Effect of Canopy Openness and Soil Depth on the Persistent Spore Bank of Cloud Forest Ferns

Spore banks can facilitate germination and establishment of gametophytes at any ecologically appropriate time and promote the persistence and coexistence of fern species. However, previous studies of fern spore banks have either failed to assess their viability or found that they persist less than six months. Therefore, the ability of tropical ferns to form persistent spore banks with a viability of over one year is unknown. Using recently collected spores of six species of terrestrial ferns from a Mexican cloud forest, we evaluated the effect of storage (in situ in forest soil and ex situ in vials under refrigeration at 5°C), canopy openness (open and closed forest), soil depth (0 and 10 cm), and time (3, 6, and 15 months) on spore germination. Spore germination of all species ranged between 33% and 77% after 15 months of burial in the soil. Except for the invasive fern Macrothelypteris torresiana, spore germination of stored samples in situ was higher than laboratory samples under refrigeration. Spore germination of Cyathea divergens, M. torresiana, and Lophosoria quadripinnata deposited at 10 cm soil depth was higher in the open, while those of Cyathea bicrenata and Parablechnum schiedeanum in the closed and those of Austroblechnum wardiae were unaffected by canopy openness. Spores deposited at 10 cm depth of three species for which enough were obtained had higher germination than those deposited on the soil surface. This work provides the first evidence of the existence of a persistent spore bank in tropical ferns.