The Relationship of Stable Isotope Accumulation in Ectomycorrhizas on Pinus sylvestris

The stable isotopes of nitrogen (15N) and carbon (13C) have been widely used to investigate nutrient transfer between ectomycorrhizal (ECM) plants and fungi. In this study, the 13CO2 was used to label mycorrhizal Pinus sylvestris saplings collected from the Culbin forest and 15N injected into the intact blocks of turf containing the saplings. The carbon allocation from the plant to ectomycorrhizas was hypothesised to be positively related to the acquisition and accumulation of nitrogen from the soil by the fungi. There were multiple colonisations of ECM fungi were found in individual sapling root systems. The analysis of stable isotopes showed that morphologically distinct groups of ECM fungi accumulated different amounts of 15N and 13C. Contrary to our hypothesis, the analysis also demonstrated a strong negative correlation between 15N and 13C in the ECM tips. This suggests the dynamics of carbon allocation and nitrogen acquisition may be offset, that some ECM fungi are using carbon from hosts to acquire other growth limiting nutrients (e. g. Phosphorus) that has not labelled, or that accumulation of carbon and nitrogen in ECM tips does not accurately reflect nutrient transfer processes.