792 AJCS 11(07):792-798 (2017) ISSN:1835-2707 doi: 10.21475/ajcs.17.11.07.pne354 Leaf gas exchange and biomass partitioning in Jatropha curcas L. young plants subjected to flooding and drought stresses Tessio Araújo de Santana *, Leandro Dias da Silva 2 , Priscila Souza de Oliveira 1 , Carolina Santos Benjamin 3 , Elmo Pereira Ramos 1 , José Olimpio de Souza Júnior¹, Fábio Pinto Gomes 1 1 State University of Santa Cruz, Department of Biological Sciences, Ilhéus, Ba 45662900, Brazil ²Federal University of Espírito Santo, Department of Plant Production, Alegre, Es 2950000, Brazil 3 Universidade Federal de Viçosa, Departamento de Fitotecnia, Viçosa, 36570000, Brazil *Corresponding author: tessiosantana@yahoo.com.br Abstract With the purpose of assessing the physiological responses of J. curcas young plants to drought and flooding, plants were subjected to three watering regimes: Control, drought and flooding. In the same period, five plants were submitted to drought (irrigation suspension), five to flooding and five were maintained near the field capacity (control). Measurements of leaf gas exchange, chlorophyll content, biomass of each organ (leaf, stem and root), biomass ratios, as well as the root:shoot ratio were made. When compared to control, drought and flooding treatments led to significant reductions (P≤.05) of gas exchange rates at 14 and 7 days after imposition treatments (DAIT), respectively. At the 16 th DAIT, significant reductions of leaf, root, stem and total biomass were observed, which resulted in changes of biomass partitioning of each organ. Significant reduction of leaf dry biomass (LDB) was observed in water deficit plants. Moreover, no significant effects of water deficit were observed in root dry biomass. Such response has led to a higher root:shoot ratio, suggesting an improved ability for water and nutrients uptake. In turn, flooding has induced a significant decrease in the dry biomass of all organs. Stem dry biomass ratio of flooded plants (0.67 g g -1 ) was significantly higher than that of control plants (0.41 g g -1 ), which, was seemingly due to leaf senescence and root system rotting of flooded plants. Altogether, present results reinforce the susceptibility of the studied genotype of J. curcas to flooding, as well as highlight some characteristics of drought tolerance in this species. Keywords: Abiotic stress; biomass allocation; Euforbiaceae; stomatal control; water use efficiency. Abbreviations: DAIT_days after imposition treatments; DBR_dry biomass ratio; LA_leaf area; LDB_leaf dry biomass; SDB_stem dry biomass ratio; SLA_specific leaf area. Introduction In the current scenario of climate changes, plants are often exposed to various stresses, such as excess (flooding) or deficiency (drought) of water, which may affect their metabolic processes and, consequently growth, development and yield (Chaves and Oliveira, 2004). Flooding-induced plant damage occur, especially by reducing the availability of O 2 and the diffusion of gases (mainly O 2 e CO 2 ) (Perata et al., 2011), inhibiting seed germination, vegetative and reproductive growth and, depending on the intensity, plant death (Kozlowski, 1997). The drought affects many physiological processes of the plants, generally by increasing the stomatal resistance, reducing transpiration and thus the supply of CO 2 (Nogueira et al., 2001). Despite the damage caused by this stress, the decrease in stomatal conductance, caused by the limited availability of water, may allow the plant to assimilate more molecules of CO 2 for each unit of water transpired, i.e., increased water use efficiency is generally observed in water stressed plants (Blum, 2009). The use of appropriate crops that may grow in such harsh environments is justified (Chaves et al., 2003; Chaves and Oliveira, 2004). Given the climate changes, coupled with need of replacing fossil fuels with renewable fuels, the physic nut (Jatropha curcas L.) has drawn scientific and economic interest. Amongst the advantages of J. curcas over other oilseed crops, one may highlight the high oil production ranging from 30-35% of seed’s weight, the easy conversion of oil into biodiesel, and the lack of competitiveness with the food industry, unlike Glycine max L. and Arachis hypogaea L. (Fairless, 2007). In addition to these agronomic characteristics, J. curcas has been considered tolerant to drought, being reported consistent changes in biomass allocation in favor of root system, allowing them to survive when subjected to water deficit (Achten et al., 2010; Díaz- Lopez et al., 2012; Maes et al., 2009). The hardiness and adaptability of J. curcas to different agro-climatic conditions justify its broad distribution (Achten et al., 2008; Divakara et al., 2010) and allows its cultivation in degraded and/or dry climate areas (Srivastava et al., 2011). Based on the possible tolerance of this species to several stressful conditions, we workout the hypothesis that J. curcas can survive, for a determined period, to drought and flooding without significant damage in terms of biomass production. Indeed, there is still the need for a better characterization of the physiological responses of this species when subjected to water stress. Taking into account the above information, this study aimed to evaluate leaf gas exchange and growth responses of J. curcas young plants to water stresses by drought and flooding. AUSTRALIAN JOURNAL OF CROP SCIENCE | SUBMITTED: 04-DEC-2016 | REVISED: 12-JAN-2017 | ACCEPTED: 06-MARCH-2017