Ecosystem respiration depends strongly on photosynthesis in a temperate heath

Abstract

We measured net ecosystem CO2 flux (F n) and ecosystem respiration (R E), and estimated gross ecosystem photosynthesis (P g) by difference, for two years in a temperate heath ecosystem using a chamber method. The exchange rates of carbon were high and of similar magnitude as for productive forest ecosystems with a net ecosystem carbon gain during the second year of 293 ± 11 g C m−2 year−1 showing that the carbon sink strength of heather-dominated ecosystems may be considerable when C. vulgaris is in the building phase of its life cycle. The estimated gross ecosystem photosynthesis and ecosystem respiration from October to March was 22% and 30% of annual flux, respectively, suggesting that both cold-season carbon gain and loss were important in the annual carbon cycle of the ecosystem. Model fit of R E of a classic, first-order exponential equation related to temperature (second year; R 2 = 0.65) was improved when the P g rate was incorporated into the model (second year; R 2 = 0.79), suggesting that daytime R E increased with increasing photosynthesis. Furthermore, the temperature sensitivity of R E decreased from apparent Q 10 values of 3.3 to 3.9 by the classic equation to a more realistic Q 10 of 2.5 by the modified model. The model introduces R photo, which describes the part of respiration being tightly coupled to the photosynthetic rate. It makes up 5% of the assimilated carbon dioxide flux at 0°C and 35% at 20°C implying a high sensitivity of respiration to photosynthesis during summer. The simple model provides an easily applied, non-intrusive tool for investigating seasonal trends in the relationship between ecosystem carbon sequestration and respiration.