Respiration fluxes of a montane cloud forest in Taiwan

Shih-Chieh Chang1, Hui-Shiang Liao1
1 Department of Natural Resources and Environmental Studies, National Dong Hwa University

O 3.4 in Fluxes between the atmosphere and ecosystems

17.07.2014, 12:00-12:20, H17

Carbon budgets of cloud forests are one of the research hotspots in the context of global warming and the resulting change in cloud formation and climatology in the mountainous region. In this paper, the results of respiration measurements using chamber methods are presented for the Chi-Lan Mountain (CLM) site of northern Taiwan.

Stem CO2 efflux was measured using an automatic closed chamber system. Four chambers were installed at different heights of one Chamaecyparis obtusa var. formosana tree. The measurement started in May 2013 and works continuously until now.

The stem CO2 efflux showed a typical diurnal pattern as well as a seasonal variation that characterizes the influence of temperature on the respiration rate. The Q10 value averaged from the four chambers was 3.8. No vertical gradient of Q10 could be found. Using 15 °C as basal temperature, the stem CO2 efflux increased significantly from stem base (0.21 μmol m-2 s-1) to the highest position (0.51 μmol m-2 s-1). In a previous study of stem CO2 efflux at the site, we demonstrated a clear hysteresis pattern of efflux-temperature relationship. The daytime CO2 efflux rate was lower than the nighttime rate under the same stem temperature. The sapflow velocity correlated positively with the depression in daytime CO2 efflux, which reveals the upward transport of respiratory CO2 by the xylem sap when transpiration takes place. To quantitatively divide the two pathways of respiratory CO2, we assumed a still stand of xylem sap at the predawn hour (4 – 5 am) and thus the CO2 efflux rates at this time represented 100% of the respiration rates. Using the efflux-temperature relationship from this dataset and assuming an dependency of respiration rate on temperature, we calculated the “theoretical” respiration rates from temperature data and estimated the internal flux rate by subtracting the respective CO2 efflux rate from the respiration rate. The calculated annual stem respiration rate of 2011 was 43.1 g C m-2 ground yr-1, of which 89% diffused out of the bark and could be measured by the chamber method.

A similar chamber system was built for the measurement of branch CO2 efflux at the CLM site. Using the preliminary result, the annual respiration rate of branches accounted for 1922 kg C ha-1 yr-1. Therefore, the respiration of the aboveground woody tissues was 2353 kg C ha-1 yr-1. We further calculated the soil respiration rate by using the previously derived empirical model, which is a function of soil temperature and soil water content at 10 cm depth. The annual soil respiration rate was 5150 kg C ha-1 yr-1 for 2011. A chamber system for measuring leaf photosynthesis and respiration is now being tested in the laboratory. Once it is installed at the CLM site, an estimation of ecosystem respiration could be accomplished and a further comparison with eddy covariance method could be performed. The data presented in this paper show that soil respiration composed 69% of the ecosystem respiration (7503 kg C ha-1 yr-1, without leaf respiration).

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Letzte Änderung 04.04.2014