Ricinus communis L.: Water Use Efficiency, Carbon Assimilation and Water Relations on Deficit Irrigation

Abstract

Aims: This study evaluated carbon assimilation, water relations, intrinsic and instantaneous water use efficiency, and water consumption of two cultivars of Ricinus communis L. cv. BRS 188 Paraguaçu and BRS Energia, subjected to regulated-deficit irrigation. Study Design: The experiment was arranged in a completely randomized scheme in a factorial arrangement of 5 x 2, with five replicates. Place and Duration of Study: The experiment was conducted in a greenhouse at the Universidade Estadual de Santa Cruz, Ilhéus, Brazil from December 2008 to February 2009. Methodology: The growing plants were subjected to different water conditions by predefined quantities of water, so as to maintain the substrate under the following matric potential (Ψm) during the experimental period: -1.6 kPa (near field capacity), -3.0 kPa, -7.3 kPa, -26.7 kPa, and -183.0 kPa. Results: The cultivars differed significantly (P = .05) in predawn leaf water potential and relative water content, showing that the tissues of BRS Energia remained more hydrated compared to  BRS 188 Paraguaçu. Under -183.0 kPa, the intrinsic water use efficiency and instantaneous water use efficiency were significantly higher in BRS Energia than in BRS 188 Paraguaçu, suggesting a conservative behavior of the cultivar BRS Energia. Non-stomatal limitations to photosynthesis were observed in BRS 188 Paraguaçu. Under greater water stress, BRS 188 Paraguaçu and BRS Energia plants had the leaf area reduced by 75.58% and 23.13%, respectively compared with the control. The water use efficiency of biomass was significantly higher in BRS Energia than in BRS 188 Paraguaçu. Conclusion: The cultivar BRS Energia was more promising in relatively drier conditions compared to BRS 188 Paraguaçu. The carbon assimilation decreased in both castor bean cultivars only under severe water stress (-183.0 kPa), suggesting that the use of the deficit irrigation technique may be viable leading to lower water consumption and higher photosynthesis efficiency.