Earth’s environment is continuously changing, owing to a variety of natural and anthropogenic events. Taxonomic and functional compositions of soil microbiome are generally sensitive to environmental disturbances, which are usually associated with notable changes in environmental variables such as climate, soil physiochemical properties and aboveground plants. As such, it remains unclear whether microbiome is sensitive to mild disturbance, which causes no immediate change to ecosystem despite possibly notable consequences in the long term. To this end, we initiated a field study with very light-intensity lamb grazing in the Xilinguole grassland, a representative temperate Eurasian grassland located in Inner Mongolia, China. For the purpose of comparison, we also examined the effects of soil erosion and dust deposition, which are frequently occurring in Xilinguole and have substantially changed the grassland ecosystem. We adopted high-throughput sequencing of 16S rRNA gene amplicons to examine bacterial taxonomy in grassland soils. We adopted GeoChip 5.0 to examine 676 gene families of soil microbiome. We measured 15 plant and soil variables, including plant species richness, plant coverage, soil temperature, soil moisture, pH, total organic carbon, ammonium and nitrate.
Results/Conclusions
Light-intensity lamb grazing changed neither plant nor soil variables. Nonetheless, most microbial functional genes, but not bacterial taxonomy, were significantly shifted. The relative abundances of both taxonomic markers and functional genes related to nitrifying bacteria were also changed. In contrast, soil total organic carbon and plant coverage were decreased by soil erosion, and soil dissolved organic carbon (DOC) was increased by soil deposition. Microbial taxonomy and functional gene compositions were altered by both soil erosion and deposition, with dramatic increase in Cyanobacteria related to increased stability in soil aggregates. amyA genes encoding α-amylases were specifically increased by soil deposition and positively correlated to DOC, which likely explained changes in DOC. Most of microbial functional genes associated with carbon, nitrogen, phosphorus and potassium cycling were decreased or unaltered by both erosion and deposition, probably arising from acceleration of organic matter mineralization. When conducting lamb grazing in the background of eroded soils or deposited soils, we still observed significant shift of most microbial functional genes, but not bacterial taxonomy. Therefore, we conclude that there is a high level of sensitivity with respect to functional traits in differentiating environmental disturbance, suggests that the key level at which to address microbial responses may not be “species” (by means of rRNA taxonomy), but rather at the functional gene level.