Arbuscular Mycorrhizal Fungi Mediate Drought Tolerance and Recovery in Two Contrasting Carob (Ceratonia siliqua L.) Ecotypes by Regulating Stomatal, Water Relations, and (In)Organic Adjustments

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.

Defense Enzymes in Mycorrhizal Tomato Plants Exposed to Combined Drought and Heat Stresses

“…This phenomenon can be attributed to the limited period of stress applications, or perhaps the different species of AMF (R. irregularis, F. mosseae, and F. coronatum) used in our experiment have high efficiency with tomato roots when exposed to abiotic stress conditions. Another study conducted by Boutasknit et al [47] explained that drought does not affect root colonization because it is linked to the unchanged carbon availability of the host plant. Moreover, this finding agrees with a study conducted by Pedranzani et al [23], where Digitaria eriantha plants were inoculated with R. irregularis and subjected to drought, salinity, and cold stress.…”

Arbuscular Mycorrhizal Symbiosis Enhances Photosynthesis in the Medicinal Herb Salvia fruticosa by Improving Photosystem II Photochemistry

“…Under drought stress AMF inoculation increased the content of compatible solutes, assisting in maintaining the relative water content, and upregulated the antioxidant system of maize plants, facilitating alleviation of oxidative effects through elimination of reactive oxygen species (ROS) [ 12 ]. Yet, under drought stress AMF promoted growth, nutrient content, and physiological and biochemical parameters in Ceratonia siliqua plants mediating drought tolerance [ 13 ].…”

“…Glomus irregulare Błaszk., Wubet, Renker & Buscot, previously known as Glomus intraradices ) [ 18 , 19 ]. R. irregularis is an endomychorrhizal fungus being one of the most popular since it stimulates the growth and development of different plant species, colonizing nearly all the important commercial crops [ 13 , 20 , 21 , 22 ]. Recently, an increasing research interest has been noticed in the utilization of AMF for improving plant growth of aromatic and medicinal plants [ 23 , 24 ].…”

“…Most researchers who have explored the mechanisms underlying the growth advantage of AMF plants have done it under stress conditions and not under normal growth ones [ 5 , 6 ]. Photosynthetic performance of plant symbiotic relationships with mycorrhizal fungi has been evaluated almost exclusively under stress conditions since soil microbes are used as inoculants to maintain crop yields under decreased water and nutrient inputs [ 7 , 13 , 21 , 22 ]. However, the mechanisms that contribute to enhanced photosynthetic performance and plant growth of plant symbiotic relationships with AMF can be better evaluated under non-stress conditions.…”

Alleviation of Detrimental Effects of Salt Stress on Date Palm (Phoenix dactylifera L.) by the Application of Arbuscular Mycorrhizal Fungi and/or Compost

“…In the saline environment, AMF improve the rhizospheric condition of the soil and enhance the mineral nutrition and the water uptake of the host plant (Augé et al, 2014;Hodge and Storer, 2014;El Kinany et al, 2019). AMF colonization has been widely reported to reduce the influx of toxic ions (sodium and chlorine) into the root system (Daei et al, 2009), and stimulate the photosynthetic apparatus and enhance the effectiveness of antioxidant defense system (Hidri et al, 2016;Boutasknit et al, 2020). These features led to in recent years the commercial production of AMF as a "biofertilizer" for field use, to reduce the intensive use of agrochemicals with no loss in yield.…”