Environmental and taxonomic controls of carbon and oxygen stable isotope composition in <i>Sphagnum</i> across broad climatic and geographic ranges Academic Article uri icon


  • <p><strong>Abstract.</strong> Rain-fed peatlands are dominated by peat mosses (<i>Sphagnum</i> sp.), which for their growth depend on nutrients, water and <span class="inline-formula">CO<sub>2</sub></span> uptake from the atmosphere. As the isotopic composition of carbon (<span class="inline-formula"><sup>12,13</sup>C</span>) and oxygen (<span class="inline-formula"><sup>16,18</sup>O</span>) of these <i>Sphagnum</i> mosses are affected by environmental conditions, <i>Sphagnum</i> tissue accumulated in peat constitutes a potential long-term archive that can be used for climate reconstruction. However, there is inadequate understanding of how isotope values are influenced by environmental conditions, which restricts their current use as environmental and palaeoenvironmental indicators. Here we tested (i) to what extent C and O isotopic variation in living tissue of <i>Sphagnum</i> is species-specific and associated with local hydrological gradients, climatic gradients (evapotranspiration, temperature, precipitation) and elevation; (ii) whether the C isotopic signature can be a proxy for net primary productivity (NPP) of <i>Sphagnum</i>; and (iii) to what extent <i>Sphagnum</i> tissue <span class="inline-formula"><i>?</i><sup>18</sup>O</span> tracks the <span class="inline-formula"><i>?</i><sup>18</sup>O</span> isotope signature of precipitation. In total, we analysed 337 samples from 93 sites across North America and Eurasia using two important peat-forming <i>Sphagnum </i>species (<i>S. magellanicum</i>, <i>S. fuscum</i>) common to the Holarctic realm. There were differences in <span class="inline-formula"><i>?</i><sup>13</sup>C</span> values between species. For <i>S. magellanicum</i> <span class="inline-formula"><i>?</i><sup>13</sup>C</span> decreased with increasing height above the water table (HWT, <span class="inline-formula"><i>R</i><sup>2</sup>=17</span><span class="thinspace"></span>%) and was positively correlated to productivity (<span class="inline-formula"><i>R</i><sup>2</sup>=7</span><span class="thinspace"></span>%). Together these two variables explained 46<span class="thinspace"></span>% of the between-site variation in <span class="inline-formula"><i>?</i><sup>13</sup>C</span> values. For <i>S. fuscum</i>, productivity was the only significant predictor of <span class="inline-formula"><i>?</i><sup>13</sup>C</span> but had low explanatory power (total <span class="inline-formula"><i>R</i><sup>2</sup>=6</span><span class="thinspace"></span>%). For<span id="page5191"/> <span class="inline-formula"><i>?</i><sup>18</sup>O</span> values, approximately 90<span class="thinspace"></span>% of the variation was found between sites. Globally modelled annual <span class="inline-formula"><i>?</i><sup>18</sup>O</span> values in precipitation explained 69<span class="thinspace"></span>% of the between-site variation in tissue <span class="inline-formula"><i>?</i><sup>18</sup>O</span>. <i>S. magellanicum</i> showed lower <span class="inline-formula"><i>?</i><sup>18</sup>O</span> enrichment than <i>S. fuscum</i> (<span class="inline-formula">?</span>0.83<span class="thinspace"></span>‰ lower). Elevation and climatic variables were weak predictors of tissue <span class="inline-formula"><i>?</i><sup>18</sup>O</span> values after controlling for <span class="inline-formula"><i>?</i><sup>18</sup>O</span> values of the precipitation. To summarize, our study provides evidence for (a) good predictability of tissue <span class="inline-formula"><i>?</i><sup>18</sup>O</span> values from modelled annual <span class="inline-formula"><i>?</i><sup>18</sup>O</span> values in precipitation, and (b) the possibility of relating tissue <span class="inline-formula"><i>?</i><sup>13</sup>C</span> values to HWT and NPP, but this appears to be species-dependent. These results suggest that isotope composition can be used on a large scale for climatic reconstructions but that such models should be species-specific.</p>