Interrelations between respiration and dormancy in buds of three hardwood species with different chilling requirements for dormancy release

Respiration in vegetative buds of mature Betula pendula, Alnus glutinosa and Prunus padus trees was measured monthly at 15°C from mid-October 1996 to natural outdoor budburst in April 1997. In B. pendula the effect of bud water content on respiration was also estimated (December–April) by artificial imbibition of buds for 24 h prior to measurement of respiration. For estimation of corresponding bud dormancy status, batches of twigs were forced at identical monthly intervals at 15°C in long days (24 h), and budburst recorded. In all species dormancy was deepest when the leaves were shed in October, and dormancy was first alleviated in P. padus followed by B. pendula and A. glutinosa. However, bud respiration capacity was not related to dormancy release as it decreased in all species from October to November and displayed no notable increase until February in P. padus, March in B. pendula and April in A. glutinosa, after completion of dormancy release. Rather, increase in respiration coincided with growth resumption prior to budburst. Artificial imbibition of B. pendula buds increased the water content by approximately 10% (FW) and induced a doubling of the respiration rate (December–February). Moreover, the seasonal variation in bud water content (October–April) explained 94% of the variation in respiration in B. pendula and P. padus, and 84% in A. glutinosa. These observations suggest an important role of water content for respiration. During a cold period from mid-December to mid-January with mean temperature of –9.7°C dormancy release was arrested in P. padus, and to some degree in A. glutinosa, whereas dormancy release progressed normally in B. pendula. This indicates species differences in lower critical temperatures for dormancy release.