The Vertical Distributions of Live and Dead Fern Spores in the Soil of a Semi-Natural Woodland in Southeast Scotland and Their Implications for Spore Movement in the Formation of Soil Spore Banks

Abstract

The changes with depth in frequency and species composition of fern spores in soil were determined for two sites within semi-natural deciduous woodland on acid soil in a fern-rich ravine in southeast Scotland. The total fern spore count (TFSC) was determined by standard palynological techniques for the extraction, quantification and identification of spores in soil. The live fern spore bank (LFSB) was determined by culturing soil samples and its relative size was estimated from the number of gametophytes developed on the surface. At both sites, live spores were found down to the maximum depth sampled (50 cm and 80 cm). At Site 1, both the TFSC and the LFSB declined with depth. At Site 2, on the steep bank of a stream, both showed an initial decrease followed by an increase towards the bottom of the profile, possibly the result of accumulation above a less permeable layer or of the burial of a previous soil surface. The species lists for the TFSC and LFSB coincide with those for the plants currently growing in the surrounding area but the large excess of Athyrium spores in the TFSC is not reflected in the LFSB or the sporophyte population. The evidence indicates that most spores move very slowly through the soil matrix but a minority is carried more rapidly by water down open channels to considerable depths, within the lifespan of the spore. If, as the total numbers of spores in the soil suggest, spores have been accumulating for several hundred years at these sites, the TFSC profile provides a stratified historical record of past floras at the site. The large excess of Athyrium spores in the TFSC at both sites would then indicate that, until recently, Athyrium filix-femina was the most abundant species. This is the first palynological study of fern spores in soil in which the live and thus most recently deposited spores have been separately identified and their movement followed.