Climate Warming Can Accelerate Carbon Fluxes without Changing Soil Carbon Stocks

The origin of soil organic matter controls its composition and bioreactivity across a mesic boreal forest latitudinal gradient

“…The depth increases in %carboxylic‐C and %alkyl‐C observed are congruent, respectively, with the oxidation of functional groups and accumulation of hydrophobic compounds (ie, plant waxes) during diagenesis (Baldock et al., ; Quideau, Anderson, Graham, Chadwick, & Trumbore, ). Accumulation of these functional groups is also consistent with the leaching of more water soluble compounds from the organic layer supported by the large soil dissolved organic C fluxes observed in these precipitation‐rich climates (Ziegler et al., ). Although some variation in these two measures was explained by climate region no significant climate region by depth interaction was observed indicating little evidence for differential diagenesis with climate.…”

“…The different response of SOM chemistry and stocks to climate warming between the mesic boreal forests studied here and previously studied continental boreal forests stresses the need for regional understanding (eg, drier, inland vs. mesic, coastal) of forest soil responses to climate change. While continental forest SOM stocks are observed to decrease from colder to warmer climates (Kane et al., ; Norris et al., ), SOM stocks in mesic boreal forests appear to be retained overall and even increase (Ziegler et al., ). It is this balanced increase of both inputs and losses in response to warming that likely led to the similarity in chemical parameters associated with diagenetic alteration observed along this transect.…”

“…). Furthermore, nutrient availability to support that productivity appears to increase with warming in these forests (Philben et al., ) enabling productivity that compensates for the accelerated decomposition with warming (Ziegler et al., ). SOM stocks therefore remain stable in contrast to more dry continental boreal forest ecosystems.…”

“…Litterfall samples were collected between June 2011 and June 2013 as described in (Ziegler et al., ). Briefly, three litter traps with an area of 0.34 m 2 were installed at each plot (9 per site).…”

“…SOM properties derived from diagenetic alteration would likely occur over time in a linear fashion, whereas SOM properties linked to a shift in litter inputs would exhibit a threshold change; and (2) The interpretation of SOM stocks and turnover using SOM chemistry which depends upon the origin of that chemistry. The mesic boreal forests of Atlantic Canada feature a climate gradient in which both mean annual temperature (MAT) and precipitation (MAP) decrease with latitude, such that greater evaporative loss of soil water at higher temperatures is compensated by greater precipitation (Ziegler et al., ). These forests are, therefore, characterized by similarly high soil moisture across a temperature gradient, enabling the study of effects of increasing temperature in the absence of greater water limitation (Appendix S2).…”