The role of Ectomycorrhizal fungi mediating soil organic matter mineralisation: Impacts of N availability and CO2 conditions

Laura Castaneda Gomez1, Johanna Wong  W-H1, Dr. Jonathan  Plett1, Dr. Krista Plett1, Dr Yolima Carrillo1

1Hawkesbury Institute for the Environment, Western Sydney University, Penrith, Australia

The role of ectomycorrhizal (EM) fungi on soil C cycling is receiving increasing attention and they are suspected to alter soil C decomposition. However, direct measurements of their impact are not available and , information on how this ,function might change with ,elevated CO2 ,(eCO2) is ,scarce. These symbiotic fungi provide nutrients to the plants in exchange for C. With eCO2 plant productivity and thus, nutrient demand, are expected to increase. Higher C allocation belowground may promote EM colonisation and nutrient mining from soil organic matter (SOM) to meet plants demands, with potential impacts on soil C. Therefore it could be expected that the impacts of EM fungi on SOM with eCO2 might dependon nutrient availability. Research so far on this matter is scarce, showing conflicting results and facing methodological constraints.


We aimed to understand the impact of two different isolates of EM fungi on soil C cycling under eCO2 and nitrogen (N) availability conditions (high/low). We used a whole plant-soil system  with Eucalyptus plants in chambers with a continuous 13C- input that allowed us to differentiate between plant and SOM-derived fractions of different C pools.Above and belowground biomass responses along with EM colonisation rates were also studied. EM fungi responses to eCO2 and N varied between the isolates, although hartig nets were generally deeper at low N and shallower with eCO2. eCO2 and high N increased plant biomass, while EM presence reduced shoot biomass. EM fungi did not have a significant effect on SOM-derived respired C.  Our direct and high resolution assessment of SOM mineralisation indicate that in this ecosystem EM fungi may not have a substantial role enhancing soil C cycling under eCO2 as generally expected.


Yolima Carrillo’s research focuses on the cycles of carbon and nutrients in the plant-soil-microbe interface in both natural and agricultural ecosystems. She is interested in the mechanisms by which these cycles are affected by environmental change and management. Her work combines field and laboratory experiments to understand how biogeochemical processes are shaped by plants, plant roots and soil biotic communities. She is  a Senior Lecturer at the Hawkesbury Institute for the Environment in Western Sydney University.


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