Isotopic (13C and 14C) tracers in ecosystem respiration

Terrestrial ecosystems are expected to respond to global warming with the very real possibility that they may add to global atmospheric anthropogenic CO[2] emissions, thus exacerbating climate change. Isotopes of carbon in ecosystem respiration provide valuable information regarding the contribution of individual sources. A portable sampling system was developed (MS[3]) incorporating zeolite molecular sieve, which can capture CO[2] for stable and radiocarbon analysis without contamination, fractionation or hysteresis. The sampling system and its application in studies of respiration and carbon cycling, both in situ and ex situ, has the potential to be applied in a wide range of ecosystems. A field experiment was performed to assess the contribution of individual components of a peatland ecosystem (peatland soil and the three main plant functional groups it supported) to total peatland ecosystem respiration. Stable carbon (delta[13]C) analysis of respired CO[2] collected using Exetainers to partition respiration sources had limited use, mainly due to methodological difficulties. A laboratory peat core experiment studied the interactive effects of abiotic regulators: temperature, moisture and substrate quality. All parameters influenced soil carbon decomposition with temperature being the primary regulator of CO[2] fluxes. Interactive effects on decomposition rates were observed, with increased temperature, decreased moisture and reduced substrate quality affecting the largest Q[10] values. The radiocarbon signature of both ecosystem and soil respiration were successfully characterised in the field using MS[3]. Modelling implied there to be a third source of respired CO[2] that contributed to total ecosystem respiration (in addition to plant and soil components). This is believed to be the first time that this third source, plant mediated catotelm CO2, has been directly observed. It is estimated to contribute ~ 20 % of the total peatland ecosystem respiration flux