Responses to water limitation are independent of light for saplings of a seasonally dry tropical forest

Abstract

Seasonally dry tropical forests (SDTFs) experience large spatial and temporal variation in water and light availability. The effect of heterogeneity in these limiting resources on species water use, physiology, and growth is still not well understood. We used a shade-house experiment to manipulate light and water availability and examine plant water uptake, leaf-level physiology, and sapling growth in four co-occurring SDTF species belonging to both evergreen and deciduous plant functional types. Water uptake varied dramatically among species with a fivefold difference in maximum whole-plant transpiration (WPT). While species differed in how WPT, leaf physiology, and growth responded to shade, there were no differences among species, or between evergreen and deciduous functional types, in responses to limited water. Importantly, responses to shade were independent of water availability in all four species. Changes in WPT in response to limited light and water were largely congruent with changes in leaf physiology and growth. However, the magnitude of change in leaf physiology was largely driven by light, while changes in WPT and growth were driven by water availability. Thus, whole-plant water uptake may be a better indicator of plant growth responses in these species. Overall, these results suggest that responses to light and water limitation may be independent of each other, allowing species in SDTFs to explore a wide range of combinations of light and water responses to adapt to heterogeneous light and water niches.