Climatic seasonality challenges the stability of microbial‐driven deep soil carbon accumulation across China

Abstract

Microbial residues contribute to the long‐term stabilization of carbon in the entire soil profile, helping to regulate the climate of the planet; however, how sensitive these residues are to climatic seasonality remains virtually unknown, especially for deep soils across environmental gradients. Here, we investigated the changes of microbial residues along soil profiles (0–100 cm) from 44 typical ecosystems with a wide range of climates (~3100 km transects across China). Our results showed that microbial residues account for a larger portion of soil carbon in deeper (60–100 cm) vs. shallower (0–30 and 30–60 cm) soils. Moreover, we find that climate especially challenges the accumulation of microbial residues in deep soils, while soil properties and climate share their roles in controlling the residue accumulation in surface soils. Climatic seasonality, including positive correlations with summer precipitation and maximum monthly precipitation, as well as negative correlations with temperature annual range, are important factors explaining microbial residue accumulation in deep soils across China. In particular, summer precipitation is the key regulator of microbial‐driven carbon stability in deep soils, which has 37.2% of relative independent effects on deep‐soil microbial residue accumulation. Our work provides novel insights into the importance of climatic seasonality in driving the stabilization of microbial residues in deep soils, challenging the idea that deep soils as long‐term carbon reservoirs can buffer climate change.

Fungal necromass is reduced by intensive drought in subsoil but not in topsoil

“…Soil C (particularly SOC) is typically a critical factor that influences the soil TNC content. The key role of TN in influencing TNC was also confirmed by the results of the meta‐analysis (Cao et al., 2023; Wen et al., 2023). It was observed that the supply and restriction of substrates (TC and TN) were the main drivers for the microbial necromass C pool (Shao et al., 2021).…”

“…Soil C (particularly SOC) is typically a critical factor that influences the soil TNC content. The key role of TN in influencing TNC was also confirmed by the results of the meta-analysis (Cao et al, 2023;Wen et al, 2023).…”

“…Since substrate restrictions typically increased with soil depth, the microbial biomass and activities in the subsoil were generally lower than those of the topsoil (Liang & Balser, 2008;Sradnick et al, 2014), which limited the accumulation of microbially derived C in the subsoil (Jia et al, 2022). These mechanisms were also found in the meta-analysis (Wen et al, 2023).…”

“…Several studies showed that drought affected the structures of soil microbial communities (Preece et al., 2019; Wen et al., 2023); thus, it may be assumed that it can influence the composition of microbial residues. It was revealed in this study that drought had a greater effect on bacterial necromass than fungal necromass, which validated our second hypothesis (Figure 2).…”

“…The BNC increased in the subsoil where bacteria dominate to a greater degree than in the topsoil (Figure 2), as they are mostly facultative anaerobes (Wen et al., 2023). Moreover, the protection of soil aggregates by clay reduced the sensitive responses of BNC to variations in soil moisture (Li et al., 2019), which protected the accumulation of subsoil BNC (Doetterl et al., 2015).…”