The potential of viruses to influence the magnitude of greenhouse gas emissions in an inland wetland

Microbes drive more carbon dioxide and nitrous oxide emissions from wetland under long-term nitrogen enrichment

Wetlands are frequently regarded as weak carbon dioxide (CO2) sinks, the largest natural sources of methane (CH4), and weak sources of nitrous oxide (N2O). Anthropogenic activities and climate change-induced nitrogen (N) enrichment may affect wetland carbon (C) and N cycling via soil microbes, consequently modifying the original greenhouse gas (GHG) emissions. However, the effects and mechanisms of the duration and rate of N inputs on wetland GHG emissions remain uncertain and controversial. Therefore, this study conducted an in situ field experiment to investigate the effects and driving mechanisms of long-term N enrichment on wetland GHG emissions throughout the 2023 growing season by using the static opaque chambers method. Soil microbial composition and function were also analyzed through metagenomic sequencing. The results showed that N enrichment significantly increased wetland CO2 emissions, which were associated with the abundance of microbial C-fixing functional genes and the soil C content. Although nitrogen enrichment tended to suppress CH4 emissions, the effect was not significant. High N enrichment created a powerful wetland N2O source driven by the abundance of microbial nitrification function genes and microbial species. Vegetation influenced wetland GHG emissions by altering soil carbon content. This study elucidates the response mechanism of wetland GHG emissions to long-term nitrogen enrichment, thereby furnishing a theoretical basis for wetland conservation and nitrogen management.

Phages Affect Soil Dissolved Organic Matter Mineralization by Shaping Bacterial Communities

Viruses are considered to regulate bacterial communities and terrestrial nutrient cycling, yet their effects on bacterial metabolism and the mechanisms of carbon (C) dynamics during dissolved organic matter (DOM) mineralization remain unknown. Here, we added active and inactive bacteriophages (phages) to soil DOM with original bacterial communities and incubated them at 18 or 23 °C for 35 days. Phages initially (1-4 days) reduced CO2 efflux rate by 13-21% at 18 °C and 3-30% at 23 °C but significantly (p < 0.05) increased by 4-29% at 18 °C and 9-41% at 23 °C after 6 days, raising cumulative CO2 emissions by 14% at 18 °C and 21% at 23 °C. Phages decreased dominant bacterial taxa and increased bacterial community diversity (consistent with a "cull-the-winner" dynamic), thus altering the predicted microbiome functions. Specifically, phages enriched some taxa (such as Pseudomonas, Anaerocolumna, and Caulobacter) involved in degrading complex compounds and consequently promoted functions related to C cycling. Higher temperature facilitated phage-bacteria interactions, increased bacterial diversity, and enzyme activities, boosting DOM mineralization by 16%. Collectively, phages impact soil DOM mineralization by shifting microbial communities and functions, with moderate temperature changes modulating the magnitude of these processes but not qualitatively altering their behavior.

Ebullition mediated transport dominates methane emission from open water area of the floating national park in Indo Burma hotspot

Ebullition is an important route of methane emission from aquatic ecosystems. Ebullitive CH4 emissions from the wetlands, particularly the mountain wetlands of Eastern Himalayan, are poorly understood. To gain insights into the role of ebullition in CH4 emissions and understand the factors influencing CH4 ebullition, we conducted field measurements of the spatial and temporal variation of ebullition in a freshwater wetland area in floating national park (40 sq. km, 780 m amsl, maximum depth < 4.5) in Northeast India. The average ebullitive CH4 flux ranged from 220.24 to 1889.35 mg m-2 d-1, while the overall CH4 fluxes varied widely ranging from 345.81 to 2240.56 mg m-2 d-1. Methane constituted 90.18% of the gas bubbles produced from the sediment, with CO2 comprising 8.82% of the total sediment gas in the wetland. This suggests that CH4 emission through ebullition plays an important role in transporting biogenic CH4 to the atmosphere. The ebullition rate was markedly higher during summer and lower during winter and exhibited a significant seasonal variation. At a spatial scale, the sites with dense aquatic vegetation growth increase CH4 emission where plants derived autochthonous sediment organic matter, substantiating the supply of carbon substrate for CH4 production. Linear mixed-effect models revealed that water temperature, organic matter, organic carbon and dissolved organic matter are the important factors affecting the ebullitive methane flux. Our results indicate that mountainous wetlands with organic-rich sediments may be potential hotspots for CH4 ebullition. However, the lack of information on these wetlands in the scientific literature emphasizes the need for further research.

