Synergistic Effects of Raised Temperature and CO2 on Strategists of Soil Enzyme and Microbial Communities

The effects of global warming and CO₂ influence on soil processes and crop growth are a major area of concern. Rhizosphere soil enzymes, mostly produced by microbes, play a pivotal role in enhancing soil nutrient accessibility for plant assimilation. Knowledge about the responses and adaptations related to the nutrient acquisition in space of microbial communities to increased temperature and CO₂ re remaining deficient. Here, we grew soybean in rhizobox mesocosms under raised temperature (+2 ℃, ET) and CO₂ (+300 ppm, ECO₂) and the combination (ECO₂+ ET). ECO₂ increased the enzymatic hotspot area from 1.8 to 3.3% of soil, while ET increased enzyme activities by 2.5%-8.7%. Notably, the combined influence of ECO2 and ET synergistically amplified both the scope (increasing by 5.3% to 10.1%) and intensity (escalating by 35.4% to 67.3%) of three concurrent enzymes. Compared to ambient, rhizosphere communities in ECO₂ were dominated by the keystone taxa of r-strategists, Acidobacteria, Proteobacteria, and Ascomycota. Conversely, ET shifted the microbial community to K- selection by increasing the relative abundance of Basidiomycota and Actinobacteria. Meanwhile, ECO₂+ ET promoted the relative abundance of bacterial keystone species (Acidobacteria, Proteobacteria, and Actinobacteria) and fungi (Ascomycota and Basidiomycota) of the total community. These observations emphasize the potentially key role of enzyme hotspot areas in mediating climate change responses. Changes in the activity and extent of enzymes observed under the experimental treatments suggest a shift in balance towards a mixed r and K strategy in the hotspot microbiota. The microbial communities showed clear shifts in composition of the structure in response to the treatments, with changes in taxonomic composition, network structuring, and the balance between r and K-designated species.