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Soil microbes are an essential component of terrestrial ecosystems and drive many biogeochemical processes throughout the soil profile. Prior field studies mainly focused on the vertical patterns of soil microbial communities, meaning their temporal dynamics have been largely neglected. In the present study, we investigated the vertical and temporal patterns of soil bacterial and archaeal communities in a wheat-soybean rotation agroecosystem at a depth of millions of sequences per sample. Our results revealed different vertical bacterial and archaeal richness patterns: bacterial richness was lowest in the deep soil layer and peaked in the surface or middle soil layer. In contrast, archaeal richness did not differ among soil layers. PERMANOVA analysis indicated that both bacterial and archaeal community compositions were significantly impacted by soil depth but unaffected by sampling time. Notably, the proportion of rare bacteria gradually decreased along with the soil profile. The rare bacterial community composition was the most important indicator for soil nutrient fertility index, as determined by random forest analysis. The soil prokaryotic co-occurrence networks of the surface and middle soil layers are more connected and harbored fewer negative links than that of the deep soil layer. Overall, our results highlighted soil depth as a more important determinant than temporal variation in shaping the soil prokaryotic community and interspecific interactions and revealed a potential role of rare taxa in soil biogeochemical function.

Abstract:The tissue compartmentalization of phosphophoryn, osteopontin (OPN) and bone sialoprotein (BSP) in dentin was biochemically analyzed. The radicular portion of rat incisor was excised and sequentially extracted; i.e., proteins non-covalently bound to matrix such as soft tissues were solubilized with 4 M guanidinium chloride (G1), mineral-binding proteins were then extracted with 0.5 M EDTA (E), proteins noncovalently bound to the collagen matrix were extracted with 4 M guanidinium chloride (G2) after E, and finally the proteins covalently bound to the collagen matrix were extracted by bacterial collagenase digestion (C). Stains-All and Rhodamine B staining, which selectively stain calciun~-binding proteins, revealed a 50~80 kDa broad band in the E extract on 10 % polyacrylamide gels. This intense band disappeared after precipitation with CaC12, indicating that the protein is phosphophoryn. After removing phosphophoryn from the E extract, 67 kDa intense and 50 kDa weak bands appeared on the gels stained with Stains-All. The 67 kDa protein was observed similarly in the G2 and C extracts. Western blots using monoclonal antibodies revealed the presence of 67 kDa BSP and 50 kDa OPN. When the tissue compartmentalization was compared, these three proteins were not detected in the G1 extract, phosphophoryn and osteopontin were localized only in the E extract, and BSP was observed not only in the E extract but also in the G2 and C extracts. These findings indicate that phosphophoryn, OPN and BSP are rapidly incorporated into the mineralized fraction and that BSP also binds to collagen-related fraction, suggesting the association with intial mineralization in the dentin.

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