Isohydricity of Two Different Citrus Species under Deficit Irrigation and Reclaimed Water Conditions.

Cristina Romero-Trigueros,Emilio Nicolás Nicolás,Juan José Alarcón Cabañero,Pedro Antonio Nortes Tortosa,Jose María Bayona Gambín

doi:10.3390/plants10102121

Cristina Romero-Trigueros, Emilio Nicolás Nicolás + Show 3 more

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https://doi.org/10.3390/plants10102121

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Abstract

Citrus species are frequently subjected to water and saline stresses worldwide. We evaluated the effects of diurnal changes in the evaporative demands and soil water contents on the plant physiology of grapefruit and mandarin crops under saline reclaimed (RW) and transfer (TW) water conditions, combined with two irrigation strategies, fully irrigated (fI) and non-irrigated (nI). The physiological responses were different depending on the species. Grapefruit showed an isohydric pattern, which restricted the use of the leaf water potential (Ψl) as a plant water status indicator. Its water status was affected by salinity (RW) and water stress (nI), mainly as the combination of both stresses (RW-nI); however, mandarin turned out to be relatively more tolerant to salinity and more sensitive to water stress, mainly because of its low hydraulic conductance (K) levels, showing a critical drop in Ψl that led to severe losses of root–stem (Kroot–stem) and canopy (Kcanopy) hydraulic conductance in TW-nI. This behavior was not observed in RW-nI because a reduction in canopy volume as an adaptive characteristic was observed; thus, mandarin exhibited more anisohydric behavior compared to grapefruit, but isohydrodynamic since its hydrodynamic water potential gradient from roots to shoots (ΔΨplant) was relatively constant across variations in stomatal conductance (gs) and soil water potential. The gs was considered a good plant water status indicator for irrigation scheduling purposes in both species, and its responses to diurnal VPD rise and soil drought were strongly correlated with Kroot–stem. ABA did not show any effect on stomatal regulation, highlighting the fundamental role of plant hydraulics in driving stomatal closure.

Highlights

Citrus species are some of the most important commercial fruit crops around the world, including in semi-arid Mediterranean regions [1], where the irrigation water is not always available due to water scarcity; many citrus orchards suffer severe drought periods [2]
An increase in vapor pressure deficit (VPD) or a reduction in soil water content leads to a decrease in stomatal conductance or a hydraulic cascade of water potential in the tree, which becomes larger and longer-lasting when high atmospheric water demand combines with soil water stress [12]
This study aims to evaluate the effects of long-term irrigation with saline reclaimed water (RW) and of the total suppression of irrigation for a period, as well as the combination of both stresses, on diurnal changes in the physiology of two citrus species with different rootstocks and productive potential, namely grapefruit [42] and mandarin [43], under field conditions

Summary

Introduction

Citrus species are some of the most important commercial fruit crops around the world, including in semi-arid Mediterranean regions [1], where the irrigation water is not always available due to water scarcity; many citrus orchards suffer severe drought periods [2]. An increase in VPD or a reduction in soil water content leads to a decrease in stomatal conductance (gs ) or a hydraulic cascade of water potential in the tree, which becomes larger and longer-lasting when high atmospheric water demand combines with soil water stress [12]. This ability of plants to regulate transpirational water loss and to minimize fluctuations in water potential defines plants as isohydric or anisohydric [13]. More isohydric species are prone to carbon starvation, while more anisohydric species are more likely to die from tissue desiccation via hydraulic failure [14]

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