Soil respiration responses to temperature are controlled more by roots than by decomposition in balsam fir ecosystems

Abstract

Concern exists that soil respiration (R s ) will increase with global warming, thereby reducing the sink strength of forest ecosystems for carbon (C) or making them sources. We measured R s at three balsam fir (Abies balsamea (L.) Mill.) sites on a climatic gradient from 1997 to 2000 to assess potential responses to global warming. Mean annual R s varied from 0.67 kg C·m -2 ·year -1 at the cool site, to 1.19 kg C·m -2 ·year -1 at the midtransect site, to 1.52 kg C·m -2 ·year -1 at the warm site. Trenched plots were installed in 1999 to partition R s into root respiration (R r ) and heterotrophic respiration (R h ). Differences in trenched-plot respiration (R t ) among sites were much less than differences in R s , because trenching reduced R s at the warm site more than at the cool site. Annual R t was 22% less than annual R s at the cool site, 36% less at the midtransect site, and 50% less at the warm site. After making adjustments for extraordinary decomposition of killed roots in trenched plots, it was estimated that annual R h varied little among sites (0.40 kg C·m -2 ·year -1 at the cool site to 0.54 kg C·m -2 ·year -1 at the warm site), but annual R r varied substantially among sites (0.24 kg C·m -2 ·year -1 at the cool site to 0.98 kg C·m -2 ·year -1 at the warm site). We conclude that R s varied among sites, because climatically driven differences in primary productivity caused greater R r and greater detrital production for R h .