Resumo Este trabalho teve como objetivo avaliar o efeito da aplicação exógena de ácido salicílico sobre o metabolismo fotossintético e a qualidade de mudas de Eugenia myrcianthes sob deficiência hídrica e seu potencial de recuperação após reidratação. Foram avaliados dois regimes hídricos: controle - plantas irrigadas diariamente (I) e déficit hídrico (S), com e sem a aplicação de 400 mg L–1 de ácido salicílico (AS), totalizando quatro tratamentos. As mudas foram avaliadas em três momentos: no início do experimento (T0) quando a irrigação foi interrompida; quando a taxa fotossintética atingiu valores próximos a zero (F0 - 15 dias após a suspensão hídrica), quando a irrigação foi reiniciada; e quando a taxa fotossintética foi recuperada (REC). Mudas de E. myrcianthes foram afetadas negativamente quando submetidas à restrição hídrica; o ácido salicílico atenuou os danos ao aparato fotossintético por agir positivamente sobre o conteúdo relativo de água nas folhas, índice SPAD, metabolismo fotossintético, atividade das enzimas superóxido dismutase e peroxidase e crescimento das mudas na F0. Eugenia myrchiantes apresentou potencial de recuperação após a retomada da irrigação. A aplicação de AS contribuiu na manutenção das trocas gasosas, processos fotoquímicas e qualidade de mudas de E. myrcianthes durante e após o deficit hídrico, sugerindo a promoção da indução de resistência de plantas.

Abstract This study aimed to evaluate the effect of exogenous application of salicylic acid on the photosynthetic metabolism and quality of Eugenia myrcianthes seedlings under water deficit and their recovery potential after rehydration. Two water regimes were evaluated, as follows: control - plants irrigated daily (I) and water deficit (S), with and without the application of 400 mg L–1 of salicylic acid (SA), totaling four treatments. Seedlings were evaluated at three times: at the beginning of the experiment (T0), that is, when the irrigation was interrupted; when the photosynthetic rate reached values close to zero (P0 - 15 days after irrigation interruption), that is, when irrigation restarted; and when the photosynthetic rate was recovered (REC). Eugenia myrcianthes seedlings were negatively affected when subjected to water restriction; salicylic acid attenuated the damage to the photosynthetic apparatus by acting positively on the relative water content in the leaves, SPAD index, photosynthetic metabolism, superoxide dismutase and peroxidase enzyme activity, and seedling growth in P0. Eugenia myrchiantes presented potential for recovery after resumption irrigation. The application of SA contributed to the maintenance of gas exchanges, photochemical processes and quality of E. myrcianthes seedlings during and after water deficit, suggesting the promotion of plant resistance induction.

Resumo O objetivo deste estudo foi avaliar o potencial do sombreamento na redução do efeito estressante do déficit hídrico sobre o metabolismo fotossintético e antioxidante, favorecendo o crescimento de mudas de Ormosia arborea e sua recuperação metabólica. Os níveis de sombreamento estudados foram: 0, 30 e 70%. Foram implantados dois regimes hídricos: controle, em que as plantas foram irrigadas a 75% da capacidade de retenção de água no solo e restrição hídrica, em que a irrigação foi suspensa até que a taxa fotossintética atingisse valores próximos a zero (F0), período em que as mudas foram re-irrigadas. Ocorreram dois períodos de avaliação: F0 e recuperação. Observamos que a restrição hídrica reduz o metabolismo fotossintético, o crescimento e a qualidade das mudas de O. arborea, aumentando a atividade de enzimas antioxidantes. As mudas apresentam maior índice de qualidade, condutância estomática, eficiência de carboxilação da Rubisco e transpiração quando cultivadas sob sombreamento de 70% na recuperação. O efeito estressante da restrição hídrica foi mitigado pelo sombreamento de 70% quando as mudas foram capazes de se recuperara, retomando seu metabolismo fotossintético e qualidade após a retomada da irrigação. Além disso, 0% de sombreamento não é indicado para essa espécie.

Abstract This study aimed to evaluate the potential of shading in reducing the stressful effect of water restriction on photosynthetic and antioxidant metabolism, favoring the growth of Ormosia arborea seedlings and the recovery metabolic. The shadings levels studied were: 0, 30 and 70%. Two water regimes were implemented: control, in which the plants were irrigated at 75% of soil water retention capacity and water restriction, in which the irrigation was suspended until the photosynthetic rate reached values close to zero (P0), period at which the seedlings were re-irrigated. There were two evaluation periods: P0 and recovery. We observed that water restriction reduced photosynthetic metabolism, growth and quality of O. arborea seedlings by increasing the activity of antioxidant enzymes. The seedlings present higher quality index, stomatal conductance, intrinsic carboxylation efficiency and transpiration when cultivated under 70% shading in recovery. The stressful effect of water restriction was mitigated by the shading of 70%, where the seedlings were able to recover, resuming their photosynthetic metabolism and quality after resumption of irrigation. In addition, 0% shading is not indicated for this species.

ABSTRACT The aim of the present study was to evaluate the effect of different concentrations of abscisic acid (ABA) on photosynthetic metabolism and antioxidant enzyme activity in seedlings of Calophyllum brasiliense grown under water deficit. The experiment was carried out in a completely randomized design with six treatments: 1) daily irrigation without ABA (I 0 ABA); 2) daily irrigation + ABA 10 µM (I 10 ABA); 3) daily irrigation + ABA 100 µM (I 100 ABA); 4) suspension of daily irrigation without ABA (E 0 ABA); 5) suspension of daily irrigation + ABA 10 µM (E 10 ABA); 6) suspension of daily irrigation + ABA 100 µM (E 100 ABA). According to results, suspending irrigation decreased gas exchange and water potential, affecting negatively the functioning of the photochemical apparatus, increasing antioxidant enzyme activity. The decrease in stomatal conductance was accompanied by a decrease in photosynthetic and transpiration rates, but seedlings treated with 10 µM ABA presented a higher photosynthetic rate than the remaining treatments under water deficit. Seedlings under water restriction showed recovery after reirrigation of all studied parameters until the end of the experiment, to values similar to those of control plants. Intermittent water deficit decreased plant water status and gas exchange, and increases the antioxidant enzyme activity. Application of 10 µM ABA minimizes the effects of water deficit and increases the antioxidant activity of superoxide dismutase (SOD) in the leaves in C. brasiliense seedlings and improve plant recovery after resuming irrigation, preserving the integrity and functioning of photosynthetic apparatus.