| Carambola (Averrhoa carambola) is a commercially important tropical fruit tree in South Florida. Little is known about carambola water requirements or its response to limited soil water supply under subtropical conditions such as those of southern Florida. The objective of this study was to determine the effects of four levels of soil water depletion (SWD) that ranged from field capacity (FC) to the first visual signs of water stress (leaf yellowing and abscission), on leaf gas exchange, stem water potential, phenology, growth, and yield of 2-year-old, container-grown carambola trees, and 8-year-old 'Arkin' carambola trees in an orchard.;Soil water depletion treatments were determined from continuous measurement of soil water content using multisensor capacitance probes (EnviroSCAN, Sentek PTY Ltd., Kent Town, Australia). Irrigation of orchard trees was initiated when SWD reached one of the following levels (where 0% SWD = FC): 0--8% SWD, 9--11% SWD, 12--14% SWD, or 15--17% SWD. Trees in 95 L containers filled with Krome very gravelly loam soil were irrigated when SWD reached one of the following levels: 0--21% SWD, 22--31% SWD, 32--50% SWD, or 51--60% SWD.;An increase in SWD resulted in a reduction in stem water potential (Psi S), net CO2 assimilation (A), transpiration (E), and stomatal conductance to water vapor (gs) of carambola trees grown in containers in a Krome very gravelly loam soil. In the orchard, SWD never reached a point where there was a decrease on PsiS, A, E, or gs. For carambola trees in containers, when SWD levels were above 50% there was a reduction in PsiS that subsequently reduced gs. A reduction in gs resulted in a linear decrease in E and a sharp decline in A when gs fell below 50 mmol·m-2 ·s-1. Leaf gas exchange was better correlated with PsiS than with SWD level. Therefore, PsiS may be a more accurate than SWD (as determined from measurements of soil water content) for irrigation scheduling of carambola in gravelly soils.;In the orchard, precipitation and possibly capillarity from the shallow water table resulted in sufficient soil water content to obtain adequate vegetative growth and yields. Adequate soil water content also resulted in no significant phenological differences among treatments. In containers where lateral water movement and capillary rise were prevented, tree trunk diameter and total dry weight were lower for trees irrigated at 32--50% SWD and 51--60% SWD than for trees irrigated at 0--21% SWD, 22--31% SWD treatments.;Based on the results of this study, irrigation of carambola trees in Krome soil at 17% SWD in an orchard and at 32% SWD in containers does not reduce tree growth, yield and fruit quality. |
