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

INTRODUCTION: Chemically 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.

METHODS: Four 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, H2 O2 , KOH, and H3 PO4 -modified biochars).

RESULTS: The 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.

DISCUSSION: The 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.

CONCLUSION: This result clearly shows the superiority of modified biochars in protecting plants from soil pollutants.