Photosynthetic responses to temperature-mediated dormancy induction in contrasting ecotypes of red-osier dogwood (Cornus sericea L.)

Dormancy development in plants is synchronized with the cessation of environmental conditions that favour plant growth. The timing of this response is important in trees for growth and survival. Woody plants, such as dogwood (Cornus sericea L.) have evolved different ecotypes that are closely adapted to local climatic conditions, which are differentiated by irradiance, photoperiod and/or temperature. While short photoperiods are well known to play a key role in dormancy induction in northern ecotypes, low temperatures alone can by-pass the photoperiodic requirement. It is well established that the combination of low temperature and even low to moderate light intensities predispose plants to photoinhibition of photosynthesis. However, plants possess numerous photoprotective mechanisms to minimize photoinhibition including increased rates of photosynthesis as well as non-photochemical dissipation of excess excitation energy, a process involving xanthophyll cycle carotenoids. We used two ecotypes of dogwood, the northern ecotype of Northwest Territories (NWT 62° N latitude) and the southern Utah, U.S.A. (42° N latitude) ecotype, which exhibit differential responses to photoperiodic- and temperature-induced dormancy. These ecotypes were exposed to various combinations of photoperiod and low temperature treatments and monitored for photosynthetic and photoprotective processes as the plants entered dormancy. Our results demonstrate differential long- and short-term responses to photoinhibition at low temperatures between the two ecotypes. The northern ecotype was more tolerant to photoinhibition of photosynthesis than the southern ecotype potentially through a zeaxanthin-independent mechanism of photoprotection. Furthermore, anthocyanin accumulation may be involved in the LD-Cold treatment through putative sugar sensing mechanisms to trigger dormancy.