Abstract
Nutrient amendment diminished bacterial functional diversity, consolidating carbon flow through fewer bacterial taxa. Here, we show strong differences in the bacterial taxa responsible for respiration from four ecosystems, indicating the potential for taxon-specific control over soil carbon cycling. Trends in functional diversity, defined as the richness of bacteria contributing to carbon flux and their equitability of carbon use, paralleled trends in taxonomic diversity although functional diversity was lower overall. Among genera common to all ecosystems, Bradyrhizobium, the Acidobacteria genus RB41, and Streptomyces together composed 45–57% of carbon flow through bacterial productivity and respiration. Bacteria that utilized the most carbon amendment (glucose) were also those that utilized the most native soil carbon, suggesting that the behavior of key soil taxa may influence carbon balance. Mapping carbon flow through different microbial taxa as demonstrated here is crucial in developing taxon-sensitive soil carbon models that may reduce the uncertainty in climate change projections.
Highlights
Nutrient amendment diminished bacterial functional diversity, consolidating carbon flow through fewer bacterial taxa
Taxon-specific growth rates were measured using quantitative stable isotope probing with 18Owater[7,10] for soils collected from desert grassland (GL), Piñon-Juniper scrubland (PJ), Ponderosa
Our methods track the incorporation of 18O-labeled water into bacterial DNA, and not carbon explicitly, these results indicate that growth of individual bacterial taxa measured through 18O assimilation can be directly associated with the movement of C through the soil
Summary
Bradyrhizobium (Alphaproteobacteria, Family: Xanthobacteraceae), RB41 (Acidobacteria, Family: Pyrinomonadaceae—Subgroup 4), and Streptomyces (Actinobacteria, Family: Streptomycetaceae) were common to all soils and treatments and in the C + N treated soils, these lineages accounted for the majority of C flux (Fig. 4a; Supplemental Table 1). These taxa represent globally ubiquitous and abundant lineages as determined across the Earth Microbiome Project database[18]. We assessed the relationship between relative C use and relative abundance in response to nutrient amendments using linear mixed modeling, accounting for random intercepts (and to limit pseudo-replication) across ecosystems and bacterial genera, and including an offset term to assess significant departure from the 1:1 line.
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