Dr Yolima Carrillo1, Laura Castaneda Gomez1, Johanna Pihlblad1, Dr. Catriona Macdonald1, Dr. Louise Andresen2, Dr. Tobias Rutting2, Dr. Klaus Jarosch3
1Hawkesbury Institute for the Environment, Western Sydney University, Penrith, Australia, 2University of Gothenburg, , , 3University of Bern, ,
Atmospheric CO2 continues to increase. There is a high degree of uncertainty on the mechanisms by which elevated CO2 will impact SOM. Elevated CO2 is expected to increase plant carbon inputs to soil, contingent on nutrient availability. While carbon input is an important factor of SOM dynamics, it is the use of this carbon by soil microbes that ultimately determines if inputs are retained in the ecosystem, lost to the atmosphere and/or if they alter the existing SOM pool. Microbial use of new plant inputs and existing soil carbon is also dependent on nutrient availability. Recent work points at contrasting responses of different C pools to CO2, but mechanisms are not clear. In conventional assessments these different pools are not distinguished, likely masking underlying mechanisms.
Our objective is a high resolution, multi-element investigation of the role of elevated CO2 on the dynamics of different carbon pools as mediated by nutrients. We have been conducting field and laboratory studies utilising stable isotopes to isolate impacts on the new C inputs and existing organic C in intact plant-soil systems. Field studies took place at the EucFACE facility, a temperate, mature Eucalypt woodland in Eastern Australia exposed to Free-air CO2 enrichment. So far, under field conditions elevated CO2 caused a greater loss of existing soil carbon, and greater gross nitrogen mineralization which, together, are consistent with SOM priming. In controlled environments, the impact of CO2 on existing C, but not on new C inputs, was highly dependent on nitrogen availability. Elevated CO2 suppressed C loss but only when nitrogen level was low. We are currently investigating impacts of phosphorus availability and SOM phosphorus mineralisation.