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 estima tion 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 full y expanded foliage) for foliage of seven species of trees and shrubs i n the northern boreal forest (near Thompson, Manitoba, Canada) and sev en species in the subalpine montane forest (near Fraser, Colorado, USA ). At 10 degrees C, average R(m) for boreal foliage ranged from 0.94 t o 6.8 mu mol kg(-1) s(-1) (0.18-0.58 mu mol m(-2) s(-1)) and for subal pine 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 o nly weakly correlated with sample weight (r = 0.11) and leaf area (r = 0.58). However, CO2 efflux per unit foliage weight was highly correla ted 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 st atistically 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 variet y of crop and wildland species growing in warmer climates.