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This study investigated the long-term effects of Bacillus thuringiensis (NL-11) and Gongronella butleri (NL-15) inoculants on soil aggregate stoichiometry under varying plant conditions over one and three years. Results indicated that microbial impacts were time-dependent and significantly influenced by the presence of plants, particularly regarding aggregate stability and nutrient cycling.

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Abstract

Functional microbial inoculation is widely applied in soil restoration; however, its effects on aggregate-scale nutrient cycling remain unclear. Based on ecological stoichiometry theory, we conducted 1-year and 3-year pot experiments using Bacillus thuringiensis (NL-11) and Gongronella butleri (NL-15) under plant-present and plant-absent conditions, with only NL-11 applied in the 1-year experiment. Aggregate size distribution, mean weight diameter (MWD), soil nutrients, microbial biomass, and enzyme activities were evaluated across aggregate classes. The results demonstrated that microbial effects were dependent on both time and plant presence. Under 3-year plant-present conditions, NL-11 and NL-15 significantly increased macroaggregate proportions and MWD, thereby enhancing aggregate stability. Under 3-year no-plant conditions, NL-15 increased organic carbon and total nitrogen in macro- and meso-aggregates by 55–59% and elevated soil C/P and N/P ratios, whereas NL-11 primarily enhanced total nitrogen. In 1-year no-plant macroaggregates, NL-11 increased microbial biomass phosphorus and reduced microbial biomass C/P and N/P ratios. Both inoculants enhanced invertase activity under plant-absent conditions, whereas plant presence stimulated acid phosphatase activity, with NAG activity increasing only under NL-15. Overall, microbial inoculation altered nutrient availability and microbial metabolic characteristics, promoted coordinated C–N–P stoichiometry, and facilitated the recovery of aggregate-scale nutrient cycling.

Key findings

  • Under 3-year plant-present conditions, both inoculants significantly increased macroaggregate proportions and mean weight diameter, enhancing aggregate stability.
  • In 3-year no-plant conditions, NL-15 increased organic carbon and total nitrogen in macro- and meso-aggregates by 55–59% while elevating soil C/P and N/P ratios.
  • NL-11 primarily enhanced total nitrogen in no-plant conditions but increased microbial biomass phosphorus and reduced microbial biomass C/P and N/P ratios in 1-year no-plant macroaggregates.

Keywords

Microbial inoculantNutrientPhosphorusBiomass (ecology)AgronomyNutrient cycle

Identifiers

DOI
10.3390/microorganisms14030583
Journal
Microorganisms
Year
2026