Soil effects of six different two-species litter mixtures that include Ulmus pumila

The tree species that contribute to decomposed leaf litter can have important effects on soil properties and thus nutrient cycling and interactions between tree species. We examined ground leaf litter and soil mixtures consisting of leaves from Ulmus pumila (Up) combined individually with leaves from one of six other species: Betula platyphylla (Bp), Quercus liaotungensis (Ql), Salix matsudana (Sm), Hippophae rhamnoides (Hr), Caragana microphylla (Cm), and Amorpha fruticosa (Af). The soil–litter mixtures were incubated for 120 days to analyse the effects of their decomposition on soil properties and to determine the interactions between the different types of litter within each mixture. The decomposed litter mixtures were composed of Up combined with Sm- or Hr-improved soil fertility relative to the pure Up mixture, but the decomposed litter mixtures were composed of Up combined with Cm-, Af-, or Ql-diminished soil properties. Three leaf mixture treatments, namely Up?×?Bp, Up?×?Sm, and Up?×?Hr, exhibited synergistic effects on soil properties (i.e. soil properties exceeding the predicted values); however, three other treatments, namely Up?×?Ql, Up?×?Cm, and Up?×?Af, exhibited antagonistic effects (i.e. properties below the predicted values). Therefore, litter from Bp, Sm, or Hr should be mixed with Up to improve soil fertility and production in plantations.