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Temporal Trends of Phosphorus Cycling in a Tropical Montane Forest in Ecuador During 14 Years

Abstract:

Increased bioavailability of P can have a negative impact on plant biodiversity. In an approximately 9-ha catchment under N + P-limited megadiverse tropical montane forest in Ecuador, we budgeted all major P fluxes and determined whether the P fluxes changed from 1999 to 2013. Furthermore, we assessed which external drivers (rainfall, total P and acid deposition) caused this potential change. Mean (±SD) annual P deposition (bulk+dry) was 240 ± 270 mg/m2, with the SD reflecting the interannual variation. The annual P flux to the soil via throughfall+stemflow+litterfall was 1,400 ± 170 mg/m2 of which 18 ± 9.2% was leached to below the organic layer. The mineral soil retained 80 ± 12% of the P leached from the organic layer. The mean annual P weathering rate was 79 ± 63 mg/m2. The sum of P fluxes was approximately 5 times larger above than below the mineral soil surface, illustrating that P was tightly cycled in the biological part of the forest. The mean annual canopy budget was negative (−120 ± 280 mg/m2); that is, P was leached from the canopy. Throughfall was the largest source of dissolved P. The P catchment budget (total deposition-streamflow) was positive (200 ± 270 mg/m2); that is, P was retained, mainly in the soil organic layer. From 1999 to 2013, P fluxes with throughfall, stemflow, and streamflow increased significantly. The strongest driver of the P budgets of the canopy and the catchment was total P deposition. Our results demonstrate that mainly biological processes retained deposited P in the vegetation and the organic layer enhancing the internal P cycle.