Root phosphatase activity is a competitive trait affiliated with the conservation gradient in root economic space

Background: The diversity of resource acquisition strategies of plant roots determines the species coexistence patterns to a certain extent. However, few root physiological traits have been investigated, such as root phosphatase activity (PA) that affects plant phosphorus (P) uptake. Methods: Root PA and classical root functional traits were investigated for 21 coexisting species in a deciduous broad-leaved forest in warm temperate-subtropical transition zone, China. We analyzed the root order variation of absorptive fine root PA, clarified the attribution of root PA in root economic space (RES) and the different P acquisition strategies of co-occurring species based on the multidimensional RES theory, and determined the dominant factors affecting interspecific variation in root PA. Results: There was no distinct pattern of PA variation with root order in the first three root orders of absorptive fine roots, and root PA was constrained by phylogeny. Root PA is a competitive trait affiliated with the conservation gradient in RES. The tight linkages among root PA, mycorrhizal colonization, diameter, specific root length, and nitrogen concentration suggested trade-offs among P acquisition strategies of co-occurring species, i.e. species with long and fine roots acquire inorganic P by actively exploring the soil and secreting phosphatase to mineralize and hydrolyze organic P, while species with short and thick roots obtain P mainly by investing C in mycorrhizal partners. Conclusions: Collectively, our study provides an insight into the forest species coexistence in climatic transition zones, i.e. species coexistence mechanisms based on diverse phosphorus acquisition strategies.