Molecular Soil Biology 2024, Vol.15, No.2, 71-73 http://bioscipublisher.com/index.php/msb 72 Figure 1 Experimental design, soil carbon, and relative microbial community growth Note: (A) Soil samples were taken from four replicated temperature gradients (n = 4 biological replicates) in a (Sub)Arctic grassland in Iceland. This grassland experienced at least 50 years of soil warming established by natural geothermal activity. Root-ingrowth and root-exclusion cores were installed in situ for 10 months (October 2019 to August 2020) at two temperature levels (ambient temperatures and +6°C above ambient temperatures). We aimed to investigate how root presence or absence affects microbial growth under warmed conditions. While extracting the in situ installed cores, we also took a fresh soil core (hereafter, undisturbed core) to examine warming effects without the disturbances associated with core installation (e.g., soil extraction, mixing, and root/stone removal). Squares depict treatment colors used for graphs. (B) Concentrations of soil carbon decreased with warming (t = 2.1, df = 18.3, *P = 0.049, n = 12), while (C) relative microbial community growth (mass-specific) increased (t = −2.5, df = 20.7, *P = 0.019, n = 12). The median is represented by the center line of the box, while the upper and lower quartiles are indicated by the box limits. The whiskers represent 1.5 times the interquartile range; any outliers are shown as separate points. We used two-sided Student’s t tests to infer differences between warming levels Figure 6 Chitinophagaceae show a higher contribution to the total community’s growth in the presence of roots Note: Heatmap showing the top 15 families based on their proportional 18O assimilation across root-ingrowth and root-exclusion cores at ambient (A) and long-term warmed conditions (B). Individual boxes represent replicates per treatment (n = 4 biological replicates). Proportional 18O assimilation ranges from 0 to 1 and estimates how much a single taxon contributes to the community’s overall growth. Hence, it can also be considered as the proportion of bacterial growth an ASV is responsible for. It was calculated using recomputed relative abundances of only growing taxa (sum: relative abundancesgrowing taxa = 1) and their RGRs. ASVs had to be active in at least two samples if detected as growing in a treatment. Proportional 18O assimilation was then agglomerated at the family level and visualized for the top 15 families. If family identity could not be assigned (NA), then phylum names were provided. Bubbles below each replicate box show the cumulative growth summarized over all displayed families. Asterisks "*" (Acidobacteriota NA: P = 0.002,Nitrosomonadaceae: P = 0.044, Chitinophagaceae: P = 0.004, Streptomycetaceae: P = 0.016) represent significant differences between root-ingrowth and root-exclusion cores agglomerated over both temperature regimes based on Wilcoxon rank tests using false detection rate correction for multiple comparisons (n = 4)
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