Localized basal area affects soil respiration temperature sensitivity in a coastal deciduous forest

• Main Authors: S. C. Pennington, N. G. McDowell, J. P. Megonigal, J. C. Stegen, B. Bond-Lamberty
• Format: Article
• Language: English
• Published: Copernicus Publications 2020-02-01
• Series: Biogeosciences
• Online Access: https://www.biogeosciences.net/17/771/2020/bg-17-771-2020.pdf
• ISSN: 1726-4170; 1726-4189

<p>Soil respiration (<span class="inline-formula"><i>R</i>_s</span>), the flow of <span class="inline-formula">CO₂</span> from the soil surface to the atmosphere, is one of the largest carbon fluxes in the terrestrial biosphere. The spatial variability of <span class="inline-formula"><i>R</i>_s</span> is both large and poorly understood, limiting our ability to robustly scale it in space. One factor in <span class="inline-formula"><i>R</i>_s</span> spatial variability is the autotrophic contribution from plant roots, but it is uncertain how the presence of plants affects the magnitude and temperature sensitivity of <span class="inline-formula"><i>R</i>_s</span>. This study used 1 year of <span class="inline-formula"><i>R</i>_s</span> measurements to examine the effect of localized basal area on <span class="inline-formula"><i>R</i>_s</span> in the growing and dormant seasons, as well as during moisture-limited times, in a temperate, coastal, deciduous forest in eastern Maryland, USA. In a linear mixed-effects model, tree basal area within a 5&thinsp;m radius (BA<span class="inline-formula">₅</span>) exerted a significant positive effect on the temperature sensitivity of soil respiration. Soil moisture was the dominant control on <span class="inline-formula"><i>R</i>_s</span> during the dry portions of the year, while soil moisture, temperature, and BA<span class="inline-formula">₅</span> all exerted significant effects on <span class="inline-formula"><i>R</i>_s</span> in wetter periods. Our results suggest that autotrophic respiration is more sensitive to temperature than heterotrophic respiration at these sites, although we did not measure these source fluxes directly, and that soil respiration is highly moisture sensitive, even in a record-rainfall year. The <span class="inline-formula"><i>R</i>_s</span> flux magnitudes (0.46–15.0&thinsp;<span class="inline-formula">µ</span>mol&thinsp;m<span class="inline-formula">⁻²</span>&thinsp;s<span class="inline-formula">⁻¹</span>) and variability (coefficient of variability 10&thinsp;%–23&thinsp;% across plots) observed in this study were comparable to values observed in similar forests. Six <span class="inline-formula"><i>R</i>_s</span> observations would be required in order to estimate the mean across all study sites to within 50&thinsp;%, and 518 would be required in order to estimate it to within 5&thinsp;%, with 95&thinsp;% confidence. A better understanding of the spatial interactions between plants and microbes, as well as the strength and speed of above- and belowground coupling, is necessary to link these processes with large-scale soil-to-atmosphere C fluxes.</p>