Effect of a dense Allium ursinum (L.) ground cover on nutrient dynamics and mesofauna of a Fagus sylvatica (L.) woodland

The aboveground biomass built up annually by Allium ursinum (L.) contains similar amounts of nutrients as the foliage of mature Fagus sylvatica (L.) stands. The decomposition of the A. ursinum stand in early summer provides N rich forage for grazing mesofauna, especially favouring collembolans and accelerating mineralization of soil organic matter. Short term decreases of soil pH had no negative effect on populations of collembolans. Synergistic effects from soil fauna and microbes may accelerate nitrogen release from decomposing leaf litter. A positive feed back may have emerged. High animal abundance and diverse mesofauna populations are capable of high rates of litter fragmentation. Consequently, favourable conditions for microorganisms are created and allow high rates of mineralization and release of nutrients. Our data show that substantial amounts of nitrogen are lost from the system. Undisturbed forest ecosystems are considered to recycle mineralized nitrogen efficiently though. But temporal uncoupling of the N cycle due to microbial activity and delayed or decreased N uptake of higher plants can cause enhanced leaching even from undisturbed systems. The tendency to loose nutrients is apparent from high nitrate concentrations in the soil solution throughout the year. When nutrient losses from A. ursinum subsystems are considered, lateral nutrient imports from adjacent parts of the ecosystem have to be taken into account. If lateral import does not counterbalance losses, maintenance of the soil nutrient status must occur by weathering or a decline is to be expected.