Night-time respiration rate and leaf carbohydrate concentrations are not coupled in two alpine perennial species

The relationship between night-time respiration rate and carbohydrate supply are measured in two alpine perennials, Bistorta bistortoides and Campanula rotundifolia. Natural populations of B. bistortoides and C. rotundifolia were subjected to high and low light treatments. During the following night, respiration rate and carbohydrate content of leaves were measured. At the beginning of the dark period, leaf carbohydrate concentrations were significantly lower in plants exposed to lower irradiance on the previous day. The night-time respiration rate in leaves of both species was rarely affected by the previous days' irradiance; over the course of the night, respiration rate remained unchanged in C. rotundifolia and decreased, but not consistently, in B. bistortoides. No significant interaction was found between irradiance and the night-time pattern of carbohydrate concentration or respiration rate. Nocturnal carbohydrate export was positively correlated with the previous days' irradiance in leaves of C. rotundifolia only. Leaf respiration rate is uncoupled from carbohydrate supply in leaves of B. bistortoides and C. rotundifolia, possibly allowing more carbohydrate to be exported to underground storage organs.