Survival strategies of <i>Centrosema molle</i> and <i>C. macrocarpum</i> in response to drought

<p>The response of a genotype each of <em>C. moll</em>e and <em>C. macrocarpum</em> 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 (<em>C. molle</em>) to 70% (<em>C. macrocarpum</em>); -1.6 (<em>C. molle</em>) to -0.9 MPa (<em>C. macrocarpum</em>); and 8 (<em>C. molle</em>) to 10 µmol/m²/s (<em>C. macrocarpum</em>), respectively. Leaf movements helped to avoid excessive solar radiation incidence, yet efficiency of chloroplast Photosystem II in stressed leaves of <em>C. molle</em> was negatively affected. Above-ground biomass and LAI were reduced only in <em>C. macrocarpum</em> (45‒50% reduction) as a result of moisture stress. Leaves of both species behaved as isohydric, though larger declines in ψ_l in <em>C. molle</em> 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.</p> <p><strong> </strong></p> <p><strong>Keywords: </strong>Acclimation, physiological response, soil transpirable water, tropical<strong> </strong>forage legumes, water stress.</p>