Exotic Rhus Typhina is Superior to Native Rhus Chinensis Due to Trait Values and Phenotypic Integration, But Not Heterogeneous Nitrogen Deposition Rates

The temporal heterogeneity of nitrogen availability in soils is increasing due to agricultural deposition. We here compared the effects of gradually increasing nitrogen deposition rate and its increasing temporal heterogeneity patterns on the exotic species Rhus typhina and the native species Rhus chinensis . Nitrogen deposition rates of 0, 8, 20 g N m -2 year -1 and constant, single peak and double peak nitrogen were added to simulate deposition rate and temporal heterogeneity. After 60 days of N-treatment, R. typhina had several dominant growth trait values, such as total biomass production, but lower phenotypic plasticity than R. chinensis . R. typhina also had higher phenotypic integration, measured as correlation among functional traits. The increased nitrogen deposition rate affected several traits of the two species differently. Thus, while R. chinensis allocated more biomass to leaves and less to roots with increasing N deposition, R. typhina had stable biomass allocation among all N treatments. Chlorophyll content, leaf phosphorus concentration and water use efficiency increased, but maximum net photosynthetic rate decreased , with N availability in R. chinensis , but not in R. typhina . Temporal heterogeneity had no significant effect on the total biomass of R. typhina and R. chinensis , and did not increase the dominance of functional traits of R. typhina . Overall, R. typhina was often superior to R. chinensis by virtue of the dominance of trait values and high phenotypic integration rather than high phenotypic plasticity, although higher nitrogen deposition rates and their increasing temporal heterogeneity would not further improve the dominance of R. typhina