Microscale spatiotemporal heterogeneities and variations of physicochemical- and biological properties of the soil environment are key manipulating microbial activity and ecological functionalities. Yet little is known about the underlying mechanisms and impacts on the functioning biogeochemical processes of the earth-surface ecosystems typically the soil-water-microbe-climate nexus. Employing microscale experiments, we illustrate how small-scale water and nutrient configurations as well as those of biological (populations) and chemical (such as O₂ and pH) gradients regulate microbial interactions and functionality, and impacts on soil carbon (C) and nitrogen (N) cycling. We firstly use pairs of fluorescently labelled bacterial strains and a hyphae-forming fungal strain that expand together across a nutrient-amended surface, and show that fungal hyphae are important regulators of bacterial diversity and promote plasmid-mediated functional novelty during range expansion in an interaction-independent manner. In addition, we employed a soil column experiment and illustrated that sufficient labile carbon from plant residues such as straw induced fast O₂ consumption with microoxic development in the straw-soil interfaces. In the meantime, the porous structure of straw materials could enhance O₂ diffusive inputs in the core area, and subsequently formed a concentric ring-like microoxic area around the straw patch. Such enriched oxic-microoxic transient zones would induce nitrification coupled denitrification, leading to high N₂O emissions. These results contribute to a better understanding of the driving factors for microbial interactions and impacts of soil health and ecosystem functions.

Spatiotemporal heterogeneity;,microbial interactions; ecological function; soil health