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Contributed Talk

Session: : Biogeochemistry: C And N Cycling In Response To Global Change 4

COS 186-2 - Effects of long-term warming on soil respiration in a southern boreal forest depend on soil moisture

Wednesday, August 9, 2023
1:45 PM – 2:00 PM PDT
Location: B115
Abstract: The effect of long-term warming on soil respiration and its drivers remains far from clear in forests, which store approximately 40% of global soil carbon (C). This uncertainty may hinder realistic predictions of the global C cycling under future climate warming. To address this knowledge gap, we conducted a long-term (13 years) climate change experiment at two southern boreal sites. Treatments included simultaneous above- and belowground warming (ambient, + 1.7 °C, and + 3.3 °C) under different rainfall scenarios (100% and 60% of summer rainfall amount) and contrasting canopy conditions (open and closed: 240 and 74 mol m-2 s-1 for photosynthetically active radiation transmitted, respectively). Across all treatments and years, when compared to the ambient temperature, soil respiration was increased by 6% and 17% under + 1.7 °C and + 3.3 °C, respectively. In all contexts (all warming levels, rainfall amounts, and canopy conditions), warming increased soil respiration more when soils were moist but less (or even decreased soil respiration) when soils were dry. Furthermore, these responses occurred regardless of whether soil moisture deficits were driven by low ambient rainfall, experimental rainfall reduction, canopy removal, or experimental warming. Our results suggest that factors affecting soil moisture should be accounted for when predicting or modeling the response of soil respiration to warming. Otherwise, warming effects on soil respiration, and thus the positive climate feedback, may be overestimated in forests that periodically experience low soil moisture.