Effects Of Drought And Nitrogen Enrichment On Leaf Nutrient Resorption And Above-/Below-Ground Nutrient Allocation In Four Tibetan Plant Species

Plant nutrient resorption,a process by which plants withdraw nutrients from senescing tissues to developing ones,can significantly affect plant growth,litter decomposition and nutrient cycling.Beside leaf nutrient resorption,plants can also allocate biomass and nutrients to roots for enhancing nutrient acquisition.Global change factors,such as nitrogen(N)deposition and precipitation,may mediate plant nutrient resorption and allocation.The ongoing global change have increased soil N availability and drought frequency in many regions.However,interactive effects of global change factors on plant nutrient-responses remain largely unclear.The Qinghai-Tibetan Plateau is known as the "World Third Pole" and "Asian Water Tower",where the ecosystems are more prone to be disturbed by global change than many other regions of the world.Low temperatures associated with high altitudes limited nutrient availability and nutrient cycling rate in the Qinghai-Tibet Plateau,and thus the ecosystems are highly sensitive to N input.Also,primary productivity in the Qinghai-Tibet Plateau is largely determined by precipitation.Many studies have shown that both the frequency of drought and the amount of N deposition in the Qinghai-Tibet Plateau will increase with global change.Therefore,studying how these environmental factors affect nutrient resorption and allocation patterns of Tibetan plant species is important,which can help us understand nutrient utilization strategies of different species and ecosystem nutrient cycling under future climate change scenarios.In this study,four common plant species from an alpine meadow in the Qinghai-Tibet Plateau were selected for a greenhouse pot experiment.Plant individuals were grown in different nitrogen and water availability levels,and the responses of leaf nutrient resorption and above-/below-ground nutrient distribution of the four species to N enrichment and drought were studied.Major results and conclusions are as follows:1.Species showed divergent nutrient resorption and allocation patterns even within the same functional group.N and P resorption of E.nutans(grass)and D.kamaonense(forb)were stronger than capillifolia(another grass)and A.diplostephioides(another forb),while nutrient allocation to roots in the latter two species was higher than the former two.2.N addition did not alter N resorption efficiencies of the four species,but increased litter N content of the species with stronger N resorption(E.nutans and D.kamaonense),and thus decreased their N resorption proficiencies.Besides,N addition facilitated P resorption in K capillifolia and D.kamaonense.3.Drought did not affect N or P resorption proficiencies,but decreased N resorption efficiency of K.capillifolia and facilitated P resorption of A.diplostephioides.4.Species with stronger N resorption allocated more biomass C or N to aboveground and enhanced their litter quality under N enrichment,while species with weaker resorption allocated more biomass C and/or N to belowground under drought conditions.5.There is an evolutionary tradeoff between foliar nutrient resorption and resource allocation to roots.Together,these results show highly species-specific responses of nutrient resorption and allocation patterns to N enrichment and drought.Current dynamical models of ecosystem nutrient cycling should incorporate the variation in resorption and allocation associated with environmental and phylogenetic factors.This would benefit to improve the assessment of productivity and nutrient status and prediction of litter decomposition and ecosystem nutrient cycling under future global environment.