Long-term productivity of Mediterranean herbaceous vegetation after a single phosphorus application

Question What is the mechanism that underlies long-term maintenance of high herbaceous productivity after a single application of phosphorus (4.5 gP m-2 and 9 gP m-2) in a hilly Mediterranean environment in a phosphorus-deficient ecosystem? Location Inland, 15 km E of the Mediterranean coast, W Galilee, Israel (35 degrees 15'E, 33 degrees 01'N; 500 m asl). Methods The experiment was established in 1988. Multi-year data on above-ground biomass, botanical composition, P content of vegetation and soil, and the grazing management context of the experiment were integrated to construct a feasible account of the P dynamics of the ecosystem. Results The productivity of the herbaceous component already responded to P application in the first year. The effect on the shrubby component of the ecosystem was marginal. The available (bicarbonate extractable) P in the upper soil layer peaked in the year after application of P and then declined to the original level within 7 years. Despite the decline in available soil P, a high, fluctuating level of herbaceous biomass production was maintained for 20 years. Legume species (Fabaceae) became a prominent constituent of the herbaceous vegetation after the P pulse. Conclusions The long-term shift in productivity of the herbaceous component of the grazed ecosystem was triggered by a nutritional pulse that induced a feedback loop based on changes in botanical composition of the herbaceous vegetation, the animal-vegetation interaction, grazing and supplementary feeding regimen of the cattle.