Low soil temperatures increase carbon reserves in Picea mariana and Pinus contorta

Abstract

Soil temperature can limit tree growth and function, but it is often unaddressed in understanding the successional status of trees. We tested how soil temperature affected carbon allocation strategies of two dominant co-occurring boreal conifer species, Pinus contorta and Picea mariana. We measured nonstructural carbon (NSC) concentrations, biomass, and photosynthesis of dormant and actively growing 2-year-old seedlings in response to three soil temperatures (5, 10, and 20 °C) under a common ambient air temperature. For both species, variation in carbon reserves with soil temperature was more pronounced following seedling growth than during dormancy. For both species and all organ types (roots, needles, and stems), NSC concentrations were highest when seedlings were grown at 5 than 20 °C. Mass adjusted for NSC content was negatively correlated with NSC concentration for all organ types of both species. Soil temperature had a marginally significant effect on photosynthesis of pine; seedlings grown at 10 or 20 °C acquired more carbon than seedlings grown at 5 °C. Spruce seedlings photosynthesized more when grown at 20 °C than at 5 or 10 °C. Interspecific differences in allocation of carbon may underlie the responses of P. mariana and P. contorta to cold soils and consequently their successional status.