Annual precipitation and soil moisture level strongly associate with the microbial community structure in Interior Douglas-fir and Sub-Boreal Spruce ecozones in British Columbia

Abstract

Soil moisture and precipitation can affect forest soil bacterial community structure and regulate important interactions between key soil microbial processes and the environment. This study examined how mean annual precipitation and soil moisture content affect the alpha and beta diversity in the soil microbiome of the Interior Douglas Fir and Sub-Boreal Spruce ecozones in British Columbia. Since soil compaction and organic matter removal could impact moisture level, their association with soil microbial structure were also examined in this study. We used 16S rRNA gene libraries from the organic soil layer of 104 samples to test whether mean annual precipitation and soil moisture are associated with differences in soil bacterial community structure. Our results showed that sites with higher mean annual precipitation had higher soil moisture content (one-way ANOVA p = 1.16  10^-7). We demonstrated that the relative abundance of Mycobacterium, Patulibacteraceae, and Bradyrhizobium were significantly impacted by higher mean annual precipitation and soil moisture content. Soil moisture content positively correlated (spearman r = 0.58, p < 0.0001) with alpha and beta diversity, and it significantly affected soil microbial community composition. Organic matter removal and soil compaction did not significantly impact soil moisture. Overall, our study highlighted that water availability is a key driver of forest soil microbial diversity in British Columbia. Thus, close monitoring of precipitation and soil moisture may provide meaningful information on forest health.