Physiological and biochemical responses of apple trees to irrigation water depth in a semiarid region of Brazil

Abstract

The present study evaluated the physiological and biochemical parameters of apple trees under different irrigation water depths in a semiarid region of Brazil. The experiment had a split-plot randomized block design. Irrigation levels (60, 80, 100, and 120% of the reference evapotranspiration - ET0) and two apple cultivars (Julieta and Princesa) were analysed in the experimental plots and the phenological stages (vegetative, flowering and fruiting) were analysed in the experimental subplots. The physiological characteristics evaluated included the chlorophyll index, relative water content, net photosynthesis, stomatal conductance, transpiration, internal CO2 concentration, leaf temperature and instant carboxylation efficiency. The biochemical characteristics evaluated included the leaf contents of reducing sugars, total soluble sugars, and non-reducing sugars and proteins. The best biochemical responses were observed in the Princesa cultivar under 80% ET0 during the flowering and vegetative stages and under 120% ET0 during the fruiting stage. The best physiological responses for all phenological stages were observed under irrigation levels of 120% ET0 for both cultivars. The cv. Princesa demonstrated osmotic adjustment under water stress conditions during the phenological stages evaluated.

Production, gas and biochemical exchanges in pear cultivated in semi-arid region under different irrigation managements

“…The reduction in water application implies a lower water availability for plant uptake, which normally promotes a reduction in stomatal opening, reducing the leaf transpiration process with a consequent decrease in CO 2 input and its availability to the mesophyll cells, affecting the photochemical and biochemical phases, which implies the reduction of photosynthetic activity (Figure 2). Thus, it is observed that both water excess and water restriction hamper the CO 2 concentration in the substomatal chamber and consequently between the cells that form leaf tissues, directly interfering in the photosynthetic process (Andrade et al, 2017;Taiz & Zeiger, 2017;Oliveira et al, 2020).…”

“…According to the variables that contribute to the determination of gas exchange, the lower the water availability, the lower the flow from the root to the shoot, the lower the volume of water that reaches the leaves, and consequently the lower the stomatal opening, transpiration and photosynthesis, leading to the decrease of WUEi, so plants suffer from water stress (Oliveira et al, 2020;Vélez-Sánchez et al, 2021).…”

Water strategy improves the inflorescence primordia formation of 'Arra 15' grapevine in the Brazilian semiarid region

“…Increasing sugars under irrigation level of 70% ETc is likely due to the reduction of translocation of these photoassimilates to the drains. Accumulation of free sugars in the leaves may be due to the disturbances caused by stressful conditions such as the reduction of water content in leaf tissues, reducing the translocation of sugars to other organs 15 .…”

“…Fahim et al 16 reported the synthesis of soluble sugars in the cytosol is probably prioritized to maintain the plant's metabolic activity, even when water deficit reduces the rate of CO 2 assimilation. Meanwhile, Oliveira et al 15 reported that the accumulation of free sugars in the leaves with decreasing water content in the soil maintains cell turgor contributing to plant functioning. However, in order to confirm osmotic adjustment, assessing other physiological parameters that were not investigated in these studies is necessary.…”

“…Reductions in chlorophyll levels may also represent an acclimation response to water restriction, as the plant tends to conserve energy and hence capture less light energy, possibly avoiding photooxidative stress 15 . Thus, given the relationship between energy absorption and transfer, the levels of photosynthetic pigments may be related to net photosynthesis as well as to the growth and adaptation of 'Arra 15' to stress condition.…”