The modified biochars influence nutrient and osmotic statuses and hormonal signaling of mint plants under fluoride and cadmium toxicities

Abstract

IntroductionChemically modified biochars are a new generation of biochars that have a great ability to absorb and stabilize environmental pollutants. In this research, the physiological performance of mint plants (Mentha crispa L.) under fluoride and cadmium toxicities and biochar treatments was evaluated.MethodsFour levels of soil toxicities including non-toxic, 600 mg NaF kg-1 soil, 60 mg Cd kg-1 soil, and 600 mg NaF kg-1 soil + 60 mg Cd kg-1 soil were applied. The biochar addition to the soil was 25 g kg-1 (non-biochar, solid biochar, H2O2, KOH, and H3PO4-modified biochars).ResultsThe results showed that the application of biochar and especially chemically modified biochars reduced fluoride (about 15-37%) and cadmium (30-52%) contents in mint leaves, while increased soil pH and cation exchange capacity (CEC), nitrogen (12-35%), phosphorus (16-59%), potassium (17-52%), calcium (19-47%), magnesium (28-77%), iron (37-114%), zinc (45-226%), photosynthetic pigments of leaves and plant biomass (about 10-25%) under toxic conditions.DiscussionThe biochar-related treatments reduced the osmotic stress and osmolytes content (proline, soluble proteins, and carbohydrates) in plant leaves. Plant leaf water content was increased by solid and modified biochar, up to 8% in toxic conditions. Furthermore, these treatments reduced the production of stress hormones [abscisic acid (27-55%), salicylic acid (31-50%), and jasmonic acid (6-12%)], but increased indole-3-acetic acid (14-31%) in plants under fluoride and cadmium stresses. Chemically modified biochars reduced fluoride and cadmium contents of plant leaves by about 20% and 22%, respectively, compared to solid biochar.ConclusionThis result clearly shows the superiority of modified biochars in protecting plants from soil pollutants.

The role of magnesium oxide foliar sprays in enhancing mint (Mentha crispa L.) tolerance to cadmium stress

“…Cadmium accumulation in plant tissues triggers osmotic stress, which leads to compromised root growth and damage to root aquaporins 63 , 64 . This stressor diminishes the availability of water for plant growth, a phenomenon substantiated by previous researchers 11 . In response to osmotic stress, plants increase the concentration of osmolytes, such as soluble carbohydrates, within their tissues.…”

“…Cadmium stress can hinder nutrient absorption and overall plant growth by reducing root activity. This metal can also inhibit the production of growth hormones such as auxins, which can lead to a decrease in root growth 11 . Applying magnesium through foliar spraying can help reduce cadmium accumulation in mint root tissues and improve root metabolism.…”

“…Wan and Zhang 9 and Loix et al 10 suggest that the stiffening of the cell wall and the decrease in cell elongation in plants exposed to high levels of Cd are likely caused by damage to the cell wall components. A recent study by Farhangi-Abriz and Ghassemi-Golezani 11 demonstrated that, in addition to mitigating oxidative stress, enhancing plant osmotic adjustment plays a crucial role in resistance to cadmium stress. Improved nutritional conditions enable plants to thrive and function more effectively under cadmium stress.…”

Cadmium Alters the Metabolism and Perception of Abscisic Acid in Pisum sativum Leaves in a Developmentally Specific Manner

“…An increase in the content of free endogenous ABA in leaves in response to cadmium exposure has been found in several plant species, including Oryza sativa [ 52 ], Zea mays [ 53 ], Phaseolus vulgaris [ 54 ] and Mentha crispa [ 55 ]. However, the changes in ABA content related to its metabolism in response to Cd in leaves at different developmental stages have not been investigated so far.…”