Partitioning of canopy and soil CO<sub>2</sub> fluxes in a pine forest at the dry timberline across a 13-year observation period
oleh: R. Qubaja, F. Tatarinov, E. Rotenberg, D. Yakir
| Format: | Article |
|---|---|
| Diterbitkan: | Copernicus Publications 2020-02-01 |
Deskripsi
<p>Partitioning carbon fluxes is key to understanding the process underlying ecosystem response to change. This study used soil and canopy fluxes with stable isotopes (<span class="inline-formula"><sup>13</sup>C</span>) and radiocarbon (<span class="inline-formula"><sup>14</sup>C</span>) measurements in an 18 km<span class="inline-formula"><sup>2</sup></span>, 50-year-old, dry (287 mm mean annual precipitation; nonirrigated) <i>Pinus halepensis</i> forest plantation in Israel to partition the net ecosystem's <span class="inline-formula">CO<sub>2</sub></span> flux into gross primary productivity (GPP) and ecosystem respiration (<span class="inline-formula"><i>R</i><sub>e</sub></span>) and (with the aid of isotopic measurements) soil respiration flux (<span class="inline-formula"><i>R</i><sub>s</sub></span>) into autotrophic (<span class="inline-formula"><i>R</i><sub>sa</sub></span>), heterotrophic (<span class="inline-formula"><i>R</i><sub>h</sub></span>), and inorganic (<span class="inline-formula"><i>R</i><sub>i</sub></span>) components. On an annual scale, GPP and <span class="inline-formula"><i>R</i><sub>e</sub></span> were 655 and 488 g C m<span class="inline-formula"><sup>−2</sup></span>, respectively, with a net primary productivity (NPP) of 282 g C m<span class="inline-formula"><sup>−2</sup></span> and carbon-use efficiency (CUE <span class="inline-formula">=</span> NPP <span class="inline-formula">∕</span> GPP) of 0.43. <span class="inline-formula"><i>R</i><sub>s</sub></span> made up 60 % of the <span class="inline-formula"><i>R</i><sub>e</sub></span> and comprised <span class="inline-formula">24±4</span> %<span class="inline-formula"><i>R</i><sub>sa</sub></span>, <span class="inline-formula">23±4</span> %<span class="inline-formula"><i>R</i><sub>h</sub></span>, and <span class="inline-formula">13±1</span> %<span class="inline-formula"><i>R</i><sub>i</sub></span>. The contribution of root and microbial respiration to <span class="inline-formula"><i>R</i><sub>e</sub></span> increased during high productivity periods, and inorganic sources were more significant components when the soil water content was low. Comparing the ratio of the respiration components to <span class="inline-formula"><i>R</i><sub>e</sub></span> of our mean 2016 values to those of 2003 (mean for 2001–2006) at the same site indicated a decrease in the autotrophic components (roots, foliage, and wood) by about <span class="inline-formula">−</span>13 % and an increase in the heterotrophic component (<span class="inline-formula"><i>R</i><sub>h</sub>∕<i>R</i><sub>e</sub></span>) by about <span class="inline-formula">+</span>18 %, with similar trends for soil respiration (<span class="inline-formula"><i>R</i><sub>sa</sub>∕<i>R</i><sub>s</sub></span> decreasing by <span class="inline-formula">−</span>19 % and <span class="inline-formula"><i>R</i><sub>h</sub>∕<i>R</i><sub>s</sub></span> increasing by <span class="inline-formula">+</span>8 %, respectively). The soil respiration sensitivity to temperature (<span class="inline-formula"><i>Q</i><sub>10</sub></span>) decreased across the same observation period by 36 % and 9 % in the wet and dry periods, respectively. Low rates of soil carbon loss combined with relatively high belowground carbon allocation (i.e., 38 % of canopy <span class="inline-formula">CO<sub>2</sub></span> uptake) and low sensitivity to temperature help explain the high soil organic carbon accumulation and the relatively high ecosystem CUE of the dry forest.</p>