Effects Of Reduced Percipitaion And Nitrogen Deposition On Biomass Of Leymus Chinensis And Its Nitrogen Allocation

Global climate change characterized by changes in rainfall patterns and nitrogen deposition has become a serious problem in the Earth's ecosystems.Leymus chinensis grassland is an excellent grassland and an important ecological barrier in China.Under the background of global climate change,the reduction of precipitation and nitrogen deposition will affect the nitrogen allocation and utilization of grassland ecosystem,and then affect grassland productivity.Therefore,it is important to study the nitrogen allocation of soil and plant in Leymus chinensis grassland.In this study,the biomass,soil nutrient and nitrogen allocation and utilization of Leymus chinensis under the conditions of precipitation reduction?-30%?and nitrogen deposition(10 g N m^-2)were studied by using ¹⁵N isotope tracer technique.The main results and conclusions are as follows:?1?Decreased rainfall amount and nitrogen deposition changed the aboveground and belowground biomass allocation.The decreased rainfall amount significantly reduced the aboveground biomass.For the belowground part,there was an interaction between precipitation and nitrogen deposition,which significantly increased the belowground biomass of Leymus chinensis.?2?The interaction of rainfall reduction and nitrogen deposition had a significant effect on soil nutrients.Nitrogen deposition increased soil ammonium nitrogen?NH₄⁺-N?content,while low rainfall decreased soil NH₄⁺-N content.The synergistic effect of rainfall reduction and nitrogen deposition increased concetrations of soil nitrate nitrogen,total nitrogen,total carbon and total organic carbon and decreased soil pH value.?3?For the nitrogen deposited in soil,the recovery rate ranged from 11.92%to 18.02%,the residual rate in soil ranged from 40.03%to 61.53%,and the unknown loss rate ranged from 26.55%to 41.95%in the first year.?4?The residual nitrogen deposited in soil were absorbed and utilized by Leymus chinensis in the following years,the range of ¹⁵N recovery rate of the second year and the third year were 18.95²0.04%and 6.83⁷.49%,respectively,and the cumulative recovery rate of three years was 38.36⁴4.89%.The cumulative recovery of ¹⁵N was 14.58²3.66%for leaf,13.78¹8.81%for belowground part and 4.97⁷.90%for stem.Low rainfall reduced the¹⁵N recovery rate of stems and leaves,and increased the ¹⁵N recovery rate of belowground part.In the second and third year,the residual rates were 24.58³1.32%and 19.79²9.79%,respectively,and the unknown nitrogen losses were 1.59¹7.40%and 1.73³.13%,respectively.In summary,under the background of future climate change?precipitation reduction and nitrogen deposition?,the nitrogen allocation and utilization of grassland under nitrogen deposition are affected by precipitation.Low rainfall amount will affect the absorption and utilization of nitrogen and change the allocation pattern of aboveground and belowground biomass of Leymus chinensis.The aboveground biomass and nitrogen recovery rate were reduced,and the belowground biomass and nitrogen recovery rate were increased.Nitrogen deposition can compensate for the decrease of biomass caused by the decrease of rainfall.Nitrogen deposition can promote the individual growth and indirectly improve the productivity of grassland by improving the availability of soil nitrogen and soil nutrients.The residual nitrogen in soil will promote the growth of Leymus chinensis in the following years.This study not only provides a theoretical basis for the adaptation mechanism of the grassland to global climate change,but also provides a reference and theoretical guidance for the scientific use of nitrogen in other grasslands in northern China.