Differential effects of several “litter” types on the germination of dry grassland species

Question: Accumulation of litter can have serious implications on the recruitment of plant species, by modifying the physical, biological and chemical features of the microenvironment or acting as a mechanical barrier for seeds and seedlings. Isolating these different effects has rarely been achieved experimentally. Location: Transylvanian Lowland, Romania. Methods: We tested the effects of different "litter" types on the germination of dry grassland species using a controlled pot experiment with three natural litter types, differing in decay state and composition (Stipa pulcherrima fresh leaves, partly decomposed leaves and mixed and partly decomposed plant material) and an artificial plastic litter, with two levels of water addition. As a complementary field study, seed sowing was conducted in grassland plots with litter removal and plastic litter application. Results: Litter effects were mainly positive (intermittent watering) or neutral (frequent watering) under controlled experimental conditions, and mostly negative in the field. Seed size and environmental conditions were the major determinants of litter effects on germination. Significant differences were found in the effect of litter type on germination, much of which could be explained by chemical factors determined by the decay state, as we confirmed a higher concentration of allelopathic compounds in fresh S. pulcherrima litter than in the senescing leaf litter. Conclusions: The effects of litter on seed germination are strongly context dependent, and it is hard to define common rules that apply consistently under various environmental conditions. "Litter" identity and quality matter, i.e. the litter composition and decay state, and influence seed germination.