Fine root production varies with climate in balsam fir (<i>Abies balsamea</i>)

Abstract

The rising global temperature will likely affect ecological processes but the extent and direction of these responses are uncertain. To reduce this uncertainty, we evaluated the environmental controls over fine root dynamics in balsam fir (Abies balsamea (L.) Mill.). Fine root production was measured over 5 years at two balsam fir sites in the southern part of its range and two sites in the northern part using the minirhizotron and soil-coring methods. The objective of the study was to quantify climatic effects on fine root production and on allocation of growth to foliage (NPPf) and fine roots (NPPfr). Year-end fine root biomass was greater in the south (800 ± 60 g·m–2) than in the north (490 ± 69 g·m–2) (p < 0.001). Similarly, NPPfr was greater in the south (557 ± 35 g·m–2) than in the north (351 ± 41 g·m–2) (p = 0.01). Differences in annual NPPfr between north and south arose because summer and autumn NPPfr was greater in the south. Fine root production did not vary interannually within regions. Annual fine root growth was correlated with air growing degree-days (r2 = 0.53, p = 0.002). The allocation to NPPf relative to NPPfr did not differ significantly between regions. Our results suggest that NPPfr will increase with an increase in mean annual air temperature but that there will be no significant changes in functional equilibrium between foliage and fine roots as global warming progresses.