Soil Amendment with Arbuscular Mycorrhizal Fungi and Biochar Improves Salinity Tolerance, Growth, and Lipid Metabolism of Common Wheat (Triticum aestivum L.)

Co-application of biochars and Piriformospora indica improved the quality of coastal saline soil and promoted the growth of forage

Soil quality is defined as the ability of soil to maintain the soil environment and the biosphere. Due to the limitation of salt and alkali stress, soil quality can be reduced, which in turn affects agricultural production. Biochar is widely used in saline-alkali land improvement because of its special pore structure and strong ion exchange ability, while Piriformospora indica is widely used in saline-alkali land improvement because it can symbiose with plants and improve plant stress resistance. However, the synergistic effect of combined biochar application and inoculation of P. indica on the quality of saline-alkali soil and plant development is uncertain. Hence, we investigated the combined influences of biochar and P. indica on the soil physicochemical characteristics, as well as the growth and chlorophyll florescence of sorghum-sudangrass hybrids (Sorghum bicolor × Sorghum sudane) in our study. The results indicated that after applying biochar and P. indica together, there was a considerable drop in soil pH, conductivity, Na+, and Cl- concentrations. Meanwhile, the soil organic matter (SOM), available phosphorus (AP), and alkaline hydrolyzable nitrogen (AN) increased by 151.81%, 50.84%, and 103.50%, respectively, when the Bamboo biochar was combined with 120 ml/pot of P. indica. Eventually, sorghum-sudangrass hybrid biomass, transpiration rate, and chlorophyll content increased by 111.69%, 204.98%, and 118.54%, respectively. According to our findings, using P. indica and biochar together can enhance soil quality and plant growth. The results also provide insights to enhance the quality of saline-alkali soils and the role of microorganisms in nutrient cycling.

The effect of AMF combined with biochar on plant growth and soil quality under saline-alkali stress: Insights from microbial community analysis

Arbuscular mycorrhizal fungi (AMF) and biochar application individually can enhance plant tolerance to saline-alkali stress and promote plant growth efficiency. However, little is known about the potential synergistic effects of their combination on improving plant growth and soil quality under saline-alkali stress. This experiment adopted the potted method to explore the effects of four treatments on switchgrass growth and soil quality: biochar (BC), Rhizophagus irregularis (Ri), biochar + Ri (BR) and a control without biochar or Ri (CK). Compared to the CK treatment, the switchgrass biomass increased by 92.4 %, 148.6 %, and 177.3 % in the BC, Ri, and BR treatment groups, respectively. Similarly, the rhizosphere soil quality index increased by 29.33 %, 22.7 %, and 49.1 % in the respective treatment groups. The BR treatment significantly altered the rhizosphere soil microbial composition and diversity. Notably, compared to the other treatments, the archaeal α-diversity in the BR group showed a significant decrease. BR treatment significantly increased the relative abundance of bacteria, fungi and archaea at the genus level (e.g., Bacillus, Trichome and candidatus_methanopenens). Network analysis showed that the complexity and closeness of interactions between different microbial taxa were stronger in the BC, Ri and BR treatments than in the CK treatment, with BR being the more prominent. In summary, biochar combined with Ri has a better effect on promoting the growth of switchgrass under saline-alkali stress, improving the quality of saline-alkali soil, and increasing soil microbial diversity. This study provides a new approach for the efficient development and utilization of saline-alkali land.

Putting Biochar in Action: A Black Gold for Efficient Mitigation of Salinity Stress in Plants. Review and Future Directions

Soil salinization is a serious concern across the globe that is negatively affecting crop productivity. Recently, biochar received attention for mitigating the adverse impacts of salinity. Salinity stress induces osmotic, ionic, and oxidative damages that disturb physiological and biochemical functioning and nutrient and water uptake, leading to a reduction in plant growth and development. Biochar maintains the plant function by increasing nutrient and water uptake and reducing electrolyte leakage and lipid peroxidation. Biochar also protects the photosynthetic apparatus and improves antioxidant activity, gene expression, and synthesis of protein osmolytes and hormones that counter the toxic effect of salinity. Additionally, biochar also improves soil organic matter, microbial and enzymatic activities, and nutrient and water uptake and reduces the accumulation of toxic ions (Na+ and Cl), mitigating the toxic effects of salinity on plants. Thus, it is interesting to understand the role of biochar against salinity, and in the present Review we have discussed the various mechanisms through which biochar can mitigate the adverse impacts of salinity. We have also identified the various research gaps that must be addressed in future study programs. Thus, we believe that this work will provide new suggestions on the use of biochar to mitigate salinity stress.

