Short-term effects of fire on soil and plant nutrients in palmetto flatwoods

Fire may have different effects on the relative availability of nitrogen (N) and phosphorus (P) because N volatilization occurs at lower temperatures than P volatilization, and fire-mediated changes in soil nutrient availability may affect foliar nutrient concentrations. We assessed the short-term effects of fire on soil and plant nutrients and ¹⁵N isotopic signatures in a palmetto flatwoods ecosystem in central Florida. Fire caused a short-term increase in extractable ammonium (NH₄⁺) and phosphate (PO₄^3-). The increase in PO₄^3- was greater than the increase in NH₄⁺, resulting in a decrease in the soil extractable N:P ratio shortly after fire. Similarly, foliar %P of the palmetto Serenoa repens (W. Bartram) Small increased more than foliar %N, resulting in a decrease in foliar N:P ratios shortly after fire. Soil δ¹⁵N and the difference between foliar and soil δ¹⁵N did not vary with time since fire; however, foliar δ¹⁵N of S. repens decreased after fire. Foliar %N of Quercus geminata Small and ericaceous shrubs was positively correlated with soil extractable inorganic N, while foliar %P of S. repens was positively correlated with soil extractable PO₄^3-. Variation in foliar δ¹⁵N after fire and the positive relationship between soil and foliar nutrients suggest that both increased soil nutrient availability and reallocation of nutrients from below- to aboveground can be important for plant nutrient status after fire in palmetto flatwoods.