Climate warming negatively affects plant water-use efficiency in a seasonal hydroperiod wetland

Climate warming has substantial influences on plant water-use efficiency (PWUE), which is defined as the ratio of plant CO2 uptake to water loss and is central to the cycles of carbon and water in ecosystems. However, it remains uncertain how does climate warming affect PWUE in wetland ecosystems, especially those with seasonally alternating water availability during the growing season. In this study, we used a continuous 10-year (2011-2020) eddy covariance (EC) dataset from a seasonal hydroperiod wetland coupled with a 15-year (2003-2017) satellite-based dataset (called PML-V2) and an in situ warming experiment to examine the climate warming impacts on wetland PWUE. The 10-year EC observational results revealed that rising temperatures had significant negative impacts on the interannual variations in wetland PWUE, and increased transpiration (Et) rather than changes in gross primary productivity (GPP) dominated these negative impacts. Furthermore, the 15-year satellite-based evidence confirmed that, in the study region, climate warming had significant negative consequences for the interannual variations in wetland PWUE by enhancing wetland Et. Lastly, at the leaf-scale, the light response curves of leaf photosynthesis, leaf Et, and leaf-scale PWUE indicated that wetland plants need to consume more water during the photosynthesis process under warmer conditions. These findings provide a fresh perspective on how climate warming influences carbon and water cycles in wetland ecosystems.

Experimental evidence for the impact of phages on mineralization of soil-derived dissolved organic matter under different temperature regimes

Microbial mineralization of dissolved organic matter (DOM) plays an important role in regulating C and nutrient cycling. Viruses are the most abundant biological agents on Earth, but their effect on the density and activity of soil microorganisms and, consequently, on mineralization of DOM under different temperatures remains poorly understood. To assess the impact of viruses on DOM mineralization, we added soil phage concentrate (active vs. inactive phage control) to four DOM extracts containing inoculated microbial communities and incubated them at 18 °C and 23 °C for 32 days. Infection with active phages generally decreased DOM mineralization at day one and showed accelerated DOM mineralization later (especially from day 5 to 15) compared to that with the inactivated phages. Overall, phage infection increased the microbially driven CO₂ release. Notably, while higher temperature increased the total CO₂ release, the cumulative CO₂ release induced by phage infection (difference between active phages and inactivated control) was not affected. However, higher temperatures advanced the response time of the phages but shortening its active period. Our findings suggest that bacterial predation by phages can significantly affect soil DOM mineralization. Therefore, higher temperatures may accelerate host-phage interactions and thus, the duration of C recycling.

Virus-to-prokaryote ratio in the Salar de Huasco and different ecosystems of the Southern hemisphere and its relationship with physicochemical and biological parameters

The virus-to-prokaryote ratio (VPR) has been used in many ecosystems to study the relationship between viruses and their hosts. While high VPR values indicate a high rate of prokaryotes' cell lysis, low values are interpreted as a decrease in or absence of viral activity. Salar de Huasco is a high-altitude wetland characterized by a rich microbial diversity associated with aquatic sites like springs, ponds, streams and a lagoon with variable physicochemical conditions. Samples from two ponds, Poza Rosada (PR) and Poza Verde (PV), were analyzed by epifluorescence microscopy to determine variability of viral and prokaryotic abundance and to calculate the VPR in a dry season. In addition, to put Salar de Huasco results into perspective, a compilation of research articles on viral and prokaryotic abundance, VPR, and metadata from various Southern hemisphere ecosystems was revised. The ecosystems were grouped into six categories: high-altitude wetlands, Pacific, Atlantic, Indian, and Southern Oceans and Antarctic lakes. Salar de Huasco ponds recorded similar VPR values (an average of 7.4 and 1.7 at PR and PV, respectively), ranging from 3.22 to 15.99 in PR. The VPR variability was associated with VA and chlorophyll a, when considering all data available for this ecosystem. In general, high-altitude wetlands recorded the highest VPR average (53.22 ± 95.09), followed by the Oceans, Southern (21.91 ± 25.72), Atlantic (19.57 ± 15.77) and Indian (13.43 ± 16.12), then Antarctic lakes (11.37 ± 15.82) and the Pacific Ocean (6.34 ± 3.79). Physicochemical variables, i.e., temperature, conductivity, nutrients (nitrate, ammonium, and phosphate) and chlorophyll a as a biological variable, were found to drive the VPR in the ecosystems analyzed. Thus, the viral activity in the Wetland followed similar trends of previous reports based on larger sets of metadata analyses. In total, this study highlights the importance of including viruses as a biological variable to study microbial temporal dynamics in wetlands considering their crucial role in the carbon budgets of these understudied ecosystems in the southern hemisphere.