Physiological factors correlated with short-term dynamic changes in a tropical forest tree community.

Abstract

Although niche differentiation has been widely observed, its driving force is still incompletely known. This project aims to determine the role of physiological traits of species in niche differentiation. Clidemia hirta and Melastoma malabathricum (Melastomataceae) were subjected to combinations of moisture and light treatments in the greenhouse and measured weekly for stomatal conductance (g), chlorophyll content, chlorophyll fluorescence and in the final week, relative water content. These, and water potential (Ѱ) were measured in field studies on Clidemia and Melastoma, and Pellacalyx saccardianus, Gynotroches axillaris and Carallia brachiata (Rhizophoraceae). Results showed that Melastoma is more light-tolerant and water-demanding than Clidemia, explaining its existence in wet, high light areas. Clidemia has a lower Ѱ and probable night transpiration that decreases risk of xylem cavitation, explaining its invasiveness into drier habitats. The Rhizophoraceae family possibly exhibit radiationless dissipation of excitation energy, and can control Ѱ to ensure noontime g without excessive water loss, explaining how these shade plants can survive in higher light intensity and swamps. The higher wood density of Gynotroches makes it more drought-tolerant than the rest, allowing it to grow in dry forests as well. I conclude that physiological factors can cause changes in a tropical forest tree community.