Soil CO2 flux was measured monthly over a year from tropical peatland of Sarawak, Malaysia using a closed‐chamber technique. The soil CO2 flux ranged from 100 to 533 mg C m−2 h−1 for the forest ecosystem, 63 to 245 mg C m−2 h−1 for the sago and 46 to 335 mg C m−2 h−1 for the oil palm. Based on principal component analysis (PCA), the environmental variables over all sites could be classified into three components, namely, climate, soil moisture and soil bulk density, which accounted for 86% of the seasonal variability. A regression tree approach showed that CO2 flux in each ecosystem was related to different underlying environmental factors. They were relative humidity for forest, soil temperature at 5 cm for sago and water‐filled pore space for oil palm. On an annual basis, the soil CO2 flux was highest in the forest ecosystem with an estimated production of 2.1 kg C m−2 yr−1 followed by oil palm at 1.5 kg C m−2 yr−1 and sago at 1.1 kg C m−2 yr−1. The different dominant controlling factors in CO2 flux among the studied ecosystems suggested that land use affected the exchange of CO2 between tropical peatland and the atmosphere.

A B S T R A C T Soil CO 2 flux was measured monthly over a year from tropical peatland of Sarawak, Malaysia using a closed-chamber technique. The soil CO 2 flux ranged from 100 to 533 mg C m −2 h −1 for the forest ecosystem, 63 to 245 mg C m −2 h −1 for the sago and 46 to 335 mg C m −2 h −1 for the oil palm. Based on principal component analysis (PCA), the environmental variables over all sites could be classified into three components, namely, climate, soil moisture and soil bulk density, which accounted for 86% of the seasonal variability. A regression tree approach showed that CO 2 flux in each ecosystem was related to different underlying environmental factors. They were relative humidity for forest, soil temperature at 5 cm for sago and water-filled pore space for oil palm. On an annual basis, the soil CO 2 flux was highest in the forest ecosystem with an estimated production of 2.1 kg C m −2 yr −1 followed by oil palm at 1.5 kg C m −2 yr −1 and sago at 1.1 kg C m −2 yr −1 . The different dominant controlling factors in CO 2 flux among the studied ecosystems suggested that land use affected the exchange of CO 2 between tropical peatland and the atmosphere.

No abstract

While wetlands are the largest natural source of methane (CH4) to the atmosphere, they represent a large source of uncertainty in the global CH4 budget due to the complex biogeochemical controls on CH4 dynamics. Here we present, to our knowledge, the first multi‐site synthesis of how predictors of CH4 fluxes (FCH4) in freshwater wetlands vary across wetland types at diel, multiday (synoptic), and seasonal time scales. We used several statistical approaches (correlation analysis, generalized additive modeling, mutual information, and random forests) in a wavelet‐based multi‐resolution framework to assess the importance of environmental predictors, nonlinearities and lags on FCH4 across 23 eddy covariance sites. Seasonally, soil and air temperature were dominant predictors of FCH4 at sites with smaller seasonal variation in water table depth (WTD). In contrast, WTD was the dominant predictor for wetlands with smaller variations in temperature (e.g., seasonal tropical/subtropical wetlands). Changes in seasonal FCH4 lagged fluctuations in WTD by ~17 ± 11 days, and lagged air and soil temperature by median values of 8 ± 16 and 5 ± 15 days, respectively. Temperature and WTD were also dominant predictors at the multiday scale. Atmospheric pressure (PA) was another important multiday scale predictor for peat‐dominated sites, with drops in PA coinciding with synchronous releases of CH4. At the diel scale, synchronous relationships with latent heat flux and vapor pressure deficit suggest that physical processes controlling evaporation and boundary layer mixing exert similar controls on CH4 volatilization, and suggest the influence of pressurized ventilation in aerenchymatous vegetation. In addition, 1‐ to 4‐h lagged relationships with ecosystem photosynthesis indicate recent carbon substrates, such as root exudates, may also control FCH4. By addressing issues of scale, asynchrony, and nonlinearity, this work improves understanding of the predictors and timing of wetland FCH4 that can inform future studies and models, and help constrain wetland CH4 emissions.