Seasonal and spatial variance of seed bank species composition in an oligotrophic wet meadow

Abstract

Seasonal and small-scale spatial variation of the seed bank in an oligotrophic wet meadow ( Molinion) was assessed by two methods: (1) direct determination of seeds extracted from soil samples (6 cm in diameter, 10 cm depth) and (2) germination of seeds according to Ter Heerdt et al. [1996. An improved method for seed bank analysis: seedling emergence after removing the soil by sieving. Funct. Ecol. 10, 144–151]. Samples were taken three times during the year (July and November 2001, March 2002) from three distinct microhabitats (moss layer, gaps, Molinia caerulea tussocks). Using the extraction method, more seeds were found in the upper 0–3 cm soil layer than in the deeper 3–7 cm layer, significant differences in the number of seeds were found among microhabitats (with the lowest seed bank densities in Molinia tussocks). The highest number of seeds was found in the spring census, but the test was not significant ( P<0.10). However, seasonal variation was found when damaged seeds were included in the analysis. Changes in damaged/undamaged and light/heavy seed ratios, and in numbers of grass/herbs/sedges seeds are also discussed. The spatial distribution of seeds is probably influenced to a great degree by abiotic factors, such as microtopography (round and heavy seeds of sedges prevail in gaps and in deeper soil layers). The species composition of the seed bank varied among microhabitats, depth, and throughout the year. No differences were found by the seed germination method.