Biologia 64/3: 585—588, 2009 Section Botany DOI: 10.2478/s11756-009-0081-z Effect of alginite amendment on microbial activity and soil water content in forest soils Erika G¨ om¨ oryová, Dionýz Vass, Viliam Pichler & Dušan G¨ om¨ ory Technical University in Zvolen, Faculty of Forestry, T.G. Masaryka 24, SK-96053 Zvolen, Slovakia; e-mail: egomory@vsld.tuzvo.sk Abstract: The effect of the amendment with alginite, an organic rock originating from the biomass of fossilized unicellular algae, on microbial activity of forest soils was tested using a pot experiment. Five variants of soil-alginite mixtures were tested in three replicates with two forest soils: a loose sandy soil and a sandy loam. Gravimetric moisture closely correlated with the dose of alginite in both soils. Basal respiration and catalase activity increased with the dose of alginite in the sandy soil, but not in the sandy loam, where the highest response was observed at intermediate doses of alginite. The correlations of microbial activity parameters with moisture in the sandy soil were also much closer than in the sandy loam. The amendment with alginite was thus effective in improving some of the selected microbial activity indicators, but the optimum dose of alginite strongly depends on soil texture. Key words: alginite; soil moisture; soil respiration; soil enzyme activity Introduction Climate scenarios for Slovakia predict an increase of the duration of drought periods. Unfavourable changes in soil water content leading to physiological weakness of forest stands could potentially occur at lower elevations, especially on soils with low water-holding capacity, in the near future (Střelcová et al. 1997; Škvarenina et al. 2004). The amendment of organic or inorganic material to topsoil is considered a way to improve physical proper- ties of soil. Such materials affect the living space of soil microorganisms and thus also their activity (Dlapa et al. 2004; Fernandez et al. 2007; Ismail & Ozawa 2007). Alginite is a sedimentary laminated rock – an oil shale (Jámbor & Solti 1975), which originated in basalt maar lakes. Dark laminae are rich in amorphous organic mat- ter and well preserved cells of green alga Botryococcus braunii. The grey laminae are composed of clay miner- als derived from weathered basaltic tuff. In addition to organic matter, the rock contains considerable amounts of macronutrients such as P, K, Ca and Mg, as well as numerous trace elements. The content of heavy metals lies below toxicity limits. A large specific surface area ranging from 300 to 650 m 2 g -1 results in a water re- tention capacity of approx. 110% (Russell 1990; Vass et al. 1997; Kulich et al. 2001). Tests of alginite from the deposits in Pula and Gerce (Hungary) showed that it can be used in agriculture and forestry to improve soil quality, soil water dynamics and nutrient content, to increase organic matter content, colloid content and to protect soil against acidification, desiccation and leak- age of nutrients (Vass et al. 2003). No negative side effects for the environment have been observed (Kulich et al. 2001). Soil microorganisms are the key agents in decom- position and mineralization of dead organic materials and in the soil nutrient balance. Because of their quick response to changes and adaptation to environmental conditions, they are often used as indicators of soil quality and soil health. Compared to higher organisms, microorganisms have a high surface-to-volume ratio, which means they are capable of a much more intense exchange of matter and energy with their environment. Therefore, soil microbiota are able to respond quickly to environmental stress. Changes in size, composition and activity of microbial communities can frequently be ob- served before detectable changes in soil physical and chemical properties occur (Nielsen & Winding 2002). The aim of this study is to assess whether the in- fluence of alginite amendment improves water retention capacity and microbial activity of soils and to what ex- tent an eventual improvement depends on soil texture. Material and methods A completely randomized container experiment was estab- lished in the facilities of the Faculty of Forestry of the Tech- nical University in Zvolen on August 4, 2004. Five soil- alginite mixtures (2 kg) with different contents of alginite originating from the deposit in Pula (Hungary) were pre- pared (0, 125, 250, 500 and 1000 g of alginite representing 0, 6.25, 12.5, 25 and 50% w/w alginite content in the mix- ture, respectively) and put into 2 L plastic pots (ø 20 cm × 15.5 cm). Prior to amendment, alginite was crushed, to c 2009 Institute of Botany, Slovak Academy of Sciences