Nitrogen is essential for seagrass productivity but excesses in nitrogen exposure contribute to declines in meadow health. This study reports baseline data of bulk nitrogen loadings and contents in surficial sediments and seagrass tissues to determine the extent of nitrogen inputs in meadows of Sungai Pulai estuary (Johor, Malaysia). The sediment contained relatively low nitrogen loadings (mean range of 91-94 g N m-2) with likely origins from land-based sources. At the meadow-level, Enhalus acoroides, Cymodocea serrulata and Thalassia hemprichii are the most important species as nitrogen sinks. The highest δ15N values of seagrass tissues were recorded for T. hemprichii (10.7 ± 0.4‰), which indicated an elevated capacity for internal recycling of nitrogen. The data demonstrates the provision of ecosystem services by the meadows in mitigating excess nitrogen imported into the estuary. Seagrasses health, however, needs to be at optimum levels for the effectiveness of the meadow as a nutrient sink.
The permeable (sandy) sediments that dominate the world's coastlines and continental shelves are highly exposed to nitrogen pollution, predominantly due to increased urbanisation and inefficient agricultural practices. This leads to eutrophication, accumulation of drift algae and changes in the reactions of nitrogen, including the potential to produce the greenhouse gas nitrous oxide (N2O). Nitrogen pollution in coastal systems has been identified as a global environmental issue, but it remains unclear how this nitrogen is stored and processed by permeable sediments. We investigated the interaction of drift algae biomass and nitrate (NO3-) exposure on nitrogen cycling in permeable sediments that were impacted by high nitrogen loading. We treated permeable sediments with increasing quantities of added macroalgal material and NO3- and measured denitrification, dissimilatory NO3- reduction to ammonium (DNRA), anammox, and nitrous oxide (N2O) production, alongside abundance of marker genes for nitrogen cycling and microbial community composition by metagenomics. We found that the presence of macroalgae dramatically increased DNRA and N2O production in sediments without NO3- treatment, concomitant with increased abundance of nitrate-ammonifying bacteria (e.g. Shewanella and Arcobacter). Following NO3- treatment, DNRA and N2O production dropped substantially while denitrification increased. This is explained by a shift in the relative abundance of nitrogen-cycling microorganisms under different NO3- exposure scenarios. Decreases in both DNRA and N2O production coincided with increases in the marker genes for each step of the denitrification pathway (narG, nirS, norB, nosZ) and a decrease in the DNRA marker gene nrfA. These shifts were accompanied by an increased abundance of facultative denitrifying lineages (e.g. Pseudomonas and Marinobacter) with NO3- treatment. These findings identify new feedbacks between eutrophication and greenhouse gas emissions, and in turn have potential to inform biogeochemical models and mitigation strategies for marine eutrophication.
The response patterns of microbial functional genes involved in biogeochemical cycles to cadaver decay is a central topic of recent environmental sciences. However, the response mechanisms and pathways of the functional genes associated with the carbon (C) and nitrogen (N) cycling to cadaveric substances such as cadaverine and putrescine remain unclear. This study explored the variation of functional genes associated with C fixation, C degradation and N cycling and their influencing factors under cadaverine, putrescine and mixed treatments. Our results showed only putrescine significantly increased the alpha diversity of C fixation genes, while reducing the alpha diversity of N cycling genes in sediment. For the C cycling, the mixed treatment significantly decreased the total abundance of reductive acetyl-CoA pathway genes (i.e., acsB and acsE) and lig gene linked to lignin degradation in water, while only significantly increasing the hydroxypropionate-hydroxybutylate cycle (i.e., accA) gene abundance in sediment. For the N cycling, mixed treatment significantly decreased the abundance of the nitrification (i.e., amoB), denitrification (i.e., nirS3) genes in water and the assimilation pathway gene (i.e., gdhA) in sediment. Environmental factors (i.e., total carbon and total nitrogen) were all negatively associated with the genes of C and N cycling. Therefore, cadaverine and putrescine exposure may inhibit the pathway in C fixation and N cycling, while promoting C degradation. These findings can offer some new insight for the management of amine pollution caused by animal cadavers.
Tropical peatlands significantly influence local and global carbon and nitrogen cycles, yet they face growing pressure from anthropogenic activities. Land use changes, such as peatland forests conversion to oil palm plantations, affect the soil microbiome and greenhouse gas (GHG) emissions. However, the temporal dynamics of microbial community changes and their role as GHG indicators are not well understood. This study examines the dynamics of peat chemistry, soil microbial communities, and GHG emissions from 2016 to 2020 in a logged-over secondary peat swamp forest in Sarawak, Malaysia, which transitioned to an oil palm plantation. This study focuses on changes in genetic composition governing plant litter degradation, methane (CH4), and nitrous oxide (N2O) fluxes. Soil CO2 emission increased (doubling from approximately 200 mg C m-2 h-1), while CH4 emissions decreased (from 200 µg C m-2 h-1 to slightly negative) following land use changes. The N2O emissions in the oil palm plantation reached approximately 1,510 µg N m-2 h-1, significantly higher than previous land uses. The CH4 fluxes were driven by groundwater table, humification levels, and C:N ratio, with Methanomicrobia populations dominating methanogenesis and Methylocystis as the main CH4 oxidizer. The N2O fluxes correlated with groundwater table, total nitrogen, and C:N ratio with dominant nirK-type denitrifiers (13-fold nir to nosZ) and a minor role by nitrification (a threefold increase in amoA) in the plantation. Proteobacteria and Acidobacteria encoding incomplete denitrification genes potentially impact N2O emissions. These findings highlighted complex interactions between microbial communities and environmental factors influencing GHG fluxes in altered tropical peatland ecosystems.IMPORTANCETropical peatlands are carbon-rich environments that release significant amounts of greenhouse gases when drained or disturbed. This study assesses the impact of land use change on a secondary tropical peat swamp forest site converted into an oil palm plantation. The transformation lowered groundwater levels and changed soil properties. Consequently, the oil palm plantation site released higher carbon dioxide and nitrous oxide compared to previous land uses. As microbial communities play crucial roles in carbon and nitrogen cycles, this study identified environmental factors associated with microbial diversity, including genes and specific microbial groups related to nitrous oxide and methane emissions. Understanding the factors driving microbial composition shifts and greenhouse gas emissions in tropical peatlands provides baseline information to potentially mitigate environmental consequences of land use change, leading to a broader impact on climate change mitigation efforts and proper land management practices.
Soybean (Glycine max L.) is one the most commonly consumed legumes worldwide, with 200 million metric tons produced per year. However, the inedible soy husk would usually be removed during the process and the continuous generation of soybean husk may represent a major disposal problem for soybean processing industries. Thus, the main aim of the present study was to investigate the possibility to convert soybean husk (S) amended with market-rejected papaya (P) into vermicompost using Eudrilus eugeniae.