Foliar nitrogen and phosphorus resorption and decomposition in the nitrogen-fixing tree Lysiloma microphyllum in primary and secondary seasonally tropical dry forests in Mexico

Abstract

The tree Lysiloma microphyllum (Fabaceae) dominates in the seasonally tropical dry forests of central Mexico. In this study foliar N and P concentrations (on leaf mass basis), foliar N and P resorption efficiency and proficiency, as well as the decomposition of senescent leaves of L. microphyllum were studied in primary and in regenerating, secondary seasonally tropical dry forests. Our study included an area of early successional forest (10 y old), with phosphorus-poor soils and comparatively abundant nitrogen, an area of late-successional forest (∼60 y old), in which soil P and N were comparatively abundant, and an area of primary forest, in which soil P was comparatively abundant and N was less abundant than in the secondary counterparts. N and P concentrations in mature leaves varied across forests, reflecting soil nutrient availability. Nitrogen concentration in senescent leaves did not change among sites, which led to very different patterns of N resorption. In contrast, P concentration in senescent leaves was lower in the early than in late-successional and primary forests, which resulted in similar patterns of resorption. Leaf decomposition increased from 70% mass loss in the first year in the early successional to ∼80% in the same period in late-successional and primary forests. The element loss during decomposition change across forests in the following order: for N, early successional = late-successional > primary forest, and for P, primary forest > late-successional > early successional forest. Overall, the pattern of variation in leaf chemistry and nutrient release on the forest floor among sites is consistent with soil nutrient availability along this sequence, while decomposition rate may be related with the P concentration in senescent leaves.