Leaf Stoichiometry And Nutrient Resorption Of Plant Communities Along Altitude In Taibai Mountain

Leaf nutrients are the basis of leaf construction and physiological function,and leaf nutrient resorption is an important nutrient conservation mechanism for plants.Species differences and environmental factors can affect the variation of leaf carbon(C),nitrogen(N),phosphorus(P)stoichiometry and leaf N and P resorption traits.However,the variation in leaf nutrient and resorption traits along environmental gradient at species and community levels is not clear.Therefore,further research on strategies of leaf nutrient investment and recycling in different plants and communities is of great significance for understanding the environmental adaptation and plasticity of plant nutrient traits and building complex ecological stoichiometry models of terrestrial ecosystems.This study investigated 6 types of plant communities and collected samples at different altitude in Taibai Mountain,based on 6 typical vegetation zones(deciduous broadleaved forest,temperate birch forest,fir forest,larch forest,alpine shrubland and alpine meadow).A total of 320 leaf samples(including green and senesced leaves)were collected from 168 species belonging to 135 genus in 63 families,and analyzed their C,N,P stoichiometry and N,P resorption traits for untangling the effects of phylogenetic factors on leaf stoichiometry and resorption traits,resolving the altitudinal patterns and environmental influence mechanisms of leaf stoichiometry and resorption traits at species and community level and comparing the variation differences between species and community levels and between 2 methods of community traits.The main results are as follows:(1)Phylogenetic factors greatly influenced the stoichiometric traits of green leaves.Except for N:P,all stoichiometric traits of green leaves showed significant phylogenetic signals(Blomberg’s K=0.32-0.40,Blomberg’s P<0.05).In results of nested-ANOVA,phylogenetic taxonomy had 30.9%-49.9%variance explanation of the stoichiometric traits for green leaves.In senesced leaves,C:P and N:P showed significant phylogenetic signals(Blomberg’s K was 0.51 and 0.49,respectively,Blomberg’s P<0.05),P content,C:P and N:P of senesced leaves were affected by phylogenetic taxonomy with 23.7%-45.2%variance explanation.All nutrient resorption traits had no significant phylogenetic signals,and slightly less influenced by phylogenetic taxonomy than differences in sampling sites.In the evolution process of plant species in Taibai Mountain,plants tended to decrease C contents but increase N and P content in green leaves with the advancement of evolution time,and some taxa with higher levels of evolution had higher green leaf N and P contents.Among different phylogenetic clades,the variation trends of leaf nutrient traits with environmental changes were significantly different.(2)At species level,when considering total species,green leaves C first increased and then decreased with the increasing altitude(P<0.05),while P contents significantly increased with the increasing altitude(P<0.05).In senesced leaves,N content first decreased and then increased with the increasing altitude(P<0.05),while P content decreased with altitude(P<0.05).Both leaf N and P resorption efficiency(NRE and PRE)increased with the increasing altitude(P<0.05).In different plant growth forms(GF),senesced leaves N of woody plants first decreased and then increased with the increasing altitude(P<0.05),while senesced leaves P had no significant altitudinal trend(P>0.05),indicating that senesced leaf N of woody plants was more sensitive to environmental change.In herbaceous plants,senesced leaf P significantly decreased with the increasing altitude(P<0.05),while senesced leaf N had no significant altitudinal trends(P>0.05),indicating that herbaceous senesced leaves P were more sensitive and preferred to resorb more P when facing environmental changes.At species level,environmental factors had small influence on nutrient traits in green leaves,and the main factors were soil bulk density(SBD)and soil available phosphorus(SAP)(3.2%-8.2%variance explanation).Traits of senesced leaves nutrient and resorption were mainly influenced by the annual mean temperature(MAT)(5.4%-24.0%variance explanation),and the change of MAT dominated the altitudinal trends of senesced leaves nutrient and resorption traits.According to the variation of allometric relationships in leaf nutrient traits among different altitudinal ranges and plant growth forms,plants at high altitude tended to simultaneously increase the investment and recycle of P in leaves.Relative to woody plants,herbaceous plants tended to resorb more P.Significant negative correlations between senesced leaf nutrient and resorption efficiency with significant difference among regression slopes in different altitudinal ranges.(3)At community level,we used two calculation methods to obtain the leaf nutrient traits of weighted mean of community dominance(community weighted value)and community accumulated quality value per unit land area(community accumulated quality).In community weighted traits,Green leaf C_C and N_C first increased and then decreased with altitude(P<0.05),while the community weighted values of the remaining leaf nutrient traits has no significant trends with altitude(P>0.05),which showed nonlinear changes.Among vegetation zones,the fir forest and alpine shrubland tended to have the community weighted traits of slow-return type on nutrient investments according to leaf economics spectrum,yet the temperate birch forest,larch forest and alpine meadow tended to have the community weighted traits of quick-return type on nutrient investments.In community accumulated quantity traits,all leaf nutrients showed significant linear altitude trends and significantly decreased with the increasing altitude(P<0.05).The comparison of leaf nutrient community accumulated quantity traits between the fir forest and the temperate birch forest showed opposite result to the community weighted traits.In the analysis of the environmental factors,precipitation and soil factors had the greatest influence on the community weighted traits of green and senesced leaf nutrient(0%-54.6%variance explanation of all traits),and environmental factors just had a little influence on the community weighted traits of resorption.The community accumulated quantity of leaf nutrients were mostly influenced by climatic factors(11.1%-46.8%variance explanation of all traits),and MAT dominated the overall altitudinal change of the community accumulated quantity.In the allometric relationships of leaf nutrient traits at community level,green leaf N_C-P_C allometric index(SMA slope was 0.39)was greatly decreased compared to species level.Most of the relationships between community accumulated quantity were extremely stable.The most stable relationship was between leaf C_Q and N_Q(R~2=0.99,P<0.0001),and the weakest stability was between N and P resorption quantity(NRQ and PRQ)(R~2=0.39,P<0.001).In summary,based on 6 typical vegetation zones at different altitudes in the Taibai Mountain,our study explores the effects of phylogenetic factors on green and senesced leaf nutrient and resorption traits and the evolutionary direction of leaf nutrients of different species,and clarifies the different altitudinal patterns and environmental impact factors of green and senesced leaf nutrient and resorption traits at the species and community levels.This study could help us to understand mechanism of leaf nutrient strategy comprehensively at species and community levels,which provides an important basis for studying ecosystem nutrient accumulation and nutrient cycling on the community scale.Our results suggest that future research need to attach importance to the relationships and differences among green leaf nutrient,senesced leaf nutrient and resorption traits,explore the variation and relationships among nutrient quantity per land area of leaf,litter and soil,which could provide a basis for establishing a stoichiometry models of macroscopic ecosystems.