Coupled abiotic-biotic cycling of nitrous oxide in tropical peatlands

Atmospheric nitrous oxide (N2O) is a potent greenhouse gas thought to be mainly derived from microbial metabolism as part of the denitrification pathway. Here, we report that in unexplored peat soils of Central and South America, N2O production can be driven by abiotic reactions (> 98 %) highly competitive to their enzymatic counterparts. Extracted soil iron positively correlated with in-situ abiotic N2O production determined by isotopic tracers. Moreover, we found that microbial N2O reduction accompanied abiotic production, essentially closing a coupled abiotic-biotic N2O cycle. Anaerobic N2O consumption occurred ubiquitously (pH 6.4-3.7), with proportions of diverse clade II N2O-reducers increasing with consumption rates. Our findings show denitrification in tropical peat soils is not a purely biological process, but rather a 'mosaic' of abiotic and biotic reduction reactions. We predict hydrological and temperature fluctuations differentially affect abiotic and biotic drivers and further contribute to the high N2O flux variation in the region.

Assessing the distribution of total Fe, Cu, and Zn in tropical peat at an oil palm plantation and their relationship with several environmental factors

Extensive utilization of fragile tropical peatlands ecosystem encourages a better understanding of spatiotemporal micronutrients distribution. The distribution of total Fe, Cu, and Zn in peat and their relationship with environmental factors were studied under oil palm plantation, Pangkalan Pisang, Koto Gasib, Riau, Indonesia. Peat samples were taken compositely inside the block using a combination of six factors, including a) the oil palm age (<6, 6-15, >15 years old), b) the peat thickness (< 3 and >3 m), c) season (rainy and dry), d) the distances from the secondary canal (10, 25, 50, 75, 100, and 150 m), e) the distances from an oil palm tree (1, 2, 3, and 4 m), and f) the depth of sample collection (0-20, 20-40, and 40-70 cm from the peat surface). Total Fe, Cu, and Zn were determined by the wet digestion method. These micronutrients observed in this study possessed high variability; however, they were within the expected range in tropical peatland. The entire micronutrients were statistically different by oil palm age, peat thickness, and distance from canal. Meanwhile, total Cu and Zn were also significantly different at each season. The oil palm age, peat thickness, and distance from the canal were the common factors controlling total Fe, Cu, and Zn in peat significantly. Moreover, total Cu and Zn were also dictated by season, distance from the oil palm tree, and depth of sample collection. Based on visual interpretation in PCA (principal component analysis), all micronutrients were categorized into two groups, separated by 2 m distance from the oil palm tree and 20 cm depth from the soil surface. Our study also highlights the dominance of the dilution over the enrichment process in peat, which requires further research to formulate micronutrients fertilization, especially for an extended cultivation time.

Socio-economic Study of Conservation and Rehabilitation of Tropical Peatland With Agroforestry Systems in Central Kalimantan, Indonesia

Current studies on tropical peatlands in Indonesia are mostly focused on the impacts of management practices on the environment. Studies on efforts to conserve and rehabilitate the degradation of tropical peatland involving farmers through agroforestry systems have been limited. By employing the qualitative survey with semi-structured interviews and field observations to agroforestry locations in two villages of Tumbang Nusa and Kalampangan, Central Kalimantan, Indonesia aims to fill those research gaps. The results showed that the main motivation of farmers in starting agroforestry activities was the understanding that there would be limited trees in the future, and planting trees with a combination of intercrops provided adequate income. Agroforestry farmers who devote considerable time to agroforestry can meet the family's economic needs. Although further guidance is not typically provided, government intervention through tree planting programs also stimulates agroforestry activities. Intensive management of intercrops in various types can provide a good income. For intensive intercropping options, farmers follow market demand, while less intensive farmers prefer plants that do not require intensive management. Trees planted in agroforestry systems are only given fertilizer at the initial planting stage. Some farms receive fertilizer subsidies from government support programmes, but fertilizers are obtained from intercropping at the following stage. The study results imply that the community needs to get knowledge and training on agroforestry, which can be a way of conserving and rehabilitating tropical peatlands and a source of income.