Arbuscular Mycorrhizal Fungi and Dry Raw Garlic Stalk Amendment Alleviate Continuous Monocropping Growth and Photosynthetic Declines in Eggplant by Bolstering Its Antioxidant System and Accumulation of Osmolytes and Secondary Metabolites

Almond shell-derived biochar decreased toxic metals bioavailability and uptake by tomato and enhanced the antioxidant system and microbial community

The effectiveness of almond shell-derived biochar (ASB) in immobilizing soil heavy metals (HMs) and its impact on soil microbial activity and diversity have not been sufficiently studied. Hence, a pot study was carried out to investigate the effectiveness of ASB addition at 2, 4, and 6 % (w/w) on soil biochemical characteristics and the bioavailability of Cd, Cu, Pb, and Zn to tomato (Solanum lycopersicum L.) plants, as compared to the control (contaminated soil without ASB addition). The addition of ASB promoted plant growth (up to two-fold) and restored the damage to the ultrastructure of chloroplast organelles. In addition, ASB mitigated the adverse effects of HMs toxicity by decreasing oxidative damage, regulating the antioxidant system, improving soil physicochemical properties, and enhancing enzymatic activities. At the phylum level, ASB addition enhanced the relative abundance of Actinobacteriota, Acidobacteriota, and Firmicutes while decreasing the relative abundance of Proteobacteria and Bacteroidota. Furthermore, ASB application increased the relative abundance of several fungal taxa (Ascomycota and Mortierellomycota) while reducing the relative abundance of Basidiomycota in the soil. The ASB-induced improvement in soil properties, microbial community, and diversity led to a significant decrease in the DTPA-extractable HMs down to 41.0 %, 51.0 %, 52.0 %, and 35.0 % for Cd, Cu, Pb, and Zn, respectively, as compared to the control. The highest doses of ASB (ASB6) significantly reduced the metals content by 26.0 % for Cd, 78.0 % for Cu, 38.0 % for Pb, and 20.0 % for Zn in the roots, and 72.0 % for Cd, 67.0 % for Cu, 46.0 % for Pb, and 35.0 % for Zn in the shoots, as compared to the control. The structural equation model predicts that soil pH and organic matter are driving factors in reducing the availability and uptake of HMs. ASB could be used as a sustainable trial for remediation of HMs polluted soils and reducing metal content in edible plants.

A Systematic Review on the Continuous Cropping Obstacles and Control Strategies in Medicinal Plants

Continuous cropping (CC) is a common practice in agriculture, and usually causes serious economic losses due to soil degeneration, decreased crop yield and quality, and increased disease incidence, especially in medicinal plants. Continuous cropping obstacles (CCOs) are mainly due to changes in soil microbial communities, nutrient availability, and allelopathic effects. Recently, progressive studies have illustrated the molecular mechanisms of CCOs, and valid strategies to overcome them. Transcriptomic and metabolomics analyses revealed that identified DEGs (differently expressed genes) and metabolites involved in the response to CCOs are involved in various biological processes, including photosynthesis, carbon metabolism, secondary metabolite biosynthesis, and bioactive compounds. Soil improvement is an effective strategy to overcome this problem. Soil amendments can improve the microbial community by increasing the abundance of beneficial microorganisms, soil fertility, and nutrient availability. In this review, we sum up the recent status of the research on CCOs in medicinal plants, the combination of transcriptomic and metabolomics studies, and related control strategies, including uses of soil amendments, crop rotation, and intercropping. Finally, we propose future research trends for understanding CCOs, and strategies to overcome these obstacles and promote sustainable agriculture practices in medicinal plants.

Effects of Drought Stress Induced by Hypertonic Polyethylene Glycol (PEG-6000) on Passiflora edulis Sims Physiological Properties

Passion fruit is known to be sensitive to drought, and in order to study the physiological and biochemical changes that occur in passion fruit seedlings under drought stress, a hypertonic polyethylene glycol (PEG) solution (5%, 10%, 15%, and 20%) was used to simulate drought stress in passion fruit seedlings. We explored the physiological changes in passion fruit seedlings under drought stress induced by PEG to elucidate their response to drought stress and provide a theoretical basis for drought-resistant cultivation of passion fruit seedlings. The results show that drought stress induced by PEG had a significant effect on the growth and physiological indices of passion fruit. Drought stress significantly decreased fresh weight, chlorophyll content, and root vitality. Conversely, the contents of soluble protein (SP), proline (Pro), and malondialdehyde (MDA) increased gradually with the increasing PEG concentration and prolonged stress duration. After nine days, the SP, Pro and MDA contents were higher in passion fruit leaves and roots under 20% PEG treatments compared with the control. Additionally, with the increase in drought time, the activities of antioxidant enzymes such as peroxidase (POD), superoxide dismutase (SOD) and catalase (CAT) showed an increasing trend and then a decreasing trend, and they reached the highest value at the sixth day of drought stress. After rehydration, SP, Pro and MDA contents in the leaves and roots of passion fruit seedlings was reduced. Among all the stress treatments, 20% PEG had the most significant effect on passion fruit seedlings. Therefore, our study demonstrated sensitive concentrations of PEG to simulate drought stress on passion fruit and revealed the physiological adaptability of passion fruit to drought stress.

