Datensatz

Zusammenfassung

Soil phosphate oxygen isotope analysis (δ18OP) emerges as an effective method to trace the
cycling of phosphorus (P) in soils. This study uses δ18OP measurements to learn how the nutrient status
(P and N) affects the biological turnover rates of P in the soil of a Mediterranean holm oak Savanna. Such
ecosystems cover >3 × 106 ha at the Iberian Peninsula. The analysis was part of a large-scale nutrient
manipulation experiment, where N and P were added. We followed the changes in δ18O values of soil
bioavailable P during incubation of soils with a pulse of P and in addition measured the δ18OP in soil sampled
at the site. In the incubations, the δ18OP values changed from the original value of the added P and
approached a steady state of 16.3‰, which is 3.8‰higher than the isotopic equilibrium with water. The
steady state was higher with 18O-enriched incubation media water. The change in δ18OP values was more
pronounced under trees, indicating a faster microbial P turnover rate. Incubation of soils fertilized with either
P or N showed faster P turnover rate than control, implying N and P colimitation. Soil samples from P-fertilized
plots displayed higher δ18OP than the fertilizer, rather than the expected decrease toward steady-state
values, found at the control and N plots. The microbial P turnover rates during incubations were slower
than the rates reported for lowland tropical forest with lower bioavailable P concentrations but resemble
ecosystems with similar concentrations.