Shift of Dominant Species in Plant Community and Soil Chemical Properties Shape Soil Bacterial Community Characteristics and Putative Functions: A Case Study on Topographic Variation in a Mountain Pasture.

Reducing management intensity according to the topography of pastures can change the dominant plant species from sown forages to weeds. It is unclear how changes in species dominance in plant community drive spatial variation in soil bacterial community characteristics and functions in association with edaphic condition. Analysing separately the effects of both plant communities and soil chemical properties on bacterial community is crucial for understanding the biogeographic process at a small scale. In this paper, we investigated soil bacterial responses in five plant communities (two forage and three weed), where >65% of the coverage was by one or two species. The structure and composition of the bacterial communities in the different microbiome were analysed using sequencing and their characteristics were assessed using the Functional Annotation of Prokaryotic Taxa (FAPROTAX) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. Firmicutes and Planctomycetes responded only to one specific plant community, and each plant community harboured unique operational taxonomic units (OTUs) at the species level. There were a large percentage of uniquely absent OTUs for specific plant communities, suggesting that a negative effect is critical in the relationship between plants and bacteria. Bacterial diversity indices were influenced more by soil chemical properties than by plant communities. Some putative functions related to C and N recycling including nitrogen fixation were correlated with pH, electrical conductivity (EC) and nutrient levels, and this also implied that some biological functions, such as ureolysis and carbon metabolism, may decline when fertilisation intensity is reduced. Taken together, these results suggest that a shift of dominant species in plant community exerts individual effects on the bacterial community composition, which is different from the effect of soil chemical properties.

Effect of vermicompost application on root growth and ginsenoside content of Panax ginseng.

Vermicomposts are valuable by-products of organic wastes and can be used to improve soil environments in ginseng production. We compared the effects of food waste vermicompost (FWV), cow manure vermicompost (CMV) and paper sludge vermicompost (PSV) on several ginseng root production variables. Interactions between soil chemical properties, root growth, ginsenoside content and plant mineral content were also investigated. In the PSV treatment, the root yield increased by 40 t ha-1 compared to the untreated control. Nitrate concentration correlated negatively with root yield, and none of the vermicompost treatments differed significantly from the control in terms of root loss. Soil pH correlated positively with root weight, and total ginsenoside content did not vary among treatments, although some individual ginsenosides did differ among treatments. Root iron content correlated strongly with total ginsenoside content, and total ginsenoside content correlated negatively with root yield. Overall, our results showed that the root yield increase was not due to nutrient increase. Vermicompost was safe to use in relation to root rot disease, and it favourably elevated the pH of fields converted from rice paddies to ginseng production. Ginsenoside was not involved in defence mechanisms against root rot disease. Root iron content may have been involved in the metabolism of ginsenoside, and there was an apparent trade-off between ginsenoside content and root yield. Finally, vermicompost application altered resource allocation and soil chemical properties, which led to novel interactions between root parameters and components.