Biotic and abiotic factors affect soil seed bank of cacti in the Caatinga, a Seasonally Dry Tropical Forest

Cacti produce fleshy fruits with seeds surrounded by a funicular pulp that are dispersed by animals that use this pulp as a food source. The aim of the present study was to investigate whether Brazilian cacti form seed banks in the soil and whether the permanence of funicular pulp and the place where seeds are deposited by dispersers affect seed longevity of eight species of two subfamilies of Cactaceae. We buried seeds with and without funicular pulp in open sites and under the canopy of the perennial tree Sarcomphalus joazeiro (Rhamnaceae) in the Caatinga, a Seasonally Dry Tropical Forest. We calculated germinative parameters at 0, 6, 12 and 24 months. We found three different responses regarding seed longevity. Species of the Cactoideae subfamily showed a significant reduction in seed germination over time and in open sites and the funicular pulp had no influence, except in Pilosocereus and Xiquexique species. We also found a significant reduction in the germinability of species from these two genera over time in open sites and germination was further reduced when we buried the seeds with funicular pulp. However, for Tacinga species, germination was not influenced by the funicular pulp and increased over time, mainly in open sites. We conclude that cacti can form soil seed banks in the Caatinga, and the presence of dispersers is essential, as the longevity of the seeds of some Cactaceae species is impaired by the presence of funicular pulp on the seeds.