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 (g_s), the maximum photochemical efficiency of PSII (F_v/F_m), 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.

The date palm is a commercially important woody crop and is a good target plant for improving agricultural yields in extreme environments. However, salinity has been the primary abiotic stress complicating its cultivation and damaging its production worldwide. This study investigated the effect of alleviating salt stress on date palm growth and development by using arbuscular mycorrhizal fungi (AMF) and/or compost. The experiment was arranged in a completely randomized design with eight treatments. The treatments comprised control without inoculation or amendment and application of compost (made from green waste) and AMF (an autochthonous consortium) individually or in combination under non-saline (0 mM NaCl) or saline (240 mM NaCl) conditions. Growth, physiological characteristics, nutrient uptake, chlorophyll content, oxidative stress markers, and antioxidant enzyme activities were assessed. Salt stress increased sodium (Na⁺) and chlorine (Cl⁻) content, lipid peroxidation and proline, soluble sugar, and H₂O₂ content. However, it reduced growth parameters, AMF colonization, leaf water potential, nitrogen (N), phosphorus (P), potassium (K⁺), calcium (Ca²⁺), and chlorophyll content. The application of AMF and compost separately or in combination mitigated the deleterious effects induced by salinity. AMF inoculation contributed to plant salt tolerance through strategies such as increased nutrient uptake (particularly P and Ca²⁺), chlorophyll content, relative water content, stomatal conductance, antioxidant enzymatic activities (superoxide dismutase, ascorbate peroxidase, catalase) and by decreasing lipid peroxidation and H₂O₂ content. Plants grown in soil amended with compost under salt stress showed an improvement particularly in K⁺ and proline content and a decrease in H₂O₂ concentration compared to controls under the saline condition. In the presence of NaCl stress, the dual application of the compost and AMF consortium maximized plant growth, stomatal conductance, leaf water potential, all antioxidant enzyme activities and P, K⁺, N, and Ca²⁺ uptake as well as proline and soluble sugar content. However, it reduced Na⁺ and Cl⁻ uptake and oxidative stress marker content. In conclusion, our study suggests that the application of AMF with compost has the potential to improve the tolerance of date palm seedlings to salt stress more than AMF or compost applied separately.

Salinity is one of the devastating abiotic stresses that cause reductions in agricultural production. The increased salinization affects alfalfa growth, metabolism, and rhizobium capacity for symbiotic N₂ fixation negatively. This study was undertaken to investigate the efficiency of green compost (C; made from green waste), arbuscular mycorrhizal fungi (M; field-sourced native consortium), and/or rhizobium (R; a salt-tolerant rhizobium strain) individually or in combination as an effective strategy to improve alfalfa productivity under non-saline and high-saline (120 mM NaCl) conditions. In addition, we aimed to understand the agro-physiological and metabolic basis as well as glomalin content in the soil of biofertilizers-induced salt tolerance in alfalfa. Here, we show that mycorrhizal infection was enhanced after MR inoculation, while C application decreased it significantly. Salinity reduced growth, physiological functioning, and protein concentration, but the antioxidant system has been activated. Application of the selected biofertilizers, especially C alone or combined with M and/or R improved alfalfa tolerance. The tri-combination CMR mitigated the negative effects of high salinity by stimulating plant growth, roots and nodules dry matters, mineral uptake (P, N, and K), antioxidant system, synthesis of compatible solutes, and soil glomalin content, sustaining photosynthesis-related performance and decreasing Na⁺ and Cl⁻ accumulation, lipid peroxidation, H₂O₂ content, and electrolyte leakage.