Relationships among plants, soils and microbial communities along a hydrological gradient in the New Jersey Pinelands, USA

Non-flooding conditions caused by water table drawdown alter microbial network complexity and decrease multifunctionality in alpine wetland soils

Several soil functions of alpine wetland depend on microbial communities, including carbon storage and nutrient cycling, and soil microbes are highly sensitive to hydrological conditions. Wetland degradation is often accompanied by a decline in water table. With the water table drawdown, the effects of microbial network complexity on various soil functions remain insufficiently understood. In this research, we quantified soil multifunctionality of flooded and non-flooded sites in the Lalu Wetland on the Tibetan Plateau. We employed high-throughput sequencing to investigate the microbial community responses to water table depth changes, as well as the relationships between microbial network properties and soil multifunctionality. Our findings revealed a substantial reduction in soil multifunctionality at both surface and subsurface soil layers (0-20 cm and 20-40 cm) in non-flooded sites compared to flooded sites. The α-diversity of bacteria in the surface soil of non-flooded sites was significantly lower than that in flooded sites. Microbial network properties (including the number of nodes, number of edges, average degree, density, and modularity of co-occurrence networks) exhibited significant correlations with soil multifunctionality. This study underscores the adverse impact of non-flooded conditions resulting from water table drawdown on soil multifunctionality in alpine wetland soils, driven by alterations in microbial community structure. Additionally, we identified soil pH and moisture content as pivotal abiotic factors influencing soil multifunctionality, with microbial network complexity emerging as a valuable predictor of multifunctionality.

Microbial Communities of Peaty Permafrost Tundra Soils along the Gradient of Environmental Conditions and Anthropogenic Disturbance in Pechora River Delta in the Eastern European Arctic

Microbial communities play crucial roles in the global carbon cycle, particularly in peatland and tundra ecosystems experiencing climate change. The latest IPCC assessments highlight the anthropogenic changes in the Arctic peatlands and their consequences due to global climate change. These disturbances could trigger permafrost degradation and intensification of the biogeochemical processes resulting in greenhouse gas formation. In this study, we describe the variation in diversity and composition of soil microbial communities from shallow peat tundra sites with different anthropogenic loads and applied restoration interventions in the landscape of remnant fragments of terraces in the Pechora River delta, the Russian Arctic, Nenets Autonomous Okrug. The molecular approaches, including quantitative real-time PCR and high-throughput Illumina sequencing of 16S RNA and ITS, were applied to examine the bacterial and fungal communities in the soil samples. Anthropogenic disturbance leads to a significant decrease in the representation of Acidobacteria and Verrucomicrobia, while the proportion and diversity of Proteobacteria increase. Fungal communities in undisturbed sites may be characterized as monodominant, and anthropogenic impact increases the fungal diversity. Only the verrucomicrobial methanotrophs Methyloacifiphilaceae were found in the undisturbed sites, but proteobacterial methanotrophs Methylobacterium-Methylorubrum, as well as different methylotrophs affiliated with Methylophilaceae, and Beijerinckiaceae (Methylorosula), were detected in disturbed sites.

Driving Factors of Microbial Community Abundance and Structure in Typical Forest Soils of Sanjiang Plain, Northeast China

Until recently, a comprehensive evaluation of the environmental drivers on the abundance and structure of the microbial community in typical forest soils has not been thoroughly conducted. In this study, the typical forest soils (Mongolian oak (Quercus mongolica) soil, MOS; white birch (Betula platyphylla) soil, WBS; and white poplar (Populus davidiana) soil, WPS) in the Sanjiang Plain were selected to ascertain the differences and the major environmental factors driving soil microbial community abundance and structure. Results indicated that differences existed in the abundance and structure of the bacterial, archaeal, and fungal community. Co-occurrence network analysis showed that the bacterial and fungal networks were more complex than those of archaeal networks. Unclassified Acidobacteria and unclassified Pyrinomonadaceae were the keystone taxa in the bacterial networks, while Pleotrichocladium and Leotia were the keystone taxa in the fungal networks. Among all environmental factors, pH, SOM, and total N exhibited dominant roles in affecting the abundance of bacteria, archaea, and fungi. The redundancy analysis (RDA) showed that pH was the vital environmental factor responsible for driving the structure of the bacterial, archaeal, and fungal community.

Habitats Are More Important Than Seasons in Shaping Soil Bacterial Communities on the Qinghai-Tibetan Plateau