Enhancing tomato plants' tolerance to combined heat and salt stress - The role of arbuscular mycorrhizae and biochar

The Mediterranean basin is highly susceptible to climate change, with soil salinization and the increase in average temperatures being two of the main factors affecting crop productivity in this region. Following our previous studies on describing the detrimental effects of heat and salt stress co-exposure on tomato plants, this study aimed to understand if substrate supplementation with a combination of arbuscular mycorrhizal fungi (AMF) and biochar could mitigate the negative consequences of these stresses. Upon 21 days of exposure, stressed tomato plants grown under supplemented substrates showed increased tolerance to heat (42 °C for 4 h/day), salt (100 mM NaCl), and their combination, presenting increased biomass and flowering rate. The beneficial effects of AMF and biochar were associated with a better ionic balance (i.e. lower sodium accumulation and higher uptake of calcium and magnesium) and increased photosynthetic efficiency. Indeed, these plants presented higher chlorophyll content and improved CO2 assimilation rates. Biochemical data further supported that tomato plants grown with AMF and biochar were capable of efficiently modulating their defence pathways, evidenced by the accumulation of proline, ascorbate, and glutathione, coupled with a lower dependency on energy-costly enzymatic antioxidant players. In summary, the obtained data strongly point towards a beneficial role of combined AMF and biochar as sustainable tools to improve plant growth and development under a climate change scenario, where soil salinization and heat peaks often occur together.

Biochar and nano biochar: Enhancing salt resilience in plants and soil while mitigating greenhouse gas emissions: A comprehensive review

Salinity stress poses a significant challenge to agriculture, impacting soil health, plant growth and contributing to greenhouse gas (GHG) emissions. In response to these intertwined challenges, the use of biochar and its nanoscale counterpart, nano-biochar, has gained increasing attention. This comprehensive review explores the heterogeneous role of biochar and nano-biochar in enhancing salt resilience in plants and soil while concurrently mitigating GHG emissions. The review discusses the effects of these amendments on soil physicochemical properties, improved water and nutrient uptake, reduced oxidative damage, enhanced growth and the alternation of soil microbial communities, enhance soil fertility and resilience. Furthermore, it examines their impact on plant growth, ion homeostasis, osmotic adjustment and plant stress tolerance, promoting plant development under salinity stress conditions. Emphasis is placed on the potential of biochar and nano-biochar to influence soil microbial activities, leading to altered emissions of GHG emissions, particularly nitrous oxide(N2O) and methane(CH4), contributing to climate change mitigation. The comprehensive synthesis of current research findings in this review provides insights into the multifunctional applications of biochar and nano-biochar, highlighting their potential to address salinity stress in agriculture and their role in sustainable soil and environmental management. Moreover, it identifies areas for further investigation, aiming to enhance our understanding of the intricate interplay between biochar, nano-biochar, soil, plants, and greenhouse gas emissions.

Alleviation of salinity stress by EDTA chelated-biochar and arbuscular mycorrhizal fungi on maize via modulation of antioxidants activity and biochemical attributes

