The data of the researches describes the were to establish the species composition of pasture cenoses and the productivity potential of light-chestnut and meadow-chestnut soils under different climatic conditions and in different periods of the year in the Terek-Kuma lowland of the North-Western Precaspian. Two peaks of productivity of phytocoenosis have been observed: the first is – ephemeral synusia in the middle of May- early June; second – motley grass and saltworts in the second half of September. The data on receipt of photosynthetically active radiation (PAR) on the soil surface and the coefficient of its use over the years and periods of the year depending on the hydrothermal conditions and dynamics of harmful salts in the soil are given. On light-chestnut soil formed cereals-wormwood, grass-cereals, wormwood-ephemeral in combination with wormwood-saltworts association, and meadow-chestnut soil – ephemera-wormwood. The phytocenosis on light-chestnut soil is inherent in the maximum species diversity – 35 species. On meadow-chestnut soil there are only 25 species. The items of the changes in the species composition of phytocenoses depending on the environmental factors are considered. The data in this article support and augment information presented in the research articles [1] , [2] , [3] , [4] , [5] , [6] , [7] .

No abstract

The purpose of the work is to determine the content and reserves of nitrogen, its balance in the ecosystems of the northern and southern expositions of the Mayak Mountain in the Highlands of Dagestan. For the first time, calculations of nitrogen reserves and balance in phytocenoses were performed for the High-mountain subprovincion of Dagestan. Methods. The study was conducted in 2012-2019 on the territory of the Gunib base of the Mountain Botanical Garden of the Russian Academy of Sciences. A protected regime was introduced at the experimental sites to exclude anthropogenic impact. The plots are located on the slopes of Mount Mayak: south (2100 m above sea level with a slope of 350), north (2070 m above sea level with a slope of 100). The nitrogen content in the phytomass was determined by wet salting. Nitrogen reserves and balance in phytocenoses were determined by the method of A. A. Titlyanova. Results. The productivity of phytomass on the slopes of Mount Mayak was at the northern and southern exposures: in the aboveground mass-69.62 and 66.50 c/ha * year; in the underground mass-2.07-2.10 times more. Most of the nitrogen reserves were on the slope of the northern exposure, which was probably due to the leaching of nitrogen from the soil, due to the great steepness of the southern slopes. The input part of the nitrogen balance in the phytocenoses of the Highlands of Dagestan during the decomposition of the underground mass was from 68.57 to 68.80%, depending on the slope exposure. During the decomposition of aboveground phytomass, 27.29-27.64% were received. Nitrogen fixation and intake with atmospheric precipitation amounted to a total of 3.69-4.32%. The main part of the expenditure item of the nitrogen balance accounts for the creation of net primary production of phytocenoses – 98.25-98.50%. Denitrification was 0.94-1.10%, leaching from the soil was 0.56-0.66%. In the studied protected areas, a positive nitrogen balance of + 8.47 and + 6.2 was found on the northern and southern slopes.

The results of a study on the content of potassium and calcium in plants of the Middle Mountain province of Dagestan are presented. The content of macroelements was determined on «Savant AA Σ» atomic absorption spectrometer. The K content in plants varied from 0.16 to 3.21%, Ca - from 0.02 to 3.47%. The content of mobile forms of elements on the northern slope is slightly higher than on the southern (1.2 times). The coefficient of biogeochemical mobility K ranges from 5 to 100.3, Bx Ca – from 1.2 to 204.1. On the southern slope, K and Ca are most actively absorbed from the herb-cereal phytocenoses Plantago media, Plantago lanceolata, Lotus corniculatus, Trifolium medium, Inula britannica, Achillea millefolium, Psephellus daghestanicus, Galium verum, Astragalus onobrychioides, Medicago glutinosa. On the northern slope, K, Ca Astrantia biebersteinii, Inula germanica, Trifolium campestre, Vicia truncatula, Vicia cracca, Betonica macrantha, Origanum vulgare, and Betonica orientalis accumulate most actively. The least accumulation of K and Ca is observed in plants of the Poaceae family. The difference in the content of K and Ca in plants depends on the content of mobile forms of elements in the soil, biological characteristics of plants, and environmental factors.