Changes in freezing tolerance and mineral uptake of oat plants grown in biochar media

In this study, the effects of biochar applications on mineral element concentrations, antioxidant enzyme activities, and physiological and molecular parameters of oat plants grown under control (25 °C) and freezing stress (-15 °C) conditions were investigated. The study was conducted in controlled conditions and pots according to a factorial experimental design with three replications. Oat plants were treated with a 4% application of biochar derived from animal and plant resources and grown under control conditions until the 3-4 leaf stage. After approximately 28 days, a portion of the plants was acclimated at +4 °C for 24 hours, while another portion was exposed to freezing stress (-15 °C) for 3, 6, and 12 hours without any acclimation. Freezing stress reduced the uptake of various nutrients, including N, P, and K. Acclimation of oat plants improved the uptake of N, P, K, Ca, Mg, Fe, Cu, Zn, and Mn. The decrease in chlorophyll content due to freezing stress was mitigated to a lesser extent by biochar application, while the membrane durability index (MDI) of biochar-treated plants was found to be higher. Lipid peroxidation (MDA) and proline content were at desired levels in both biochar-treated and acclimated plants. The increase in enzyme activities (SOD, CAT, GR, APX) induced by freezing stress and biochar applications was determined to be sufficient to counteract the freezing stress. The change in gene expressions indicated that the expected upregulation in stress response was achieved in acclimated plants with animal-derived biochar during the 3-hour freezing period. Given the emergence of HSP90 protein, it was concluded that animal-derived biochar application would be more effective in reducing short-term freezing stress in oat plants.