The priming effect patterns linked to the dominant bacterial keystone taxa during different straw tissues incorporation into Mollisols in Northeast China

Abstract

The incorporation of crop residues (e.g., maize straw) into the soil could promote or inhibit soil organic carbon (SOC) mineralization by affecting microbial activity, which is known as the priming effect (PE), and is a pivotal mechanism of the soil C cycle. However, the microbial community structure underlying PE remains elusive. Furthermore, the effects of crop residues on PE are poorly understood. Therefore, we conducted a 120-day laboratory experiment using the Mollisols of China and the addition of 13 C-labeled maize stems (ST), leaves (LE), and sheaths (SH) residues (1 %) to investigate PE and keystone taxa at different stages. Results showed that the ST, LE, and SH treatments significantly increased total CO 2 - and SOC-derived CO 2 emissions by 73.55–77.13 % and 54.67–62.55 %, respectively, compared to the control ( p < 0.05). The ST, LE, and SH treatments resulted in a negative PE during the first 20 days, which subsequently changed to a positive PE. Furthermore, the threshold for a significant increase in PE increase occurred at 20.81 %, 39.19 %, and 46.51 % of the mineralization of sheaths, stems, and leaves, respectively. Co-occurrence network analysis showed that the keystone taxa were from Sphingomonas to Nitrospira then to Subgroup_10 and Gemmatimonas, from Sphingomonas, Nitrospira to Steroidobacter then to Subgroup_10 , and from Sphingomonas to Subgroup_10 , then to Chitinophaga , delta_proteobacterium in ST, LE, and SH during three stages, respectively. Furthermore, structural equation model (SEM) analysis showed that these potential keystone species and their specific functions significantly influenced the PE ( p < 0.05). In conclusion, these findings highlight the critical roles of bacterial keystone taxa in regulating PE under different straw tissue incorporation into soil, which provides a better understanding of the influences of residues quality on soil C cycle. Additionally, the findings contribute to the promotion of the proper utilization of different straw tissues in the future. • Straw stem, leaves and sheath could trigger a two-stage priming effect with different mechanism. • A threshold of the decomposition function indicated that a drastic increase in PE occurred when ca. 20.81%, 39.19%, and 46.51% of straw sheath, stem and leaves decomposed, respectively. • The putative keystone taxa were associated with PE due to their different functional traits.

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