Effects Of Warming And Increased Precipitation On Plant Community Characteristics And Soil Of Desert Steppe In Inner Mongolia

Global climate change has become a worldwide issue of high concern.As the key ecological factors affecting grassland ecosystem,the changes of temperature and water will affect the soil,vegetation type and distribution,community structure and function of ecosystem,and then change the potential feedback of ecosystem to climate change.The desert steppe ecosystem is extremely fragile and highly sensitive to climate change.Previous studies on global climate change in this region mostly focused on the impacts of temperature and nitrogen increase,precipitation and nitrogen addition,CO₂concentration increase and their interaction on the desert steppe ecosystem.However,there is a lack of experimental studies on the effects of warming and increased precipitation and their interactions on desert steppe by field controlled experiments under natural conditions.Climate change simulation with temperature and precipitation as the main variables is helpful to clarify the uncertainty of climate change in desert steppe.We examined the effects of warming and increased precipitation on plant community characteristics in a desert steppe ecosystem by simulating climate change control experiments.We examined the relationships among soil condition,community structure and composition,species diversity,and productivity under climate change.Our results would help to improve the understanding of the responses and adaptation strategies of plant communities in desert steppe to warming,increased precipitation and their interactions,provide scientific basis and data support for how to ensure ecological security of desert steppe ecosystem under the severe challenge of global climate change,and provide scientific basis and data support for the development of management plans to deal with climate change.A three-year field experiment of warming and increased precipitation was conducted in Stipa breviflora desert steppe in Siziwang Banner Research Base of Inner Mongolia Academy of Agricultural and Animal Husbandry Sciences.The experiment used a randomized block design,with three temperature gradients（no warming,1.5℃warming,3.0℃warming）and three precipitation gradients（natural precipitation,25%increase precipitation,50%increase precipitation）,a total of nine treatments with four replicates per treatment.In addition,we carried out pot experiments on the growth and reproductive characteristics of S.breviflora under the warming and increased precipitation（May 2017—September 2017）to further explore the response and adaptation mechanism of dominant species to climate change in desert steppe at the species level.The main results and conclusions of this study are as follows:1.Warming and increased precipitation have a significant effect on soil physical and chemical properties in desert steppe.warming effectively increased soil temperature（p<0.05）,and the effect of increased precipitation on soil temperature was closely related to the annual precipitation,soil temperature was significantly decreased under the condition of increased precipitation in wet years（p<0.05）.The response of soil water content to warming and increased precipitation was more rapid and significant,soil water content decreased by 7.9%under 3.0℃warming,increased by8.2%under 50%increased precipitation treatment,and increased by 6.7%under the interactive treatment of warming and increased precipitation.The effects of warming and increased precipitation on the contents of soil total carbon,soil total nitrogen and soil total phosphorus had an obvious time lag.The interactive treatment of warming and increased precipitation was more conducive to the improvement of soil total carbon,soil total nitrogen and soil total phosphorus.2.Warming decreased plant community density and coverage in desert steppe,and significantly increased community height（p<0.05）,while increased precipitation treatment significantly increased community density,coverage and height（p<0.05）.After 3 years of warming and increased precipitation,the proportion of plants in different functional groups changed significantly in desert steppe.The proportion of Perennial Grasses decreased significantly from 57.6%to 38.1%,the proportion of Annuals and Biennials increased significantly from 3.3%to 6.0%,and the proportion of Perennial Forbs,Shrubs and Semi-shrubs did not change significantly.The changes of species composition of plant community were mainly caused by the increases of the proportions of Artemisia scoparia and Neopallasia petinata.The Perennial Grasses were significantly negatively correlated with Annuals and Biennials,with an obvious trend that goes up and down.Warming decreased species diversity,but did not reach the significant level（p>0.05）.Increased precipitation significantly increased Shannon-Wiener index and Simpson index（p<0.05）,but the interaction between warming and increased precipitation had no significant effect on species diversity index（p>0.05）.Compared with warming and increased precipitation,inter-annual climate variability had a more significant impact on species diversity.3.The above ground biomass of the community was significantly reduced by the3.0℃warming treatment（p<0.05）,and significantly increased by the 50%water addition treatment（p<0.05）.The interaction of warming and increased precipitation had a positive effect on the above ground biomass of the community,but the effect was not significant（p>0.05）.The response of underground biomass of plant community to warming and increased precipitation was not significant（p>0.05）.The root/shoot ratio of plant community was significantly increased by warming in drought year（2015）（p<0.05）,and significantly decreased by 50%increased precipitation treatment in wet year（2016）（p<0.05）.This study found that soil water content and plant community height were the direct key factors determining above ground biomass,with significant positive correlation.4.Both growth and reproduction characteristics of S.breviflora changed due to climate warming and increased precipitation.Increased precipitation promoted sexual reproduction of S.breviflora,while the effects of warming on reproductive and vegetative ramet of S.breviflora might change from negative to positive depending on the changes of precipitation conditions.We found that the reproductive ramet of S.breviflora were more sensitive to simulated climate change.In conclusion,warming,increased precipitation and their interactions had significant effects on soil physical and chemical properties,plant community structure and composition,species diversity and biomass in desert steppe ecosystems.The change of soil water availability caused by warming and increased precipitation is the most important factor affecting the plant community in desert steppe.At the same time,in the process of plant communities responding to warming and increased precipitation,the change of species composition leads to the change of biodiversity and ecosystem function,and the competition and interrelationship between species play a key role in regulating.At the same time,the inter-annual climate variability also has an inestimable impact on the whole experiment results.Therefore,in the context of future climate change,we need to focus on species relationships and the effects of inter-annual climate variability.