Interactions of r/K-strategist bacteria and bacterivorous nematodes regulate herbivorous nematodes abundances under organic and inorganic fertilization practices

Long-term organic fertilization promoted the positive rhizosphere effects on r-strategist bacteria and K-strategist bacterivorous nematodes. Long-term inorganic fertilization facilitated the positive rhizosphere effects on Kstrategist bacteria and r-strategist bacterivorous nematodes. The r/K-strategist bacteria interact with r/K-strategist bacterivorous nematodes to suppress herbivorous nematodes abundances. Microbial food web organisms’ responses to fertilization are influenced by their r/K-strategies. The roles of r/K-strategist microbes and their associated microbivorous nematodes in regulating herbivorous nematodes abundances remain unexplored, especially under different fertilization regimes. Filling this knowledge gap is critical for enhancing agricultural sustainability through optimization of microbial food web. Here, the microbial food web community structure was analyzed in two soil compartments (bulk/rhizosphere soil) from oilseed rape (Brassica napus L.) season to investigate interactions between r/K-strategist microbes and nematodes under organic and inorganic fertilization regimes. Fertilization regimes, rather than soil compartments, predominantly controlled the microbial food web community structure. Under organic fertilization, the relative abundances of r-strategist bacteria and bacterivores of cp-3 guild were greater in the rhizosphere than in the bulk soil. In contrast, under inorganic fertilization regimes, K-strategist bacteria and bacterivores of cp-2 guild were enriched in the rhizosphere versus the bulk soil. Differential r/K-strategist bacteria controlled the microbial food web network, with r- and K-strategist bacteria predominating under organic and inorganic fertilization, respectively. Soil organic carbon from organic fertilization stimulated the growth of r-strategist bacteria, which interacted with bacterivores of cp-3 guild to reduce the relative abundance of herbivores in the rhizosphere soil. Acidification from inorganic fertilization enriched K-strategist bacteria, which interacted with bacterivores cp-2 or cp-3 guilds to suppress herbivores abundances in the rhizosphere soil. Overall, our findings highlight the importance of cross-kingdom interactions among r/K-strategist organisms for the biocontrol of herbivores, providing guidance for harnessing microbial food web to create a healthy plant rhizosphere.