Salinity stress adversely affects agricultural productivity by disrupting water uptake, causing nutrient imbalances, and leading to ion toxicity. Excessive salts in the soil hinder crops root growth and damage cellular functions, reducing photosynthetic capacity and inducing oxidative stress. Stomatal closure further limits carbon dioxide uptake that negatively impact plant growth. To ensure sustainable agriculture in salt-affected regions, it is essential to implement strategies like using biofertilizers (e.g. arbuscular mycorrhizae fungi = AMF) and activated carbon biochar. Both amendments can potentially mitigate the salinity stress by regulating antioxidants, gas exchange attributes and chlorophyll contents. The current study aims to explore the effect of EDTA-chelated biochar (ECB) with and without AMF on maize growth under salinity stress. Five levels of ECB (0, 0.2, 0.4, 0.6 and 0.8%) were applied, with and without AMF. Results showed that 0.8ECB + AMF caused significant enhancement in shoot length (~ 22%), shoot fresh weight (~ 15%), shoot dry weight (~ 51%), root length (~ 46%), root fresh weight (~ 26%), root dry weight (~ 27%) over the control (NoAMF + 0ECB). A significant enhancement in chlorophyll a, chlorophyll b and total chlorophyll content, photosynthetic rate, transpiration rate and stomatal conductance was also observed in the condition 0.8ECB + AMF relative to control (NoAMF + 0ECB), further supporting the efficacy of such a combined treatment. Our results suggest that adding 0.8% ECB in soil with AMF inoculation on maize seeds can enhance maize production in saline soils, possibly via improvement in antioxidant activity, chlorophyll contents, gas exchange and morphological attributes.

The influence of a soil amendment on the abundance and interaction of arbuscular mycorrhizal fungi with arable soils and host winter wheat

Arbuscular mycorrhizal (AM) fungi have been shown to be associated with an estimated 70 % of vascular terrestrial plants. Such relationships have been shown to be sensitive to soil disturbance, for example, tillage in the preparation of a seed bed. From the application of arable soil management, AM fungal populations have been shown to be negatively impacted in abundance and diversity, reducing plant growth and development. The present study aims to utilise two sources (multipurpose compost and a commercial inocula) of mycorrhizal fungi for the amendment of arable soils supporting Zulu winter wheat under controlled conditions and quantify plant growth responses. A total of nine fields across three participating farms were sampled, each farm practicing either conventional, reduced, or zero tillage soil management exclusively. Soil textures were assessed for each sampled soil. Via the employment of AM fungal symbiosis quantification methods, AM fungi were compared between soil amendments and their effects on crop growth and development. The present study was able to quantify a mean 6 cm increase to crop height (P<0.001), 10 cm reduction to root length corresponding with a 2.45-fold increase in AM fungal arbuscular structures (P<0.001), a 1.15-fold increase in soil glomalin concentration corresponding to a 1.26-fold increase in soil carbon, and a 1.32-fold increase in the relative abundance of molecular identified AM fungal sequences for compost amended soils compared to control samples. Mycorrhizal inocula, however, saw no change to crop height or root length, AM fungal arbuscules were reduced by 1.43-fold, soil glomalin was additionally reduced by 1.55-fold corresponding to a reduction in soil carbon by 1.31-fold, and a reduction to relative AM fungal species abundance by 1.26-fold. The present study can conclude the addition of compost as an arable soil amendment is more beneficial for the restoration of AM fungi beneficial to wheat production and soil carbon compared to the addition of a commercial mycorrhizal inocula.

Variability in morpho-biochemical, photosynthetic pigmentation, enzymatic and quality attributes of potato for salinity stress tolerance

Salt stress has emerged as a growing global concern, exerting a significant impact on agricultural productivity. The challenges of salt stress on potatoes are crucial for ensuring food security and sustainable agriculture. To address this issue a pot trial was executed to evaluate the impacts of NaCl in the soil on the growth, photosynthetic pigments, and quality attributes of potato, plants were grown in soil spiked with various concentrations of NaCl (0, 1, 3, 5, 7 g kg-1 of soil). Results revealed that salt stress have negative impacts on the growth, biomass, photosynthesis and quality attributes of potato. Lower level of salt stress 1 g kg-1 of soil improved the fresh and dry biomass of leaves (78.70 and 47.74%) and tubers (86.04 and 88.92%) as compared to control, respectively. Higher levels of salt stress (7 g kg-1) increased lipid peroxidation in leaves and improved the enzymatic antioxidants. It was observed that enzyme activities i.e., SOD (134.97%), POD (101.02%), and CAT (28.87%) increased in leaves and are inversely related to the NaCl concentration. The combination of reduction in chlorophyll contents and soluble sugars resulted in lower levels of quality attributes i.e., amylose (68.90%) and amylopectin (16.70%) of potato. Linear relationship in growth, biomass and physiological attributes showed the strong association with increased salt stress. Furthermore, the PCA-heatmap synergy offers identifying clusters of co-regulated attributes, which pinpoint the physiological responses that exhibit the strongest correlation with increasing salt stress levels. Findings indicate that potato can be grown successfully with (1 g kg-1 of NaCl in soil) without negative impacts on plant quality. Furthermore, this study contributes valuable insights into the complexities of salt stress on potato plants and provides a foundation for developing strategies to enhance their resilience in salt-affected environments.

