Quantal Response of Fruit and Seed Germination Rate inQuercus roburL. andCastanea sativaMill, to Constant Temperatures and Photon Dose

Abstract

A linear relationship between constant temperatures in the sub-optimal temperature range and germination rate is shown in both Quercus robur L and Castanea sativa Mill germinated under nominal dark conditions. The mean base temperature was interpolated for Q robur as 0 8 ° or 2-4 °, depending on seed lot provenance, and for C. sativa as 1 -4° The optimum temperature for germination in Q. robur was about 20° compared with around 28 ° in C. sativa Over the sub-optimal temperature range the distribution of thermal times was log-normal for each population studied their spread varying both between Q robur seed lots and between species However, in C. sativa germinated close to the mean base temperature, the distribution in thermal times was reduced Thermal times to germination were decreased in Q. robur and C sativa by approximately 0 3 and 0-5 log-units, respectively, when the pericarp was removed, i.e in the seeds, but the sensitivity of the response remained relatively unaltered In both species the germination rate was the same when nominal dark or safe green light conditions were employed during the germination test. However, at 21 ° Q robur exhibited the high irradiance reaction (HIR) at photon doses above 30mmol m−2 d−1. HIR first affected the germination rate by an inhibition of radicle extension The sensitivity of the response to thermal time was reduced as photon dose increased. This photo-inhibition was exacerbated at supra-optimal temperatures. In contrast, C. sativa germination rate at 26 ° was little influenced by light at a photon dose of 752 mmol m−2 d−1