HIGHLIGHTS:
Irrigation water electrical conductivity of less than 3.5 dS m-1 does not damage the photosynthetic apparatus in guava.
The maximum and variable fluorescence is reduced when electrical conductivity of irrigation water is above 0.3 dS m-1.
Excessive doses of N and K reduce the quantum efficiency of photosystem II.
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.
Key words:
Psidium guajava L.; salt stress; physiology
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ns, *, ** - not significant, significant at p ≤ 0.05 and p ≤ 0.01 by the F test, respectively; C1 = 70% N + 50% K2O, C2 = 100% N + 75% K2O, C3 = 130% N + 100% K2O, and C4 = 160% N + 125% K2O
ns, * - not significant, significant at p ≤ 0.05 by the F test, respectively; C1 = 70% N + 50% K2O, C2 = 100% N + 75% K2O, C3 = 130% N + 100% K2O, and C4 = 160% N + 125% K2O
ns, *, ** - not significant, significant at p ≤ 0.05 and p ≤ 0.01 by the F test, respectively; C1 = 70% N + 50% K2O, C2 = 100% N + 75% K2O, C3 = 130% N + 100% K2O, and C4 = 160% N + 125% K2O
ns, *, ** - not significant, significant at p ≤ 0.05 and p ≤ 0.01 by the F test, respectively; C1 = 70% N + 50% K2O, C2 = 100% N + 75% K2O, C3 = 130% N + 100% K2O, and C4 = 160% N + 125% K2O. Means followed by different letters indicate significant difference between treatments by Tukey test (p ≤ 0.05)