Soil respiration: implications of the plant-soil continuum and collar insertion depth on measurement and modelling of soil CO2 efflux rates in three major ecosystems.

摘要

Key uncertainties remain in accurately measuring soil respiration, including how the commonly-used technique\udof collar insertion affects measured soil and root-derived CO2 fluxes. We hypothesized that total soil respiration\udis frequently under-estimated because soil collar insertions sever surface roots, which coupled with the\udpreferential practice of taking daytime measurements, leads to the autotrophic (root-derived) component\udfrequently being missed. We measured root distribution and soil CO2 efflux in three contrasting ecosystems:\uda Lodgepole pine (Pinus contorta) plantation, an upland heather-dominated peatland and a lowland sheep-\udgrazed grassland, where we combined shallow surface collars with collars at different soil insertion depths for\udoccasional and continuous hourly flux measurements. Collar insertion by only a few centimetres reduced total\udsoil CO2 efflux in all three ecosystems by an average of 15% but at times by up to 30–50%, and was directly\udproportional to the quantity of cut fine roots. Most reduction occurred in the shallow-rooted peatland system\udand least in the deep-rooted grassland. In the forest and grassland, soil temperatures explained most of the\uddeep-collar (largely heterotrophic) variation and did not relate to the root-derived (largely autotrophic) flux\udcomponent, whilst the opposite was true for the peatland site. For the forest, the autotrophic flux component\udpeaked at night during moist periods and was drought-limited. Mean flux estimates differed between sampling\udtime and insertion depth. Our results suggest strongly that accurate measurement and modelling of soil\udrespiration needs explicitly to consider collar insertion, and the root-derived flux component, with its own\udtemperature sensitivity and potential time-lag effects.