A decade of free‐air CO2 enrichment increased the carbon throughput in a grass‐clover ecosystem but did not drastically change carbon allocation patterns
2014
Staddon, Philip L. | Reinsch, Sabine | Olsson, Pål A. | Ambus, Per | Lüscher, Andreas | Jakobsen, Iver | Briones, Maria Jesus
The response of the soil carbon cycle to increasing atmospheric CO₂concentration has far reaching consequences for the ecosystem carbon balance under future climatic conditions. We report on work carried out in the Swiss free‐air CO₂enrichment (FACE) experiment, where we used in situ¹³CO₂labelling to determine whether elevated CO₂(+230 μL L⁻¹) concentration changes the fate of recently assimilated carbon in the soil microbial community. Elevated CO₂(eCO₂) concentration had an overall positive effect on microbial abundance (P < 0·001) with the gram‐negative bacteria showing significantly increased quantities. Gram‐negative bacteria and saprotrophic fungi tended to utilize a higher amount of recently assimilated carbon under eCO₂. Arbuscular mycorrhizal fungi (AMF) utilized plant‐assimilated carbon within 1 day after the¹³CO₂pulse and¹³C uptake patterns in AMF suggest that carbon transfer is faster under eCO₂concentration than under ambient CO₂(aCO₂). Additionally, the respiration of recently assimilated carbon was significantly higher under eCO₂than aCO₂concentration. Our data suggest that elevated atmospheric CO₂concentration accelerated and increased the utilization of recently assimilated carbon by the microbial community without changing the microbial community composition drastically. We conclude that a higher standing soil microbial biomass under eCO₂concentration was the key cause for the higher carbon flow through the plant–soil system. Carbon utilization by microbial functional groups was only little affected by a decade of CO₂enrichment.
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