Effect of shungite application on the temperature sensitivity of Allium cepa respiration under two soil water regime

For agricultural soils with low natural fertility, the possibility of using rock powders as an alternative source of nutrients and/or improver of soil physical parameters is under discussion and study. Shungite rocks, volcanic sedimentary rock formed mainly on a silicate basis, are characterized by the high content of carbon and nutrients. This study aimed to evaluate if shungite application to Umbric Podzols may affect leaf and root mitochondrial respiratory pathways, and leaf response to a temperature change. A pot culture experiment was conducted with Allium cepa L. seedlings, using soil shungite concentrations of 0, 5, 10, and 20 g kg^-1 and two soil water regimes: well-watered (WW) and drying-wetting (DW) cycles. Soil water deficit increased total respiration (V_t) of onion leaves, but not roots, under low (13°C) and high (33°C) measurement temperature. Shungite application affected leaf V_t only at 13°C: it increased the V_t rate under WW and decreased one under DW. An increase in measurement temperature enhanced the sensitivity of leaf respiration to the inhibitor of the alternative respiratory pathway (salicylhydroxamic acid, SHAM). Shungite application increased the contribution of SHAM-sensitive pathway to the leaf V_t rate under WW, but not DW regime, regardless of the leaf temperature. In contrast to SHAM-resistant pathway, the temperature sensitivity of the SHAM-sensitive rate decreased following the decrease in soil water availability. Shungite application increased the temperature sensitivity of both SHAM-sensitive and SHAM-resistant pathways under DW, and significantly decreased these parameters under WW. In summary, the decrease of temperature sensitivity of alternative SHAM-sensitive respiratory pathway with a decrease of soil water availability or shungite-related decrease of both SHAM-sensitive and SHAM-resistant leaf respiration may play an important role in enhancing the resistance of plant respiration to stress temperature.