Maintenance respiration correlates with sugar but not nitrogen concentration in dormant plants

The range and source of variation in foliage respiration rate in the dormant season were investigated for plants of Lycopodium annotinum L,, Pinus contorta Dougl, var. latifolia Engelm,, Picea abies (L,) Karst,, Andromeda polifolia L,, Calluna vulgaris (L,) Hull, Vaccinium myrtillus L,, Vaccinium vitis-ideae L, and Empetrum hermaphroditum Hagerup. Field-grown plants were transferred to a cold room kept at 5 degrees C in late autumn and then analysed for the foliage respiration rate in relation to nitrogen and sugar concentration over a period of many weeks. Respiration rate varied 1.6-fold among species at a given time, and decreased with time as long as plants remained dormant. Most of both sources of variation were accounted for by the same linear and positive correlation with total soluble sugar concentration, whereas no relationship with nitrogen concentration was found. The hypothesis presented is that respiration rate correlates with sugar concentration in the dormant season because cellular sugar concentrations are much increased and, thereby, the costs of maintaining concentration gradients. Pinus contorta had a significantly higher respiration rate for a given sugar concentration than any other species, and therefore suffered larger relative losses of sugars when kept at 5 degrees C; possible reasons and consequences of this are discussed in relation to field performance.