Total belowground carbon and nitrogen partitioning of mature black spruce displaying genetic × soil moisture interaction in growth

Abstract

Total belowground biomass, soil C, and N mass were measured in plots of 32-year-old black spruce ( Picea mariana (Mill.) Britton, Sterns & Poggenb.) from four full-sib families studied previously for drought tolerance and differential productivity on a dry and a wet site. Stump root biomass was greater on the wet than on the dry site; however, combined fine and coarse root biomass was greater on the dry than on the wet site, resulting in no site root biomass differences. There were no site differences in root distribution by soil depth. Drought-tolerant families had greater stump root biomass and allocated relatively less to combined coarse and fine roots than drought-intolerant families. Fine roots (<2 mm) made up 10.9% and 50.2% of the belowground C and N biomass. Through 50 cm soil depth, mean total belowground C mass was 187.2 Mg·ha–1, of which 8.9%, 3.4%, 0.7%, and 87.0% were from the stump root, combined fine and coarse roots, necromass, and soil, respectively. Here, we show that belowground C sequestration generally mirrors (mostly from stump roots) aboveground growth, and thus, trends in genetic and genetic × environment productivity effects result in similar effects on belowground C sequestration. Thus, tree improvement may well be an important avenue to help stem increases in atmospheric CO2.