The natural grasslands in South America have soils with low phosphorus (P) availability (1.0 to 7.5 mg kg−1), possibly altering the absorption and accumulation of P in grasses. We evaluated the chemical fractionation of P in the leaves of the most important grasses present in these grasslands to better understand the mechanisms involved in the storage of P. The grasses studied were Axonopus affinis and Paspalum notatum (fast tissue cycling and high nutrient demand) and Andropogon lateralis and Aristida laevis (slow tissue cycling and low nutrient demand). They were grown in pots filled with an Ultisol with two levels of P: control, and addition of 50 mg P kg–1. The main P fractions were the inorganic soluble (44%) and P in RNA (26%). Addition of P increased the total P concentration, following the order A. affinis (140%) > P. notatum (116%) > A. lateralis (81%) > A. laevis (21%). In conclusion, the species A. affinis and P. notatum responded to P fertilization with high variation and accumulating P in less-structural chemical forms, such as inorganic P. The species A. lateralis and A. laevis showed low variation in the concentration of P forms, with higher P concentrations in structural forms.

Isotopic composition of leaf carbon (δ13C) and nitrogen (δ15N) is determined by biotic and abiotic factors. In order to determine the influence of leaf habit and site on leaf δ13C and δ15N in the understorey of two Atlantic forests in Brazil that differ in annual precipitation (1200 and 1900 mm), we measured these isotopes in the shaded understorey of 38 tropical tree species (20 in the 1200-mm site and 18 in the 1900-mm site). Mean site values for δ15N were significantly lower at the 1200-mm site (−1.4‰) compared with the 1900-mm site (+3.0‰), and δ13C was significantly greater in the 1200-mm site (−30.4‰) than in the 1900-mm site (−31.6‰). Leaf C concentration was greater and leaf N concentration was lower at 1200-mm than at 1900-mm. Leaf δ15N was negatively correlated with δ13C across the two sites. Leaf δ13C and δ15N of evergreen and deciduous species were not significantly different within a site. No significant phylogenetic signal for any traits among the study species was found. Overall, site differences were the main factor distinguishing traits among species, suggesting strong functional convergence to local climate and soils within each site for individuals in the shaded understorey.

Leaf traits of tropical tree species are known to operate as intrinsic determinants of insect herbivory. However, we know little about how habitat fragmentation affects these traits and what, if any, are the consequences of this process on herbivory. We tested the effects of forest fragmentation on the leaf traits of sapling of four light-demanding species: Acalypha diversifolia, Hampea nutricia, Myriocarpa longipes, Siparuna thecaphora, and two shade-tolerant species: Pseudolmedia glabrata and Garcinia intermedia, in Los Tuxtlas, Mexico. We also conducted an acceptability assay with a generalist herbivore Spodoptera frugiperda. Plant traits did not change with forest fragmentation, but did with plant regeneration mode and species identity. Light-demanding species had significantly higher water content, nitrogen concentration and specific leaf area than shade-tolerant species. The latter had significantly higher leaf strength, carbon concentration and carbon:nitrogen ratio. Acceptability was affected by fragmentation but only in P. glabrata; plant tissue from forest fragments was consumed 2.6 times more than that from continuous forest. We conclude that forest fragmentation did not affect leaf traits in this site.

In order to understand the stoichiometric balance between foliar nitrogen (N) and phosphorus (P) on P-poor soils, we investigated how foliar N and P attributes (i.e. N and P concentrations in green and senesced leaves, N and P resorption efficiencies) of 30 tropical tree species co-vary along a gradient of soil P availability across three forests on Mount Kinabalu, Borneo. We found strong and positive correlations between foliar N and P in the concentrations and resorption efficiencies within each forest and across the three forests. Slopes of standardized major axis between foliar N and P concentrations for both green and senesced leaves were not different among the three forests, although the values of the scaling exponent in the relationships of foliar N to P across the three forests were significantly lower than 1. We suggest that down-regulation of N concentrations in green leaves on P-poor soils is one of several possible mechanisms explaining why N concentrations decrease with decreasing P concentrations in both green and senesced leaves toward a lower P availability in soils. On the other hand, the physiological and ecological reasons why N and P resorption efficiencies are positively correlated with each other across tree species remain unclear.