Partitioning of soil CO2 flux components in a temperate grassland ecosystem

We deployed an automated multiplexed soil-respiration (SR) system to monitor partitioned soil CO2 componentfluxes (from roots, mycorrhizal hyphae and heterotrophs) in a UK grassland using a combination of shallowsurface (total SR flux), deep (excluding roots and mycorrhizal fungi) and 20-μm pore mesh window soilcollars (excluding roots only). Soil CO2 efflux was monitored during a 3-month period during summer.Repeated cutting of mycorrhizal connections in some of the mycorrhizal treatments enabled assessment ofsubsequent recovery of mycorrhizal fluxes and a comparison with deep collar fluxes. After soil collar insertion,fluxes in the deep collars were significantly reduced, by approximately 40%. Whereas fluxes in the uncut,mycorrhizal collar treatments remained close to those from the surface collar, cut mycorrhizal treatmentsshowed an immediate reduction after cutting to values close to those from the deep collar with a subsequentrecovery of around 4 weeks. Overall, the autotrophic root and mycorrhizal flux was relatively stable throughout.Whereas root fluxes contributed about 10–30% of the total flux during the initial larger flux period, thisdeclined and there was an increased mycorrhizal contribution during the latter part of the measurement period.Moreover, SR flux components differed in their response to key climatic factors, with root fluxes respondingequally to temperature and light. Importantly, whereas the heterotrophic flux component responded stronglyto temperature and soil moisture, the mycorrhizal component responded much less to those factors, but moreto light. We also investigated treatment impacts over time on soil biochemical variables such as microbialbiomass C, extractable C, microbial quotient and metabolic quotient, and bacterial community structure, anddiscussed these in relation to measured SR fluxes and the partitioning technique.