SOIL CONDITION ON THE BORDER OF NATURAL HABITAT OF ENGLISH AOK IN SOUTHERN FOREST-STEPPE (EUROPEAN PART OF RUSSIA)

Abstract

Introduction. The topicality of the problem is determined with significant reduction of the area of oak groves in Europe and the necessity to study in detail the limits of adaptation of English oak to the unfavourable factors of environment, in whole, and soil conditions, in particular. Oak groves of water-parting of southern forest-steppe are of particular interest. Such oak groves grow on the border of English oak habitat and are adapted to soil salination. The goal of the research is to reveal the indices of the state of the soil, determining English oak development and preventing from growing the trees in the south of forest-steppe zone. Objects and methods. The object of research is located in Tellermanovskoe division of forestry of  the Institute of Forest Science, RAS. One cut and three pores were made in the upper part of water-parting under a 80-year old stand of English oak (I quality class),established with  sowing of acorns of late phenological form. Two cuts and eight pores made the catena, which was going through the oak stand of IV and V quality class, under shrub-like oaks and on the  meadow with grassland vegetation. In soil-water extract (1:5), the content of Ca²⁺ and Mg²⁺ was determined with trilonometry, Na⁺ – by flame-photometric method, Cl^- – by titrimetric method, sulfates (SO₄^2-) – by the method of Kamorovskiy, С and N – on the analyzer of elemental composition, active forms of potassium and phosphorus (available for the plants) – by the method of Machigin. Results. The soils in the studied ecotopes were significantly different in content of highly soluble salts which may be explained with the influence of groundwater reservoirs and with their drawing from underlying  layer caused by  consumption of soil water by plants. In the catena  in the part from oak grove of V quality class to the middle of the meadow taper, НСО₃^- and СО₃^2- ionic concentration is observed. Gray forest soil of upland were described with high content of  С and N, and medium and low content of К and Р. The soils of catena under forest and  grassland vegetation were significantly different with the indices of fertility and soils of water-parting. Conclusion. Sodium-carbonate salinization of soils is the major factor, limiting dispersion of oaks in the studied ecosystems. Extreme concentration of carbonate - and bicarbonate ions is about 2 mmol /100 g of soil. Thickness of soil layer, free from ions with such concentration in the studied ecosystems, is about 100-130 сm. High concentration of sulfates in the soil (up to 21 mmol/100 g), influencing physiological drought and worsening water status of plants, does not stop dispersion of English oak in the studied area. Very low content of potassium and phosphorus is one of the factors to decline the state of trees in the studied salinized ecosystems. Low content of nitrogen in the soil contributes to  decrease of phytomass of English oak.