Land-Use Changes Associated with Oil Palm Plantations Impact PLFA Microbial Phenotypic Community Structure throughout the Depth of Tropical Peats

Tropical peatlands are complex and globally-important ecosystems that are increasingly threatened by anthropogenic disturbances, primarily via agricultural development. Microbes in peatlands play important roles in governing overall ecosystem functions and sustenance, with specific population dynamics governing carbon sink or source dynamics. We determined phenotypic microbial community structures under forest, drained, burned and oil palm plantation peatlands, using phospholipid fatty acid (PLFA) profiling. Communities were distinct under each land-use type, varied consistently with depth down to two metres, but with a distinct characteristic shift at circa one metre depth. There was bacterial dominance across all land-use types and depths. The burnt peatland showed the greatest contrast relative to forest, possibly due to the difference in water table level. Gram-positive bacteria was the most dominant group in surface layers under all land-use types except burnt, and their relative abundance decreased with depth, replaced by Gram-negative groups in deeper layers. Fungal relative abundance remained low across both land-use types and depth ranges. Our results shed light on a hitherto virtually unknown tropical peat microbial phenotypic community structure and indicate that anthropogenic disturbance in tropical peatlands severely alter microbial communities

Methane emissions from tree stems in neotropical peatlands

1.Neotropical peatlands emit large amounts of methane (CH4) from the soil surface, but fluxes from tree stems in these ecosystems are unknown. In this study we investigated CH4 emissions from five tree species in two forest types common to neotropical lowland peatlands in Panama.2.Methane from tree stems accounted for up to 30% of net ecosystem CH4 emissions. Peak CH4 fluxes were greater during the wet season when the water table was high and temperatures were lower. Emissions were greatest from the hardwood tree Campnosperma panamensis, but most species acted as emitters, with emissions declining exponentially with height along the stem for all species. 3.Overall, species identity, stem diameter, water level, soil temperature and soil CH4 fluxes explained 54% of the variance in stem CH4 emissions from individual trees. On the landscape level, the high high emission from Campnosperma panamensis forest these emitted comparable amounts of CH4 from tree stems as mixed forests at 340 kg CH4 day‐1 during flooded periods despite their substantially lower areal cover. 4.We conclude that emission from tree stems is an important emission pathway for CH4 flux from Neotropical peatlands, and that these emissions vary strongly with season and forest type

Nutrient and trace element concentrations influence greenhouse gas emissions from Malaysian tropical peatlands

Tropical peatlands are unique and globally important ecosystems for carbon storage that are generally considered nutrient poor. However, different nutrient and trace element concentrations in these complex ecosystems and their interactions with carbon emissions are largely unknown. The objective of this research was to explore the concentrations of macro- and micronutrients and othertrace elements in surface peats, and their relationship with greenhouse gas emissions in North Selangor peatlands subjected to different land use. All nutrient and trace element concentrations except chromium exhibited significant differences between sites. Most macronutrients and some micronutrients showed significant differences between seasons, typically with a reduction over time from wet to dry seasons, possibly due to leaching. CO2 emissions were positively related to organic matter content and manganese concentrations and negatively correlated with selenium. CH4 emissions were positively correlated with organic matter content, manganese, copper, barium, cobalt and aluminium, and negatively correlated with molybdenum, selenium, lithium and vanadium. This research has detected loss of essential nutrients over time, aiding to increase nutrient limitation in tropical peatlands due to drainage. The observed significant correlation between trace elements and greenhouse gas emissions strengthens the importance of including trace element analyses in understanding the biogeochemical functions of these understudied peatlands

To what extent can zero tillage lead to a reduction in greenhouse gas emissions from temperate soils?

Soil tillage practices have a profound influence on the physical properties of soil and the greenhouse gas (GHG) balance. However there have been very few integrated studies on the emission of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) and soil biophysical and chemical characteristics under different soil management systems. We recorded a significantly higher net global warming potential under conventional tillage systems (26–31% higher than zero tillage systems). Crucially the 3-D soil pore network, imaged using X-ray Computed Tomography, modified by tillage played a significant role in the flux of CO2 and CH4. In contrast, N2O flux was determined mainly by microbial biomass carbon and soil moisture content. Our work indicates that zero tillage could play a significant role in minimising emissions of GHGs from soils and contribute to efforts to mitigate against climate change

Root oxygen mitigates methane fluxes in tropical peatlands

Tropical peatlands are a globally important source of methane, a potent greenhouse gas. Vegetation is critical in regulating fluxes, providing a conduit for emissions and regular carbon inputs. However, plant roots also release oxygen, which might mitigate methane efflux through oxidation prior to emission from the peat surface. Here we show, using in situ mesocosms, that root exclusion can reduce methane fluxes by a maximum of 92% depending on species, likely driven by the significant decrease in root inputs of oxygen and changes in the balance of methane transport pathways. Methanotroph abundance decreased with reduced oxygen input, demonstrating a likely mechanism for the observed response. These first methane oxidation estimates for a tropical peatland demonstrate that although plants provide an important pathway for methane loss, this can be balanced by the influence of root oxygen inputs that mitigate peat surface methane emissions

Monitoring tropical peat related settlement using ISBAS InSAR, Kuala Lumpur International Airport (KLIA)

