Effects of litter on seedling establishment: an indoor experiment with short-lived Brassicaceae species

Recruitment by seeds is essential both in vegetation dynamics and in supporting biodiversity in grasslands. The recruitment by seeds is feasible in suitable vegetation gaps from the seed rain and/or by establishment from persistent soil seed banks. Cessation of grassland management results in litter accumulation, which leads to the decline of species diversity by the decreased availability of open patches. Low amounts of litter is often beneficial, while high amounts of litter is detrimental for seed germination and seedling establishment of short-lived species. In a designed indoor experiment, we explored the effect of litter on seedling establishment by germinating six short-lived Brassicaceae species with both increasing seed mass and litter cover. We found that both seed mass and litter had significant effect on germination and establishment of the sown species. Small-seeded species were significantly negatively affected by the 300 and/or 600 g/m(2) litter layers. No negative litter effect was detected for species with high seed masses (Lepidium spp.). No overall significant positive litter effect was found, although for most of the species cumulative seedling numbers were not the highest at the bare soil pots. Our results suggest that the negative effects of litter are less feasible on the large-seeded short-lived species than on that of small-seeded ones.