Hydrologically-Influenced Feedbacks Between Phosphorus and Vegetation in Dry Tropical Forests

DeLonge, Marcia Susan, Department of Environmental Sciences, University of Virginia
D’Odorico, Paolo, Department of Environmental Sciences, University of Virginia
Lawrence, Deborah, Department of Environmental Sciences, University of Virginia
Fuentes, José

This research investigates the potential for hydrologically-influenced feedbacks between phosphorus and vegetation to induce ecosystem state changes in dry tropical forests. Since many of these forests are phosphorus (P) limited, any disturbance that influences available P may directly impact vegetation (V). I hypothesized that vegetation also influences P-cycling, and that P-V feedbacks lead to reduced resiliency and state changes in dry tropical forests, especially when disturbed. I designed a model to explore the interactions between P and V dynamics in tropical forests. Using published data to define the relationships between P and V, I determined that feedbacks in these systems (i.e., the role of vegetation in "trapping" P deposition) could be sufficient to induce state shifts. Based on this result, I investigated three regions of P-cycling where I expected to find hydrologically-influenced P-V feedbacks: deposition, leaching, and soil P bioavailability. Associated studies were primarily undertaken in the Mexican dry forest of the Southern Yucatan Peninsular Region. I found that: 1) throughfall [P] was significantly higher in old forests than in young forests after a dry period, supporting the idea that greater plant area in old forests makes them more efficient at "trapping" deposition. However, collection time and storm size also affected throughfall [P]. 2) Deep leachate [P] decreased with increasing forest age, suggesting that old forests lose less P via leachate. There was also a significant negative relationship between forest age and the difference between deep and shallow leachate [P); leachate [P] may decrease down the soil profile in old forests, implying that these forests are highly efficient at conserving P. 3) Soil P bioavailability increased with ii moisture and was strongly pulsed after re-wetting dried soils. Wet-dry pulses may become more common with reduced canopy cover (e.g., less shading) or climate change; plants may be inefficient at conserving strongly pulsed P, increasing the risk for P losses under these conditions.

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MS (Master of Science)
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