Abstract
Irregular precipitation and drought caused an increase in tree mortality rates in multiple forest biomes with alterations in both ecosystem services and carbon balance. Carob (Ceratonia siliqua) growth and production in arid and semi-arid ecosystems are likely affected by climate change-induced droughts. Understanding the physiological responses of drought-induced early-stage tree death and strategies to enhance drought tolerance and optimize growth will help tree improvement programs. Mycorrhizal inoculation has a pronounced impact on plant growth, water absorption, mineral nutrition, and protection from abiotic stresses. However, a better understanding of these complex interconnected cellular processes and arbuscular mycorrhizal fungi (AMF)-mediated mechanisms regulating drought tolerance in plants will enhance its potential application as an efficient approach for bio-amelioration of stresses. The objectives of this work were to elucidate the different effects of autochthone AMF on inorganic solute and water content uptakes, organic adjustments (sugar and proteins content), leaf gas exchange (stomatal conductance and efficiency of photosystems I and II), and oxidative damage of two contrasting ecotypes of carob seedlings: coastal (southern ecotype (SE)) and in-land (northern ecotype (NE)) under control (C), drought (by cessation of irrigation for 15 days (15D)), and recovery (R) conditions. Our findings showed that AMF promoted growth, nutrient content, and physiological and biochemical parameters in plants of both ecotypes during C, 15D, and R conditions. After four days of recovery, stomatal conductance (gs), the maximum photochemical efficiency of PSII (Fv/Fm), water content, and plant uptake of mineral nutrients (P, K, Na, and Ca) were significantly higher in shoots of mycorrhizal (AM) than non-mycorrhizal (NM) control plants. Consequently, AMF reduced to a greater degree the accumulation of hydrogen peroxide (H2O2) and oxidative damage to lipid (malondialdehyde (MDA)) content in AM than NM plants in NE and SE, after recovery. Altogether, our findings suggest that AMF can play a role in drought resistance of carob trees at an early stage by increasing the inorganic solutes (P, K, Na, and Ca), water content uptake, organic solutes (soluble sugars and protein content), stomatal conductance, and defense response against oxidative damage during re-watering after drought stress.
Highlights
Drought is one of the most frequent and severe abiotic stresses negatively affecting many physiological and biochemical parameters, plant growth, and development in arid and semi-aridMediterranean ecosystems [1,2]
The frequency (F) and intensity (I) of the root seedlings inoculated with arbuscular mycorrhizal fungi (AMF) showed no significant differences among the mycorrhizal–carob seedlings in control (C), drought by cessation of irrigation for 15 days (15D), and recovery (R) conditions in both ecotypes (Table 1)
We demonstrated a beneficial effect of AMF at the physiological and cellular levels on improving carob growth, reducing drought damage, and enabling rapid recovery once the stress is removed
Summary
Mediterranean ecosystems [1,2] These ecosystems are subject to particular climatic conditions and anthropogenic pressure, leading to a decline in forest cover and irreversibly to serious environmental consequences such as rapid soil erosion and desertification [3]. Drought in these regions is becoming extreme, longer, and more frequent. This alters the biodiversity of vegetation, and often makes the reforestation with original species difficult [2]. The use of pioneering tree species, adapted to climatic hazards and able to settle on eroded soils, remains the most recommended solution
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