The problem of the lack of adequate water resources for agriculture has intensified in recent years, making it necessary to use waters with relatively high concentration of salts for the irrigation of crops all over the world. The objective of this study was to evaluate the influence of potassium (K) fertilization as a salt stress attenuator on gas exchanges and photochemical efficiency of West Indian cherry. The crop was cultivated under greenhouse conditions in the municipality of Campina Grande, PB, in lysimeters filled with 250 kg of sandy loam soil. Treatments were distributed in randomized blocks, in a 2 x 4 factorial scheme, with two levels of electrical conductivity of irrigation water - ECw (0.8 and 3.8 dS m^-1) and four K doses (50, 75, 100 and 125% of recommendation), in which the dose corresponding to 100% was equal to 19.8 g of K₂O, with three replicates and one plant per repetition. Seedlings of the West Indian cherry cultivar BRS 366-Jaburu, grafted onto a locally developed rootstock from the clonal garden of the EMBRAPA Tropical Agroindustry, Pacajus, CE, were used. Irrigation with salinized water (electrical conductivity of 3.8 dS m^-1) compromised the gas exchange and the photochemical efficiency of West Indian cherry plants. Potassium fertilization was not efficient at reducing the stress caused by water salinity on West Indian cherry plants.

Objetivou-se estudar os mecanismos fisiológicos de percepção e tolerância ao estresse salino de híbridos de citros em cultivo hidropônico. O experimento foi realizado em ambiente protegido do Centro de Ciências e Tecnologia Agroalimentar - CCTA, da Universidade Federal de Campina Grande - UFCG, Pombal, PB. Foram avaliados, em blocos casualizados, em esquema fatorial (2x5), dois níveis de salinidade da água de irrigação (0,3 e 4,0 dS m^-1) e cinco híbridos recomendados para uso como porta-enxerto [HTR - 069, HTR - 116, HTR - 127, LCR x TR - 001 e TSKC x (LCR x TR) - 040)], com três repetições. Os genótipos foram cultivados em sistema hidropônico adaptado em vasos de Leonard, utilizando solução de Hoagland. O início da aplicação da solução nutritiva com uso de águas salinas ocorreu aos 90 dias após a semeadura, quando se procedeu as avaliações quanto às trocas gasosas e fluorescência do PSII às 0, 24 e 48 horas após aplicação dos tratamentos a fim de determinar o efeito do estresse salino sobre os atributos fisiológicos. A fluorescência inicial, a condutância estomática e a eficiência no uso da água foram as variáveis que mais permitem evidenciar a percepção do estresse neste trabalho. O híbrido TSKC x (LCR x TR) - 040 foi o mais tolerante à salinidade, seguido do híbrido HTR - 069. O híbrido LCR x TR - 001 foi o mais sensível à salinidade, por ter sua atividade do PSII comprometida.

Nitrogen (N) fertilization has been tested for the mitigation of salt stress in some species including fruit crops. However, special attention should be paid to the source of N, due to the different compositions and saline indices of the fertilizers, particularly when irrigation is conducted using waters with salinity levels that are restrictive to agriculture. Thus, this study evaluated the effect of fertilization with N sources on the growth and gas exchanges of soursop irrigated with saline water after transplanting. The experiment was carried out in greenhouse at the Center of Technology and Natural Resources of the Federal University of Campina Grande, and treatments were arranged in randomized blocks, in 4 x 4 factorial scheme, corresponding to electrical conductivity of water - 0.5, 1.1, 2.5 and 3.5 dS m^-1, and the N sources urea, ammonia sulfate, calcium nitrate and potassium nitrate, with three replicates. Growth and gas exchanges of soursop at 110 days after transplanting were not influenced by either the interaction between water salinity and N sources or the individual action of N, but were inhibited by the increase in water salinity from 0.5 dS m^-1. Increasing water salinity inhibited stomatal opening and carboxylation in the leaves.

The objective of this study was to evaluate the interaction between water salinity and doses of nitrogen and phosphorus on chlorophyll a fluorescence and on the growth of West Indian Cherry (‘acerola’) plants in the initial growth stage. The research was carried out in a protected environment, in lysimeters filled with Regolithic Neosol of loamy clay texture and low initial phosphorus content. The experiment was conducted in a randomized block design, arranged in a factorial scheme with two factors, five levels of electrical conductivity of the irrigation water - ECw (0.6, 1.4, 2.2, 3.0 and 3.8 dS m^-1) and four proportions of the recommendation of phosphorus/nitrogen - P/N (100:100, 140:100, 100:140 and 140:140% P/N of recommendation), with three replicates, and each plot consisted of one plant. Water salinity above 2.2 dS m^-1 decreases the quantum efficiency of photosystem II and the growth of west indian cherry plants. Increase in nitrogen and/or phosphorus supply improves the energy stability of west indian cherry plants by reducing the effects of salt stress on the quantum efficiency of photosystem II. The increase of 40% in the nitrogen dose increased the chlorophyll a fluorescence, but did not influence the plant growth.