Temporal and spatial dynamics of bacterial and fungal microbiomes in nursery soils post-steaming

A major concern for plant nurseries and land stewards is managing pathogens that induce soilborne diseases. Plant diseases cost nurseries millions of dollars in lost revenue. Plant pathogens spread into the environment from nursery soil used for out-plantings. Recent research shows that steaming soil at high temperatures can effectively kill plant pathogens, however, few studies investigate the influence of steaming on the soil microbiome, an essential component of plant health. We conducted a controlled experiment where nursery soil underwent a steaming event within a rectangular mesocosm (2.04 x 3.55 x 0.25 m) located at the National Ornamentals Research Site at Dominican University (NORS-DUC) (San Raphael, CA, US). Soil samples were collected at four time points post-steaming. Thirty-two soil samples were used for DNA extraction and 18 for chemical analysis. The 16S rRNA gene and ITS genetic markers were used for amplicon-based sequencing methods to identify the bacterial and fungal soil communities. Results indicate that microbial diversity and composition shifted overtime, but that soil depth was not an important factor. Important bacterial taxa were the Firmicutes, especially 1 day post-steaming, and common fungal taxa included Aspergillus sp., Cladosporium sp., and Pseudallescheria sp.. Plant nutrients such as B, C, Cl, K, Mg, SO4, and Zn in addition to essential soil properties such as CEC, gypsum, moisture, and SAR changed significantly with soil recovery. These results can help nursery practitioners make informed decisions for biotic and nutrient amendments post-steaming to promote soil and plant health.