Maintenance of Leaf Water Potential by Tropical Dry Forest Tree and Liana Species During a Severe Drought

Abstract:

In 2014, tropical dry forest (TDF) ecosystems in northwestern Costa Rica experienced the most severe drought on record since 1950, in which precipitation in the first four months of the rainy season (May-August) was 43% of normal. We used this opportunity to quantify the impact of soil water availability on the maintenance of diurnal leaf water potential (LWP) in a diverse set of tree and liana taxa. Across sites spanning a large soil texture and water potential gradient, we measured pre-dawn (pdLWP) and mid-day leaf water potential (mdLWP) of 79 individuals of 14 tree and 7 liana species both during the peak of the drought (early August), and well after the onset of wet season rains (late September). In addition, we quantified a suite of resource-acquisition related leaf traits for every individual. The maintenance of leaf water potential throughout the day (deltaLWP = mdLWP – pdLWP) varied dramatically among species (Figure 1). During the drought, evergreen species experienced significantly higher drought stress overall (larger deltaLWP) than deciduous species, but trees did not differ from lianas in their responses. The ability of TDF trees or lianas to maintain LWP did not depend on site-specific soil water potential, indicating that soil water retaining characteristics may not be good predictors of overall community responses to drought. We found that TDF tree and liana species have a wide range of responses to severe drought, and future integration of both leaf trait and physiological data (turgor loss point, stomatal conductance) will allow us to determine if specific leaf traits or physiological metrics are good predictors of tree and liana drought responses in TDF.