Effects Of Nitrogen Addition,Warming And Rainfall Increase On Stoichiometry Of Alfalfa Leaves In The Loess Plateau Of China

In the context of increasing global climate change,such as rising temperatures,atmospheric nitrogen deposition,and extreme precipitation events,there will be a non-negligible impact on a region or even a global ecosystem.Especially in the fragile Loess Plateau region of China,natural ecosystems are more sensitive to climate change.In addition,the carbon,nitrogen and phosphorus cycle and ecological stoichiometry of plants are closely related to global climate change.At present,the research on the ecosystem of the Loess Plateau mainly focuses on the influence of the interaction of single factors or two factors on the structure and function of ecosystems.The ecological impacts of simultaneous changes in rainfall,nitrogen addition and warming require further research.Studying the response of ecological stoichiometric characteristics of C,N and P in the semi-arid region of the Loess Plateau to rainfall,nitrogen addition and warming is helpful to predict the response of the stoichiometric characteristics of grassland ecosystems to global climate change in semi-arid areas.Therefore,this study set up three factors experiments on the effects of rainfall?R?,nitrogen addition?N?and warming?W?on alfalfa.Each factor has two levels,a total of 8 treatments,and each treatment was repeated four times.The increase of rainfall is the addition of 100 mm on the basis of natural rainfall,sprayed in 5 months?May-September?,spraying 20 per month,spray twice a month,each time 10 mm;The nitrogen addition is to spray NH₄NO₃ according to the nitrogen deposition amount of 10 g/m² per year,and the average annual distribution is 5 times in the middle of May-September;Warming adopts open top OTC warming frame.Research indicates:1.The aboveground biomass was significantly increased by warming,the interactions between rainfall and nitrogen addition?R*N?,rainfall and warming?R*W?,nitrogen addition and warming?N*W?had no significant effect on aboveground biomass.However,the effects of interactions between rainfall,nitrogen addition,and warming?R*N*W?on biomass were different between years.2.In May,the warming and nitrogen addition had no significant effect on the carbon,nitrogen and phosphorus and their ratios of alfalfa leaves;In July,the content of total nitrogen and total phosphorus in alfalfa leaves was significantly reduced by warming,and C:N and C:P were significantly increased,but there was no significant effect on organic carbon and N:P,rainfall and nitrogen addition had no significant effect on C,N,P and their ratios in alfalfa leaves.The interaction of rainfall and nitrogen addition?R*N?,rainfall and warming?R*W?,nitrogen addition and warming?N*W?had no significant effect on organic carbon,total nitrogen,total phosphorus and their ratios in alfalfa leaves.3.There was a significant positive correlation between the content of N and P in the leaves,while there was no significant correlation between N:P and the content of N in the leaves,and there was a significant negative correlation between N:P and the content of P in the leaves?p<0.001?.There was no significant correlation between the content of C and P in leaves,and there was no significant correlation between C:P and the content of C in leaves,but there was a significant negative correlation between C:P and the content of P in leaves?p<0.001?.4.In May,there was no significant correlation between the content of C and N in leaves,but there was a significant positive correlation between C:N and the content of C in leaves?p<0.05?,and a very significant negative correlation between C:N and the content of N in leaves?p<0.001?.In July,there was no significant correlation between the content of C and N in leaves and between the content of C:N and the content of C in leaves,but there was an extremely significant negative correlation between the content of C:N and the content of N in leaves?p<0.001?.