Unaltered soil microbial community composition, but decreased metabolic activity in a semi-arid grassland after two years of passive experimental warming

Soil microbial communities regulate soil carbon feedbacks to climate
warming through microbial respiration (i.e. metabolic rate). A thorough
understanding of the responses of composition, biomass and metabolic rate
of soil microbial community to warming is crucial to predict soil carbon
stocks in a future warmer climate. Therefore, we conducted a field
manipulative experiment in a semi-arid grassland on the Loess Plateau of
China to evaluate the responses of the soil microbial community to
increased temperature from April 2015 to December 2017. Soil temperature
was 2.0 oC higher relative to the ambient when open-top chambers (OTCs)
were used. Warming did not affect microbial biomass or the composition of
microbial functional groups. However, warming significantly decreased
microbial respiration, directly resulting from soil pH decrease driven by
the co-mediation of aboveground biomass increase, inorganic nitrogen
increase and moisture decrease. These findings highlight that the soil
microbial community structure of semi-arid grasslands resisted the
short-term warming by 2 oC, although its metabolic rate declined.