Coordinated interannual change in NEON soil bacterial communities across continental North America

Daniel Tang , Jihong Liu

Soil bacterial communities change from year to year, but whether these changes are coordinated across distant ecosystems has not been well investigated. We leveraged publicly available soil data from the National Ecological Observatory Network (NEON), and applied statistical analyses to evaluate the temporal changes of soil bacterial communities across continental North America. Data were collected from 2020 to 2024, across 20 NEON sites spanning arctic tundra, tropical forest, grassland, and desert ecosystems. Bacterial composition, profiled by 16S rRNA gene amplicon sequencing, differed significantly among years in 16 of the 21 strata across the 1,253 cores with non-zero reads (between-year minus within-year Bray-Curtis dissimilarity, 999 within-stratum year-label permutations, pooled P = 0.001). PERMANOVA agreed in significance on 20 of the 21 strata. After applying a 50,000-read minimum depth floor and rarefaction, 1,212 cores remained across 21 strata. Fifteen of these strata met the temporal change criterion and formed the analytical set for synchrony analysis. Genus-level temporal trajectories were positively correlated among these strata (mean Spearman ρ = 0.167 across 105 pairs, rising to 0.218 when the single boundary stratum was excluded); no permutation of 999 reached the observed value, giving p = 0.001 and indicating coordinated interannual change across geographically separated sites. Among the prespecified predictors, more similar median soil pH was weakly associated with greater synchrony (ρ = -0.181, one-sided P = 0.043), while geographic distance was not (ρ = -0.143, P = 0.08, across separations of 110 to 9,193 km). None of the four declared climate-synchrony windows was associated with bacterial synchrony (ρ = +0.034 to +0.069, all P > 0.20 before correction for four tests). Overall, these results provide evidence for coordinated interannual dynamics of soil bacterial communities at continental scale, while the environmental drivers of that coordination remain undetermined and should be the focus of future work.