The Interspecies Difference Of Terrestrial Plant Biomass In Response To Nitrogen Addition And Its Pattern Analyses

Plant biomass is the basis of estimating terrestrial vegetation carbon storage,and important for the carbon cycle under global changes.Terrestrial plant biomass and productivity are commonly limited by nitrogen(N)availability.With increasing atmospheric N deposition,how plant biomass responds to N deposition would be beneficial to understand and predict the vegetation dynamic and carbon cycle under future climate changes.However,the responses of plant biomass to N deposition are interspecific different for the differences of environments,N treatments and species among studies.Therefore,this study investigated the interspecific differences of terrestrial plant biomass in response to nitrogen addition and studied influencing factors at global and site scales by using the method of global data synthesis and field experiments.The global synthesis included 519 species from 348 publications reporting the responses of plant biomass to N addition.The site experiment collected 13 evergreen species in a subtropical forest.In addition,the effects of biotic(phylogeny and nitrogen use efficiency(NUE))and abiotic factors(environment factors and N treatment factors)on the responses of terrestrial plant biomass to N addition across global and site scales were studied.(1)Across the 348 publications of N addition experiments,N addition enhanced plant biomass with an average of 45.02% at global scale.However,plant biomass responses varied with plant functional types(PFTs)and tissues.For example,herb biomass was increased by 56.11%,greater than 36.15% in woody biomass.Aboveground biomass(59.13%)was stimulated more than belowground biomass(29.71%)across different PFTs,except for legume plants.The stem was greater than leaf in the biomass responses to N addition,especially for woody plants.In addition,coarse roots had greater biomass responses than fine roots for most PFTs.As a result,N addition stimulated the biomass accumulation of terrestrial plants and tissues,and the effects are interspecific different.(2)Global responses of plant biomass were affected by multiple environmental factors.Mean annual precipitation(MAP)contributed the most to plant biomass responses,while soil total N and p H were the smallest contributors.The correlation between plant biomass responses and MAP is generally positive,but there are interspecific differences.For example,the biomass response of woody plants increased with the increased MAP,and the opposite is true for herbaceous plants.Due to the differences in water and phosphorus(P)availability,planting patterns and N treatments between field and controlled experiments,plant biomass responses in controlled experiments(58.11%)were greater than in field experiments(22.96%),and great interspecific differences were observed.Therefore,when considering the plant biomass response and its interspecific differences under N addition,it is necessary to pay attention to the important effects of water and experimental conditions.(3)N treatment factors have affected plant biomass responses at a global scale,of which N treatment duration played the most important role,followed by amount and form.Plant biomass responses decreased with increasing duration.The same was for woody and herb plants.In addition,the responses of plant and tissues biomass to various N treatment forms are different.Urea promoted plant biomass(11.00% per g N),followed by ammonium-N(6.27% per g N)and ammonium nitrate(5.51% per g N),and nitrate-N had the smallest effects(1.07% per g N).Nitrate-N exacerbated the interspecific differences of plant biomass responses relative to ammonium-N.In addition,nitrate-N stimulated greater enhancements of aboveground biomass(8.42%per g N)relative to belowground biomass(-2.00% per g N),and ammonium-N had the opposite effects.These results show that the interspecific differences of plant biomass responses would be more changeable under the increasing N deposition and the rapid changes of reduced and oxidized N deposition.(4)Phylogeny significantly affected the global responses of species biomass to N addition.In addition,phylogeny explained 31.34% of the biomass responses,greater than environment(6.03%)and N treatment factors(7.25%).The relative contributions of phylogeny,environment and N treatment factors to the biomass of various PFTs were consistent with the overall results.However,the contribution of abiotic factors was greater than phylogeny for leaf and stem biomass responses.In addition,leaf biomass,rather than stem and root biomass,evolved toward a weaker response to N addition.Therefore,phylogeny should be considered in explaining biomass changes under N deposition in experiments and models,and more studies are required to investigate the mechanism of phylogeny effects.(5)In the subtropical forest,the responses of plant DBH to N and P addition varied with species.Environment factors are related to species DBH relative to phylogeny,which is contrary to the global results of greater phylogeny effects on biomass responses.In addition,N addition reduced NUE,and the NUE responses of species were negative correlated with its biomass responses both at the global and site scale.Therefore,it indicates that N addition stimulated biomass accumulation at the expense of decreased NUE,and suggests that the factors in influencing plant growth responses to N addition varied with spatial scales.By combining global data and the field experiment of N and P addition in a subtropical evergreen broad-leaved forest,focusing the interspecific differences on species and PFTs scale,this study clarified the responses of plant biomass to N addition and its interspecific differences,and revealed the important role of water,N treatment duration and form in affecting biomass responses.In addition,this study also emphasized the considerable effects of phylogeny at global scale,while insignificant at site scale.It also stated that the negative correlation between NUE responses and biomass responses.This study demonstrates the interspecies differences of terrestrial plant biomass in response to nitrogen addition,and reveals the main influencing factors and their changing patterns.It provides a strong scientific basis for terrestrial productivity and biomass in the context of global changes.