Different leafy vegetable cropping systems regulate growth, photosynthesis, and PSII functioning in mono-cropped eggplant by altering chemical properties and upregulating the antioxidant system

Continuous cropping of eggplant threatened regional ecological sustainability by facilitating replanting problems under mono-cropping conditions. Therefore, alternative agronomic and management practices are required to improve crop productivity at low environmental cost for the development of sustainable agricultural systems in different regions. This study examined changes in soil chemical properties, eggplant photosynthesis, and antioxidant functioning in five different vegetable cropping systems over a 2-year period., 2017 and 2018. The results showed that welsh onion-eggplant (WOE), celery-eggplant (CE), non-heading Chinese cabbage-eggplant (NCCE), and leafy lettuce-eggplant (LLE) rotation systems significantly impacted growth, biomass accumulation, and yield than fallow-eggplant (FE). In addition, various leafy vegetable cropping systems, WOE, CE, NCCE, and LLT induced significant increases in soil organic matter (SOM), available nutrients (N, P, and K), and eggplant growth by affecting the photosynthesis and related gas exchange parameters with much evident effect due to CE and NCCE. Moreover, eggplant raised with different leafy vegetable rotation systems showed higher activity of antioxidant enzymes, resulting in lower accumulation of hydrogen peroxide and hence reduced oxidative damage to membranes. In addition, fresh and dry plant biomass was significantly increased due to crop rotation with leafy vegetables. Therefore, we concluded that leafy vegetable crop rotation is a beneficial management practice to improve the growth and yield of eggplant.

Biomass, Essential Oil Yield, and Composition of Marjoram as Influenced by Interactions of Different Agronomic Practices under Controlled Conditions

Origanum marjorana L. has been valued for centuries for its flavoring attributes and therapeutic properties. The growing demand for its various applications necessitates optimizing agronomic practices for its production. A glasshouse pot trial was conducted to identify optimum agronomic practices for increased herbage and oil yield, as well as oil quality. The effects of varying air temperature regimes (low, medium, and high levels), irrigation (low, medium, and high levels), nitrogen fertilizer application (N = 100, 150, and 200 kg/ha), and soil type (sandy loam, sandy clay loam, and loamy sand) on the productivity of marjoram plants were investigated. The results showed an increase in plant growth and herbage yield as well as chlorophyll content under conditions of high air temperature, low irrigation, and moderate to high nitrogen level applied to sandy loam soil, with an increase in oil yield with loamy sand soil. The major compounds observed in marjoram essential oil were terpinene-4-ol (22.63-36.72%) and (Z)-β-terpineol (6.85-16.60%), in which terpinene-4-ol was not found to be within the International Organization for Standardization (ISO) limits of acceptability while (Z)-β- terpineol had no reference limits available. A promising performance of marjoram cultivation under high regimes of air temperature (16.7 to 36.6 °C), nitrogen fertilization (200 kg ha^-1 N), and low irrigation (up to 60% soil water depletion from field capacity) on sandy loam soils was demonstrated for improved crop productivity.

Effects of Arbuscular Mycorrhizal Fungi and Biochar on Growth, Nutrient Absorption, and Physiological Properties of Maize (Zea mays L.)

Arbuscular mycorrhizal fungi (AMFs) and biochar are two common alternatives to chemical fertilizers applied to soil to improve crop growth. However, their interactive effects on maize (Zea mays L.) growth, nutrient absorption, and physiological properties remain poorly understood. In this study, maize plants were grown in pots treated with biochar and AMFs Diversispora eburnea, alone or in combination. The results showed that the individual application of AMFs or biochar increased maize growth and mineral contents in shoots and roots (including P, K, Ca, Na, Mg, Fe, Mn, and Zn). The chlorophyll a, chlorophyll b, and total chlorophyll contents in AMF-treated leaves were significantly higher than those in the control treatment group. However, AMFs had no synergistic effects with biochar on maize growth, nutrient absorption, nor photosynthetic pigments. The application of biochar to the soil significantly reduced mycorrhizal colonization by 40.58% in the root tissues, accompanied by a significant decline in mycorrhizal dependency from 80.57% to -28.67%. We conclude that the application of biochar and AMFs can affect maize growth, nutrient uptake, and physiological properties. Our study can provide vital information for further resource use optimization in agroecosystems.

How Carbon Nanoparticles, Arbuscular Mycorrhiza, and Compost Mitigate Drought Stress in Maize Plant: A Growth and Biochemical Study

Drought negatively affects crop growth and development, so it is crucial to develop practical ways to reduce these consequences of water scarcity. The effect of the interactive potential of compost (Comp), mycorrhizal fungi (AMF), and carbon nanoparticles (CNPS) on plant growth, photosynthesis rate, primary metabolism, and secondary metabolism was studied as a novel approach to mitigating drought stress in maize plants. Drought stress significantly reduced maize growth and photosynthesis and altered metabolism. Here, the combined treatments Com-AMF or Com-AMF-CNPs mitigated drought-induced reductions in fresh and dry weights. The treatments with AMF or CNPS significantly increased photosynthesis (by 10%) in comparison to the control plants. Results show that soluble sugars were accumulated to maintain the osmotic status of the maize plant under drought stress. The level and metabolism of sucrose, an osmo-protectant, were increased in plants treated with Com (by 30%), which was further increased under the triple effect of Com-AMF-CNPs (40%), compared to untreated plants. This was inconsistent with increased sucrose-phosphate synthase and sucrose-P-synthase activity. The combined treatment Com-AMF-CNPs increased the levels of oxalic and succinic acids (by 100%) and has been reflected in the enhanced levels of amino acids such as the antioxidant and omso-protectant proline. Higher increases in fatty acids by treatment with CNPS were also recorded. Com-AMF-CNPs enhanced many of the detected fatty acids such as myristic, palmitic, arachidic, docosanoic, and pentacosanoic (110%, 30%, 100%, and 130%, respectively), compared to untreated plants. At the secondary metabolism level, sugar and amino acids provide a route for polyamine biosynthesis, where Com-AMF-CNPs increased spermine and spermidine synthases, ornithine decarboxylase, and adenosyl methionine decarboxylase in treated maize. Overall, our research revealed for the first time how Cmo, AMF, and/or CNPS alleviated drought stress in maize plants.