Abiotic drivers of CO2 fluxes in the transition from the winter-to-spring in coniferous forest and bog in central Siberia

Abstract

<p>The transition winter-to-spring is essential for understanding the seasonal dynamics of CO2 flux in high northern latitudes. However, the latest CO2 flux measurements in the two dominant boreal ecosystems, i.e. coniferous forests and bogs are still insufficient. We investigated interannual variability of CO2 fluxes and their major drivers measured in a coniferous forest and a bog from 2013-2017 in Zotino, Russia. To better understand the controlling factors, we utilized the  Multivariate Adaptive Regression Splines (MARS) model. The two ecosystems showed clear differences in the timing of the start of CO2 uptake and CO2 flux rates before and after snowmelt. Both ecosystems started the net CO2 uptake even the snowmelt was incompleted. CO2 flux variations of coniferous forest were more sensitive to changes in air temperature than soil temperature than that of the bog. It is likely that intermittent frost events can reduce the magnitude of CO2 uptake rates of both ecosystems, however, CO2 uptake rates increased with a similar level as pre-frost within a few days. In 2015, both ecosystems reached the highest cumulative net ecosystem exchange of CO2 because of the unusually warm temperature in May compared to the study period. Our findings reveal that continuous and long-term monitoring of the effects of air and soil temperatures on vegetation productivity as well as their legacy effect in subarctic ecosystems required further to be studied.</p>