Manure application affects microbial metabolic quotient through DOM recalcitrance and microbial strategy shifts in a Mollisol

Abstract

Microbial metabolic quotient (qCO₂) is an essential predictor for the dynamic of carbon storage in global soil. Dissolved organic matter (DOM) acts as a primary OC source for microbial respiration, and microbial life strategy acts as an important factor in controlling organic carbon utilization, but numerous uncertainties persist regarding their association with qCO₂ under long-term manure application. To fill this knowledge gap in current understanding, this study measured the qCO₂ in a Mollisol after a long-term (40 years) fertilisation, and assessed its correlation with the DOM chemodiversity and microbial life strategy (A- and Y-strategies). Results suggested that long-term manure amendments, in comparison to the application of mineral fertilisers and no fertilisers, notably decreased the qCO₂, but enhanced the recalcitrance of DOM which was demonstrated by increased humification (HIX and the relative proportion of humic-like components) and aromaticity (SUVA₂₅₄). Microbial life strategy analysis showed the mineral and manure amendments promoted the increase in the relative percentage of Y-strategies, while decreased that of A- strategies. The correlation and Random Forest analysis suggested that the recalcitrant DOM components and Y-strategies might be directly implicated in the qCO₂. Redundancy analysis evidenced that soil pH was the most important regulator for change in microbial strategy and DOM chemodiversity. Partial least squares path modeling revealed that long-term manuring directly reduced the soil pH, and then increased the proportion of Y-strategies and DOM recalcitrance, ultimately resulting in the decreased qCO₂. These findings elucidate the mechanism and novel insights regarding microbial metabolic quotient under long-term manure fertilisation, which are critical for more accurately forecasting microbial carbon utilization efficiency and proposing effective management strategies for carbon sequestration.