Interannual variability of the ecosystem CO₂ fluxes at paludified spruce forest and ombrotrophic bog in southern taiga

Abstract

Abstract. Climate warming in high latitudes impacts CO2 sequestration of northern peatlands through the changes in both production and decomposition processes. The response of the net CO2 fluxes between ecosystems and the atmosphere to the climate change and weather anomalies can vary across the forest and non-forest peatlands. To better understand the differences in CO2 dynamics at forest and non-forest boreal peatlands induced by changes in environmental conditions the estimates of interannual variability of the net ecosystem exchange (NEE), total ecosystem respiration (TER) and gross primary production (GPP) was obtained at two widespread peatland ecosystems – paludified spruce forest and adjacent ombrotrophic bog in the southern taiga of west Russia using 6-year of paired eddy covariance flux measurements. The period of measurements (2015–2020) was characterized by both positive and negative annual and growing season air temperature and precipitation anomalies. Flux measurements showed that in spite of the lower growing season TER (332…339 gC∙m−2) and GPP (442…464 gC∙m−2) rates the bog had a lower NEE (−132…−108) than the forest excepting the warmest and the wettest year of the period and was a sink of atmospheric CO2 in the selected years while the forest was a CO2 sink or source between years depending on the environmental conditions. Growing season NEE at the forest site was between −142 and 28 gC∙m−2, TER between 1135 and 1366 gC∙m−2 and GPP between 1207 and 1462 gC∙m−2. Annual NEE at the forest was between −62 and 145 gC∙m−2, TER between 1429 and 1652 gC∙m−2 and GPP between 1345 and 1566 gC∙m−2 respectively. Anomalously warm winter with sparse and thin snow cover lead to the increased GPP as well as lower NEE in early spring at forest and to the increased spring TER at the bog. Also, the shifting of the compensation point to the earlier dates at the forest and to the later dates at the bog following the warmest winter of the period was detected. This study suggest that the warming in winter can increase CO2 uptake of the paludified spruce forests of southern taiga in non-growing season.

Response of Spruce Forest Ecosystem CO2 Fluxes to Inter-Annual Climate Anomalies in the Southern Taiga

“…The hydrological regime of the site may be the key factor that determines the response of a forest ecosystem to climate extremes and anomalies. The results obtained from the flux measurements performed in the southern taiga nemorose spruce forest were different from the results obtained from an old paludified spruce forest (Ru-Fyo FLUXNET ID) located 1.5 km from the study site [51]. While the ecosystem CO 2 uptake in the nemorose spruce forest substantially increased in 2018, the annual GPP/TER ratio in the paludified spruce forest was less sensitive to the warm, dry, and sunny environmental conditions (Figure 7).…”

“…In the nemorose forest, the early start of the CO 2 uptake, as well as the TER dynamics, did not lead to an increase in the annual GPP/TER ratio. The annual sums of the CO 2 fluxes seen at the sites in the 2016-2020 period had a similar order of magnitude: NEE in the paludified forest varied between −95 ± 12 and 145 ± 41 gC•m −2 , TER varied between 1366 ± 92 and 1652 ± 44 gC•m −2 , and GPP varied between 1408 ± 45 and 1592 ± 112 gC•m −2 , respectively [51]. However, the daily CO 2 fluxes in the nemorose spruce forest varied within a wider range (Figure 8).…”

“…According to the meteorological observations at the meteostations nearest to the CFSBR, "Toropets" and "Lesnoy Zapovednik", positive air temperature (+0.73 °C per 10 years) and precipitation (+3.6 mm•month −1 per 10 years) trends were detected in the study area during the 1991-2020 period; moreover, the growing season length is mostly increasing due to the shifting of the start of the growing season in spring to earlier dates [51]. This region has a humid continental climate (Dfb type according to the Köppen-Geiger climate classification) [48] with cool winters and warm summers.…”

“…According to the observations made at meteorological station "Toropets", five of six years of the 2015-2020 period were warmer in relation to the long-term means (Table 1); moreover, no years with a negative annual temperature anomaly were observed in the period [51]. The coolest year was 2017, when the mean annual air temperature was equal to the long-term annual mean, and the warmest year was 2020, when the mean annual temperature anomaly reached 1.9 • C. According to the observations made at the meteorological station "Lesnoy Zapovednik", the annual precipitation in 2015 and 2018 was lower than the mean long-term annual sum.…”

“…According to the observations made at meteorological station "Lesnoy Zapovednik" in the selected years, the surface was covered by snow from November to April with a maximum snow depth of about 40 cm. Under the exceptionally warm conditions that occurred in winter 2019/2020, snow cover was detected only in January and February 2020, with a maximum snow depth of 10 cm [51].…”