Biochar and Seed Priming Technique with Gallic Acid: An Approach toward Improving Morpho-Anatomical and Physiological Features of Solanum melongena L. under Induced NaCl and Boron Stresses

Dynamic shifts in climatic patterns increase soil salinity and boron levels, which are the major abiotic factors that affect plant growth and secondary metabolism. The present study assessed the role of growth regulators, including biochar (5 g kg-1) and gallic acid (GA, 2 mM), in altering leaf morpho-anatomical and physiological responses of Solanum melongena L. exposed to boron (25 mg kg-1) and salinity stresses (150 mM NaCl). These growth regulators enhanced leaf fresh weight (LFW) (70%), leaf dry weight (LDW) (20%), leaf area (LA), leaf area index (LAI) (85%), leaf moisture content (LMC) (98%), and relative water content (RWC) (115%) under salinity and boron stresses. Physiological attributes were analyzed to determine the stress levels and antioxidant protection. Photosynthetic pigments were negatively affected by salinity and boron stresses along with a nonsignificant reduction in trehalose, GA, osmoprotectant, and catalase (CAT) and ascorbate peroxidase (APX) activity. These parameters were improved by biochar application to soil and presoaking seeds in GA (p < 0.05) in both varieties of S. melongena L. Scanning electron microscopy (SEM) and light microscopy revealed that application of biochar and GA improved the stomatal regulation, trichome density, epidermal vigor, stomata size (SS) (13 381 μm), stomata index (SI) (354 mm2), upper epidermis thickness (UET) (123 μm), lower epidermis thickness (LET) (153 μm), cuticle thickness (CT) (11.4 μm), trichome density (TD) (23 per mm2), vein islet number (VIN) (14 per mm2), vein termination number (VTN) (19 per mm2), midrib thickness (MT) (5546 μm), and TD (27.4 mm2) under salinity and boron stresses. These results indicate that the use of inexpensive and easily available biochar and seed priming with GA can improve morpho-anatomical and physiological responses of S. melongena L. under oxidative stress conditions.

Arbuscular mycorrhiza differentially adjusts central carbon metabolism in two contrasting genotypes of Vigna radiata (L.) Wilczek in response to salt stress

The study aimed at investigating Arbuscular Mycorrhiza (AM) mediated metabolic changes in two genotypes of mungbean (Vigna radiata) differing in their salt tolerance in presence of salt stress (100 mM NaCl). Colonisation by Claroideoglomus etunicatum resulted in higher growth, photosynthetic efficiency, total protein content, and lower levels of stress markers, indicating alleviation of stress in mungbean plants. AM differentially upregulated the components of Tricarboxylic acid (TCA) cycle in salt tolerant (ST) and salt sensitive (SS) genotypes that could be correlated to AM-mediated moderation in nutrient uptake. Under salt stress, while maximum increase in the activity of α-ketoglutarate dehydrogenase (65%) was observed in mycorrhizal (M)-ST; the increase in isocitrate dehydrogenase (79%) and fumarase (133%) activities was maximum in M-SS plants over their non-mycorrhizal (NM) counterparts. Apart from TCA, AM also affected gamma-aminobutyric acid (GABA) and glyoxylate pathways. Activities of enzymes implicated in GABA shunt increased in both the genotypes under stress resulting in increase in GABA concentration (46%). Notably, glyoxylate pathway was induced by AM in SS only, wherein M-SS exhibited significantly higher isocitrate lyase (49%) and malate synthase (104%) activities, reflected in higher malic acid concentration (84%), than NM under stress. The results suggest that AM moderates the central carbon metabolism and strategizes towards boosting the formation of stress-alleviating metabolites such as GABA and malic acid, especially in SS, bypassing the steps catalysed by salt-sensitive enzymes in TCA cycle. The study, therefore, advances the understanding on mechanisms by which AM ameliorates salt stress.

