How Does Zinc Improve Salinity Tolerance? Mechanisms and Future Prospects

Residual effects of biochar and nano-modified biochar on growth and physiology under saline environment in two different genotype of Oryza sativa L

Soil salinity is represent a significant environmental stressor that profoundly impairs crop productivity by disrupting plant physiological functions. To mitigate this issue, the combined application of biochar and nanoparticles has emerged as a promising strategy to enhance plant salt tolerance. However, the long-term residual effects of this approach on cereal crops remain unclear. In a controlled pot experiment, rice straw biochar (BC) was applied in an earlier experiment at a rate of 20 t/ha, in conjunction with ZnO and Fe2O3 nanoparticles at concentrations of 10 mg L-1 and 20 mg L-1. Two rice genotypes, Jing Liang You-534 (salt-sensitive) and Xiang Liang You-900 (salt-tolerant), were utilized under 0% NaCl (S1) and 0.6% NaCl (S2) conditions. Results showed that, application of residual ZnOBC-20 significantly enhanced rice biomass, photosynthetic assimilation, relative chlorophyll content, SPAD index, enzyme activities, K+/Na+ ratio, hydrogen peroxide (H2O2) levels, and overall plant growth. Specifically, ZnOBC-20 increased the tolerance index by 142.8% and 146.1%, reduced H2O2 levels by 27.11% and 35.8%, and decreased malondialdehyde (MDA) levels by 33% and 57.9% in V1 and V2, respectively, compared to their respective controls. Residual of ZnOBC-20 mitigated oxidative damage caused by salinity-induced over-accumulation of reactive oxygen species (ROS) by enhancing the activities of antioxidant enzymes (SOD, POD, CAT, and APX) and increasing total soluble protein (TSP) content. Xiang Liang You-900 exhibited a less severe response to salinity compared to Jing Liang You-534. Additionally, residual of ZnOBC-20 significantly enhanced the anatomical architecture of both root and leaf tissues and regulated the expression levels of salt-related genes. Residual of ZnOBC-20 also improved salt tolerance in rice plants by reducing sodium (Na+) accumulation and enhancing potassium (K+) retention, thereby increasing the K+/Na+ ratio under saline conditions. The overall results of this experiment demonstrate that, residual effects of ZnOBC-20 not only improved the growth and physiological traits of rice plants under salt stress but also provided insights into the mechanisms behind the innovative combination of biochar and nanoparticles residual impacts for enhancing plant salt tolerance.

Valorization of sewage sludge incineration ash as a novel soilless growing medium for urban agriculture and greenery

Limited open areas for urban agriculture and greenery have led to the search for innovative, sustainable growing media to strengthen the food supply and improve atmospheric quality for a resilient city. Rampant land developments have caused soil to become increasingly scarce. Sewage sludge incineration ash (SSIA), the by-product of waste-to-energy (WtE) incineration of sewage sludge, is a major municipal waste containing phosphorus-fertilizing nutrients. For the first time, we investigated the novel application of SSIA as a soilless plant-growing medium with built-in fertilizer. SSIA outperformed topsoil in bulk density, water-holding capacity, porosity, and nutrient content. However, it was found that SSIA has a high salinity and should be treated first. Wheatgrass (Triticum aestivum L.), a fast-growing glycophyte, thrived in the desalinated SSIA, showing growth and nutrient content comparable to the topsoil case. Simultaneously, it demonstrated phytoremediation. The SSIA residue was then recycled into cementitious materials, using desalinating water for mixing. SSIA upcycle into a growing medium facilitates urban resource management by utilizing nutrients in sewage waste for eco-friendly plant cultivation, benefiting urban agriculture and greenery. It is also a prudent valorization step before further recycling SSIA to reduce landfill requirements.

Mitigation of Salinity Stress and Lead Toxicity in Maize by Exogenous Application of the Sorghum Water Extract

The increased concentration of lead (Pb) in soils is a serious threat to human beings and plants all over the world. Salinity stress is also a major issue across the globe, which limits crop productivity. The use of allelochemicals has become an effective strategy to mitigate the toxic effects of abiotic stresses. Sorghum is an important crop grown across the globe, and it also possesses an appreciably allelopathic potential. Therefore, this study was planned to determine the impacts of the sorghum water extract (SWE) on improving maize growth under Pb and salinity stress. The experiment included different treatments; control, SWE (3%), and different levels of Pb and salinity stress; T1: control, T2: 50 mM NaCl, T3: 100 mM NaCl, T4: 250 μM Pb, and T5: 500 μM Pb. Lead and salinity stress reduced the maize growth by the genesis of reactive oxygen species (ROS), as evidenced by higher production of malondialdehyde (MDA: 39.1 and 32.28%) and hydrogen peroxide (H2O2: 20.62 and 17.81%). Spraying plants with SWE improved the maize growth by increasing antioxidant activities (ascorbate peroxidase: APX, catalase: CAT, peroxidase: POD and superoxide dismutase: SOD), photosynthetic pigments, relative water contents (RWC), osmolyte accumulation (proline, total soluble proteins: TSP, free amino acids: FAA), potassium accumulation, and decreasing MDA, H2O2, sodium, chloride, and Pb accumulation. In conclusion, the application of SWE mitigates adverse impacts of Pb and salinity stresses by improving chlorophyll synthesis and osmolyte accumulation, activating the antioxidant defense system, and preventing the entry of toxic ions.

Antioxidant Defense and Ionic Homeostasis Govern Stage-Specific Response of Salinity Stress in Contrasting Rice Varieties

Salt stress is one of the most severe environmental stresses limiting the productivity of crops, including rice. However, there is a lack of information on how salt-stress sensitivity varies across different developmental stages in rice. In view of this, a comparative evaluation of contrasting rice varieties CSR36 (salt tolerant) and Jaya (salt sensitive) was conducted, wherein NaCl stress (50 mM) was independently given either at seedling (S-stage), tillering (T-stage), flowering (F-stage), seed-setting (SS-stage) or throughout plant growth, from seedling till maturity. Except for S-stage, CSR36 exhibited improved NaCl stress tolerance than Jaya, at all other tested stages. Principal component analysis (PCA) revealed that the improved NaCl stress tolerance in CSR36 coincided with enhanced activities/levels of enzymatic/non-enzymatic antioxidants (root ascorbate peroxidase for T- (2.74-fold) and S+T- (2.12-fold) stages and root catalase for F- (5.22-fold), S+T- (2.10-fold) and S+T+F- (2.61-fold) stages) and higher accumulation of osmolytes (shoot proline for F-stage (5.82-fold) and S+T+F- (2.31-fold) stage), indicating better antioxidant capacitance and osmotic adjustment, respectively. In contrast, higher shoot accumulation of Na+ (14.25-fold) and consequent increase in Na+/K+ (14.56-fold), Na+/Mg+2 (13.09-fold) and Na+/Ca+2 (8.38-fold) ratio in shoot, were identified as major variables associated with S-stage salinity in Jaya. Higher root Na+ and their associated ratio were major deriving force for other stage specific and combined stage salinity in Jaya. In addition, CSR36 exhibited higher levels of Fe3+, Mn2+ and Co3+ and lower Cl- and SO42-, suggesting its potential to discriminate essential and non-essential nutrients, which might contribute to NaCl stress tolerance. Taken together, the findings provided the framework for stage-specific salinity responses in rice, which will facilitate crop-improvement programs for specific ecological niches, including coastal regions.