FOLIAR MAINTENANCE RESPIRATION OF SUB-ALPINE AND BOREAL TREES AND SHRUBS IN RELATION TO NITROGEN-CONTENT

A nitrogen-based model of maintenance respiration (R(m)) would link R(m) with nitrogen-based photosynthesis models and enable simpler estimation of dark respiration flux from forest canopies. To test whether an N-based model of R(m) would apply generally to foliage of boreal and subalpine woody plants, I measured R(m) (CO2 efflux at night from fully expanded foliage) for foliage of seven species of trees and shrubs in the northern boreal forest (near Thompson, Manitoba, Canada) and seven species in the subalpine montane forest (near Fraser, Colorado, USA). At 10 degrees C, average R(m) for boreal foliage ranged from 0.94 to 6.8 mu mol kg(-1) s(-1) (0.18-0.58 mu mol m(-2) s(-1)) and for subalpine foliage it ranged from 0.99 to 7.6 mu mol kg(-1) s(-1) (0.28-0.64 mu mol m(-2) s(-1)). CO2 efflux at 10 degrees C for the samples was only weakly correlated with sample weight (r = 0.11) and leaf area (r = 0.58). However, CO2 efflux per unit foliage weight was highly correlated with foliage N concentration [r = 0.83, CO2 flux at 10 degrees C (mol kg(-1) s(-1)) = 2.62 x foliage N (mol kg(-1))], and slopes were statistically similar for the boreal and subalpine sites (P = 0.28), CO2, efflux per unit of foliar N was 1.8 times that reported for a variety of crop and wildland species growing in warmer climates.