Contrasting seasonal plasticity of photosynthesis in evergreen and
deciduous tree species from a tropical forest
Abstract
Microclimate differences in water availability can diversify seasonal
water use and photosynthetic strategies among co-occurring tropical tree
species, especially in forests with strongly seasonal climates. We
studied a tropical forest site in the Western Ghats, India, and
characterised seasonal differences in photosynthetic CO
2 assimilation rates ( A net)
among three tree species groups spanning leaf habit and topographic
affinity: deciduous species in dry hilltops, dry-affinity evergreens on
slopes, and wet-affinity evergreens in valleys. As expected, deciduous
species on dry hilltops showed higher P opt (
A net at optimal temperature, T
opt) during the wet period, while evergreen species
showed no overall seasonal differences. Interestingly, dry-affinity
slope evergreens showed higher P opt during the
dry period compared to the wet period despite lower soil moisture,
suggesting sufficient water availability and warmer thermal niche
preference. Across species, stomatal conductance ( g
s) at T opt was generally higher
during the wet period, except for one evergreen species. Surface soil
moisture was lowest in hilltops, intermediate on slopes, and highest in
valleys, with higher levels during the wet period compared to the dry
period. Our findings highlight the diverse seasonal photosynthetic
strategies among tropical tree species with different leaf habits and
water affinities.