Abstract: Soil viral community dynamics along a naturally occurring organic carbon gradient in temperate desert
Understanding the impact of microbial processes on soil carbon (C) cycling is critical to predicting the effects of future climate change, as terrestrial ecosystems contribute about half of global C efflux. Thus, their inclusion is a current focus of climate model improvement, however substantial unexplained variation remains. We hypothesized that soil viruses could account for a significant proportion of that unexplained variation. This premise was based on previous research that demonstrated that viruses play a major role in marine C cycling by killing and lysing 25-50% of marine microbial biomass daily, releasing host cell contents into the environment, where the C is then either sequestered or respired into the atmosphere. To assess the impact of viruses in terrestrial ecosystems, we combined techniques from microbial ecology, meta-âomics, and bioinformatics. To this aim, we collected 12 soil samples along elevational gradients of mountains in northern New Mexico that encompass a natural organic C gradient. We then sequenced metagenomes and virus-enriched âmetaviromesâ extracted from the same soil samples for a comprehensive view into virus-host interactions and soil community dynamics. Illumina sequencing resulted in a total of 4.1 trillion reads from 12 metavirome and 12 metagenome samples. Next, we customized a bioinformatics pipeline to analyze the paired virus-microbial community data and recovered a diverse set of viral contigs and bacterial MAGs, which were further analyzed to investigate virus-host interactions, examine spatial patterning in viral and microbial community structures, and relate community dynamics to ecosystem functioning. Our results suggest viral diversity has strong positive correlations to more favorable soil conditions with higher concentrations of organic C and higher rates of microbial respiration. Additionally, we found evidence of divergent patterns of genes in putative viral genomes that could influence host cell metabolism based on soil conditions. We have also expanded our work from field-based observations and correlations to more controlled systems in laboratory microcosms, which have allowed us to directly test for causal relationships between viral communities and C flux. Our work can be incorporated into quantifying potential impact of virus-host dynamics on a global scale and improve our understanding of the drivers of terrestrial C cycling, enabling the development of more accurate climate models.