Nutrient acquisition, soil phosphorus partitioning and competition among trees in a lowland tropical rain forest

Summary We hypothesized that dinitrogen (N 2 )‐ and non‐N 2 ‐fixing tropical trees would have distinct phosphorus (P) acquisition strategies allowing them to exploit different P sources, reducing competition. We measured root phosphatase activity and arbuscular mycorrhizal ( AM ) colonization among two N 2 ‐ and two non‐N 2 ‐fixing seedlings, and grew them alone and in competition with different inorganic and organic P forms to assess potential P partitioning. We found an inverse relationship between root phosphatase activity and AM colonization in field‐collected seedlings, indicative of a trade‐off in P acquisition strategies. This correlated with the predominantly exploited P sources in the seedling experiment: the N 2 fixer with high N 2 fixation and root phosphatase activity grew best on organic P, whereas the poor N 2 fixer and the two non‐N 2 fixers with high AM colonization grew best on inorganic P. When grown in competition, however, AM colonization, root phosphatase activity and N 2 fixation increased in the N 2 fixers, allowing them to outcompete the non‐N 2 fixers regardless of P source. Our results indicate that some tropical trees have the capacity to partition soil P, but this does not eliminate interspecific competition. Rather, enhanced P and N acquisition strategies may increase the competitive ability of N 2 fixers relative to non‐N 2 fixers.