Fósforo e salinidade da água no crescimento, trocas gasosas e osmólitos em mudas de pinheira

Abstract

The salinity of irrigation water becomes a problem for irrigation of crops, including custard apple, however, the adoption of specific techniques should contribute to use of saline water in agriculture. Phosphorus is an important nutrient, because under deficient conditions it limits the growth of seedlings. The aim of this study was to evaluate the influence of water salinity and triple superphosphate doses (TSP) on growth, gas exchange and osmolytes in Annona squamosa L. seedlings. The experiment was carried out under greenhouse conditions, from January to March, 2017 at the UFPB, Campus II, Areia, PB, in a randomized block design based on the Central Composite Box Design, referring to triple superphosphate doses (TSP) (0.0, 0.87, 3.0, 5.1, 6 g.dm-3 ) and CEai (0.5, 1.1, 2.5, 3.9 and 4.5 dS.m-1 ). Were evaluated: plant height, stem diameter, shoot dry matter mass, total dry matter mass, Na+ , K+ , Ca+2, P leaf content, net photosynthesis, transpiration rate, stomatal conductance, internal CO2 concentration, water use efficiency, carboxylation efficiency, proline, glycine-betaine, reducing and non-reducing sugars. It was observed interaction effect on stem diameter, carboxylation efficiency (A / Ci), glycine-betaine, reducing sugars and non-reducing sugars. Plant height, total shoot dry matter mass, absolute growth rate, relative growth rate, Dickson quality index, Na+ , K+ , Ca+2, phosphorus and proline had an effect when they were submitted to doses of TSP. And the Na+ , K+ , Ca+2, phosphorus, gaseous exchange and proline variables had an isolated CEwi effect. The interaction of phosphorus and CEwi promotes higher levels of glycine-betaine, reducing sugars and non-reducing sugars in custard apple seedlings. Triple x superphosphate and CEwi high doses reduced K+ leaf content and increased Na+ /K+ ratio. Triple superphosphate doses promote greater growth in custard apple seedlings, so at 78 days, it is recommended to apply 2.24 g dm-3 of triple superphosphate in the substrate. Triple superphosphate doses did not attenuate the negative effects of the electrical conductivity of irrigation water. The dose of 3.2 g dm-3 of TSP promoted greater leaf content of proline. The salinity of irrigation water impairs gas exchange in custard apple seedlings and increases leaf proline content. Both the high electrical conductivities of the irrigation water, and the high doses of TSP caused stress to the custard apple seedlings.