Morphophysiology and gas exchange of pomegranate under salt stress and foliar application of nitrogen¹

Morfofisiologia e trocas gasosas da romãzeira sob estresse salino e aplicação foliar de nitrogênio

HIGHLIGHTS:

Salinity reduces growth and gas exchange of pomegranate.

Foliar-applied N dose of up to 1.31 g L^-1 reduces the harmful effect of salinity on pomegranate growth.

Foliar nitrogen fertilization up to 1.59 g L^-1 increases net photosynthesis.

ABSTRACT

Salinity is one of the abiotic stresses that affect gas exchange and growth of pomegranate. In this context, the application of nitrogen fertilizer through the leaves can minimize these effects. Thus, the objective of present study was to evaluate the effect of foliar nitrogen fertilization on pomegranate seedlings irrigated with brackish water. The design used was randomized blocks, in an incomplete factorial scheme (Central Composite Design) with five electrical conductivities of irrigation water - ECw (0.50, 1.15, 2.75, 4.35, and 5.00 dS m^-1) and five doses of foliar nitrogen fertilization - FNF (0, 0.33, 1.15, 1.97, and 2.30 g L^-1), with four replicates and two plants per experimental plot. Plant height, number of leaves, stem diameter, and gas exchange (stomatal conductance, net photosynthesis, intercellular CO₂ concentration, transpiration rate, instantaneous carboxylation efficiency, instantaneous water use efficiency, and intrinsic water use efficiency) were evaluated at 60 days after the beginning of irrigation with saline water. Salinity of irrigation water negatively affects the gas exchange of pomegranate seedlings. Foliar nitrogen fertilization up to 1.31 g L^-1 improves plant height and number of leaves in pomegranate seedlings under salt stress. Foliar nitrogen fertilization up to 1.59 g L^-1 increases the net photosynthesis of pomegranate seedlings.

Key words:
Punica granatum L.; photosynthesis; nitrogen; salinity