Nutrient resorption is associated with leaf vein density and growth performance of dipterocarp tree species

Nutrient resorption is important for the nutrient budget of plants, but little is known about which plant traits mediate nutrient resorption, how resorption efficiency is associated with other leaf traits and whether nutrient resorption has an impact on plant growth. In this study, 17 dipterocarp tree species were compared in a common garden experiment. N and P resorption efficiencies were regressed against suites of traits associated with phloem transport capacity (i.e. leaf vein density; D-vein), leaf nutrient conservation traits (e.g. leaf mass per area; LMA) and species growth rate. Across the dipterocarp species studied, N resorption efficiency (percentage N resorbed) was positively correlated with D-vein and leaf thickness. N resorption efficiency was also correlated with D-vein after considering phylogenetic effects. N resorption proficiency (N remaining in senesced leaves) was negatively correlated with D-vein, LMA, leaf thickness and palisade and spongy mesophyll thickness. Senesced-leaf N concentration was still negatively correlated with LMA and leaf thickness after considering phylogenetic effects. N resorption efficiency was positively correlated with both height and diameter growth rates. After considering phylogenetic effect, N resorption efficiency was marginally correlated with diameter growth rate. Green-leaf N concentration was positively correlated with height growth rate after considering phylogenetic effect. P resorption efficiency and proficiency were not related to any of the leaf morphological and anatomical traits, or to species growth rates.Synthesis. These results indicate that higher phloem transport capacity of the dipterocarp species is positively correlated with greater N resorption efficiency and that N resorption proficiency is closely linked with leaf nutrient conservation traits. Growth rates of the dipterocarps are more likely governed by photosynthetic rates associated with green-leaf N concentration than N resorption rates per se. Although P is generally deficient in tropical soils, it appears that N rather than P availability is the key limiting factor for the growth of the dipterocarp species.