Atmospheric measurements of the terrestrial O<sub>2</sub> : CO<sub>2</sub> exchange ratio of a midlatitude forest
oleh: M. O. Battle, J. W. Munger, M. Conley, E. Sofen, R. Perry, R. Hart, Z. Davis, J. Scheckman, J. Woogerd, K. Graeter, S. Seekins, S. David, J. Carpenter
| Format: | Article |
|---|---|
| Diterbitkan: | Copernicus Publications 2019-07-01 |
Deskripsi
<p>Measurements of atmospheric <span class="inline-formula">O<sub>2</sub></span> have been used to quantify large-scale fluxes of carbon between the oceans, atmosphere and land since 1992 <span class="cit" id="xref_paren.1">(<a href="#bib1.bibx19">Keeling and Shertz</a>, <a href="#bib1.bibx19">1992</a>)</span>. With time, datasets have grown and estimates of fluxes have become more precise, but a key uncertainty in these calculations is the exchange ratio of <span class="inline-formula">O<sub>2</sub></span> and <span class="inline-formula">CO<sub>2</sub></span> associated with the net land carbon sink (<span class="inline-formula"><i>α</i><sub><i>B</i></sub></span>). We present measurements of atmospheric <span class="inline-formula">O<sub>2</sub></span> and <span class="inline-formula">CO<sub>2</sub></span> collected over a 6-year period from a mixed deciduous forest in central Massachusetts, USA (42.537<span class="inline-formula"><sup>∘</sup></span> N, 72.171<span class="inline-formula"><sup>∘</sup></span> W). Using a differential fuel-cell-based instrument for <span class="inline-formula">O<sub>2</sub></span> and a nondispersive infrared analyzer for <span class="inline-formula">CO<sub>2</sub></span>, we analyzed airstreams collected within and <span class="inline-formula">∼5</span> m above the forest canopy. Averaged over the entire period of record, we find these two species covary with a slope of <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M14" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>-</mo><mn mathvariant="normal">1.081</mn><mo>±</mo><mn mathvariant="normal">0.007</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="76pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="60c94e7ccf831b61c3286393a3d5d90d"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-19-8687-2019-ie00001.svg" width="76pt" height="10pt" src="acp-19-8687-2019-ie00001.png"/></svg:svg></span></span> mol of <span class="inline-formula">O<sub>2</sub></span> per mole of <span class="inline-formula">CO<sub>2</sub></span> (the mean and standard error of 6 h periods). If we limit the data to values collected on summer days within the canopy, the slope is <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M17" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>-</mo><mn mathvariant="normal">1.03</mn><mo>±</mo><mn mathvariant="normal">0.01</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="64pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="c59ec2e0c2d5081d82e370fcc637b96e"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-19-8687-2019-ie00002.svg" width="64pt" height="10pt" src="acp-19-8687-2019-ie00002.png"/></svg:svg></span></span>. These are the conditions in which biotic influences are most likely to dominate. This result is significantly different from the value of <span class="inline-formula">−</span>1.1 widely used in <span class="inline-formula">O<sub>2</sub></span>-based calculations of the global carbon budget, suggesting the need for a deeper understanding of the exchange ratios of the various fluxes and pools comprising the net sink.</p>