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Volume 2, issue 3
SOIL, 2, 403–419, 2016
https://doi.org/10.5194/soil-2-403-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
SOIL, 2, 403–419, 2016
https://doi.org/10.5194/soil-2-403-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Original research article 12 Aug 2016

Original research article | 12 Aug 2016

Soil CO2 efflux in an old-growth southern conifer forest (Agathis australis) – magnitude, components and controls

Luitgard Schwendenmann1 and Cate Macinnis-Ng2 Luitgard Schwendenmann and Cate Macinnis-Ng
  • 1School of Environment, University of Auckland, Private Bag 92019, 1142 Auckland, New Zealand
  • 2School of Biological Sciences, University of Auckland, Private Bag 92019, 1142 Auckland, New Zealand

Abstract. Total soil CO2 efflux and its component fluxes, autotrophic and heterotrophic respiration, were measured in a native forest in northern Aotearoa–New Zealand. The forest is dominated by Agathis australis (kauri) and is on an acidic, clay rich soil. Soil CO2 efflux, volumetric soil water content and soil temperature were measured bi-weekly to monthly at 72 sampling points over 18 months. Trenching and regression analysis was used to partition total soil CO2 efflux into heterotrophic and autotrophic respiration. The effect of tree structure was investigated by calculating an index of local contribution (Ic, based on tree size and distance to the measurement location) followed by correlation analysis between Ic and total soil CO2 efflux, root biomass, litterfall and soil characteristics. The measured mean total soil CO2 efflux was 3.47 µmol m−2 s−1. Autotrophic respiration accounted for 25 % (trenching) or 28 % (regression analysis) of total soil CO2 efflux. Using uni- and bivariate models showed that soil temperature was a poor predictor of the temporal variation in total soil CO2 efflux (<  20 %). In contrast, a stronger temperature sensitivity was found for heterotrophic respiration (around 47 %). We found significant positive relationships between kauri tree size (Ic) and total soil CO2 efflux, root biomass and mineral soil CN ratio within 5–6 m of the sampling points. Using multiple regression analysis revealed that 97 % of the spatial variability in total soil CO2 efflux in this kauri-dominated stand was explained by root biomass and soil temperature. Our findings suggest that biotic factors such as tree structure should be investigated in soil carbon related studies.

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This is the first study quantifying total soil CO2 efflux, heterotrophic and autotrophic respiration in an old-growth kauri forest. Root biomass explained a high proportion of the spatial variation suggesting that soil CO2 efflux in this forest is not only directly affected by the amount of autotrophic respiration but also by the supply of C through roots and mycorrhiza. Our findings also suggest that biotic factors such as tree structure should be investigated in soil carbon related studies.
This is the first study quantifying total soil CO2 efflux, heterotrophic and autotrophic...
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