Temperature Control of Spring CO2 Fluxes at a Coniferous Forest and a Peat Bog in Central Siberia

Abstract

Climate change impacts the characteristics of the vegetation carbon-uptake process in the northern Eurasian terrestrial ecosystem. However, the currently available direct CO2 flux measurement datasets, particularly for central Siberia, are insufficient for understanding the current condition in the northern Eurasian carbon cycle. Here, we report daily and seasonal interannual variations in CO2 fluxes and associated abiotic factors measured using eddy covariance in a coniferous forest and a bog near Zotino, Krasnoyarsk Krai, Russia, for April to early June, 2013–2017. Despite the snow not being completely melted, both ecosystems became weak net CO2 sinks if the air temperature was warm enough for photosynthesis. The forest became a net CO2 sink 7–16 days earlier than the bog. After the surface soil temperature exceeded ~1 °C, the ecosystems became persistent net CO2 sinks. To change into the full spring photosynthesis recovery, the forest is likely to need a minimum accumulated air temperature of ~80 to 137 °C, and the bog requires 141 to 211 °C. During these periods, soil temperature in the forest still remained nearly 0 °C, suggesting that it is likely that forests appear more sensitive to the rise of air temperature than bogs. Net ecosystem productivity was highest in 2015 for both ecosystems because of the anomalously high air temperature in May compared with other years. Our findings demonstrate that long-term monitoring of flux measurements at the site level, particularly during winter and its transition to spring, is essential for understanding the responses of the northern Eurasian ecosystem to spring warming.

Warming response of peatland CO2 sink is sensitive to seasonality in warming trends

“…4c). There, increased net CO 2 uptake occurring with warming in early summer months approximately balances losses occurring with warming in late summer and winter months, which is supported by in situ NEE observations 32 . The largest differences were observed for regions experiencing more than 2 °C of June (early summer) warming (Extended Data Fig.…”

“…The weak relationships might be caused by small interannual temperature variability compared with warming experiments 25 , by seasonally varying and compensating effects of peatland NEE sensitivity to temperature 29 or by complex interactions with other environmental drivers (for example, water table influencing phenology) 14 . For example, increased net CO 2 uptake in response to earlier snowmelt [30][31][32] and to warmer air temperatures in the early growing season has been observed in some peatlands 29,33,34 . Other studies report decreased net CO 2 uptake or even net CO 2 loss during periods of drier conditions with lower water-table positions, particularly in the late growing season [34][35][36][37] .…”

Nongrowing Season CO2 Emissions Determine the Distinct Carbon Budgets of Two Alpine Wetlands on the Northeastern Qinghai—Tibet Plateau

“…Such a phenomenon indicates that GPP and RES at XBH should be to some extent water-stressed, which agrees well with previously reported positive relationships between CO 2 fluxes and water availability at the same site from 2012 to 2013 [29]. Indeed, recent studies have suggested that the response of soil carbon decomposition to water-table manipulation in LHZ is controlled by ferrous iron, in contrast to the classic "enzyme latch" theory seen in other wetlands [21,48]. Therefore, the different responses of CO 2 fluxes to promoted precipitation between peatlands and swamplands should be taken into full consideration in predicting the feedback of alpine wetlands to climate change on the QTP.…”

“…Meanwhile, the easily degradable labile carbon from plant litter, induced by higher vegetation coverage (e.g., twofold higher EVI at LHZ), will stimulate enhanced microbial growth, carbon mineralization, and soil respiration at LHZ [11]. However, the temperature sensitivity of RES was much higher at XBH (Figure 8), which also indicated lower stability of soil organic matter at this site [21].…”

“…Vascular plant coverage has an asymptotic relationship with GPP, and an incremental relationship with RES, but their sensitivity varies by leaf area index and vegetation type [17,18]. Under the context of climate warming scenarios, recent studies have shown that plant productivity outweighs ecosystem respiration, and alpine peatlands have become more efficient carbon sinks because of a higher sensitivity of GPP compared to RES, longer growing season, and more plant carbon input [19][20][21]. Contrarily, other studies have suggested that decreased moisture availability caused by warming could stimulate more soil respiration and potentially reverse the carbon sink function [6,22,23].…”