**5. AMF and abiotic stresses**

#### **5.1 Drought**

Drought is the dearth of sufficient levels of water in the root zone for normal functioning of plant. It is also referred as water deprivation or water stress. Drought stress effects in plants emerge due to deficiency of water in the rhizospheric region, a high transpiration rate, or the rapid formation of reactive oxygen species (ROS), and the subsequent onset of oxidative stress [31]. Drought stresses have a negative impact on expansion on plants owing to alteration in enzymatic activity, Ion and mineral absorption [32]. Symbiotic associations are thought to govern a number of physio-biochemical processes in plants, including greater osmotic adjustment,

stomatal regulation through modulating ABA metabolism, increased proline buildup, and higher glutathione levels**.** Under drought conditions, the symbiotic connection of numerous plants with AMF may eventually boost biomass, LAI, length of roots and efficiency [33]. Li et al. [34], reported that in C3 plants viz. *Leymus chinensis* and C4 plants viz. *Hemarthria altissima* the growth and photosynthesis was enhance by AMF mediation through up-regulation of antioxidant system. Abiotic stressors like salt and drought generate significant decline in agricultural return. Furthermore, mineral depletion, water stress, salt stress and increase in pH, the existence of trace elements, and elevated temperatures are major issues in numerous regions of the world, especially in dry regions [35]. This mutualistic interaction has been reported to participate in a variety of biochemical and physiological activities, including (1) direct absorption and transfer of water and minerals by mycorrhizal fungi, (2) enhanced osmotic regulation, (3) improved gas exchange and Efficiency of water utilization, and (4) strong defense in opposition to oxidative destruction [36]. In contrast to non-mycorrhizal plants, mycorrhizal fungus can also change water control in plant growth by altering hormonal equilibrium signaling or by stimulating osmolytes in mycorrhizal plants (increased vigor or volume of products of photosynthesis and dissolvable sugars in the foliage symplasm). In drought conditions, AM inoculation of plants improved size and density of root hairs. These plants also have higher concentrations of methyl jasmonate, IAA, calmodulin, and nitric oxide in their roots, resulting in enhanced resistance to drought stress [37].

### **5.2 Salinity**

Soil salinization is a well-known environmental phenomenon that poses a serious danger to international food safety. Salinity stress is common for suppressing plant growth by altering vegetative development and overall absorption rate, leading to lower quantity of yield. It also stimulates the extravagant production of reactive oxygen species. The resistance to salinity involves Na + and Cl- storage in cell vacuoles, which prevents Na + entry into the cell and its removal by transpiration. Efforts are being undertaken to investigate potential methods of increasing agricultural output on salt-affected soils. One such option is to apply AMF sparingly to reduce the negative effects of salinity on plants. Some research investigations have established the effectiveness of AMF in initiating growth and increasing production in plants subjected to salt stress [38]. EL-Nashar [39], demonstrated that MF increased enlargement rate. Foliage water potential, water utilization potential of *Antirrhinum majus* plant. Under saline conditions, mycorrhizal inoculation significantly increased rate of photosynthesis and other gas exchange properties, chlorophyll concentration, and water utilization potential in Ocimum basilicum L. [40]. Furthermore, Plants with AMF produce more jasmonic acid, salicylic acid, and other vital inorganic nutrients. Under salt stress conditions, for instance, total N, P, K+, Ca2+, and Mg2+ concentrations were more in AMF-treated Cucumis sativus plants than in untreated plants [41]. AMF inoculation can efficiently modulate critical growth regulator levels. Furthermore, AMF inoculation increased the build up of different organic acids, leading to enhanced osmoregulation mechanism in plant growth under salt stress. Salinity has an impact on crop morphology, physiological function, and yield, as well as a large amount of arable land. It has been discovered that tomato plant production is maximum at salinity concentration of 5 dSm−1, however Salinity has been shown to reduce foliage area and dry matter concentration. Furthermore, the foliage was shown to be

#### *AM Fungi as a Potential Biofertilizer for Abiotic Stress Management DOI: http://dx.doi.org/10.5772/intechopen.108537*

more vulnerable to salinity stress than the fruits because they contained more proline and Na [42]. Salinity influences all stages of plant growth, including germination, seedling, vegetative phase, and maturity. Salinity disrupts plant ionic adjustment and osmotic pressure, as well as cell membrane selectivity [43]. Salinity disrupts plant ionic homeostasis by amplifying ROS (reactive oxygen species), that negatively influences nutrient absorption, cell membranes, and different ultra structures, resulting in ionic and osmotic stress [44].

