Effect of nitrogen and phosphorus addition on leaf nutrient concentrations and nutrient resorption efficiency of two dominant alpine grass species

Nitrogen(N)and phosphorus(P)are two essential nutrients that determine plant growth and many nutrient cycling processes.Increasing N and P deposition is an important driver of ecosystem changes.However,in contrast to numerous studies about the impacts of nutrient addition on forests and temperate grasslands,how plant foliar stoichiometry and nutrient resorption respond to N and P addition in alpine grasslands is poorly understood.Therefore,we conducted an N and P addition experiment(involving control,N addition,P addition,and N+P addition)in an alpine grassland on Kunlun Mountains(Xinjiang Uygur Autonomous Region,China)in 2016 and 2017 to investigate the changes in leaf nutrient concentrations(i.e.,leaf N,Leaf P,and leaf N:P ratio)and nutrient resorption efficiency of Seriphidium rhodanthum and Stipa capillata,which are dominant species in this grassland.Results showed that N addition has significant effects on soil inorganic N(NO_(3)^(-)-N and NH_(4)^(+)-N)and leaf N of both species in the study periods.Compared with green leaves,leaf nutrient concentrations and nutrient resorption efficiency in senesced leaves of S.rhodanthum was more sensitive to N addition,whereas N addition influenced leaf N and leaf N:P ratio in green and senesced leaves of S.capillata.N addition did not influence N resorption efficiency of the two species.P addition and N+P addition significantly improved leaf P and had a negative effect on P resorption efficiency of the two species in the study period.These influences on plants can be explained by increasing P availability.The present results illustrated that the two species are more sensitive to P addition than N addition,which implies that P is the major limiting factor in the studied alpine grassland ecosystem.In addition,an interactive effect of N+P addition was only discernable with respect to soil availability,but did not affect plants.Therefore,exploring how nutrient characteristics and resorption response to N and P addition in the alpine grassland is important to understand nutrient use strategy of plants in terrestrial ecosystems.

Effects of Thermal Annealing on the Solvent Additive P3HT PC61BM Bulk Heterojunction Solar Cells

Effects of thermal annealing on the optical, electrical and structural properties of 3 vol% 1,8-diiodoctane added P3HT：PC61BM active layers are investigated, concerning the performance of the bulk heterojunction polymer so- lar cells by changing the heat temperature. The structure information of the active layer is analyzed by using the grazing incidence wide angle scattering diffraction combined with the optical microscope, light absorption, pho- toluminescence and the external quantum efficiency spectra. The relationship between the detail of morphology and the optical, electrical properties is investigated.

Divergent responses of plant biomass and diversity to short-term nitrogen and phosphorus addition in three types of steppe in Inner Mongolia,China

Background:Understanding the response of the plant community to increasing nitrogen(N)and phosphorus(P)inputs is helpful for managing and protecting grassland ecosystems in semiarid areas.However,information about different types of steppe responses to N and P availability in semiarid grasslands is limited.In 2017-2018,two field experiments were conducted with six levels of N(from 5 to 30 g N m^(−2)yr^(−1))and P(from 2.5 g to 15 g P m^(−2)yr^(−1))additions in three different temperate steppes,including meadow steppe(MS),typical steppe(TS),and desert steppe(DS),in northern China to study the effects of these addition rates on community biomass and diversity.Results:Our results showed that plant biomass and diversity in the three steppe types in Inner Mongolia responded differently to elevated N and P inputs.Increasing P promoted aboveground and belowground biomass more than increasing N in the three temperate steppes.Short-term N and P additions reduced plant diversity to some extent,with the most pronounced decreases in MS and DS.It is noteworthy that there were response thresholds for plant diversity and biomass in response to N and P inputs in different steppe types(e.g.,10 g P m^(−2)yr^(−1)).Furthermore,redundancy analysis and stepwise regression analysis revealed that changes in soil properties induced by nutrient addition and climate conditions jointly regulated changes in vegetation biomass and diversity.Conclusions:The plant biomass and diversity of three steppe types in Inner Mongolia respond divergently to elevated N and P inputs.Our results indicate that regional differences in climate and soil substrate conditions may jointly contribute to the divergent responses of plant biomass and diversity to short-term N and P addition.Our analyses provide new insights into managing and protecting grassland ecosystems.Considering that the effects of nutrient addition on plant diversity and productivity may have increasing effects over time,studies on long-term in situ nutrient addition are necessary.