The cycling of readily available phosphorus in response to phosphate additions

Phosphorus (P), being vital to biological processes, is an important factor in ecosystem productivity. While nitrogen has long been the focus of biogeochemical cycling and budgeting studies in temperate systems, the understanding of P cycling in temperate zones is limited. The objective of this study was to quantify labile P flux in North American Eastern deciduous forests. Additionally, we sought to contextualize this quantification with potential indicators of labile P stress in a P amendment regime with enzyme studies. To quantify P flux, we deployed anion exchange membranes (AEMs), in situ, in nine elevated P plots and nine control plots in Southeast Ohio for two weeks, twice over two months. To contextualize P flux, resin P pools were measured at the time of deployment and harvest of the AEMs. Phosphomonoesterase (PM) and phosphodiesterase (PD) activities were measured to assess P limitation. We found that the resin P pool was almost 200% greater in the elevated P treatments (10.6 mg/kg) than the control (3.6 mg/kg). The flux available P flux was 1.0 ± 0.4 μg P/day for the control treatment, but 310% (3.9 ± 0.9 μg P/day) greater in the elevated P treatment. Furthermore, P mineralization was similar (P = 0.06) between treatments and averaged -0.22 ± 0.09 (mg P/kg/day), suggesting mild P immobilization. As a comparison, we observed that Net N mineralization was around 0.84 ± 0.18 mg N/kg/day. These results suggest that P is more limiting than N. Elevated P significantly decreased phosphatase enzyme activity, suggesting reduced P deficiency, but not complete alleviation of P stress, as suppression was modest at 13% (PM) and 34% (PD). The resin P pool, while small, is cycling very rapidly and is only a partial indicator of P dynamics in North American Eastern deciduous forests. Results indicate that P flux is as rapid as N flux, and P is likely a scarcer soil resource.