Effects Of Warming And Nitrogen Addition On Plant Nutrient Resorption In A Desert Steppe

Climate warming and increased atmospheric nitrogen(N)deposition,as two important components of global climate change,can influence the nutrient cycle process between plant and soil.Based on a 12-year simulated warming and N addition experiment in the field,we explored the responses of plant and soil nutrient characteristics to warming and N deposition in contrasting wet(2016,52%above the long-term mean precipitation)and dry(2017,16%below the long-term mean precipitation)years in desert steppe.We selected three dominant species(Stipa breviflora,Artemisia frigida and Cleistogenes songorica)and two other common species(Convolvulus amma and Kochia prostrata).We measured N and phosphorus(P)concentrations in green and senesced leaves from the five studied species,and correspondingly calculated N resorption efficiency(NRE)and P resorption efficiency(PRE).We measured soil available N and P contents,soil moisture,soil temperature,natural precipitation and air temperature.The aim of this study is to uncover how plant nutrient resorption responds to long-term warming and N addition.These findings may need to be considered in global climate change models,in order to provide improved predictions and assessment of the effects of climate change on nutrient cycling.The main research results are shown as followings:(1)In a relatively wet year(2016),warming,N addition and combined warming and N addition significantly increased soil inorganic N and available P(P<0.001).On the contrary in a relatively dry year(2017),there were no significant effect(P>0.10).(2)In 2016,warming,N addition and combined warming and N addition significantly increased N and P concentrations in green and senesced leaves of the studied five species,and decreased plant NRE and PRE(P<0.01).While in 2017,warming,N addition and combined warming and N addition did not significanly affect these plant nutrient resorption efficiency(P>0.10).Both NRE and PRE were lower in 2016 than in 2017(P<0.001).(3)In 2016,warming significantly reduced N:P ratios of green and senesced leaves from C.songorica and that of senesced leaves from K.prostrata(P<0.05).Nitrogen addition significantly reduced the N:P ratio of green leaves from K.prostrata.In 2017,warming,N addition and combined wanning and N addition had no significant impact on leaf N;P ratios(P>0.10).(4)Regression analysis showed that plant NRE and PRE were negatively correlated with leaf N concentration and leaf P concentration respectively(P<0.001).The N:P ratios of green and senesced leaves were not related to NRE,but were negatively correlated PRE(P<0.001).Nitrogen concentrations in green and senesced leaves increased with increasing soil inorganic N,and leaf P concentrations increased with increasing soil available P.Leaf N and P concentrations were positively correlated with soil water content.Both NRE and PRE decreased with increasing soil nutrient and water availability.In conclusion,in the wet year,warming and N addition increased plant N and P concentrations and soil available N and P,and decreased N and P resorption efficiency.Nevertheless,in the dry year,these effects were not found in a desert steppe that was sensitive to abrupt changes in weather patterns.These results suggested that the impacts of climate change on nutrient characteristics of plants and soils can be mediated by natural precipitation variations in water-limited arid and semiarid regions.