The critical role of biochar to mitigate the adverse impacts of drought and salinity stress in plants

Drought stress (DS) is a potential abiotic stress that is substantially reducing crop productivity across the globe. Likewise, salinity stress (SS) is another serious abiotic stress that is also a major threat to global crop productivity. The rapid climate change increased the intensity of both stresses which pose a serious threat to global food security; therefore, it is urgently needed to tackle both stresses to ensure better crop production. Globally, different measures are being used to improve crop productivity under stress conditions. Among these measures, biochar (BC) has been widely used to improve soil health and promote crop yield under stress conditions. The application of BC improves soil organic matter, soil structure, soil aggregate stability, water and nutrient holding capacity, and the activity of both beneficial microbes and fungi, which leads to an appreciable increase in tolerance to both damaging and abiotic stresses. BC biochar protects membrane stability, improves water uptake, maintains nutrient homeostasis, and reduces reactive oxygen species production (ROS) through enhanced antioxidant activities, thereby substantially improving tolerance to both stresses. Moreover, BC-mediated improvements in soil properties also substantially improve photosynthetic activity, chlorophyll synthesis, gene expression, the activity of stress-responsive proteins, and maintain the osmolytes and hormonal balance, which in turn improve tolerance against osmotic and ionic stresses. In conclusion, BC could be a promising amendment to bring tolerance against both drought and salinity stresses. Therefore, in the present review, we have discussed various mechanisms through which BC improves drought and salt tolerance. This review will help readers to learn more about the role of biochar in causing drought and salinity stress in plants, and it will also provide new suggestions on how this current knowledge about biochar can be used to develop drought and salinity tolerance.

Mycorrhizal symbiosis alleviate salinity stress in pistachio plants by altering gene expression and antioxidant pathways

This study investigated how inoculation of salt-stressed Pistacia vera seedlings with Rhizophagus irregularis, an arbuscular mycorrhizal fungus (AMF), affects their biomass, oxidative damage, antioxidant enzyme activity, and gene expression. Pistachio seedlings (N:36) were randomly assigned to AMF inoculation and non-inoculation groups in a pot experiment with 9 replications. Each group was further divided and randomly assigned to two salinity treatments (0 and 300 mM NaCl). At the end of week 4, three pistachio plantlets were randomly selected from each group for Rhizophagus irregularis colonization inspection, physiological and biochemical assays, and biomass measurements. Salinity activated enzymatic and non-enzymatic antioxidant systems in the pistachio plants were studied. The negative effects of salinity included reduced biomass and relative water content (RWC), increased O2 ·-, H2O2, MDA, and electrolytic leakage. Generally, Rhizophagus irregularis was found to mitigate the adverse effects of salinity in pistachio seedlings. AMF inoculation resulted in even further increases in the activities of SODs, POD, CAT, and GR enzymes, upregulating Cu/Zn-SOD, Fe-SOD, Mn-SOD, and GR genes expression in plants under salinity stress. Moreover, AMF significantly increased AsA, α-tocopherol, and carotenoids under both control and salinity conditions. The study concludes with a call for future research into the mechanisms of mycorrhiza-induced tolerance in plants under salinity stress.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-023-01279-8.

Potential of plant growth promoting bacterial consortium for improving the growth and yield of wheat under saline conditions

