THE BALANCE OF CALCIUM IN THE GRASS ECOSYSTEMS OF THE TEREK-KUMA LOWLAND
Terek-Kuma lowland occupies the North-Western part of the Precaspian lowland. The soil-plant cover of the territory is determined by the aridity of the climate with frequent winds, light granulometric and saline soils, high pasture load. In this study, for the first time in the Terek-Kuma semidesert conditions, the productivity of structural parts of grass ecosystems and calcium reserves during the most favorable (April) and arid (August) periods are determined for the main soil types. The work aimed to determine the accumulation, distribution and reserves of calcium in the structure of phytomass with regard to a soil type. The research was performed at the Kochubey Biosphere Station, Precaspian Institute of Biological Resources of the Dagestan Scientific Center RAS in 2011-2016 on grass phytocenoses of light chestnut and meadow-chestnut soils and saline typical automorphic soils. Assessment of plant matter and Ca accumulation in green mass, rags, steppe felt, and roots, and calculation of the Ca budget of the ecosystems were carried out according to A.A. Titlyanova et al. (1988). The content of Ca in plants was determined by capillary electrophoresis (a Drops-105M system, Lumex, Russia) with special software Elforan (Lumex, Russia). The greatest amount of phytomass accumulated on light chestnut soil. On meadow-chestnut soil photosynthesizing parts, rags, steppe felt and roots accumulated 2.3, 1.5, 2.3 and 2.2 times less, respectively, and on typical saline soil 2.6, 1.7, 2.5 and 2.7 times less than on light chestnut soil. This was likely caused by a decrease in projective coverage from 77.0 % on light chestnut soil to 48.5 % on meadow chestnut soil and 43.5 % on typical saline soil. In the species patterns the dominants were Poaceae (51 % for light chestnut soil) and Asteraceae (30 % and 17 % for meadow chestnut soil and saline soil, respectively). The root weight for meadow-chestnut soil and typical saline soil was 2.2 and 2.9 times less than for light chestnut soil. Their share in the total phytomass depending on soil types ranged from 85.0 to 87.2 %. In green parts, the concentration of Ca, depending on the season and the soil type, was in the range of 0.40-0.48 %, in rags it was 0.50-0.54 %, in felt 1.00-1.31 %, and in underground parts 1.14-1.38 %. By soil types, it decreased as light chestnut soil > meadow-chestnut soil > saline soil due to pH changes (8.6 > 8.2 > 8.0), an increase in the degree of salinity and the shift of salinity from the sulfate type to the sulfate-chloride type. Reserves of Ca in the above-ground parts during the growing season on light chestnut soil amounted to 2.32 kg/ha per year and exceeded 2.7- and 3.1-fold, respectively, similar indicators for meadow-chestnut soil and typical saline soil. Ca reserves in the root mass for all types of soils were 12.6 times more than in the aboveground parts. After plant matter decomposition, steppe felt and underground organs contribute to light chestnut soil 42.0 and 58.0 % of the calcium consumed from the soil, to meadow chestnut soil 36.0 and 64.0 %, respectively; for the typical saline soil these amounts are 1.1- and 2.3-fold, respectively. It was revealed that the difference in the dynamics of Ca accumulation in components of a semi-desert plant community (green mass, rags, steppe felt, and roots) depends on the plant species composition, soil type and season.