Effects Of Short-term Warming On Plant Community Characteristics Of Semi-arid Leymus Secalinus Grassland In Northern Shanxi

Over the past 100 years,the global climate tends to be warming.Global warming affects the environment and community characteristics of terrestrial ecosystems.As one of the important ecosystems,the structural characteristics and ecological functions of grassland ecosystems are profoundly affected.However,the change of ecosystem structure and characteristics is a slow process,so simulating the impact of climate warming on grassland ecosystem function can predict the trend of grassland ecosystem in the future.This study is focused on the semi-arid Leymus secalinus grassland in northern Shanxi.In March 2018,OTCs(the open top chambers)were set to simulate five gradient warming experiments,namely CK(quadrilateral edge length 200cm,height 0cm),W1(bottom edge length 100cm,height 40cm),W2(bottom edge length 110cm,height 60cm),W3(bottom edge length 120cm,height 80cm),W4(bottom edge length 130cm,height 100cm)and the top edge length of OTCs was 80cm.Random block design was used in the experiment with five replicates.The changes of environmental factors and plant community characteristics of semi-arid Leymus secalinus grassland in northern Shanxi during the growing season from2018 to 2020 were observed,and the correlation between environmental factors and plant communities was analyzed.The effects of short-term warming on the community structure characteristics of semi-arid Leymus secalinus grassland in northern Shanxi were discussed.The results are summarized as follows :1.Short-term warming significantly increased air temperature and soil temperature(0-10cm),and decreased soil moisture(0-10cm)(P<0.001).The changes of air temperature,soil temperature and soil moisture under different gradient warming treatments were consistent,showing an asymmetric single peak curve.In 2019,compared with the CK,the air temperature of W1,W2,W3 and W4 increased by 1.3℃,1.6℃,2.2℃ and 3.7℃,respectively.Soil temperature increased by 0.66℃,0.73℃,0.80℃ and 0.98℃,respectively.Soil moisture decreased by 1.6%,1.9%,2.4% and 2.9%,respectively.In 2020,compared with the CK,the air temperature of W1,W2,W3 and W4 increased by 3.0℃,3.2℃,4.2℃ and 5.5℃,respectively.Soil temperature increased by 0.40℃,0.41℃,0.53℃ and 0.85℃,respectively;Soil moisture decreased by 1.07%,1.29%,2.18% and 2.39% respectively.Short-term warming leads to the increase of shallow soil temperature and drying of soil.2.Short-term warming significantly reduced the plant community density(P<0.001),height and coverage of grassland without significant difference(P>0.05).The density,height and coverage increased first and then decreased with the passage of the month,the highest in August.Plant community density was the highest under CK treatment and the lowest under W4 treatment;Plant community height was the highest under W2 treatment and the lowest under CK treatment;Plant community coverage was the highest under W1 treatment and the lowest under W3 treatment;Gradient warming treatment had a significant effect on plant community density(P<0.001),and there were significant differences in plant community density,height and coverage between years(P<0.001).The importance value of grass plant community increased first and then decreased along the warming gradient.Appropriate warming promoted the growth of grass,while excessive temperature promoted the growth of hybrid grass.3.Short-term warming had no significant effect on grassland species richness and diversity(P>0.05).The species richness in 2019 was higher than in 2018 and 2020.The species richness and diversity of grassland species were significant between years(P<0.001).4.Short-term warming had no significant effect on plant community biomass(P>0.05).5.Air temperature had a significantly negatively correlated with species richness and species diversity index(P<0.001).Soil temperature had a significantly positively correlated with plant community coverage(P<0.001),but had no relationship with species richness and diversity index(P>0.05).Soil moisture had a significantly positively correlated with plant community density,coverage and height,species richness and diversity index(P<0.001).Correlation analysis showed that soil moisture was the driving factor of plant community composition change in arid environment.In summary,warming changed grassland environmental factors,making it more and more warm and drought.Warming changed the composition and structure of plant communities.Appropriate warming can promote the growth of plants,and too high temperature can inhibit the growth of plants,so that the plant community tends to be unitary.Air temperature and soil moisture are related to plant community diversity.