Tužinský, L., Bublinec, E., Tužinský, M., 2017. Development of soil water regime under spruce stands. Folia Oecologica, 44: 46-53.The aim of this paper is to analyse the water regime of soils under spruce ecosystems in relation to long-lasting humid and drought periods in the growing seasons 1991-2013. The dominant interval humidity in observing growing seasons is semiuvidic interval with soil moisture between hydro-limits maximal capillary capacity (MCC) and point of diminished availability (PDA). Gravitationally seepage concentrated from accumulated winter season, water from melting snow and existing atmospheric precipitation occurs in the soil only at the beginning of the growing season. The supplies of soil water are significantly decreasing in the warm climate and precipitant deficient days. The greatest danger from drought threatens Norway spruce during the summer months and it depends on the duration of dry days, water supply at the beginning of the dry days, air temperature and the intensity of evapotranspiration. In the surface layers of the soil, with the maximum occurrence of active roots, the water in semiarid interval area between hydro-limits PDA and wilting point (WP) decreases during the summer months. In the culminating phase occurs the drying to moisture state with capillary stationary and the insufficient supply of available water for the plants. Physiological weakening of Norway spruce caused by set of outlay components of the water balance is partially reduced by delivering of water by capillary action from deeper horizons. In extremely dry periods, soil moisture is decreasing also throughout the soil profile (0-100 cm) into the bottom third of the variation margin hydro-limits MCC-PDA in the category of capillary less moving and for plants of low supply of usable water (60-90 mm). The issue of deteriorated health state of spruce ecosystems is considered to be actual. Changes and developments of hydropedological conditions which interfere the mountain forests represent the increasing danger of the drought for the spruce.
Mountain forests are among the main components of natural environment in Slovakia. They grow mainly in areas with cold climate, on poor soils with unfavorable reaction, often very acidic (pH in H<sub>2</sub>O < 4.5) and with nutrient deficit. Immissions and acid rain attack forests to a great extent. Global climate changes also represent a new threat. Extremes in air temperatures, excessive amounts of precipitation or on the other hand the lack of water from precipitation, torrential rains or long-lasting drought periods are recorded as a result of a higher amount of heat energy accumulation from the greenhouse effect. Spruce forests are most endangered. Spruce with its root system concentrated in the upper soil layers, where also the highest amount of toxic elements accumulates, suffers more and more from dry and warm periods and it begins to wither due to drought. The occurrence of hydropedological cycles with a low or insufficient supply of available water in the soil is most frequent during summer (July, August). If the soil water potential values approach the value of the wilting point, an expressive decrease in transpiration is observed during the day, whereas its daily course is also suppressed. Gradual soil drying up from the upper layers towards the deepest ones of the physiological profile of soil represents a change in soil moisture stratification, especially after moistening the upper layers of soil with water from atmospheric precipitation. The deeper soil layers need not be re-saturated in such a case. Under drought the whole physiological profile of soil dries up in a relatively short time. Trees are exposed to a strong physiological stress in such conditions and after longlasting drought periods they can get into the state of total exhaustion.
ABSTRACT:The paper describes the regime and dynamics of the soil moisture content of sandy soils in Záhorská lowland during different growing seasons. Research plots are situated near Kamenný mlyn, approximately 3 km from Plavecký Štvrtok and 8 km southward from the town of Malacky. Changes in the soil moisture content are described by soil moisture constants (MCC, PDA, WP) and its relation to atmospheric precipitation and to the character of undergrowth is shown. The low water-holding capacity of sandy soils and their high drainage together with dense root system do not allow the sufficient saturation of soil during the growing season. The low wilting point value (2%) leads to the consumption of all available water in the soil. The most frequent is the semiarid interval of soil moisture (PDA -WP) with reduced availability of water to plants (> pF 3.1). The arid interval (< WP) occurrence on hot summer days results in a decrease in transpiration and assimilation intensity of plants, their physiological weakening and premature fall of assimilation organs.
The paper presents the research results of soil water regime under the spruce stand in the Upper Orava, in Oravská Polhora - Borsučie in the growing seasons of 2012 and 2013. There are characterized different ranges of soil moisture, soil water categories and its accessibility for plants, particularly for the surface layer from 20 cm to 100 cm deep physiological soil profile. Dominant interval of moisture during the growing season is the semiuvidic interval with the soil moisture between hydrolimits MCC and PDA. Amount of water presents mostly capillary less moving water, in the surface layer of soil sufficient, for short time insufficient supply of usable water. The amount of water decreseases for a short time after dry days. Semiaridic interval with the soil moisture between hydrolimits PDA and WP, up to the upper third of the variation range means that the vegetation has available stationary capillary water in the surface layer. In prolonged dry season such humidity condition can be one of the main causes of physiological weakening of spruce.
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