Diverse phosphorus acquisition strategies contributed to dominant species coexistence under nitrogen enrichment

Background/Question/Methods: Understanding how reactive nitrogen (N) enrichment influences community structure, such as species diversity and dominant species, is essential to predict the responses of ecosystem functions to the increasing N deposition. Under the background of N-induced aggravation in light and phosphorus (P) limitation, the dominant species which remained in the community could change a series of resource acquisition strategies to maintain their own dominance and interspecific coexistence, but the underlying mechanisms are poorly understood. In this study, we focused on two dominant species Stipa purpurea and Carex stenophylloides in a Tibetan alpine steppe, and assessed the effect of N-induced changes in acquired light and P resources on species important values as well as the linkages between resource acquisition and leaf and root morphology, P reabsorption, mycorrhizal colonization, root vigor, root phosphatase activities, root carboxylate exudation, and utilization of various soil P compounds.

Results/Conclusions: Our results showed that, the important value of Stipa purpurea increased with increasing acquired light resource, while the important value of Carex stenophylloides was regulated by the joint effect of light and P. Under high levels of N fertilization, utilizing of moderately labile P components by increasing phosphatase activities and carboxylate exudation is the key for Carex stenophylloides to maintain its dominant position and coexiste with Stipa purpurea. These results demonstrate that the difference in resource acquisition strategies is important for maintaining species coexistence under continuous N input.