Daily and season transpiration intensive of Calluna vulgaris (L.) Hill in the trans-Ural south area

Abstract

The Trans-Ural region is the southern point of the common heather (C. vulgaris) range. Field ecophysiological study of C. vulgaris plants transpiration intensity (IT) was carried out in connection with the problem of marginal populations adaptation to arid climate. The research was carried out in the forest-steppe of the Trans-Ural region (Kurgan region), where an abundant population of heather grows. The dailyvariation of IT was studied taking into account a set of recorded ecoclimate limiting factors (wind speed, illumination, dynamics of air temperature and humidity, soil temperature) during one growing season (from April to September 2016) under the canopy of a pine forest and in the adjacent clearing. To study IT, annual apical shoots of plants 4 cm long were used in triplicate for each time period. The total sample size on one day of measurements ranged from 30-35 shoots. The transpiration rate was determined by the rapid weighing method, which takes into account the water lost by the shoot over a certain time period. When processing the data, we used correlation analysis (Pearson's correlation coefficient r), which made it possible to clarify the strength and direction of two continuous (metric) variables interaction. Differences in IT daily changes were revealed in plants growing under the forest canopy and in the open areas. Under conditions of long-term atmospheric and soil drought, which is common for the region, in 2016 a sharp decrease in heather water content was observed, starting from 10 a.m. throughout the entire growing season, with the exception of April, when the moisture deficit in the soil and heather tissues was still minimal. In May, maximum IT values in the clearing were noted at 14:00 (8.5 mg/h×10 –4) whereas under the canopy of the tree stand, peak IT values begin at 10 a.m. (12.7 mg/h×10 –4). Daytime summer transpiration in common heather (C. vulgaris) is even less intense than spring transpiration ((3–5 mg/h×10–4).It was revealed that meteorological factors play a decisive role in IT in various types of forest. In open felled areas, the determining factor is PAR (0.81, p < 0.05) and, to a lesser extent, atmospheric temperature (0.69, p < 0.05), and under the canopy - only PAR (0.96, p <0.05). A decrease in IT and, accordingly, photosynthesis leads to a decrease in the population’s vitality and non-ripening of seeds, which is an ecophysiological factor of the heather absence south of Kurgan city.