Microbial mechanisms of carbon priming effects revealed during the interaction of crop residue and nutrient inputs in contrasting soils

Abstract

Agronomic practices such as crop residue return and additional nutrient supply are recommended to increase soil organic carbon (SOC) in arable farmlands. However, changes in the priming effect (PE) on native SOC mineralization in response to integrated inputs of residue and nutrients are not fully known. This knowledge gap along with a lack of understanding of microbial mechanisms hinders the ability to constrain models and to reduce the uncertainty to predict carbon (C) sequestration potential. Using a C-labeled wheat residue, this 126-day incubation study examined the dominant microbial mechanisms that underpin the PE response to inputs of wheat residue and nutrients (nitrogen, phosphorus and sulfur) in two contrasting soils. The residue input caused positive PE through "co-metabolism," supported by increased microbial biomass, C and nitrogen (N) extracellular enzyme activities (EEAs), and gene abundance of certain microbial taxa (Eubacteria, β-Proteobacteria, Acidobacteria, and Fungi). The residue input could have induced nutrient limitation, causing an increase in the PE via "microbial nutrient mining" of native soil organic matter, as suggested by the low C-to-nutrient stoichiometry of EEAs. At the high residue, exogenous nutrient supply (cf. no-nutrient) initially decreased positive PE by alleviating nutrient mining, which was supported by the low gene abundance of Eubacteria and Fungi. However, after an initial decrease in PE at the high residue with nutrients, the PE increased to the same magnitude as without nutrients over time. This suggests the dominance of "microbial stoichiometry decomposition," supported by higher microbial biomass and EEAs, while Eubacteria and Fungi increased over time, at the high residue with nutrients cf. no-nutrient in both soils. Our study provides novel evidence that different microbial mechanisms operate simultaneously depending on organic C and nutrient availability in a residue-amended soil. Our results have consequences for SOC modeling and integrated nutrient management employed to increase SOC in arable farmlands.

Interactive carbon priming, microbial response and biochar persistence in a Vertisol with varied inputs of biochar and labile organic matter

“…Biochar and LOM contain different forms of C for use by various microorganisms; hence, the input of biochar and LOM can influence the microbial community and consequently the interactive priming effects. For example, the easily available C (such as glucose-type C) increases bacterial growth but might decrease fungal growth (Meidute, Demoling, & Bååth, 2008), whereas crop residues increase growth of both bacterial and fungal communities (Fang, Nazaries, Singh, & Singh, 2018;Meidute et al, 2008). Biochar increases the fungal community (Farrell et al, 2013;Steinbeiss, Gleixner, & Antonietti, 2009) and Gram-positive bacteria in soil (Farrell et al, 2013;Santos, Torn, & Bird, 2012), which might be related to the use of labile-C in biochar over the short term (Farrell et al, 2013).…”

Enhancing Carbon Sequestration Using Organic Amendments and Agricultural Practices

“…There three mechanisms, which are classified by different researchers based on the stabilization of SOM, include chemical, biochemical and physical stabilization [76]. Agricultural practices such as the addition of crop residues increase the SOM as well as nutrients contents in the soil by integrated nutrient management [77]. Most studies focus on the fact that the change of crop residue traits has positive effects of the soil CS in organic farming system [78].…”

Litter carbon and nutrient chemistry control the magnitude of soil priming effect

“…More specifically, the balance in microbial competition between micro‐organism communities specialized in the decomposition of easily degradable organic compounds and those feeding on polymerized SOC may further explain differences in soil PE (Fontaine et al, ). In this context, the chemical composition of fresh litter inputs could be a critical driver of SOC degradation by regulating the balance between different functional types of soil microbial communities (Fang, Nazaries, Singh, & Singh, ; Fanin, Hättenschwiler, & Fromin, ). Despite this, the relationship between litter chemistry and PEs remains largely unexplored.…”