The involvement of environmental factors in dormancy cycling is well known in temperate annual species, but it is not known how interaction between soil temperatures and humidity can modulate dormancy in perennial tropical species. In this study the effects were evaluated of substrate temperature and humidity on the modulation of the acquisition and overcoming of secondary dormancy in the buried seeds of two endemic Eriocaulaceae species from the rocky fields (campos rupestres) vegetation in south-eastern Brazil. Fresh seeds of Comanthera bisulcata and Syngonanthus verticillatus were buried and subsequently maintained at temperatures of 15, 20, 25 and 30°C, under three substrate humidity levels (boggy, humid and humid/dry). The seeds were exhumed every 3 months and tested for germination (20°C, 12 h photoperiod) and viability (tetrazolium test). The seeds of both species acquired dormancy after burial in all of the treatments. During the experimental period they demonstrated cycles of acquisition and overcoming of dormancy that were most evident in the treatments involving alterations of the substrate humidity (humid/dry regime) that coincided with the environmental conditions found naturally in the region of origin of the species. The seeds gradually lost dormancy during the dry period and re-acquired it when exposed again to humidity; dormancy would once again be overcome during the subsequent dry period. Burial promoted the acquisition of dormancy in C. bisulcata and S. verticillatus seeds; the lowest temperature tested favoured overcoming dormancy; and varying the humidity regime signalled the acquisition and the overcoming of secondary dormancy.

Seeds can synchronize their germination and dormancy cycles to regular seasonal environmental changes. The present work sought to evaluate the in-situ longevity of the buried seeds of two species of Syngonanthus and two species of Comanthera (Eriocaulaceae) in the region of natural occurrence (Serra do Cipó Range, south-eastern Brazil), and to relate their germination responses to seasonal climatic changes. Samples were exhumed bimonthly and germination was tested under a 12-h photoperiod (30 μmol m− 2s− 1) at optimal germination temperature. The seeds of Comanthera showed high deterioration after the first year of burial, especially C. elegans, which reflects their incapacity to form viable soil seed banks. The buried seeds of C. bisulcata, S. anthemidiflorus and S. verticillatus acquired secondary dormancy during the rainy season (spring/summer, higher temperatures) which was alleviated during the subsequent dry season (autumn/winter, lower temperatures). It is concluded that C. bisulcata, S. anthemidiflorus, and S. verticillatus form seed banks of the persistent type and demonstrate consecutive cycles of germination/dormancy, accompanying annual seasonal changes for at least 2 years.