Morphophysiological and Ecological Characteristics of Melilotus officinalis (Fabaceae, Magnoliopsida) under Conditions of the Republic of Tatarstan

Abstract—The morphological variability of the aerial vegetative and generative organs of yellow sweet clover (Melilotus officinalis) was studied in the ecotone communities of the forest–steppe and the forest zones of the Republic of Tatarstan including the disturbed parts of the forest zone. The ascorbic acid content was also analyzed in various parts of the plants growing in these habitats. It was revealed that the implementation of the morphophysiological potential of the plants was determined by the conditions of particular botanical and geographical zones. The sweet clover plants growing on chernozem soils under the conditions of the ecotone communities of the forest–steppe zone were found to display higher levels of the total biomass, leaf biomass, and inflorescence biomass as compared with the plants growing in similar communities on gray soils in the forest zone. The content of ascorbic acid was also higher in all parts of the plants taken from the ecotone communities of the forest-steppe zone. The M. officinalis plants growing under the conditions of a damaged soil layer and weak competition with other herbal species exhibited the maximal accomplishment of their biomorphological potential. Here, the coefficient of variation (CV) was low, which indicates a stronger homogeneity of the samples. In the plants growing under extreme conditions, the concentration of ascorbic acid increased sharply in all their parts. This may be interpreted as an important adaptive mechanism to withstand dramatic changes in the substrate temperature. Along with a prolongation of the generative period, the adaptation of the species was characterized by a weak correlation between the biomass of inflorescences and their content of ascorbic acid and between the inflorescence biomass and the ascorbic acid concentration in the leaves. These relationships show the stable process of formation of the generative system of sweet clover. All the coenopopulations studied were characterized by an incomplete ontogenetic spectrum with the absolute maximum (95%) corresponding to the plants of the middle-age ontogenetic status