Gas exchange and photochemical efficiency of guava under saline water irrigation and nitrogen-potassium fertilization

ABSTRACT The objective of this study was to evaluate the effects of different combinations of nitrogen and potassium fertilization on gas exchange and chlorophyll a fluorescence in seedlings of guava cv. Paluma irrigated with water of different salinity levels. The experiment was set up in a randomized block design and analyzed in 5 × 4 factorial scheme, with four replicates. The treatments were composed of the combination of the factor electrical conductivity of irrigation water - ECw (0.3, 1.1, 1.9, 2.7, and 3.5 dS m-1), with the factor combinations (C) formed from recommended doses of nitrogen (N) and potassium (K2O), 70% N + 50% K2O, 100% N + 75% K2O, 130% N + 100% K2O, and 160% N + 125% K2O. The fertilization combination 130% N + 100% K2O mitigated the effects of salt stress up to mean ECw of 1.3 dS m-1, resulting in increments in CO2 assimilation rate, transpiration, instantaneous carboxylation efficiency, and electron transport rate. For maximum quantum efficiency of photosystem II, only treatment irrigated with ECw 3.5 dS m-1 under the combination 160% N + 125% K2O showed damage to the photosynthetic apparatus.摘要 本研究旨在评估不同氮钾肥配施组合对以不同盐度水体灌溉的Paluma品种番石榴（guava cv. Paluma）实生苗气体交换与叶绿素a荧光（chlorophyll a fluorescence）的影响。试验采用随机区组设计，设置5×4因子试验方案，共设4次重复。试验处理由灌溉水电导率（electrical conductivity of irrigation water, ECw）因子与因子组合C组构成：其中ECw因子设置梯度为0.3、1.1、1.9、2.7与3.5 dS·m⁻¹；因子组合C组则基于推荐施氮（N）量与钾（K₂O）量设置4种配施方案，分别为70% N + 50% K₂O、100% N + 75% K₂O、130% N + 100% K₂O及160% N + 125% K₂O。研究结果显示，130% N + 100% K₂O的施肥组合可在灌溉水电导率均值不超过1.3 dS·m⁻¹的条件下缓解盐胁迫效应，提升CO₂同化速率、蒸腾速率、瞬时羧化效率与电子传递速率。针对光系统II（photosystem II）最大量子效率这一指标，仅当采用160% N + 125% K₂O施肥组合且灌溉水ECw为3.5 dS·m⁻¹时，供试番石榴实生苗的光合机构才会受到损伤。