Variability in above- and belowground carbon stocks in a Siberian larch watershed Academic Article uri icon

abstract

  • <p><strong>Abstract.</strong> Permafrost soils store between 1330 and 1580<span class="thinspace"></span>Pg carbon (C), which is 3 times the amount of C in global vegetation, almost twice the amount of C in the atmosphere, and half of the global soil organic C pool. Despite the massive amount of C in permafrost, estimates of soil C storage in the high-latitude permafrost region are highly uncertain, primarily due to undersampling at all spatial scales; circumpolar soil C estimates lack sufficient continental spatial diversity, regional intensity, and replication at the field-site level. Siberian forests are particularly undersampled, yet the larch forests that dominate this region may store more than twice as much soil C as all other boreal forest types in the continuous permafrost zone combined. Here we present above- and belowground C stocks from 20 sites representing a gradient of stand age and structure in a larch watershed of the Kolyma River, near Chersky, Sakha Republic, Russia. We found that the majority of C stored in the top 1<span class="thinspace"></span>m of the watershed was stored belowground (92<span class="thinspace"></span>%), with 19<span class="thinspace"></span>% in the top 10<span class="thinspace"></span>cm of soil and 40<span class="thinspace"></span>% in the top 30<span class="thinspace"></span>cm. Carbon was more variable in surface soils (10<span class="thinspace"></span>cm; coefficient of variation (CV)<span class="thinspace"></span>?=?<span class="thinspace"></span>0.35 between stands) than in the top 30<span class="thinspace"></span>cm (CV<span class="thinspace"></span>?=?<span class="thinspace"></span>0.14) or soil profile to 1<span class="thinspace"></span>m (CV<span class="thinspace"></span>?=?<span class="thinspace"></span>0.20). Combined active-layer and deep frozen deposits (surface – 15<span class="thinspace"></span>m) contained 205<span class="thinspace"></span>kg<span class="thinspace"></span>C<span class="thinspace"></span>m<sup>?2</sup> (yedoma, non-ice wedge) and 331<span class="thinspace"></span>kg<span class="thinspace"></span>C<span class="thinspace"></span>m<sup>?2</sup> (alas), which, even when accounting for landscape-level ice content, is an order of magnitude more C than that stored in the top meter of soil and 2 orders of magnitude more C than in aboveground biomass. Aboveground biomass was composed of primarily larch (53<span class="thinspace"></span>%) but also included understory vegetation (30<span class="thinspace"></span>%), woody debris (11<span class="thinspace"></span>%) and snag (6<span class="thinspace"></span>%) biomass. While aboveground biomass contained relatively little (8<span class="thinspace"></span>%) of the C stocks in the watershed, aboveground processes were linked to thaw depth and belowground C storage. Thaw depth was negatively related to stand age, and soil C density (top 10<span class="thinspace"></span>cm) was positively related to soil moisture and negatively related to moss and lichen cover. These results suggest that, as the climate warms, changes in stand age and structure may be as important as direct climate effects on belowground environmental conditions and permafrost C vulnerability.</p>