Soil microorganisms are the drivers of major nutrient cycles on Earth. However, as most soil microorganisms are dormant, it is important to elucidate the active participants in soil processes. In this project, we explored the active microorganisms involved in two major processes in soil - degradation of plant polymeric material (cellulose) and fixation of atmospheric N2 gas. Cellulose is a key component of plant material, and one of the major constituents of the soil carbon pool. Bacteria and fungi work in tandem to mediate the decomposition of this polymer, yet their activities, interactions and ecological niches have yet to be explored. To that end, we investigated microbial-mediated cellulose degradation to explore the influence of background nutrient on process dynamics and niche availability for the bacterial-fungal cellulose-degrading consortium. We found that the cellulose-degrading consortium had a clear niche differentiation depending on carbon- and nitrogen-availability and time. Although historically fungi are presumed to be the most important participants of this process, our data suggest that bacteria exploit a clear, yet context-dependent functional niche. Network analysis further revealed, that there are in fact stable co-occurrence patterns between fungi and bacteria independent of nutrient amendments and time underlining the consortia nature of cellulose degradation in soil. In the process of N2 fixation, we investigated the dependence of active diazotrophs on different C and thus energy sources, which in soil are provided via plant root exudation. Active diazotrophs were identified in the vicinity of plant roots, which represent a reactivation hotspot for diazotrophs. Sequence analysis revealed that the active diazotroph community was plant-specific and differed significantly from the diazotroph seedbank, suggesting plant-specific resuscitation effects. Another goal of the project was to investigate dormancy strategies of soil microorganisms inhabiting arid soils, namely biological soil crusts in the Negev Desert. We used meta-omics techniques in combination with single-cell activity assays to understand the genetic mechanisms for dormancy and the resuscitation dynamics of microorganisms inhabiting these crusts, which explain their capability to persist in this inhospitable environment. The results of this project were disseminated via scientific publications and presentations at scientific conferences by the team to the scientific audience and to the non-scientific public in articles, interviews and other outreach activities.
