Stomatal size and density trade-off varies with leaf phenology and species shade tolerance in a South Asian moist tropical forest

The density and guard cell length of stomata regulate the physiological processes in plants. Yet, the variation of stomatal characteristics among different functional groups of trees is not been well understood. Particularly, a comprehensive understanding of stomatal behaviour in Bangladeshi moist forest trees is lacking. The study investigated how abaxial stomatal density (SD) and guard cell length (GCL) vary among tree functional types and leaf phenological groups in a moist tropical forest of Bangladesh. Cluster dendrogram revealed three groups of species based on SD and GCL. The independent sample t-test showed that there was a significant difference in SD between evergreen and deciduous tree species (t = 4.18, P < 0.001) but no significant difference in GCL between the two phenological groups. ANOVA revealed no significant difference in SD among the light demanding, intermediate shade tolerant and shade tolerant species (F = 0.76, P = 0.47). However, GCL significantly differed among the three functional groups (F = 3.3, P < 0.05). Maximum theoretical stomatal conductance (gmax) varied between evergreen and deciduous species but did not vary with species shade tolerance. In general, there was a significant trade-off between SD and GCL. However, the inverse relationship was stronger in deciduous and shade tolerant species than in evergreen and shade intolerant species. Leaf dry matter content was positively related with SD and negatively related with GCL. Specific leaf area and leaf thickness were not related to the stomatal traits. Our analyses suggest that leaf phenology and species shade tolerance need to be considered while estimating gas exchange through the stomata in tropical moist forests.