Global subsoil organic carbon turnover times dominantly controlled by soil properties rather than climate

Abstract

Soil organic carbon (SOC) in the subsoil below 0.3 m accounts for the majority of total SOC and may be as sensitive to climate change as topsoil SOC. Here we map global SOC turnover times ( τ ) in the subsoil layer at 1 km resolution using observational databases. Global mean τ is estimated to be yr (mean with 95% confidence interval), and deserts and tundra show the shortest ( yr) and longest ( yr) τ respectively. Across the globe, mean τ ranges from 9 (the 5% quantile) to 6332 years (the 95% quantile). Temperature is the most important factor negatively affecting τ , but the overall effect of climate (including temperature and precipitation) is secondary compared with the overall effect of assessed soil properties (e.g., soil texture and pH). The high-resolution mapping of τ and the quantification of its controls provide a benchmark for diagnosing subsoil SOC dynamics under climate change.

Warming‐induced global soil carbon loss attenuated by downward carbon movement

“…where NPP is the observed total NPP, f BNPP the fraction of total NPP allocated belowground and fr 0-0.2 the fraction of root biomass in the 0-0.2 m soil layer; while the aboveground plant litter carbon is correspondingly estimated as NPP ⋅ 1 − f BNPP . The detailed datasets and approach for estimating NPP allocation aboveground and to different soil layers can be found in Luo, Wang, et al (2019).…”

“…These limits were determined based on prior knowledge about the decay rate of aboveground plant litter k a (Zhang et al, 2008), microbial carbon use efficiency (e; Manzoni et al, 2012;Sinsabaugh et al, 2016), residence time (i.e. the reciprocal of decay rate) of SOC in different soil layer depths (He et al, 2016;Luo, Wang, et al, 2019;Todd-Brown et al, 2013;Trumbore, 2000), the PE (Cheng et al, 2014;Luo et al, 2016) and the downward movement coefficient mainly leaching (Kindler et al, 2011).…”

“…A number of challenges inhibit explicit assessment of whole‐soil profile SOC dynamics. First, the subsoil SOC change is more difficult to detect than topsoil SOC change, because subsoil SOC may have much longer residence times than topsoil SOC (Balesdent et al., 2018; Luo, Wang et al., 2019; Mathieu et al., 2015). For this reason, much longer‐term monitoring of subsoil than topsoil SOC dynamics is required, but it is usually unaffordable.…”

Simulating the spatiotemporal variations in aboveground biomass in Inner Mongolian grasslands under environmental changes

“…In addition, in most existing studies, the mean annual climate attributes (e.g. temperature and precipitation) have widely been treated as potential drivers on spatiotemporal variations in grassland biomass (Fan et al, 2009;Ma et al, 2008). However, growing evidence has demonstrated the importance of seasonality and intra-annual variability of climate in regulating the biomass dynamics (Godde et al, 2020;Grant et al, 2014).…”

No solid evidence of soil carbon loss under warming in tropical forests along a 3000 m elevation gradient

“…Considering normal funding cycles and the difficulty to reach the remote areas of the tropical forests, the experiment should be appreciated. However, five years are too short to observe statistically significant trends of soil carbon changes, particularly for recalcitrant pools (if these pools really exist) which usually have residence times of decades or centuries (Luo, Wang, & Wang, 2019; Schmidt et al, 2011). We would suggest to last the experiment as long as possible to detect clear response of SOC to temperature changes.…”