Owing to inconsistent results of a single bacterial strain, co-inoculation of more than one strain under salinity stress could be a more effective strategy to induce salt tolerance. Co-inoculation of more than one bacterial strain could be more effective due to the presence of several growths promoting traits. This study was conducted to evaluate the effectiveness of multi-strains bacterial consortium to promote wheat growth under salinity stress. Several plant growth promoting rhizobacteria (PGPR) had been isolated and tested for their ability to grow in increasing concentrations of sodium chloride (NaCl). Those rhizobacterial strains having tolerance against salinity were screened to evaluate their ability to promote wheat growth in the presence of salinity by conducting jar trials under axenic conditions. The rhizobacteria with promising results were tested for their compatibility with each other before developing multi-strain inoculum of PGPR. The compatible PGPR strains were characterized, and multi-strain inoculum was then evaluated for promoting wheat growth under axenic conditions at different salinity levels, i.e., 2.1 (normal soil), 6, 12, and 18 dS m^–1. The most promising combination was further evaluated by conducting a pot trial in the greenhouse. The results showed that compared to a single rhizobacterial strain, better growth-promoting effect was observed when rhizobacterial strains were co-inoculated. The multi-strain consortium of PGPR caused a significant positive impact on shoot length, root length, shoot fresh weight, and root fresh weight of wheat at the highest salinity level in the jar as well as in the pot trial. Results showed that the multi-strain consortium of PGPR caused significant positive effects on the biochemical traits of wheat by decreasing electrolyte leakage and increasing chlorophyll contents, relative water contents (RWC), and K/Na ratio. It can be concluded that a multi-strain consortium of PGPR (Ensifer adhaerens strain BK-30, Pseudomonas fluorescens strain SN5, and Bacillus megaterium strain SN15) could be more effective to combat the salinity stress owing to the presence of a variety of growth-promoting traits. However, further work is going on to evaluate the efficacy of multi-strain inoculum of PGPR under salt-affected field conditions.

Organic Amendments: Direct Application and Residual Effects on Vegetative and Reproductive Growth of Hot Pepper

The high production potential of coffee and animals in the Gedeo zone that could produce huge amounts of coffee pulp and animal manure wastes has been polluting the environment. In this sense, this study was aimed at averting pollution and managing plant and animal wastes, focusing on the effect of coffee pulp and animal manure in the form of vermicompost, biochar, and ordinary compost on hot pepper vegetative and reproductive growth. A 15 ton per hectare of each treatment was applied in a randomized complete block design replicated three times. Vegetative and reproductive growth parameters (plant height, leaf number, number of branches, days to 50% flowering, total fresh biomass, number of fruits per plant, single fruit length, and fruit yield per hectare) were recorded, and the statistical difference was determined at 5% significance level using R-program. The result showed that there was a significant difference among treatments. Coffee pulp vermicompost prepared using Eisenia fetida earthworm had significantly ( $P<0.05$ ) higher results in plant height, leaf number, number of branches, total fresh biomass, number of fruits per plant, single fruit length, and total yield, while the minimum values were recorded in topsoil (control treatment) and animal manure compost. The direct and residual effects of vermicompost and biochar organic amendments were the potential organic fertilizers for hot pepper fast growth and to produce enormous yield, which might be due to their nature in improving soil physicochemical and biological properties as well as nutrient uptake.

Arbuscular Mycorrhizal Fungi Induce Tolerance to Salinity Stress in Taro Plantlets (Colocasia esculenta L. Schott) during Acclimatization

Soil salinity is a problem that affects soil fertility and threatens agri-food crop production worldwide. Biotechnology, through plant micropropagation and the use of biofertilizers such as arbuscular mycorrhizal fungi (AMF), is an alternative to increase productivity and induce tolerance to salinity stress in different crops. This study aimed to evaluate the effect of different doses of the fungus Glomus intraradices on the ex vitro development of taro (Colocasia esculenta L. Schott cv. Criolla) plantlets under salinity stress during the acclimatization stage. In vitro-obtained C. esculenta plantlets were inoculated at different doses (0, 100, and 200 spores per plantlet) of G. intraradices during acclimatization. At 60 d of acclimatization in the greenhouse, plantlets were exposed to 100 mM NaCl salinity stress for 10 d. After the stress period, plantlet development, colonization percentage, and biomass were evaluated. In addition, the content of chlorophyll, carotenoids, proteins, proline, glycine-betaine, soluble phenols, and antioxidant capacity were quantified. The results showed differences in the developmental, physiological, and biochemical variables evaluated; however, no changes in total protein content were observed. Spore colonization showed that the symbiotic association has positive effects on the development of plantlets with or without salinity stress. This symbiotic interaction contributes to salinity stress tolerance in C. esculenta plantlets. The early application of AMF in in vitro-obtained taro plantlets is an alternative to increase or maintain the productivity of this crop in saline soils.