Integrating perennial bahiagrass into the conventional rotation of cotton and peanut enhances interactions between microbial and nematode communities

Integrating two years of bahiagrass (Paspalum notatum Flugge) into the peanut (Arachis hypogea L.) and cotton (Gossypium hirsutum L.) cropping system improves soil quality and crop production as compared to a conventional peanut-cotton-cotton rotation (CR). However, it is unclear if this system, known as a sod-based rotation (SBR), affects soil biological communities (e.g., soil microorganisms and nematodes) and their trophic interactions. Furthermore, how soil trophic groups respond to agricultural management (e.g., irrigation) is understudied. In April 2017, we collected pre-planting soil samples (0-30 cm) from cotton plots located in Quincy (Florida, United States) that had been under CR (cotton grown in two consecutive years) and SBR (cotton grown only once) for 17 years. We used amplicon sequencing to investigate soil microbial communities and an inverted microscope technique to quantify nematodes. Compared to CR, SBR significantly increased nematode alpha diversity (one-way ANOVA; P < 0.05) and induced different nematode communities. In contrast, there were no significant differences in the diversity and structure of bacterial communities between SBR and CR. SBR plots were significantly enriched in Nitrospira, while the second of two consecutive years of cotton growth in CR had a higher relative abundance of Alphaproteobacteria (one-way ANOVA; P < 0.05). Plant-parasitic (848 counts per 100 g dry soil) and bacterial-feeding nematodes (798 counts per 100 g dry soil) had a similar abundance in SBR, while plant-parasitic nematodes (7772 counts per 100 g dry soil) were predominant in CR (<1000 counts per 100 g dry soil for all other taxa). SBR exhibited a greater number of significant paired Pearson correlations (P < 0.05) among functional groups of bacteria and nematodes compared to CR systems. Irrigation had no effect on the diversity and structure of bacterial and nematode communities in SBR, although some soil bacterial and nematode groups responded to irrigation. Overall, these results suggest that integrating bahiagrass to diversify the conventional peanut-cotton rotation is a sustainable approach to enhance soil biodiversity, with more diverse nematode communities and complex soil trophic interactions that will affect the response to crops and irrigation. Thus, future crop rotations should increase plant functional trait diversity (e.g., by adding perennial grasses) to maximize benefits to soil communities.