Survival strategies of Centrosema molle and C. macrocarpum in response to drought

Abstract

The response of a genotype each of C. moll e and C. macrocarpum to drought (low soil moisture availability) was studied in a seasonally dry tropical environment throughout 3 consecutive years. Changes in soil water content, leaf water relations and gas exchange, chlorophyll fluorescence, forage yield and leaf area index (LAI) were compared in well-watered and droughted plots. Soil water depletion during the study occurred mostly at 0‒20 cm depth. Minimum values of leaf relative water content, water potential (ψ l ) and net photosynthesis in unwatered plants were within the ranges: 68 ( C. molle ) to 70% ( C. macrocarpum ); -1.6 ( C. molle ) to -0.9 MPa ( C. macrocarpum ); and 8 ( C. molle ) to 10 µmol/m 2 /s ( C. macrocarpum ), respectively. Leaf movements helped to avoid excessive solar radiation incidence, yet efficiency of chloroplast Photosystem II in stressed leaves of C. molle was negatively affected. Above-ground biomass and LAI were reduced only in C. macrocarpum (45‒50% reduction) as a result of moisture stress. Leaves of both species behaved as isohydric, though larger declines in ψ l in C. molle may suggest a less effective control of water loss; this promoted more leaf senescence. Drought survival in these species depends on a combination of avoidance and tolerance strategies; the relative importance of both mechanisms depends on species and the duration and intensity of water deficit. Further studies with a higher number of accessions/ecotypes of each species are suggested in order to corroborate our findings. Keywords: Acclimation, physiological response, soil transpirable water, tropical forage legumes, water stress.