Características fotossintéticas da palmeira macaúba (Acrocomia aculeata (Jacq.) Lodd. ex Mart.) submetidas a deficiência hídrica

• Autor(a) principal: Mota, Clenilso Sehnen
• Data de Publicação: 2011
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/988
• topic: Acrocomia aculeata; Défict hídrico; Recuperação; Trocas gasosas; Arecaceae; Estresse cíclico; Acrocomia aculeata; Water deficit; Recovery; Gas exchange; Arecaceae; Cyclic stress; CNPQ::CIENCIAS BIOLOGICAS::BOTANICA::FISIOLOGIA VEGETAL

Two experiments were carried out in a greenhouse with the objective to evaluate water relations, photosynthetic parameters, osmotic adjustment capacity and recovery of these characteristics in young macaúba plants submitted to water shortage. In both experiments, macaúba seedlings arrived at the age of 10 months, and they were grown in containers with 150 L of substrate, with daily irrigationuntil the age of 18 and 19 months, in experiments I and II, respectively, when it was started dry/recovery (DR) cycles. Experiment I was conducted with the objective to evaluate behavior of different macaúba accessions in response to a DR cycle. The plants used in the experiment were seedlings from accessions 43, 55, 57 and 63. Five plants per accession, after suspension of irrigation, and variables of water potential before dawn (Ψam), CO2 net assimilation rate (A) and transpiration (E) were evaluated in periods with approximately 10 days until accessions presented A close to zero, and at this moment irrigation was resumed, and variables were evaluated after six days. Linear regression fitted for variables A, E, water use efficiency (WUE) and Ψam in each accessions, was y=α+βx+δx2+θex (equation 1), in which y represent variable A, E, WUE or Ψam, x meaning days after suspension of irrigation, α is y value on the day when irrigation was suspended, β is curve slope after suspension of irrigation, δ is the quadratic effect of x on y and θ meaning y intensity recovery. The relationship between variables A and E in function of Ψam, for each accession, was fitted by the following quadratic equation, y=a+bx+cx2 (equation 2), in which y = A or E, x = Ψam, and a = y when Ψam is zero, b = y reduction slope in function of Ψam decrease and c expresses curve convexity. In each variable, parameters α, β and θ from equation 1 and a, b and c from equation 2 were compared among accessions of macaúba by using the model identity test. Experiment II were carried out to analyze the effect of successive DR cycles on photosynthetic parameters, water relations and osmotic adjustment. In this experiment, ten plants of FL access were submitted to three DR successive cycles and the other ten were irrigated as usual. Each cycle consisted in suspending irrigation until A was less than 95% regarded to plants without water shortage (SD), resuming irrigation until A recovered at least 85% in relation to SD plants. With the results from experiment I, values of α, β and θ from Ψam equations did not differ among accessions. But, for A and E, accessions presented differences only for α, in which A was the greatest in accession 57 and 63 in comparison to accession 43, and E was superior in accession 57 in comparison to accessions 43 and 55. WUE was the only variable that present difference among accessions for θ, in which accession 63 was superior to 55, but accession 55 was the one which presented a trend of smaller WUE reduction in severe water shortage. Parameter a from the linear equation did not present difference among accessions, for A and E. However, b and c differed among accessions, in which 57 presented the smallest A fall inclination, in relation to accessions 43 and 63, but for E, accession 57 showed less convexity than accession 43. Regarding regression convexity, accession 57 presented less convexity in relation to accession 43. In accession 57, reduction of A and E by 50% occurred at Ψam from -1.28 to -1.18 Mpa, respectively and both Ψam were lower than the other accessions. Reduction of 50% in A and E in smaller Ψam at accession 57 and the lower value of b in comparison to the other accessions, demonstrates that it is more resistant to water shortage. In experiment II, which used successive DR cycles, reductions of A, stomatal conductance (gs) and E above 95% were obtained at water potential before dawn (Ψam) of -1.9 MPa, and A decreased was preceded by gs and E. At rehydration, gs, E and Ψam did not present differences among plants with and without water shortage, which was not observed with A. A reduction is linear and proportional to decrease of Ψam, and reduction of A by 50% occurs at Ψam of -1.1 MPa. gs shows the same behavior of A in relation to Ψam, but reduction of gs by 50% occurs at Ψam of -0.8 MPa. The maximum value of WUEi occurs at Ψam of -1.5 MPa; for reductions below this value, WUEi falls sharply. Relative mesophyll limitation ranged from 91 to 94% on maximum stress point (MEP). SD plants presented relative stomatal limitation between 37 and 41%; for CD plants, CO2 increment did not affect A on MEP. Minimal fluorescence adapted to dark (F0) increased, and PSII maximum quantum efficiency (Fv/Fm) reduced in severe stress, showing damage to PSII and showed no recovery after the second cycle. Apparent electron transport rate (TTE) and PSII quantum yield of photochemical energy conversion (фPSII) showed reduction at moderate and severe levels of water shortage, but they recovered during rehydration periods. Macaúba plants showed no osmotic adjustment, however, there was accumulation of proline, with peak at the points of maximum stress. Reducing the accumulation of plant dry matter CD was 56 and 48% for roots and shoots, respectively, root/shoot was not affected by disability. Access 57 showed more tolerance to water shortage than 43, 55 and 63 access. Intermittent periods of water availability may promote photosynthesis acclimatation as shown in experiment 2. Gas exchange, in experiment 2, show recovery during rehydratation period, and the leaf water potential of -1.5 Mpa could be a limit between moderate and severe water stress.