Ecophysiological characteristics of crambe under water stress conditions

Abstract

As sementes produzidas pela espÃcie Crambe abyssinica Hoscht (crambe) apresentam grande potencial na indÃstria do biodiesel que, atualmente, procura novas fontes de biomassa vegetal para atingir as metas de produÃÃo. Por ser uma espÃcie de cultivo pouco desenvolvida, pesquisas sobre seu comportamento ecofisiolÃgico sÃo importantes para auxiliar a implementar tal cultura na matriz energÃtica brasileira. A fim de caracterizar o comportamento ecofisiolÃgico do crambe, o presente estudo avaliou o crescimento e a potencialidade alelopÃtica do crambe em condiÃÃes de estresse hÃdrico em dois estÃdios de desenvolvimento. Plantas de crambe foram submetidas a diferentes nÃveis (4, 8, 12, 16 e 20 dias) de suspensÃo de irrigaÃÃo durante o estÃdio vegetativo e a floraÃÃo. Em cada nÃvel, foram analisados os seguintes parÃmetros: nÃmero de folhas, altura das plantas, Ãrea foliar e massa seca total e calculados os Ãndices fisiolÃgicos de razÃo de Ãrea foliar (RAF), Ãrea foliar especÃfica (AFE), taxa de assimilaÃÃo liquida (TAL) e taxa de crescimento relativa (TCR), submetidos à anÃlise de regressÃo linear exponencial. AlÃm disso, fez-se anÃlise da constituiÃÃo foliar de micro e macronutrientes por espectrofotometria de absorÃÃo atÃmica. Para avaliar a potencialidade alelopÃtica do crambe em condiÃÃes de estresse hÃdrico, foi preparado extrato aquoso estÃtico a partir de suas partes aÃreas, em concentraÃÃo de 2 e 4%, os quais foram adicionados em placas de Petri contendo 25 sementes de alface em cada uma. Os experimentos foram conduzidos em cÃmara de germinaÃÃo, com testemunha de Ãgua destilada e de potencial osmÃtico (PEG 6000) e delineamento inteiramente casualizado. Obtiveram-se porcentagem (%G), Ãndice de velocidade de germinaÃÃo (IVG), comprimento mÃdio de raiz (CMR) e de parte aÃrea (CMPA) das plÃntulas e as mÃdias comparadas pelo teste Tukey a 5% de significÃncia. As plantas de crambe apresentaram reduÃÃo de Ãrea foliar e massa seca total no estÃdio vegetativo, no Ãltimo nÃvel de estresse. Para o mesmo estÃdio de desenvolvimento, foi observado efeito do estresse hÃdrico nos Ãndices RAF, AFE, TAL e TCR, haja vista esse estÃdio de desenvolvimento ser mais sensÃvel aos efeitos do dÃficit hÃdrico. Os extratos preparados a 4% de concentraÃÃo apresentaram maiores efeitos alelopÃticos. Durante o desenvolvimento vegetativo, observou-se reduÃÃo na potencialidade alelopÃtica das plantas ao longo do estresse. PorÃm, na floraÃÃo, as plantas afetaram negativamente o processo de germinaÃÃo e desenvolvimento inicial das plÃntulas de alface durante o 4 e 16 dia de estresse hÃdrico. Assim, conclui-se que os efeitos da suspensÃo de irrigaÃÃo sobre as plantas de crambe variaram quanto ao perÃodo de desenvolvimento e à intensidade do estresse hÃdricoThe seeds produced by Crambe abyssinica Hochst (crambe) species have great potential in the biodiesel industry that currently searches for new sources of biomass to reach its production goals. As this culture species is rarely developed, it is essential to carry out researches on ecophysiological behavior to implement it in the Brazilian energy matrix. In order to characterize the ecophysiological behavior of crambe, this study evaluated the growth and allelopathic potential of crambe under conditions of water stress in two stages. vi Crambe plants were submitted to different levels (4, 8, 12, 16 and 20 days) of irrigation cancelation during the vegetative and flowering stages. At each level, the following parameters were analyzed: number of leaves, plants heights, leaf area and total dry weight and calculated physiological indexes of leaf area ratio (LAR), specific leaf area (SLA), net assimilation rate (NAR) and relative growth rate (RGR), all analyzed by linear exponential regression. In addition, it was carried out a leaf constitution analysis of micro and macronutrients by atomic absorption spectrophotometry. The static aqueous extract was prepared from its shoots to evaluate the allelopathic potential of crambe under water stress, at 2 and 4% concentration and then added to Petri dishes with 25 seeds of lettuce for each one. Experiments were carried out in a germination chamber with distilled water and osmotic potential (PEG 6000) as control treatments, based on a completely randomized design. The obtained data were percentage (%G) and germination speed index (GSI), root (RL) and shoot lengths (SL) of seedlings and averages were compared by Tukey test at 5% significance level. Crambe plants showed some decrease on leaf area and total dry matter in the vegetative stage, in the last level of stress. For the same developmental stage, an effect of water stress was observed at LAR, SLA, NAR and RGR indexes, concluding that this stage of development is more sensitive to drought effects. The extracts that were prepared at 4% concentration showed higher allelopathic effects. During vegetative development, there was a decrease in allelopathic potential of plants along the stress, but, during flowering, crambe plants affected negatively germination and seedling initial development of lettuce during the 4th and 16th days of water stress. Thus, it was concluded that the cancelation of irrigation on crambe plants differed in terms of development period and intensity of water stres