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

Seasonally dry tropical forests (SDTFs) experience large spatial and
temporal variation in water and light, and how heterogeneity in
availability of these limiting resources affect species water use,
physiology, and growth is still not well understood. We examined plant
water uptake in saplings of four co-occurring SDTF species, including
evergreen and deciduous plant functional types. We asked how water uptake
responded to experimentally imposed water and light limitations, and how
these responses were related to leaf-level physiology and plant growth.
Water uptake varied dramatically among species with a five-fold 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 by
water availability, suggesting that 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 limitations may be
independent of each other, and this would allow species in SDTFs to
explore a wider range of combinations of light and water responses to
adapt to heterogeneous light and water niches.