The net annual exchange of carbon between the atmosphere and terrestrial ecosystems is of prime importance in determining the concentration of CO₂ ([CO₂]) in the atmosphere and consequently future climate. Carbon loss occurs primarily through soil respiration; it is known that respiration is sensitive to the global changes in [CO₂] and temperature, suggesting that the net carbon balance may change in the future. However, field manipulations of temperature and [CO₂] alter many important environmental factors so it is unclear how much of the observed alterations in soil respiration is due to changes of microbial function itself instead of changes to the physical and chemical environment. Here we focus on resolving the importance of changes in the microbial community in response to warming and elevated [CO₂] on carbon mineralisation, something not possible in field measurements. We took plant material and soil inocula from a long running experiment where native grassland had been exposed to both warming and elevated CO₂ and constructed a reciprocal transplant experiment. We found that the rate of decomposition (heterotrophic respiration) was strongly determined by the origin of the microbial community. The combined warming + elevated CO₂ treatment produced a soil community that gave respiration rates 30% higher when provided with shoot litter and 70% for root litter than elevated CO₂ treatment alone, with the treatment source of the litter being unimportant. Warming, especially in the presence of elevated CO₂, increased the size of the apparent labile carbon pool when either C₃ or C₄ litter was added. Thus, the metabolic activity of the soil community was affected by the combination of warming and elevated CO₂ such that it had an increased ability to mineralise added organic matter, regardless of its source. Therefore, soil C efflux may be substantially increased in a warmer, high CO₂ world. Current ecosystem models mostly drive heterotrophic respiration from plant litter quality, soil moisture and temperature but our findings suggest equal attention will need to be paid to capturing microbial processes if we are to accurately project the future C balance of terrestrial ecosystems and quantify the feedback effect on atmospheric concentrations of CO₂.

Item Type:	Refereed Article
Keywords:	decomposition, soil respiration, carbon cycling, carbon mineralisation, soil ecology, microbial ecology, ecosystem function
Research Division:	Biological Sciences
Research Group:	Other biological sciences
Research Field:	Global change biology
Objective Division:	Expanding Knowledge
Objective Group:	Expanding knowledge
Objective Field:	Expanding knowledge in the environmental sciences
UTAS Author:	Osanai, Y (Ms Yui Osanai)
UTAS Author:	Janes, J (Ms Jaz Janes)
UTAS Author:	Hovenden, MJ (Professor Mark Hovenden)
ID Code:	101949
Year Published:	2015
Funding Support:	Australian Research Council (DP0984779)
Web of Science® Times Cited:	15
Deposited By:	Plant Science
Deposited On:	2015-07-20
Last Modified:	2017-11-03
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