Rising Temperature May Trigger Deep Soil Carbon Loss Across Forest Ecosystems

Abstract

Significantly more carbon (C) is stored in deep soil than in shallow horizons, yet how the decomposition of deep soil organic C (SOC) will respond to rising temperature remains unexplored on large scales, leading to considerable uncertainties to predictions of the magnitude and direction of C-cycle feedbacks to climate change. Herein, short-term temperature sensitivity of SOC decomposition (expressed as Q 10) from six depths within the top 1 m soil from 90 upland forest sites (540 soil samples) across China is reported. Results show that Q 10 significantly increases with soil depth, suggesting that deep SOC is more vulnerable to loss with rising temperature in comparison to shallow SOC. Climate is the primary regulator of shallow soil Q 10 but its relative influence declines with depth; in contrast, soil C quality has a minor influence on Q 10 in shallow soil but increases its influence with depth. When considering the depth-dependent Q 10 variations, results further show that using the thermal response of shallow soil layer for the whole soil profile, as is usually done in model predictions, would significantly underestimate soil C-climate feedbacks. The results highlight that Earth system models need to consider multilayer soil C dynamics and their controls to improve prediction accuracy.

High microbial diversity stabilizes the responses of soil organic carbon decomposition to warming in the subsoil on the Tibetan Plateau

“…The functional redundancy in the decomposition processes was shown to decrease with increasing C recalcitrance (Maron et al, 2018). Third, the failure to capture causal relations between the tested biotic and abiotic variables and Q 10 by the SEM analysis in the topsoil implies that the relative importance of soil microbes is attenuated by other factors, for example, climate, soil environments, substrate availability (Gillabel et al, 2010; Li, Pei, et al, 2020; Suseela et al, 2012), regulating the stability of SOC decomposition. For example, using soils from 90 upland forest sites, Li, Pei, et al (2020) showed that climate but not microbes was the primary regulator of Q 10 in shallow soils.…”

“…Third, the failure to capture causal relations between the tested biotic and abiotic variables and Q 10 by the SEM analysis in the topsoil implies that the relative importance of soil microbes is attenuated by other factors, for example, climate, soil environments, substrate availability (Gillabel et al, 2010; Li, Pei, et al, 2020; Suseela et al, 2012), regulating the stability of SOC decomposition. For example, using soils from 90 upland forest sites, Li, Pei, et al (2020) showed that climate but not microbes was the primary regulator of Q 10 in shallow soils. We did not observe a significant correlation between Q 10 and mean annual temperature or growing season precipitation, suggesting the complexity in the controlling factors of Q 10 in different regions.…”

“…Some studies report that Q 10 increased with soil depth (Wang et al, 2013; Xu et al, 2010) likely due to the decreasing substrate quality with increasing soil depth (Fierer et al, 2003), but other studies have found the opposite results (Xu, Li, Jiang, et al, 2014). Data synthesis from 90 upland forests sites across China showed that Q 10 significantly increased with soil depth (Li, Pei, et al, 2020). However, there is a lack of the information for the Tibetan Plateau, where deep soil layers contain considerable amounts of SOC, for example, 7.4 Pg C in the top 1 m of alpine grasslands (Yang et al, 2008).…”

Temperature adaptation of soil microbial respiration in alpine, boreal and tropical soils: An application of the square root (Ratkowsky) model

“…Soil carbon quality has long been recognized as a control on the temperature response of soil microbial respiration (Conant et al, 2008; Craine et al, 2010; Fierer et al, 2006; Li et al, 2017; Li, Pei, Pendall, Reich, et al, 2020; Wang et al, 2018). The carbon quality‐temperature (CQT) hypothesis suggests that decomposition of low‐quality carbon requires high activation energy and thus is more sensitive to temperature change (Davidson & Janssens, 2006).…”

“…To do this, soils (passed through a 0.15 mm mesh sieve) was dried at 60°C and homogenized by grinding. Reflectance spectra (400–4000 cm −1 ) were obtained using a FT‐IR (Nicolet iS5, Thermo Scientific; Li, Pei, Pendall, Reich, et al, 2020) and relative peak areas were calculated, which represent the relative abundance of different organic carbon functional groups, such as carbohydrates (1024 cm −1 ) and aromatic carbon groups (1637 cm −1 ; Hodgkins et al, 2018). A higher ratio of carbohydrates to aromatics is usually considered as higher soil carbon quality (Tfaily et al, 2014).…”