Leaf turgor loss point varies among tree species, habitats, and seasons in a bottomland hardwood forest

Key message

Tree species in a temperate floodplain forest had leaf turgor loss point values similar to those of upland forest trees, suggesting physiological drought tolerance in this generally non-water-limited system.

Abstract

Leaf turgor loss point (TLP) is a key plant trait associated with drought tolerance. In the bottomland hardwood (BLH) forests that grow in floodplains of the southeastern USA, drought stress is generally low but may increase with climate change. To address drought tolerance among BLH trees, we measured TLP among 20 species in a BLH forest in Louisiana, USA. We tested whether (1) TLP is higher in BLH tree species than in upland temperate-zone trees; (2) lower TLP is associated with higher drought tolerance among BLH species; (3) TLP drops during the growing season within BLH trees; and (4) within species, TLP is lower in more water limited, non-flooded BLH habitats than in seasonally flooded habitats. Among BLH tree species, TLP was −2.23 ± 0.28 (mean ± SD) and, contrary to our hypothesis, weakly positively correlated with drought tolerance. Within BLH species, TLP was lower in non-flooded habitats than seasonally flooded habitats and TLP decreased between the early and late growing season, more so in the non-flooded habitat. Overall, our results show that TLP among BLH trees is relatively low and plastic for a system that is generally not water limited, which may contribute to drought tolerance in future scenarios.