Influence of soil fauna and habitat patchiness on plant (Betula pendula) growth and carbon dynamics in a microcosm experiment

We tested (1) how the presence of a diverse soil faunal community affects e cosystem carbon balance and (2) whether habitat patchiness modifies the inf luence of soil fauna on plant growth and carbon dynamics. We constructed cy lindrical microcosms that contained coniferous forest humus and different l itter materials either mixed or in separate patches, and in the presence or absence of diverse soil mesofauna. A birch seedling was planted in the cen tre of each microcosm. The experiment continued for two growing periods dur ing which net carbon assimilation was measured continuously. At the end of the experiment, the microcosms were destructively sampled for plant biomass , soil fauna, and soil physical and chemical properties. All systems, indep endently of treatment, were net CO2 producers in the beginning. In the pres ence of a diverse fauna, the plant growth was drastically increased, and th e mixed-litter systems respired more than the patchy ones. During the secon d season, the patch effect disappeared, while the birch seedlings and mosse s continued to grow better in the microcosms with diverse fauna. In the lon g term, patchiness did not modify the effect of fauna on plant growth or ca rbon balance. By the end of the experiment, the carbon balance approached z ero in the refaunated microcosms, while it remained negative in the "simple " systems. The weak impact of patchiness in comparison to the faunal effect may be due to a homogenising role of plant roots and progressive decay of the substrates.