PNNL

Abstract

The fate of soil organic carbon (SOC) in boreal forests is dependent on the integrative ecosystem response to climate change. For example, boreal forest productivity is often nitrogen (N) limited, and climate warming can enhance N cycling and primary productivity. However, the net effect of this feedback on the SOC reservoir and its longevity with climate change remains unclear. Here, we (1) applied lignin biomarkers to assess the diagenetic alteration of SOC in boreal forest organic soils across a climate gradient; and (2) investigated the coupling of soil C and N cycling and the influence of enhanced N availability on soil C stocks along this boreal forest climate transect. The lignin diagenetic state remained constant with climate warming, indicating a balance between the input and removal of lignin in these mesic boreal forests. When combined with previous knowledge of these forest ecosystems, including the diagenetic state of soil organic nitrogen and direct measures of carbon fluxes and stocks, the results indicate a coupled increase in carbon and nitrogen cycling with climate warming that supports forest productivity and maintains SOC stocks. Our observations are consistent with several lines of evidence in other biomes not limited by water availability, although the mechanisms for the maintenance of SOC stocks during climate warming appear to be ecosystem dependent.