Soil, microbial abundance and enzymatic activities to asymmetrical warming and N-inputs from a dry tropical grassland

In the present Anthropocene, climate change has been felt as a serious threat to nutrient cycling and ecosystem functioning. Soil microbial communities and enzymatic activity are crucial for nutrient cycling, although the effects of asymmetric warming and nitrogen (N) input are still unclear. A three-year field experiment (2021-2023) at Banaras Hindu University, Varanasi, India, examined the effects of daytime and nighttime warming and N inputs (0, 30, and 60 kg N ha⁻¹ yr⁻¹) on soil temperature, moisture, pH, C:N, microbial abundance, β1,4-glucosidase (BG), urease (URE), and dehydrogenase (DHA) activities in tropical grassland. Data were statistically analyzed. Asymmetrical warming and N inputs changed soil moisture, temperature, pH, and C:N. These changes affected microbial community structure. Asymmetric warming reduced soil moisture, especially during the night, impacting BG, URE, and DHA activities. N inputs lowered soil pH while enhancing microbial biomass and enzyme activity by alleviating nutritional constraints. Nighttime warming benefited Gram-positive bacteria, but daytime warmings promoted fungi. N input boosted bacterial populations and reduced the fungi-to-bacteria ratio, signifying copiotrophic communities. Microbial and enzymatic activities reached their peak during the wet season and declined in the arid summer. Structural equation modeling and stepwise regression indicated that soil moisture influenced BG and URE, but soil pH impacted DHA. Our results suggested that asymmetrical warming and nitrogen input may influence soil carbon and the nitrogen cycles through moisture and pH pathways and pointed to the incorporation of seasonal hydrothermal dynamics and asymmetrical warming into projections of nitrogen and carbon cycles in arid regions.