Global covariation of carbon turnover times with climate in terrestrial ecosystems

Abstract

The response of the terrestrial carbon cycle to climate change is among the largest uncertainties affecting future climate change projections. The feedback between the terrestrial carbon cycle and climate is partly determined by changes in the turnover time of carbon in land ecosystems, which in turn is an ecosystem property that emerges from the interplay between climate, soil and vegetation type. Here we present a global, spatially explicit and observation-based assessment of whole-ecosystem carbon turnover times that combines new estimates of vegetation and soil organic carbon stocks and fluxes. We find that the overall mean global carbon turnover time is 23(+7)(-4) years (95 per cent confidence interval). On average, carbon resides in the vegetation and soil near the Equator for a shorter time than at latitudes north of 75° north (mean turnover times of 15 and 255 years, respectively). We identify a clear dependence of the turnover time on temperature, as expected from our present understanding of temperature controls on ecosystem dynamics. Surprisingly, our analysis also reveals a similarly strong association between turnover time and precipitation. Moreover, we find that the ecosystem carbon turnover times simulated by state-of-the-art coupled climate/carbon-cycle models vary widely and that numerical simulations, on average, tend to underestimate the global carbon turnover time by 36 per cent. The models show stronger spatial relationships with temperature than do observation-based estimates, but generally do not reproduce the strong relationships with precipitation and predict faster carbon turnover in many semi-arid regions. Our findings suggest that future climate/carbon-cycle feedbacks may depend more strongly on changes in the hydrological cycle than is expected at present and is considered in Earth system models.

More than a century of Grain for Green Program is expected to restore soil carbon stock on alpine grassland revealed by field 13 C pulse labeling

“…However, they were similar to the results from a nearby Kobresia meadow in Xinghai (Hafner et al, 2012), where values of 4.2 and 5.5 days were reported for grazed and ungrazed grasslands, respectively. The results suggest differences in grassland types and climate (i.e., alpine steppe in the present study vs. alpine meadow in previous studies) attributable to a clear dependence of the TR on temperature (Carvalhais et al, 2014).…”

“…In terrestrial ecosystems, the size of the C reservoir for the whole ecosystem equals the C stocks in the vegetation and soil (Carvalhais et al, 2014), and is an ecosystem property that indicates C sequestration capability of an ecosystem (Zhao et al, 2015). This was represented by the C stocks in the shoots, roots, and soil in the present study.…”

“…(10)-(12); Table 2). Soil C stock in the natural grassland is in a steady state, and there is a balance between assimilation and losses of ecosystem C (Carvalhais et al, 2014). The SOC sequestration rate of the GfGP to restore cropland should take account of the C losses.…”

“…Carvalhais et al (2014) reported total ecosystem C turnover times of 32. 8-54.6, 44.7-78.0 and 17.0-30.1 yr in temperate grasslands and shrublands, tundra, and croplands, respectively.…”

Effects of temperature, soil substrate, and microbial community on carbon mineralization across three climatically contrasting forest sites

“…Among the treatment factors, temperature had the strongest effect on the temporal dynamics of soil C mineralization; a decrease in the incubation temperature from 25 to 5°C resulted in a delayed peak and reduced magnitude of the maximum rate of C mineralization during the study period. This is consistent with previous findings that climate exerts dominant controls on SOM decomposition (Carvalhais et al., 2014; Kirschbaum, 2004; Sun et al., 2004). A recent synthesis by Luo, Feng, Luo, Baldock, and Wang (2017) showed that climate (precipitation and temperature) accounted for as much as 25% of the relative influence on SOC by various environmental, soil biotic, and abiotic factors.…”