### **5.3 Heavy metals**

AMF is commonly thought to reinforce plant development in heavy metalcontaminated soil owing to their ability to build up defense system of host plants and growth and development promotion. These trace elements accrete in all crops viz., (food crops, fruits, vegetables) and soils, giving rise to a variety of health risks. Under aluminum stress, the interaction of AMF with whet improved nutrition absorption [45]. Plants planted in soil augmented with Cd and Zn showed remarkable inhibition of under and above ground growth, chlorosis, and even mortality [46]. The significant effect of AMF on plant development and growth under acute stressful circumstances is usually due to the tendency of fungi to augment morphological and physiological processes that enhance plant biomass and, as a result, absorption of critical immobile elements like Cu, Zn, and P, resulting in decrease in harmful effects of metals on the host plants [47]. Decrease in concentration of metals by dilution in plant tissues and chelation in the root zone is believed to cause enhanced growth. AMF blend with Cd and Zn in the cell walls of mantle hyphae and cortical cells, limiting their absorption and leading in increased growth, yield, and nutritional status. AMF were highly effective in decreasing Cd detoxifying levels in rice [48]. Numerous processes occur as a result of the AMF, including metal compound immobilization/ restriction, polyphosphate granule formation in the soil, adsorption to fungal cell wall chitin, and heavy metal chelation within the fungus.

#### **5.4 Temperature**

Plant community reactions to rising soil temperatures may be based on AMF interactions for long-term yield and production [49]. Heat stress has a remarkable affect on plant growth and development through different processes viz. (1) drop in plant vigor and seed germination inhibition, (2) retarded growth potential, (3) diminishing biomass (4) wilting and burning of foliage and reproductive parts, (5) abscission and senescence of foliage, (6) fruit destruction and change in color, (7) yield loss and cell death, and (8) increased oxidative stress. AMF-inoculated plants typically develop faster under heat stress than non-AMF-inoculated plants. Maya and Matsubara [50] demonstrated the symbiosis of AMF Glomus fasciculatum with plant expansion and enlargement, resulting in favorable alterations in growth under high temperature situations.

AMF can help plants tolerate cold stress. Furthermore, according to the majority of reports, diverse plants inoculated with AMF at low temperatures show good growth than non-AMF-inoculated plants [51]. AMF helps crops fight cold stress and subsequently improves plant development. Furthermore, AMF can regulate moisture content in the host plant, leading to escalation in plant secondary metabolites, so strengthening the plant defense system, and enhanced protein concentration, thereby assisting plants in combating cold stress situations [52]. During cold stress,

#### **Figure 2.**

*Temperature stress in plants is alleviated by AMF inoculation.*




#### **Table 1.**

*Brief overview of various fungal species and their recorded responses.*

for example, AMF injected plants demonstrated higher water saving ability as well as usage efficiency [53]. The symbiotic AMF connection boosts the water-plant relationship while increasing gas exchange potential and osmotic balance. AMF improves chlorophyll production, resulting in a remarkable increase in the concentrations of different metabolites in plants exposed to cold stress conditions [54]. Low temperatures have a deleterious impact on plant metabolism. It can cause substantial harm to plant tissue, including yellowing of leaves, membrane damage, cell death, and changes in enzyme action and cytoplasm viscosity in vegetable plants. Chilling stress reduces photosynthetic efficiency and increases electrolyte leakage in watermelon seedlings [55] (**Figure 2**) (**Table 1**).

### **6. Conclusion**

Arbuscular mycorrhizal fungi have cosmopolitan distribution in soil environment and live in mutualistic association with the roots of angiosperms and other plants. The mutualistic association between fungi and plant roots assist in absorption of macronutrients viz., P, N as well as trace elements viz. Zn, Fe, Cu. The various ways to achieve these functions effectively are increment in absorption area of plants, liberation of biochemical substances. These have significant role in cycling of nutrients by mobilizing the fixed elements as well as serving as sink for various elements. Furthermore, they have ability to decrease various biotic and abiotic stresses like drought, saline, water, temperature and resistance to diseases. These increase the availability of less accessible elements to plants. The significance of
