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

Nitrous oxide (N 2 O) emissions were measured monthly over 1 year in three ecosystems on tropical peatland of Sarawak, Malaysia, using a closed-chamber technique. The three ecosystems investigated were mixed peat swamp forest, sago (Metroxylon sagu) and oil palm (Elaeis guineensis) plantations. The highest annual N 2 O emissions were observed in the sago ecosystem with a production rate of 3.3 kg N ha −1 year −1 , followed by the oil palm ecosystem at 1.2 kg N ha −1 year −1 and the forest ecosystem at 0.7 kg N ha. The N 2 O emissions ranged from -3.4 to 19.7 μg N m −2 h −1 for the forest ecosystem, from 1.0 to 176.3 μg N m −2 h −1 for the sago ecosystem and from 0.9 to 58.4 μg N m −2 h −1 for the oil palm ecosystem. Multiple regression analysis showed that N 2 O production in each ecosystem was regulated by different variables. The key factors influencing N 2 O emissions in the forest ecosystem were the water table and the concentration at 25-50 cm, soil temperature at 5 cm and nitrate concentration at 0-25 cm in the sago ecosystem, and water-filled pore space, soil temperature at 5 cm and concentrations at 0 -25 cm in the oil palm ecosystem. R 2 values for the above regression equations were 0.57, 0.63 and 0.48 for forest, sago and oil palm, respectively. The results suggest that the conversion of tropical peat swamp forest to agricultural crops, which causes substantial changes to the environment and soil properties, will significantly affect the exchange of N 2 O between the tropical peatland and the atmosphere. Thus, the estimation of net N 2 O production from tropical peatland for the global N 2 O budget should take into consideration ecosystem type.

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.

No abstract

Soil carbon dioxide (CO 2) efflux was measured continuously for two years using an automated chamber system in an oil palm plantation on tropical peat. This study investigated the factors controlling the CO 2 efflux and quantified the annual cumulative CO 2 emissions through soil respiration and heterotrophic respiration, which is equivalent to oxidative peat decomposition. Soil respiration was measured in close-to-tree (<2.5 m, CT) and far-from-tree (>3 m, FT) plots, and heterotrophic respiration was measured in root-cut (RC) plots by a trenching method. The daily mean CO 2 efflux values (mean ± 1 standard deviation) were 2.80 ± 2.18, 1.59 ± 1.18, and 1.94 ± 1.58 µmol m −2 s −1 in the CT, FT, and RC plots, respectively. Daily mean CO 2 efflux increased exponentially as the groundwater level or water-filled pore space decreased, indicating that oxidative peat decomposition and gas diffusion in the soil increased due to enhanced aeration resulting from lower groundwater levels. Mean annual gap-filled CO 2 emissions were 1.03 ± 0.53, 0.59 ± 0.26, and 0.69 ± 0.21 kg C m −2 yr −1 in the CT, FT, and RC plots, respectively. Soil CO 2 emissions were significantly higher in the CT plots (P < 0.05), but did not differ significantly between the FT and RC plots. This implies that root respiration was negligible in the FT plots. Heterotrophic respiration accounted for 66% of soil respiration. Annual CO 2 emissions through both soil and heterotrophic respiration were smaller than those of other oil palm plantations on tropical peat, possibly due to the higher groundwater levels, land compaction, and continuous measurement of soil CO 2 efflux in this study. Mean annual total subsidence was 1.55 to 1.62 cm yr −1 , of which oxidative peat decomposition accounted for 72 to 74%. In conclusion, water management to raise groundwater levels would mitigate soil CO 2 emissions from oil palm plantations on tropical peatland.

Using a soilless culture system mimicking tropical acidic peat soils, which contained 3 mg of gellan gum and 0.5 mg NO3−-N per gram of medium, a greenhouse gas, N2O emitting capability of microorganisms in acidic peat soil in the area of Palangkaraya, Central Kalimantan, Indonesia, was investigated. The soil sampling sites included a native swamp forest (NF), a burnt forest covered by ferns and shrubs (BF), three arable lands (A-1, A-2 and A-3) and a reclaimed grassland (GL) next to the arable lands. An acid-tolerant Janthinobacterium sp. strain A1-13 (Oxalobacteriaceae, β-proteobacteria) isolated from A-1 soil was characterized as one of the most prominent N2O-emitting bacteria in this region. Physiological characteristics of the N2O emitter in the soilless culture system, including responses to soil environments, substrate concentration, C-source concentration, pH, and temperature, suggest that the N2O emitting Janthinobacterium sp. strain A1-13 is highly adapted to reclaimed open peatland and primarily responsible for massive N2O emissions from the acidic peat soils. Regulation of N2O emitters in the reclaimed peatland for agricultural use is therefore one of the most important issues in preventing the greenhouse gas emission from acidic peat soil farmlands