Ecosystem warming does not affect photosynthesis or aboveground autotrophic respiration for boreal black spruce

Abstract

We measured light-saturated photosynthesis (Anet), foliage respiration (Rfol) and stem respiration (Rstem) of black spruce (Picea mariana (Mill.) B.S.P.) in heated (+5 °C) and control plots during 2005, 2006 and 2007 in Thompson, MB, Canada. Large greenhouses and soil-heating cables were used to maintain air and soil temperature 5 °C above ambient air and soil temperature. Each greenhouse contained approximately nine black spruce trees and the majority of their fine root mass. Treatments were soil and air warming, soil-only warming, greenhouses maintained at ambient air temperature and control. Gas exchange rates ranged 0.71-4.66, 0.04-0.74 and 0.1-1.0 mol m-2 s-1 for A net, Rfol and Rstem, respectively. Treatment differences for Anet, Rfol and Rstem were not significant in any of the 3 years of measurements. The results of this experiment suggest that in a warmer climate, black spruce may not have significant changes in the rate of photosynthesis or respiration.