The relationship between the morphological traits of the medicinal plant Stachys inflata Benth and environmental factors

Background and purpose: Stachys inflata Benth from Lamiaceae family, as one of the most important medicinal species widely used among people and industries, and the aerial parts of this plant are used as an anti-inflammatory and pulmonary infection medicine. This species is widely distributed in the world and especially in different parts of the country. Considering the significant distribution and importance of this species from a medicinal point of view, it is necessary to investigate and evaluate the growth conditions of the species and the factors affecting its growth. Knowing the factors affecting the growth traits of this species facilitates the principled management and multi-purpose exploitation of rangelands. Therefore, the present research was conducted in order to investigate the effect of soil and topographical factors on the morphological traits of medicinal plant (Stachys inflata Benth) in the northern rangelands of West Azerbaijan province. Materials and methods: Sampling and data recording of crown cover of this plant species was conducted in eight rangeland sites in Chaipareh and Khoy counties in the north of West Azerbaijan province by a systematic-random method with the establishment of 80 plots along linear transects. In each of the mentioned ecological units, for each of the bases in the ten plots, the traits such as the percentage of the canopy of the species, the length of the flowering stem, the length, width and area of the leaf, the length and width of the canopy, the height of the plant, the depth of rooting, the number main branches, root dry weight and leaf and stem dry weight were measure. Soil samples were taken from each of the sites at five points from 0 to 20 cm depth and were taken to the laboratory to measure soil parameters. Changes in the morphological traits of S. inflata species due to soil and topographical factors were done by using the Redundancy Analysis (RDA) and checking the similarity of ecological units and different traits by clustering analysis (CA). Results: The results of Detrended Correspondence Analysis on the matrix of plant traits showed that the average length of the gradient is less than three and therefore the changes of these traits among the sites follow linear relationships. The results of the DCA showed that the importance of the axes based on the specific value has decreased from the first to the second axis, as a result, the major contribution of changes in plant traits is related to the first axis. Examining the factors affecting the extraction of the components shows that the first axis is mainly the result of the chemical characteristics of the soil and the second axis is the result of the topographical characteristics of the slope. The results of ordination for plant traits and environmental factors using RDA showed that crown length, leaf width and leaf area located in the first quarter of the coordinate axis are more influenced by K and Na. Considering that the root depth vector matches with the sand vector, then with the increase in the amount of sand, root growth also increases significantly. But root depth and root dry weight have a negative correlation with silt, clay, saturated moisture percentage, soil pH and lime percentage. Canopy density, leaf length and plant height are positively correlated with elevation and organic carbon and negatively correlated with Na, K and EC. The results related to the correlation between the traits showed that the canopy percentage of S. inflata has a significant direct relationship with the dry weight of leaves and stems, the dry weight of roots and the number of branches, and a significant inverse relationship with the length of the flowering stem.  The dendrogram related to the classification of traits also divides the traits into 12 separate clusters based on the similarity of 22.5 negative traits. The first cluster includes root depth, the second cluster includes dry weight of leaves and stems, the third cluster includes crown length, the fourth cluster includes crown width, the fifth cluster includes the percentage of crown cover of St. inflata species and the number of branches, the sixth cluster includes height, and the seventh cluster includes root dry weight. The eighth cluster includes the length of the flowering stem and canopy density, the ninth cluster includes the leaf width, and the tenth cluster includes the leaf area and leaf length. Discussion and conclusion: The results of this study showed that the functional traits of St. inflata species are under the combined influence of soil and topographical factors and its growth undergoes complicated changes. Considering the importance of the amount of biomass produced by this plant as a measure of the production that can be collected by the operators, it seems that the greater the amounts of sand, electrical conductivity and cations of the rangelands and less amount of the elevation values, exposure of the range to the sun, organic carbon, silt, clay, lime and acidity, the amount of biomass production of the site will increase. Therefore, it can be stated that, at least in terms of biomass production, this species likes harsher environmental conditions, therefore, in degraded sites, as a suitable species can be recommended to increase its abundance.