| The extremely important strategic ecological position of desert grassland ecosystem,and its sensitivity and inevitability to climate change determine that it is very important to study the response of desert grassland ecosystem to climate change.Therefore,in this experiment,the desert grassland in Yanchi County,Ningxia,on the southern edge of Mu Us Sandy Land,was taken as the research object,and five precipitation gradients and two temperature gradients were simulated by using the precipitation shelter technology and the OTC(Open-Top Chamber).The five precipitation gradients were 33%,66%,100%,133%,and 166%of the normal precipitation(R33,R66,RCK,RCK).The temperature gradient is natural temperature,and non-directional warming(X,X+1.5℃),and the interaction of precipitation and warming is TR33,TR66,TRCK,TR133,and TR166.The ecological response of vegetation,soil,microorganism and their coupling relationship to precipitation change and warming in desert steppe was studied(2018-2021),and the main results were as follows:(1)Under the precipitation change,increasing precipitation(R166)will significantly increase the diversity,evenness,and richness of vegetation,and increase the density and frequency of Agropyron mongolicum,Lespeseza bicolor,and Polygala tenuifolia;Precipitation has significant effects on the contents of organic carbon,total nitrogen and total phosphorus in leaves and roots of Agropyron mongolicum,Lespeseza bicolor and Polygala tenuifolia.Increasing precipitation is beneficial to the enrichment of organic carbon,total nitrogen,and total phosphorus in the litter,and promotes the increase of vegetation biomass.Reducing the nitrogen content in plant leaves inhibited the net photosynthetic rate of vegetation.There is a significant positive correlation between precipitation and vegetation biomass,litter organic carbon,litter total phosphorus,and the vegetation diversity index.The soil water content in 0-40cm soil layer is the fastest and most sensitive to the precipitation change.Under RCK treatment,the soil water content in this soil layer is higher than in other treatments,and the soil water retention capacity is relatively stable.Meanwhile,the increase in precipitation promotes soil respiration and carbon emission.There was a significant positive correlation with soil respiration,soil organic carbon,total nitrogen,total phosphorus and their stoichiometric ratio.The response of microbial diversity to precipitation changes slightly in 1-2 years,and the β diversity of soil fungi was significant increased by R166 treatment in the third year of precipitation increase.The precipitation is mainly negative correlated with the abundance and coverage of bacteria.(2)Under the warming,warming by 1.5℃(the average warming measured by OTC is 1.5℃)can improve the diversity,richness and evenness of vegetation;Warming reduced the coverage and density of Lespeseza bicolor and Agropyron mongolicum,but increased the density and height of Polygala tenuifolia.Warming increased the accumulation of organic carbon content in leaves and roots ofAgropyron mongolicum,Lespeseza bicolor,and Polygala tenuifolia,and decreased the total nitrogen content in leaves,roots of Lespeseza bicolor,and Polygala tenuifolia.Warming makes the aboveground biomass of vegetation decrease year by year,while the root biomass of vegetation increases significantly.There was a significant negative correlation between temperature,litter organic carbon,and litter total phosphorus.Warming reduces the fractal dimension of soil,promotes the accumulation of organic carbon in 20-30cm soil,and reduces the ratio of soil organic carbon to total nitrogen and soil respiration;Warming is negative correlated with soil total nitrogen and soil respiration.Grassland soil microbes are extremely sensitive to temperature changes,and warming significantly improves the richness and evenness of soil fungal communities,and promotes the bacterial β diversity.There is a significant positive correlation with the diversity and richness of bacteria.(3)Precipitation and warming decrease vegetation diversity,TR166 increases the density of Agropyron mongolicum,Lespeseza bicolor,and Polygala tenuifolia,increases the frequency of Agropyron mongolicum and Lespeseza bicolor,but inhibits the frequency of Polygala tenuifolia and height ofAgropyron mongolicum;The interaction of increasing precipitation and warming increased the organic carbon content of Agropyron mongolicum,Lespeseza bicolor and Polygala tenuifolia,while the interaction of decreasing precipitation and increasing temperature(TR33)significantly reduced the total nitrogen content of Agropyron mongolicum root.TR133 and TR166 can increase the total phosphorus in leaves and roots of Lespeseza bicolor,and the contents of organic carbon,total nitrogen,and total phosphorus in the litter,increase the aboveground biomass of vegetation,and significantly reduce the underground biomass;The interaction between precipitation and warming is positive correlated with the aboveground biomass of vegetation.The interaction of increasing precipitation and warming significantly increased soil organic carbon content,soil fractal dimension,soil pH,and promoted soil respiration.In the soil layer of 20-30cm,the ratio of soil nitrogen to phosphorus is higher than in other treatments under the interaction of increasing temperature and precipitation.The interaction between precipitation and warming is positively correlated with soil respiration and soil C/P ratio.The interaction of precipitation and warming on soil microbial characteristics showed that TR33 increased the a diversity of fungi,and TR166 promoted the β diversity of soil bacteria and fungi;The interaction between precipitation and warming is negative correlated with bacterial evenness,bacterial richness,bacterial coverage,fungi richness and fungi coverage.(4)SEM analysis shows that R166 has a significant influence on the correlation among vegetation,soil,and microorganisms,while R33 is the weakest under the precipitation change.Vegetation,soil,and microbial characteristics are negative correlated with each other,which the richness and evenness of vegetation have a positive effect on vegetation diversity,and dominance has a negative regulatory effect on vegetation diversity.Soil respiration has a negative impact on aboveground biomass,soil total phosphorus,and soil nitrogen-phosphorus ratio.Bacterial diversity mainly positively promoted the ratio of soil carbon to nitrogen,but negatively affected the total nitrogen of litter.There is a significant linear correlation between fungal diversity and plant diversity.Under increasing temperature,the correlation effect of increasing temperature by 1.5℃ on vegetation,soil and microorganism is lower than that of natural temperature.There is a negative correlation between vegetation and soil and soil microbes,but a positive correlation between soil and soil microbes,among which vegetation evenness and dominance promote vegetation diversity;Bacterial diversity mainly positively affects soil pH,but negatively feeds back vegetation dominance;Fungi diversity was positively correlated with soil fractal dimension and litter total nitrogen,but negatively correlated with vegetation diversity.Under the interaction of precipitation and warming,TR133 and TR166 have more potent correlation effects on vegetation,soil,and microorganism than other treatments.It is positively correlated with soil and microorganism,but negative correlated with soil and microorganism,in which soil respiration is high in summer and gradually decreases in autumn.It is mainly positively correlated with underground biomass of vegetation.Soil fractal dimension and total nitrogen in the litter positively affects bacterial and fungal diversity,while vegetation diversity negatively feeds back bacterial and fungal diversity.To sum up,the characteristics of vegetation-soil-microorganism are interrelated under the change in precipitation.Precipitation affects the characteristics of vegetation,and then affects the characteristics of microorganism and soil.Warming first affects soil microorganism,and then acts on vegetation and soil characteristics;The interaction between precipitation and warming affects vegetation,and then regulates microbial and soil characteristics.The results of this study not only provide a reference for simulating and predicting the response and feedback of vegetation-soilmicroorganism system to climate change in the desert steppe,but also provide scientific support for formulating reasonable strategies to deal with climate change in this region. |
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