(1) Background: Nitrogen (N) fertilization on drained tropical peatland will likely stimulate peat decomposition and mineralization, enhancing N₂O emission from the peat soil. (2) Methods: A field experiment was conducted to quantify the N₂O emissions from soil in an oil palm plantation (Elaeis guineensis Jacq.) located in a tropical peatland in Sarawak, Malaysia, under different rates of N fertilizers. The study was conducted from January 2010 to December 2013 and resumed from January 2016 to December 2017. Nitrous oxide (N₂O) flux was measured every month using a closed chamber method for four different N rates; control—without N (T1), 31.1 kg N ha⁻¹ yr⁻¹ (T2), 62.2 kg N ha⁻¹ yr⁻¹ (T3), and 124.3 kg N ha⁻¹ yr⁻¹ (T4); (3) Results: Application of the N fertilizer significantly increased annual cumulative N₂O emissions for T4 only in the years 2010 (p = 0.017), 2011 (p = 0.012), 2012 (p = 0.007), and 2016 (p = 0.048). The highest average annual cumulative N₂O emissions were recorded for T4 (41.5 ± 28.7 kg N ha⁻¹ yr⁻¹), followed by T3 (35.1 ± 25.7 kg N ha⁻¹ yr⁻¹), T1 (25.2 ± 17.8 kg N ha⁻¹ yr⁻¹), and T2 (25.1 ± 15.4 kg N ha⁻¹ yr⁻¹), indicating that the N rates of 62.2 kg N ha⁻¹ yr⁻¹ and 124.3 kg N ha⁻¹ yr⁻¹ increased the average annual cumulative N₂O emissions by 39% and 65%, respectively, as compared to the control. The N fertilization had no significant effect on annual oil palm yield (p = 0.994). Alternating between low (deeper than −60 cm) and high groundwater level (GWL) (shallower than −60 cm) enhanced nitrification during low GWL, further supplying NO₃⁻ for denitrification in the high GWL, and contributing to higher N₂O emissions in high GWL. The emissions of N₂O ranged from 17 µg N m⁻² hr⁻¹ to 2447 µg N m⁻² hr⁻¹ and decreased when the water-filled pore space (WFPS) was between 70% and 96%, suggesting the occurrence of complete denitrification. A positive correlation between N₂O emissions and NO₃⁻ at 70–96% WFPS indicated that denitrification increased with increased NO₃⁻ availability. Based on their standardized regression coefficients, the effect of GWL on N₂O emissions increased with increased N rate (p < 0.001). Furthermore, it was found that annual oil palm yields negatively correlated with annual N₂O emission and NO₃⁻ for all treatments. Both nitrification and denitrification increased with increased N availability, making both processes important sources of N₂O in oil palm cultivation on tropical peatland.; and (4) Conclusions: To improve understanding of N₂O mitigation strategies, further studies should consider plant N uptake on N₂O emissions, at least until the completion of the planting.

Nitrogen (N) fertilization improves crop productivity. However, the long-term effects of N application on methane (CH₄) emissions in drained peat soils, particularly under different hydrological conditions, remain poorly understood. Accurate quantification of CH₄ emissions from peatlands is essential for assessing carbon losses and formulating effective climate change mitigation strategies. This study was conducted to investigate the impact of N fertilization on CH₄ emissions and identify the main factors influencing CH₄ emissions from drained tropical peatlands. This study was conducted on an oil palm plantation in Sarawak, Malaysia, a randomized block design included four N fertilizer treatments: Control (0 kg N ha^− 1 yr^− 1) (T1); low (31.1 kg N ha⁻¹ yr⁻¹) (T2), moderate (62.2 kg N ha⁻¹ yr⁻¹) (T3), and high (124.3 kg N ha⁻¹ yr⁻¹) (T4). Soil CH₄ fluxes showed no statistically significant differences between treatments or across years, with emissions ranging from − 163.6 to 320.7 µg C m^− 2 hr^− 1 at T1, -86.7 to 285.8 µg C m^− 2 hr^− 1 at T2, -131.6 to 274.1 µg C m^− 2 hr^− 1 at T3 and − 125.7 to 185.9 µg C m^− 2 hr^− 1 at T4 (p > 0.05). Although ammonium sulfate fertilization did not significantly alter CH₄ emissions, its pronounced acidifying effect on soil pH, particularly at application rates above 62.2 kg N ha⁻¹ yr⁻¹ along with elevated sulfate (SO₄²⁻) inputs and nitrogen pools exceeding the critical threshold (> 400 ppm), likely suppressed methanogenic activity and constrained soil organic matter decomposition. Water-filled pore space (WFPS) influenced CH₄ emissions more than groundwater level (GWL), with the low GWL at the site limiting its impact. Increased WFPS (60–80%) reduced nitrate (NO₃⁻) through enhanced denitrification, lowering its inhibition on CH₄ production and thus increasing emissions. This study highlights the key role of soil moisture and nitrogen cycling in regulating CH₄ emissions in peatland.

