The Role of Photoperiodism in Alpine Plant Development
Franziska Keller, Christian Körner
Is alpine plant development in spring controlled by photoperiod irrespective of actual temperatures at the time following snowmelt? We investigated phenological responses to day length and temperature in 33 high-elevation species of the Central Alps (2600-3200 m a.s.l.), Austria. Plants were collected in the field in August, potted, and overwintered in a freezer at -1°C. Released from dormancy, plants experienced various photoperiods (12, 14.5, 15, and 16 h) and two temperature regimes (6/11°C and 8/18°C). Day length was extended with tungsten lamps, which do not contribute a significant dose of photosynthetically active photon flux density but provide a day-length signal. Only 23 species produced sufficient flowers to be included in the analysis. Flowering (yes or no) was sensitive to photoperiod in 54% of the species. Surprisingly, only 24% of the species showed temperature sensitivity at longer photoperiods, whereas at shorter photoperiods, 65% of the species were sensitive to an increase in temperature. The number of days between thawing of soil and flowering is sensitive to photoperiod in 46% of the species. Cerastium uniflorum, Elyna myosuroides, Saxifraga oppositifolia, Saxifraga seguieri, and Ranunculus glacialis are insensitive to both photoperiod and temperature and thus flower as soon as released from the snow irrespective of co-occurring light and temperature conditions. Specific leaf area and the duration of leafing were responsive to photoperiod and temperature in forbs but not in grasses. These results suggest that about half of the tested alpine species are sensitive to photoperiod and may not be able to fully utilize periods of earlier snowmelt.