Transplanting boreal soils to a warmer region increases soil heterotrophic respiration as well as its temperature sensitivity

Published in Soil Biology and Biochemistry 116: 203-212. https://doi.org/10.1016/j.soilbio.2017.10.018

Under a warming climate, the boreal forest could become one of the largest terrestrial net CO₂ sources, as increasing disturbances and soil organic matter decomposition rates (heterotrophic respiration, Rh) could offset net primary production. Since soil represents the boreal forest's largest C pool, it is critical of correctly predicting future changes in Rh, as well as its sensitivity to temperature (Q₁₀ of Rh). We simulated a soil warming by transplanting soil cores from boreal balsam fir (Abies balsamea, BF) and black spruce (Picea mariana, BS) stands to a more southern Eastern hemlock stand (Tsuga canadensis, EH). We measured Rh and soil properties over 3 years, from June to October. Over three snow-free seasons, soil temperature (first 10 cm, including the FH organic layers) and Rh increased for BF (+3.2 °C, +60% of Rh) and BS cores (+2.3 °C, +27% of Rh). Microbial C concentration decreased by 54–73% in the FH layers of warmed and control cores relative to initial values, despite unchanged chemically labile C, probably due to excised roots and mycorrhizal hyphae. This suggests a possible underestimation of Rh during the experiment. In BF soils only, the increase in Rh was accompanied by an increase in its sensitivity to temperature. Under a +5 °C soil warming, mean predicted Rh of BF soils would increase by 83% rather than by 56%. Relative to BS soils, such increase in sensitivity could be partly due to a higher fraction of chemically labile C (+52%) in the FH layers and a higher mean warming effect. It suggests that for BF forest soils, predicting decomposition rates for a warmer climate based on current temperature sensitivities could be inadequate. However, longer-term studies are needed to see if this increase in Q₁₀ of Rh for BF soils would be maintained for longer periods.

Forests

Scientific Article

Ecosystems and Environment, Forestry Research, Forests

Houle, Daniel, Lambert, Marie-Claude, Tremblay, Sylvie

TREMBLAY, Sylvie L., Loïc D'ORANGEVILLE, Marie-Claude LAMBERT and Daniel HOULE

2017

PDF available upon request

Available at the Direction de la recherche forestière

0038-0717

Abies balsamea, Picea mariana, ecosystems and environment, organic matter decomposition, Q10, CO2 flux, climate change, balsam fir, black spruce, forestry research scientific article