggravation of grassland degradation,the ratio of length to width of S.breviflora leaves increased,while the other single leaf functional traits showed a decreasing trend;C.ammannii was greatly affected by grassland degradation,and the index value changed greatly.(2)With the aggravation of grassland degradation,the thickness of leaf anatomical structure of the three plants increased.Overall,the thickness of leaf anatomical structure of the three plants showed severe degradation > moderate degradation > mild degradation.Because of the different cross-sectional morphology of the leaves of three plants,the change trend of leaf anatomical structure is different among different degradation degrees.The thickness of the upper cuticle of S.breviflora and C.ammannii is less than that of the lower cuticle,and the thickness of the upper cuticle is larger than that of the lower cuticle.On the contrary,the thickness of the upper cuticle of C.squarrosa(2.56-4.99 um)is larger than that of the lower cuticle(1.16-3.50 um).The mid-vein thickness of C.ammannii and S.breviflora increased with the degree of grassland degradation,while the mid-vein thickness of C.squarrosa did not change significantly.C.squarrosa leaf thickness was less affected by grassland degradation,and increased by 6.11 um.C.squarrosa leaf thickness was insensitive to grassland degradation,while C.ammannii was more affected by grassland degradation,with 46.4% increase in leaf thickness and high sensitivity.(3)With the aggravation of grassland degradation,the daily average transpiration rate and net photosynthetic rate of the three plants increased,the peak values of S.breviflora and C.ammannii net photosynthetic rate advanced,and the photosynthetic mechanism of C.squarrosa changed from stomatal limitation of photosynthesis in slightly degraded plots to non-stomatal limitation in moderately and severely degraded plots;the three plants all had certain adaptability to soil water,and S.breviflora had certain adaptability to soil water change.S.breviflora had higher photosynthetic rate and water use efficiency,and had stronger drought resistance.(4)The interception measurement method has some influence on the interception results.S.breviflora immersion interception is lower than simulated rainfall interception,while C.squarrosa and C.ammannii simulated rainfall interception is lower than simulated rainfall interception.There is a negative correlation between the amount of plant interception and the degree of grassland degradation.The amount of plant interception decreases with the degree of grassland degradation.