Abstract
Freshwater and marine sediments often harbor reservoirs of plant diaspores, from which germination and establishment may occur whenever the sediment falls dry. Therewith, they form valuable records of historical inter- and intraspecific diversity, and are increasingly exploited to facilitate diversity establishment in new or restored nature areas. Yet, while ferns may constitute a considerable part of a vegetation’s diversity and sediments are known to contain fern spores, little is known about their longevity, which may suffer from inundation and - in sea bottoms - salt stress. We tested the potential of ferns to establish from a sea or lake bottom, using experimental studies on spore survival and gametophyte formation, as well as a spore bank analysis on sediments from a former Dutch inland sea. Our experimental results revealed clear differences among species. For Asplenium scolopendrium and Gymnocarpium dryopteris, spore germination was not affected by inundated storage alone, but decreased with rising salt concentrations. In contrast, for Asplenium trichomanes subsp. quadrivalens germination decreased following inundation, but not in response to salt. Germination rates decreased with time of storage in saline water. Smaller and less viable gametophytes were produced when saline storage lasted for a year. Effects on germination and gametophyte development clearly differed among genotypes of A. scolopendrium. Spore bank analyses detected no viable spores in marine sediment layers. Only two very small gametophytes (identified as Thelypteris palustris via DNA barcoding) emerged from freshwater sediments. Both died before maturation. We conclude that marine, and likely even freshwater sediments, will generally be of little value for long-term storage of fern diversity. The development of any fern vegetation on a former sea floor will depend heavily on the deposition of spores onto the drained land by natural or artificial means of dispersal.
Highlights
As large parts of the earth surface consists of freshwater or sea water, plant diaspores regularly end up in the water
Apart from a spore bank experiment based on sediment cores from the bottom of the IJsselmeer, we collected spores from three species occurring in the Dutch IJsselmeer polders, to be used in two different storage experiments: Asplenium trichomanes ssp. quadrivalens, Asplenium scolopendrium and Gymnocarpium dryopteris
When drystored spores were compared to spores stored in tap water without additional NaCl (Table 1), no effect on germination or gametophyte growth was observed for A. scolopendrium
Summary
As large parts of the earth surface consists of freshwater or sea water, plant diaspores regularly end up in the water. [1]), eventually most will sink to the bottom, where they will end up in the river, lake or sea bottom sediment. These sediments may contain a reservoir of viable diaspores, from which species may germinate and establish whenever the sediment falls dry. In this way, sediments can play an important role in the local maintenance of biodiversity. The diaspore bank may accumulate diaspores of new or locally rare species and allow them to establish when a dry lake or river bed is (re)vegetated The diaspore bank may accumulate diaspores of new or locally rare species and allow them to establish when a dry lake or river bed is (re)vegetated (e.g. [8])
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