Stimulation of soil microbial functioning by elevated CO2 may surpass effects mediated by irrigation in a semiarid grassland

The functioning of microbial communities in response to elevated atmospheric carbon dioxide (eCO(2)) is one of the most important, but poorly understood, contributors to climate change feedbacks. The effect of soil moisture caused by eCO(2) on soil microbial communities and functioning may be of high importance in water limited ecosystems. To address this knowledge gap, we measured the functional composition, structure, and functional processes of soil microbial communities under eCO(2) and an irrigation treatment simulating water availability with eCO(2) at two soil depths (0-5 cm and 5-15 cm) in a mixed-grass semiarid prairie. The overall functional diversity increased and the microbial composition and structure were significantly (P < 0.01) altered in response to eCO(2) and irrigation treatments. A greater number of key functional genes involved in soil, i.e. carbon (C), nitrogen (N), phosphorus (P), and sulfur (S) cycling were stimulated under eCO(2) than under irrigation treatment. Structural equation modeling (SEM) suggested that eCO(2) significantly impacted soil microbial community structure by mediating both soil moisture and plant biomass, while irrigation influenced soil microbial community structure merely via regulation of soil moisture. Moreover, in this water-limited system, soil moisture mediated eCO(2) effects on soil microbial functional structure were relatively more important than those mediated by plant activity. The present study further improves our understanding of how global climate change regulates soil microbial functional processes in a semiarid grassland ecosystem.

Automated summary

This study found that eCO2 and irrigation treatments significantly impacted the functional composition and structure of soil microbial communities, leading to increased functional diversity and stimulation of key functional genes involved in carbon, nitrogen, phosphorus, and sulfur cycling in the soil.