Abstract
Tropical forests are experiencing reduced productivity and will need restoration with suitable species. Knowledge of species-specific responses to changing environments during early stage can help identify the appropriate species for sustainable planting. Hence, we investigated the variability in whole-tree canopy conductance and transpiration (Gt and EL) in potted saplings of common urban species in Thailand, viz., Pterocarpus indicus, Lagerstroemia speciosa, and Swietenia macrophylla, across wet and dry seasons in 2017–2018. Using a Bayesian modeling framework, Gt and EL were estimated from sap flux density, informed by the soil, atmospheric and tree measurements. Subsequently, we evaluated their variations with changing vapor pressure deficit (VPD) and soil moisture across timescales and season. We found that Gt and EL were higher and highly variable in L. speciosa across seasons than S. macrophylla and P. indicus. Our results implied that water-use in these species was sensitive to seasonal VPD. L. speciosa may be suitable under future climate variability, given its higher Gt and EL across atmospheric and soil moisture conditions. With their lower Gt and EL, P. indicus and S. macrophylla may photosynthesize throughout the year, maintaining their stomatal opening even under high VPD. These findings benefit reforestation and reclamation programs of degraded lands.
Highlights
Tropical forests are experiencing reduced productivity and will need restoration with suitable species
For P. indicus and L. speciosa during the wet season, the variations in sap flux density were best explained by storage time which was around half of that during the dry season, while S. macrophylla had a higher storage time in the wet season
vapor pressure deficit (VPD) and soil moisture could explain a large portion of the variability in the sap flux density of the three species, as indicated by mean R 2 during wet seasons; 0.64 (0.65) for P. indicus, 0.70 (0.57) for L. speciosa, and 0.81 (0.78)
Summary
Tropical forests are experiencing reduced productivity and will need restoration with suitable species. We investigated the variability in whole-tree canopy conductance and transpiration (Gt and EL) in potted saplings of common urban species in Thailand, viz., Pterocarpus indicus, Lagerstroemia speciosa, and Swietenia macrophylla, across wet and dry seasons in 2017–2018. L. speciosa may be suitable under future climate variability, given its higher Gt and EL across atmospheric and soil moisture conditions. With their lower Gt and EL, P. indicus and S. macrophylla may photosynthesize throughout the year, maintaining their stomatal opening even under high VPD. The robustness of a given tree species for forest establishment is inferred by investigating its physiological responses to variations in atmospheric demand (i.e., seasonal variations) and soil water availability, especially during the early stages of growth. Canopy conductance may be used to infer a tree’s ability in capturing the atmospheric carbon dioxide and to impute the responses of whole-tree photosynthesis to environmental changes
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