Effect of light and temperature on germination of spores of four tropical fern species

The effects of light and temperature (constant and fluctuating) on fern spore germination in Tectaria heracleifolia, Tectaria incisa, Tectaria mexicana, and Tectaria transiens were studied using plastic filters or filters made from leaves, both of which reduced the red:far red ratio (R:FR) and photon flux density (PFD) in different magnitudes. Under filters, the PFD was constant during a 12 h photoperiod or increased at noon, as takes place in forest gaps. To evaluate spore sensitivity to light quality, non-pre-imbibed and pre-imbibed spores were studied. The results for all studied species were (a) germination did not occur at any temperature under plastic far red filters or in darkness, (b) independent of the light condition, germination did not occur or was greatly reduced with fluctuating temperature (20–30 °C), (c) at constant temperature (25 °C), germination was high (>70%) under white light conditions, (d) under light filtered by leaves, germination was high when the PFD was higher at noon, (e) pre-imbibition increased spore sensitivity to light filtered by leaves, and (f) germination was correlated with PFD, independent of the light quality under the filters, which suggests that PFD in combination to light quality is an important signal for spore germination. Thus, the small gaps found in the forest canopy could play an important role in the germination and establishment of fern gametophytes.