Water-spender strategy is linked to higher leaf nutrient concentrations across plant species colonizing a dry and nutrient-poor epiphytic habitat

Abstract

Resource availability for plants in dry ecosystems is largely controlled by the occurrence of irregular rainfall pulses, which means that they must be able to rapidly take up water and nutrients during the narrow windows of opportunity following rainfall when resources become available. Epiphytic plant communities in Mediterranean climates provide useful model systems for investigating the diversity and effectiveness of contrasting resource use strategies in dry habitats with pronounced pulse-driven dynamics.We assessed resource use strategies in a facultative epiphytic plant community growing on Phoenix dactylifera trees, and examined how these strategies are linked to species abundance in this extreme habitat. We collected leaves from 31 species and measured their macro- and micro-nutrient concentrations and isotopic composition, as well as their relative frequency in the epiphytic habitat.Large interspecific differences in leaf stoichiometry and isotopic ratios revealed the coexistence of sharply contrasting resource use strategies in the epiphytic community, ranging from opportunistic and resource-acquisitive species with higher leaf nutrient concentrations and lower δ13C, water use efficiency and C:N ratios, to resource-conservative species with opposite traits. Multivariate analysis revealed strong co-variation among leaf nutrient concentrations and isotopic ratios across species. Opportunistic species capable of faster acquisition and more profligate use of ephemeral resources were more frequent in the harsh epiphytic habitat, even after discounting the significant effect of seed size on species frequency. Leaf N and δ15N were tightly positively correlated across species, thus extending the universality of this relationship (widely reported for terrestrial habitats) to epiphytic habitats, and suggesting that this correlation is primarily driven by variations in N demand to supply ratios linked to differences in plant productivity.Synthesis. This study highlights how an opportunistic, water-spender strategy is advantageous for maximizing nutrient capture and for successful colonization of dry and nutrient-poor habitats with extreme fluctuations in resource availability. Given that this acquisitive strategy enables plants to avoid climatic extremes, we propose that species capable of faster and more profligate water and nutrient use during short wet pulses are better preadapted to cope with increasingly irregular rainfall and more frequent drought associated with ongoing climate aridification in many dryland regions.