PS 11-97 - The effect of water and nutrient availability and the interaction between them on the composition and structure of herbaceous Mediterranean plant communities
Terrestrial ecosystems are considered to be limited by water, but in most cases, nutrients are limited as well. These limitations affect the growth at the individual level and conspecific and heterospecific plant interactions and thus shape the structure and composition of the plant community. We examined how the availability of water and nutrients affected the organization of the herbaceous plant community. We focused on two families: grasses and legumes, since these two differ in their species richness, abundance, life history traits, and in the mechanisms, these have evolved to cope with water and nutrients limitations.
Research question: How does water and nutrient limitations and their interaction shape the composition and structure of herbaceous Mediterranean plant communities?
Methods: We conducted semi-controlled fertilization experiments in four sites along the Israeli rainfall gradient (600 to 230 mm per year). In all the sites, the vegetation community was mainly herbaceous, and all of them were grazed for years. We examined the effects of nitrogen and phosphorus additions combined with inter-annual rainfall variability on the structure and composition of the plant community.
Results/Conclusions
Results: We found a positive relationship between the amount of precipitation and productivity, and no effect on species richness. The strongest positive effect of fertilizer treatments was that of nitrogen and phosphorus fertilization together, which greatly increased grass productivity. In contrast, phosphorus fertilization mainly increased the productivity of legumes. The combination of a change in the availability of water and nutrients influenced species diversity, but not their composition.
In the rainiest site, we found that nutrients limited productivity, the addition of nutrients increased productivity but compared to the drier sites the percentage of change was small. In the drier sites, we found no nutrient limitations; productivity was affected more by an increase in water availability and less by nutrient supply.
Discussion and Conclusions:
Productivity increases in response to increasing availabilities of both water and nutrients, indicating that both are limited in dry-land habitats, but the effect of each is different. Productivity is strongly related to water availability in dry-land habitats, but the positive effect of increasing water availability is further limited by nutrient availability in some soils more than in other.
