Changes in Some Physiological Characteristics of Bean with the Application of Biochar and Salicylic Acid under Saline Soil Conditions

Abstract

Introduction Phaseolus vulgaris L., commonly known as the common bean, is an important legume crop, responsible for 85% of global bean production. Nevertheless, soil salinity represents a significant challenge that severely impairs its productivity. Soil salinity represents one of the most detrimental constraints on crop growth and production. Conversely, beans are regarded as one of the most susceptible crops to salinity stress. However, the detrimental effects of salinity on crops can be significantly mitigated by the use of certain substances. Salinity exerts a significant negative influence on the primary plant processes, including photosynthesis and the production of photoassimilates, which ultimately results in a reduction in plant production. The application of an appropriate quantity of salicylic acid (SA) enhances the plant's tolerance to abiotic stresses, thereby reducing the destructive effects of stress and increasing tolerance to abiotic stresses. It has been demonstrated that the external application of salicylic acid can induce the tolerance of crop plants to a range of abiotic stresses, including salt, drought, heat, cold, and heavy metals. Furthermore, SA can be an effective substance against plant abiotic stresses, as it can regulate a variety of phytohormones, and it may play a key role in free radical scavenging and nutrient uptake. Furthermore, the utilization of biochar represents an efficacious approach to mitigating the consequences of abiotic stresses, such as salinity. Biochar, a carbon-rich material, is employed to enhance soil carbon sequestration, reduce CO₂ emissions, and augment soil microbial diversity and activity. It has been postulated that biochar has the capacity to adsorb some of the toxic ions, such as Na and Cl, thereby reducing the toxic effects of salinity. Materials and Methods A two-year glasshouse study was conducted using a randomized complete block design, with four replicates in each treatment. The study was conducted at the Faculty of Agriculture, University of Mohaghegh Ardabili, Iran over two consecutive years (2022-2023). The experiment included three levels of salicylic acid (SA): SA0 (0 mM), SA0.5 (0.5 mM) and SA1 (1 mM), four levels of biochar, including no biochar application as the control treatment (B0), recommended biochar (Rb) by application of 2.5% biochar. The treatments included 5% (w/w) of modified biochar with phosphoric acid (PA), 1.25% of modified biochar with sulfuric acid (Sb), and salt stress (SS) using NaCl in three levels: SS0 (distilled water), SS4 (4 dS m-1), and SS8 (8 dS m-1). In this experiment, the salinity treatment was applied in two stages: at the planting time and when the seedlings had fully established themselves in the soil. Salicylic acid was applied foliarly at two stages: early and late flowering, according to the predetermined levels. Results and Discussion 70 Salinity had a detrimental impact on the biochemical attributes of bean plants, yet this effect was alleviated by the application of the SA treatment. Furthermore, salt stress resulted in a reduction in relative water content, membrane stability index, leaf area and photosynthetic pigments, which in turn led to a reduction in current photosynthesis and remobilisation of photoassimilates. Nevertheless, the application of biochar and the use of SA were found to alleviate the negative effects, resulting in a higher grain yield compared with the control plants, i.e. at the absence of biochar and SA application at the end of the experiment. The combined application of biochar and SA resulted in a higher relative water content, photosynthetic pigments and an enhanced rate of photosynthesis. The greatest accumulation of chlorophyll-a and carotenoids was observed in response to the application of SA1 without biochar in non-stress conditions. Furthermore, the lowest photosynthetic rate was observed in response to SS8. Moreover, the greatest anthocyanin accumulation was observed in response to the addition of biochar to the soil in the absence of SA under salt stress conditions. Our research has demonstrated that the combined application of biochar and SA can significantly mitigate the adverse effects of salinity stress on common beans. Furthermore, the results demonstrated that SA significantly enhanced grain yield of plants under both saline and non-saline soils. The results indicate that the excessive use of biochar and SA may lower the mentioned effectiveness, as the biochar increases soil porosity, which negatively impacts water availability. Furthermore, application of high doses of SA has been shown to have a negative impact on the biochemical and enzymatic attributes of the plant under salinity conditions. Conclusions Although the study on the effects of biochar and SA on common beans under salinity stress provides valuable insights, it is important to consider the limitations of the study. Consequently, the findings may not be directly extrapolated to the natural agricultural settings, where multiple environmental factors interact.

Keywords

• anthocyanin
• chlorophyll
• photosynthesis
• relative leaf water content