Trophic selectivity of litter saprophages (Diplopoda, Isopoda) in natural forests in the steppe conditions

The forest litter serves as a bridge between the above ground forest flora and fauna with the soil. Trophic activity of soil invertebrates affects the decomposition processes of plant organic residues and, thus, on the forest soils fertility. It is a natural mechanism that positively influences on maintenance and improvement of natural soils properties. The object of this study is the representatives of Diplopoda Rossiulus kessleri (Lohmander, 1927) and Isopoda Porcellio scaber (Latreille, 1804). The aim of the paper is to qualify the trophic preferences of the saprophages, as soil invertebrate representatives, of natural forest ecosystems in conditions of the steppe zone of Ukraine. To identify the ecological role of millipedes and woodlice as primary destructors of leaf litter, we made a field experiment studying their trophic preferences with the use of microcosms. Microcosms (containers) were filled with soil free from invertebrates; after it added a certain mixture of leaf litter and saprophages representatives. To analyze the decomposition rate of leaf litter the percentage of consumed litter was determined by calculating air-dry mass of leaf litter in the beginning and at the end of experiment. A regression model that reflects the trophic selectivity of saprophages for the following mixture components of such tree species as the common maple (Acer campestre (L.), little-leaved linden (Tilia cordata (Mill.), common oak (Quercus robur (L.), European white elm (Ulmus laevis (Pall.), European ash (Fraxinus excelsior (L.) is proposed. Among other regression model types (linear, quadratic, special cubic), permissible statistical estimates revealed a special cubic mathematical model and it allowed to conclude on the saprophages trophic selectivity. The special cubic regression model has a relatively high performance (the determination coefficient is 87.5 %) and adequately approximates empirical data with a significance level of less than 0.05. It was found out that common maple and European white elm litter is consumed in a greater quantity than any other litter from suggested. It is confirmed by their main effects coefficients in the regression equation. Thus, the saprophages trophic selectivity  persistence in natural forests under the conditions of the steppe zone has been proved. Consequently, the saprophages trophic activity increases with the presence of the maple and European white elm in natural forests, which makes expedient the use of these tree species, in the design of forest stands.