Viruses are highly abundant in soils with their numbers exceeding those of cooccurring bacterial cells by 10- to over 1000-fold. Water and organic matter content influence the magnitude of the viral-to-bacterial ratio in soils; thus, ecosystem type and land use shape interactions between viral and host microbial communities in soils. Less understood are the shorter term interactions between viral and host communities that ultimately maintain the large viral standing stock within soils. This study examined short-term dynamics of viral and bacterial communities in soils to determine whether the growth of soil bacterial communities results in the production of soil viruses, and if viral community responses occur within specific populations. In microcosms amended with different carbon sources, increases in viral abundance (VA) accompanied increases in bacterial abundance (BA) and bacterial respiration rate (BRR). The timing and intensity of increases in BA, VA and BRR were different across C sources suggesting differences in the predominant mode of viral replication within growth-stimulated bacterial populations. Moreover, compositional changes occurred in soil bacterial and viral communities indicating that new viral production arose from a subset of host populations. To our knowledge, these are the first observations of soil viral populations responding to short-term changes in soil bacterial communities.

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Dam decommissioning projects, although numerous, rarely include complete sets of data before and after restoration for evaluating the ecological consequences of such projects. In this study, we used a before-after control-impact (BACI) design to assess changes in leaf litter decomposition and associated macroinvertebrate and fungal decomposers following dam decommissioning in Fossil Creek, Arizona, USA. Leaf litterbags were deployed in a relatively pristine site above the dam and a highly disturbed site below the dam where over 95% of the flow was previously diverted for hydropower generation. Leaf litter decomposition was significantly slower below the dam both measurement years (pre-and postrestoration) with no site-year interaction, indicating that decomposition in this stream section was not affected by increased flow. In contrast, both macroinvertebrates and fungi differed significantly above and below the dam prior to restoration but were similar post-restoration, supporting the concept that decomposer communities can quickly rebound following reintroduction of full flow. Our results indicate that some aquatic ecosystem variables can return to a more natural state following ecological restoration activities such as water flow restoration.