Anthropogenic activities, and in particular the use of synthetic nitrogen (N) fertilizer, have a significant influence on soil nitrous oxide (N2O) emission from oil palm plantation on tropical peatland. Finding a suitable N rate for optimum N uptake efficiency and yield with low environmental impact and production cost is crucial for the economic growth of Malaysia’s oil palm sector. However, studies on the impact of N fertilizers on N2O emissions from tropical peatland are limited. Thus, long-term monitoring was conducted to investigate the effects of N fertilization on soil N2O emissions. This study was conducted in an oil palm (Elaeis guineensis Jacq.) plantation located in a tropical peatland in Sarawak, Malaysia. Monthly soil N2O fluxes were measured using the closed-chamber method in a control (T1, without N fertilization), and under three different N treatments: low N (T2, 31.1 kg N ha−1), moderate N (recommended rate) (T3, 62.2 kg N ha−1), and high N (T4, 124.3 kg N ha−1), from January 2010 to December 2013 and from January 2016 to December 2017. The only N fertiliser rate to significantly increase (p<0.05) annual cumulative N2O emissions was 124.3 kg N ha-1 (T4). Increased in water-filled pore space (WFPS) (>70%) with a decrease in both N2O flux and nitrate (NO3−) implies that complete denitrification has taken place. Increased in NO3- uptake by oil palm with an increase in WFPS decreased NO3- concentration in soil, resulting in the reduction of N2O emission. This study highlights the importance of WFPS on denitrification and N uptake by oil palm in tropical peatland. This needs to be taken into account for the accurate assessment of N dynamics in oil palm plantations on tropical peatland in order to enhance N fertilization management strategies and counteract anthropogenic activities that produce greenhouse gases.Keywords: WFPS, oil palm yield, NO3-, N uptake

Orchid conservation effort in Sarawak is constructive but hampered by limited understanding of diversity and ecology for peat swamp forests (PSF). Thus, this study evaluated the current state of orchids in Sarawak PSF and the factors influencing their occurrence. Beyond literature compilation, an orchid survey conducted in Maludam PSF covered four phasic communities (PCs): Mixed Peat Swamp (MPS), Alan Batu (ABt), Alan Bunga (ABg), and Padang Alan (PA). Observations and sampling in each PC used convenience and stratified random sampling. Biotic and abiotic data were collected and examined with orchid occurrence using R software. Approximately 86 species of orchids with 35 genera were recorded in Sarawak PSF, wher 35 species from 14 genera were found in Maludam PSF. Most species belonged to Bulbophyllum genera from the Epidendroideae family. Over 96% of Sarawak peatland orchids were yet to be evaluated in the IUCN Red List. ABg had the highest species richness and diversity but the lowest evenness, while PA had the highest abundance of orchids. Terrestrial orchids appeared only in MPS, while Bulbophyllum cf. gracillimum and B. membranaceum dominated ABg and PA. These phenomena are influenced by tree structure and microclimate. Such knowledge is crucial to enhance conservation strategies for both Orchidaceae and PSF.