Increasing terrestrial ecosystem carbon release in response to autumn cooling and warming

Abstract

Part of the Northern Hemisphere has experienced widespread autumn cooling during the most recent decades despite overall warming, but how this contrasting temperature change has influenced the ecosystem carbon exchange remains unclear. Here, we show that autumn cooling has occurred over about half of the area north of 25° N since 2004, producing a weak cooling trend over the period 2004–2018. Multiple lines of evidence suggest an increasing net CO2 release in autumn during 2004–2018. In cooling areas, the increasing autumn CO2 release is due to the larger decrease of gross primary productivity (GPP) growth than total ecosystem respiration (TER) growth suppressed by cooling. In the warming areas, TER increased more than GPP because the warming and wetting conditions are more favourable for TER growth than GPP increase. Despite the opposite temperature trends, there has been a systematic increase in ecosystem carbon release across the Northern Hemisphere middle and high latitudes.

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

“…CO 2 source in response to even a moderate warming treatment 25 . By contrast, historical air-temperature records reveal seasonal differences in warming trends 2,26 (Extended Data Fig. 1) that are not mimicked in most warming experiments 27 .…”

“…A t northern latitudes (>45° N), air temperatures are increasing rapidly, with winter temperatures rising faster than summer temperatures 1 . Warming is not spatially and seasonally uniform, with some areas of North America and Eurasia even experiencing cooling trends in the fall since the early 2000s despite annual warming 2 . Peatlands at northern latitudes store large amounts of organic carbon 3 and are long-term carbon dioxide (CO 2 ) sinks 4,5 exerting a global climate cooling effect 6 .…”

Peatlands and their carbon dynamics in northern high latitudes from 1990 to 2300: a process-based biogeochemistry model analysis

“…A previous study found that peatland WTD deepening benefits shrub dominance, while it suppresses forbs and mosses (Mäkiranta et al, 2018). Meanwhile, shrub expansion is reported in Alaska, Siberian and across the pan-Arctic region under historical climate warming (Tape et al, 2006;Blok et al, 2010). Furthermore, the simulation based on LPJ-GUESS also predicts a higher proportion of shrub NPP in lower-latitude regions due to high insolation and deep WTD (Chaudhary et al, 2020).…”

Saturation response of enhanced vegetation productivity attributes to intricate interactions

“…First, asymmetric diurnal–nocturnal warming has implications for carbon assimilation and consumption, as night‐time warming enhances autotrophic respiration and stimulates photosynthesis in a subsequent daytime (Peng et al, 2013). Second, the increasing CO 2 release is due to cooling in autumn, which can reduce ecosystem respiration accompanied by productivity suppression (Tang et al, 2022). The increasing carbon loss in autumn is attributed to respiration growth faster than productivity, albeit with warming–wetting condition in some regions.…”