Divergent mechanisms of rhizosphere and non-rhizosphere soil organic carbon sequestration under precipitation variability: Evidence from microbial life-history strategies
Abstract
Background: Climate change-induced precipitation variability has profound impacts on soil carbon dynamics in agricultural ecosystems in arid regions.
Methods: To elucidate the carbon retention mechanisms of rhizosphere and non-rhizosphere soils under precipitation variability, we conducted an eight-year precipitation manipulation experiment (50% reduction, 25% reduction, control, 25% increase, 50% increase) in farmland on the Loess Plateau in China. This study comprehensively assessed the dynamics of carbon components and the driving factors behind these mechanisms.
Results: Our results indicate that increased precipitation significantly enhanced organic carbon (SOC) in both rhizosphere (20.5% increase) and non-rhizosphere (22.5% increase) soils, although carbon accumulation patterns exhibited spatial differences. Rhizosphere carbon accumulation primarily originated from mineral-associated organic carbon (MAOC) (MAOC/SOC ratio increased from 80.3% to 88.8%), while non-rhizosphere soils relied on contributions from particulate organic carbon (POC) (POC/SOC ratio increased from 12.5% to 17.5%). Additionally, microbial communities displayed functional group decoupling. Increased precipitation shifted bacteria towards r-strategies in both habitats (evidenced by a decrease in the ratio of oligotrophic/mesotrophic bacteria and an increase in rrn copy numbers), while fungal life strategies remained unchanged. Bacterial α-diversity increased in both regions, but the response of fungal α-diversity diverged, increasing in rhizosphere soils while decreasing in non-rhizosphere soils. Partial least squares path modeling (PLS-PM) revealed habitat-specific carbon sequestration mechanisms. In rhizosphere soils, precipitation stimulated root carbon secretion (70.7%) and increased the carbon-to-nitrogen ratio of exudates (119.8%), promoting the proliferation of r-strategists, enhancing MAOC formation and SOC accumulation. In contrast, non-rhizosphere soils depended on precipitation-mediated microbial diversity regulation and aggregate protection to promote POC formation and SOC accumulation.
Conclusion: This study proposes carbon sequestration models for rhizosphere and non-rhizosphere soils under variable precipitation conditions, providing key insights for predicting carbon trajectories in climate-sensitive agricultural ecosystems.
Main Determinants and Analytical Methods
1. Determination of soil physicochemical properties
2. Determination of soil enzyme activity
3. Microbial nutrient limitation
4. DNA extraction and high-throughput sequencing
5. Evaluation of microbial life strategies
6. Higher rrn copy numbers represent a preference for the r-strategy, and lower rrn copy numbers represent a preference for the K-strategy. The average rrn copy number of each OTU was estimated from the rrnDB database
7. Two-way ANOVA and Duncan’s multiple comparisons
8. Regression analyses
9. Random forest and Pearson correlation analyses
10. Partial least squares models (PLS-PM)
Main Results
1. Characteristics of the response of rhizosphere and non-rhizosphere soil organic carbon pools to changes in precipitation.
2. Characterization of the response of soil rhizosphere and non-rhizosphere microbial diversity and life strategies to changes in precipitation.
3. PLS-PM modelling showing potential direct and indirect relationships between soil properties (or root secretion), nutrient limitation, microbial diversity and life strategies on SOC under changes in precipitation.
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