The enhancement of root biomass increases the competitiveness of an invasive plant against a co-occurring native plant under elevated nitrogen deposition

Nitrogen (N) is one of the most important nutrition controlling plant functioning and ecological stability, which is predicted to increase rapidly in the future. Despite numerous attempts to clarify the effects of N deposition on the growth and physiological processes of plants, the difference in the effects of N deposition on biomass allocation between invasive and native species have not been fully understood. We conducted simulated N deposition experiments on a co-occurring species pair in a greenhouse to examine the plant invasion mechanisms from the patterns in plant biomass allocation. The results showed that the invasive Solidago canadensis and native Artemesia argyi have the similar response trend in N addition, where leaf mass fraction (LMF) significantly decreased and stem mass fraction (SMF) significantly increased. The root mass fraction (RMF) strongly increased in invasive S. canadensis but there was a decrease in native A. argyi respond to N addition. These findings indicated that increased nutrients, such as soil N, may shift the plant allocation structure due to unequal effects of N among different organs and species. And provided an invasion mechanism where a change in the environment leads to the potential exclusion of native competitors via a significant increase in root biomass fraction of invasive plants. We also found that the optimal partitioning theory rather than the allometric partitioning theory, better explains the N-induced changes in biomass allocation strategies in the poor-resource environment. These could lead to an increased competitive ability of invasive plants for resource acquisition and profit from neighboring species, coupled with greater biomass accumulation and higher competitiveness in its new habitat (N addition in poor resource environment) compared to A. argyi, could give S. canadensis a substantial advantage over its co-occurring native species.