Rapid population growth in South-East Asia has placed immense pressure upon lowland regions both to supply food and employment and space for residential, commercial and infrastructure development. This pressure has led to sites on tropical peatland previously considered unsuitable for development to be revisited. One such site, the KLIA2 terminal and runway, Kuala Lumpur International Airport which opened in May 2014 at a cost of 3.6 billion MYR has been beset by well documented subsidence problems. Coverage of the tropics by the Sentinel-1 satellite constellation presents an opportunity to monitor the ongoing subsidence at KLIA 2, identify potential knowledge gaps and help inform more sustainable infrastructure development in tropical peatland regions. Our results show that the ISBAS InSAR method produces reproducible ground deformation maps which can clearly identify the patterns of deformation across both urban infrastructure and adjacent rural plantations and tropical peat swamp. This is particularly well defined around the terminal building at KLIA-2 where different ground preparation and foundation design have resulted in stable terminal buildings and subsidence of surrounding pavement. Deformation is greatest in the runway area where alternate bands of uplift and subsidence presumably accompany the greatest loads associated with landing aircraft. In contrast, areas where peat replacement was the primary form of ground preparation, ground motion is stable, however this comes at high economic and environmental cost

Quality not quantity: organic matter composition controls of CO₂and CH₄fluxes in neotropical peat profiles

Tropical peatlands represent an important source of carbon dioxide (CO₂) and methane (CH₄) to the atmosphere. However, we do not know where in the peat profile these gases are produced and how controlling factors, such as substrate quality, which can vary substantially with peat age, and anoxic-oxic conditions, interact to determine production rates. To address this knowledge gap, this study investigated if substrate limitation of CO₂ and CH₄ production differs under anoxic-oxic peat conditions using entire peat profiles, from tropical peatlands in Panama. We determined the variation in peat organic chemistry through stratigraphic profiles using tetramethylammonium-pyrolysis-gas chromatography-mass spectrometry (TMAH-Py-GC/MS). To explore how variation in peat organic chemistry through the depth profile impacted on CO₂ and CH₄ production rates under anoxic-oxic conditions we carried out a series of incubation experiments. The TMAH-Py-GC/MS analysis showed high concentrations of long chain fatty acids (>C₂₀) in surface peat, and variation in the distribution of the lignin monomers through the peat profile. Both anoxic CH₄ and CO₂ production was greatest from the surface of the peat profile with surface peat accounting for 92 ± 1.7 and 54 ± 2.9% of the cumulative CH₄ and CO₂ production, respectively. The high CO₂ and CH₄ production rate under anoxic conditions, in surface peat, was strongly related to greater concentrations of lignin, but also long chain fatty acids and polysaccharides, in this section of the peat profile. As expected, CH₄ production decreased, and became decoupled from peat organic chemistry, following peat aeration. In contrast, aeration dramatically increased CO₂ emissions throughout the entire peat profile. This demonstrates that the recalcitrance of buried peat does not protect C stocks in tropical peatlands, if their water tables are lowered in response to drainage or prolonged drought. In conclusion, our work highlight that information on both labile substrate availability and water table fluctuation are needed to predict CO₂ and CH₄ fluxes from tropical peatlands

Is Intercropping an Environmentally-Wise Alternative to Established Oil Palm Monoculture in Tropical Peatlands?

Tropical peatlands in Southeast Asia are important ecosystems that play a crucial role in global biogeochemical cycles, with a potential for strong climate feedback loops. The degradation of tropical peatlands due to the expansion of oil palm plantations and their impact on biodiversity and the carbon balance is a global concern. The majority of conversion of Southeast Asian peatlands to agriculture has been by smallholder oil palm farmers, who follow more varied cropping systems compared to industrial plantations, and have better scope for expansion of other alternative varied cropping systems if supported and encouraged. Using previously-published data on peat physicochemical properties, biodiversity and greenhouse gas emissions from small-holder oil palm plantations, we determined that prolonged oil palm monocropping for two generations would result in loss of carbon and peat functional properties that may lead to potential declassification of peatlands. We propose intercropping during the early stages of oil palm as a wise alternative for already-existing plantations in tropical peatlands to ameliorate some of the negative environmental impacts of oil palm on the physio-chemical properties of peat. However, we emphasize the need to more fully explore the sustainability of intercropping systems throughout the life cycle of palm plantations on peatlands, and integrate with current management practices. We also emphasize the further need for research to fully assess the impacts of oil palm intercropping compared to widely-practiced oil palm monocropping. Finally, we suggest changes in government certification policies to encourage intercropping practices by smallholders

Immediate environmental impacts of transformation of an oil palm intercropping to a monocropping system in a tropical peatland

The expansion of oil palm plantations is one of the greatest threats to carbon-rich tropical peatlands in Southeast Asia. More than half of the oil palm plantations on tropical peatlands of Peninsular Malaysia are smallholder-based, which typically follow varied cropping systems, such as intercropping. In this case study, we compare the immediate biogeochemical impacts of conversion of an oil palm and pineapple intercropping to an oil palm monocropping system. We also assess how these changes affect the subsequent temperature sensitivity of greenhouse gas (GHG) production. We found that peat bulk density is unchanged, while organic matter content, pH and temperature is slightly yet significantly altered after conversion from oil palm intercropping to monocropping. Both in-situ and ex-situ CO2 emissions and temperature sensitivity of CO2 and CH4 production did not significantly vary between conversion stages; however, in-situ CO2 emissions in monocropping system exhibited a unique positive correlation with moisture. The findings show that some of the defining peat properties, such as bulk density and organic matter content, were mostly conserved immediately after conversion from intercropping to oil palm monocropping. However, there were signs of deterioration in other functional relationships, such as significantly greater CO2 emissions observed in the wet season to that of the dry season, showing moisture limitation to CO2 emissions in monocropping, postconversion. Nevertheless, there is a need for further research to identify the long-term impacts, and also the sustainability of intercropping practices in mature oil palm plantations for the benefit of these peat properties