Growth and gas exchanges in soursop under irrigation with saline water and nitrogen sources/ Crescimento e trocas gasosas em gravioleira sob irrigacao com aguas salinas e fontes de nitrogenio

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.sup.-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.sup.-1]. Increasing water salinity inhibited stomatal opening and carboxylation in the leaves. Key words: Annona muricata L. salinity nitrogen photosynthesis A adubacao nitrogenada vem sendo testada na mitigacao do estresse salino, em algumas especies inclusive em frutiferas; todavia, atencao especial deve ser dada a fonte de N devido as diferentes composicoes e os indices salinos dos fertilizantes, principalmente quando se irriga com aguas de salinidade restritiva a agricultura. Neste sentido, estudou-se o efeito da adubacao com fontes de nitrogenio sobre o crescimento e trocas gasosas de gravioleira irrigada com aguas salinas apos o transplantio. O experimento foi desenvolvido em casa de vegetacao do Centro de Tecnologia e Recursos Naturais da Universidade Federal de Campina Grande, com os tratamentos distribuidos em blocos casualizados, em esquema fatorial 4 x 4, correspondente aos niveis de condutividade eletrica da agua de 0,5; 1,1; 2,5 e 3,5 dS [m.sup.-1] e as fontes de nitrogenio: ureia, sulfato de amonia, nitrato de calcio e nitrato de potassio, com tres repeticoes. O crescimento e as trocas gasosas da gravioleira aos 110 dias apos o transplantio nao foram influenciados pela interacao entre a salinidade da agua e as fontes de nitrogenio e nem pela acao isolada de N, mas foram inibidos