Physiological and morphological responses of young mahogany ( Swietenia macrophylla King) plants to drought

Abstract

Young mahogany ( Swietenia macrophylla King) plants were grown under either well-watered (pre-dawn leaf water potential, Ψ pd, ca. −0.40 MPa) or drought ( Ψ pd, ca. −3.52 MPa) conditions to examine some physiological strategies that allow the maintenance of leaf turgor. In well-watered plants, stomatal conductance ( g s) was nearly constant (440 mmol m −2 s −1) between 7:00 and 13:00 h. This was accomplished by significant increases in transpiration ( E) and apparent total hydraulic conductance ( K T), in which averages were higher at 13:00 h. From 13:00 to 17:00 h, g s, E, and K T decreased sharply, reaching their lower values at 17:00 h. In these plants, significant increases in height (116%), stem diameter (50%) and leaf area (200%) were registered over the experimental period (20 days). Analyses of linear regression between g s or E and leaf-to-air vapor pressure deficit ( Δ w) were not significant. In water-stressed plants, g s and E were higher at 7:00 h and lower from 9:00 to 17:00 h, while K T was higher in early morning (7:00 h) and in late afternoon (17:00 h) than between 9:00 and 15:00 h. Moreover, both g s and E decreased potentially ( P < 0.001) with the diurnal increases on Δ w. Drought also decreased leaf and leaflet numbers and reduced total leaf area, but had no effect on stem height and diameter. Leaf proline was higher (ca. 400%, between 13:00 and 15:00 h) in water-stressed plants, suggesting osmotic adjustment under drought. Twelve hours after resumption of irrigation, Ψ pd was similar ( P > 0.05) between well-watered and drought-stressed plants, suggesting an ability of plants to recover turgor after stress cessation. Altogether, our data support the hypothesis that young mahogany plants have the ability to satisfactorily tolerate or postpone drought.