Both habitats and seasons can determine the dynamics of microbial communities, but the relative importance of different habitats and seasonal changes in shaping the soil bacterial community structures on a small spatial scale in permafrost areas remains controversial. In this study, we explored the relative effect of four typical alpine meadow habitats (swamp wetland, swamp meadow, meadow and mature meadow) versus seasons on soil bacterial communities based on samples from the Qinghai-Tibetan Plateau in four months (March, May, July and September). The results showed that habitats, rather than seasons explained more variation of soil bacterial composition and structure. Environmental cofactors explained the greatest proportion of bacterial variation observed and can help elucidate the driving force of seasonal changes and habitats on bacterial communities. Soil temperature played the most important role in shaping bacterial beta diversities, followed by soil total nitrogen and pH. A group of microbial biomarkers, used as indicators of different months, were identified using random forest modeling, and for which relative abundance was shaped by different environmental factors. Furthermore, seasonality in bacterial co-occurrence patterns was observed. The data showed that co-occurrence relationships changed over months. The inter-taxa connections in May and July were more pronounced than that in March and September. Bryobacter, a genus of subgroup_22 affiliated to Acidobacteria, and Pseudonocardia belonging to Actinobacteria were observed as the keystone taxa in different months in the network. These results demonstrate that the bacterial community was clustered according to the seasonal mechanism, whereas the co-occurrence relationships changed over months, which indicated complex bacterial dynamics in a permafrost grassland on the eastern edge of Qinghai-Tibetan.

Palustrine forested wetland vegetation communities change across an elevation gradient, Washington State, USA

Background

Forested wetlands support distinct vegetation and hydrology relative to upland forests and shrub-dominated or open water wetlands. Although forested wetland plant communities comprise unique habitats, these ecosystems’ community structure is not well documented in the U.S. Pacific Northwest. Here I surveyed forested wetland vegetation to identify changes in community composition and structure across an elevation gradient that corresponds to flooding stress, asking: (1) How do forested wetland plant communities change across an elevation gradient that corresponds to flood frequency and duration? (2) At what relative elevations do different plant species occur within a wetland?

Methods

I measured overstory tree basal area and structure and understory vascular plant composition in three zones: wetland buffers (WB) adjacent to the wetland, an upper wetland (UW) extent, and a lower wetland (LW) extent, surveying individual trees’ root collar elevation relative to the wetland ordinary high-water mark (OHWM). I estimated understory plant species abundance in sub-plots and surveyed these plots’ height above the OHWM. I used non-metric multidimensional scaling ordination to identify patterns in vegetation communities relative to wetland elevation, and tested for compositional differences between the WB, UW and LW zones using PERMANOVA. I calculated overstory and understory indicator species for each wetland zone using indicator species analysis.

Results

Forest overstory composition changed across the elevation gradient, with broad-leaved trees occupying a distinct hydrologic niche in low-lying areas close to the OHWM. Conifer species occurred higher above the OHWM on drier microsites. Pseudotsuga menziesii (mean elevation = 0.881 m) and Tsuga heterophylla (mean elevation = 1.737 m) were overstory indicator species of the WB, while Fraxinus latifolia (mean elevation = 0.005 m) was an overstory indicator for the upper and lower wetland. Understory vegetation differed between zones and lower zones’ indicator species were generally hydrophytic species with adaptations that allow them to tolerate flooding stress at lower elevations. Average elevations above the OHWM are reported for 19 overstory trees and 61 understory plant species. By quantifying forested wetland plant species’ affinities for different habitats across an inundation gradient, this study illustrates how rarely flooded, forested WB vegetation differs from frequently flooded, LW vegetation. Because common management applications, like restoring forested wetlands and managing wetland responses to forest harvest, are both predicated upon understanding how vegetation relates to hydrology, these data on where different species might establish and persist along an inundation gradient may be useful in planning for anticipated forested wetland responses to restoration and disturbance.

The role of wetland microorganisms in plant-litter decomposition and soil organic matter formation: a critical review

New soil organic matter (SOM) models highlight the role of microorganisms in plant litter decomposition and storage of microbial-derived carbon (C) molecules. Wetlands store more C per unit area than any other ecosystem, but SOM storage mechanisms such as aggregation and metal complexes are mostly untested in wetlands. This review discusses what is currently known about the role of microorganisms in SOM formation and C sequestrations, as well as, measures of microbial communities as they relate to wetland C cycling. Studies within the last decade have yielded new insights about microbial communities. For example, microbial communities appear to be adapted to short-term fluctuations in saturation and redox and researchers have observed synergistic pairings that in some cases run counter to thermodynamic theory. Significant knowledge gaps yet to be filled include: (i) What controls microbial access to and decomposition of plant litter and SOM? (ii) How does microbial community structure shape C fate, across different wetland types? (iii) What types of plant and microbial molecules contribute to SOM accumulation? Studies examining the active microbial community directly or that utilize multi-pronged approaches are shedding new light on microbial functional potential, however, and promise to improve wetland C models in the near future.

Effects of environmental variation on stable isotope abundances during typical seasonal floodplain dry season litter decomposition

Unique hydrological characteristics and complex topography can create wide-ranging dry season environmental heterogeneity in response to groundwater level across China's Jiangxi Province Poyang Lake wetland. Soil traits are one of several fluctuating environmental variables. To determine the effects of soil variables on stable isotope (δ¹³C and δ¹⁵N) abundances during decomposition, we performed a field experiment using Carex cinerascens along a groundwater level gradient (GT-L: -25 to -50cm, GT-LM: -15 to -25cm, GT-MH: -5 to -15cm, GT-H: 5 to -5cm) in a shallow lake. Twelve soil properties-including total organic carbon (TOC), nitrogen (N), pH, moisture, bulk density, clay, silt, sand, peroxidase, cellulase, microbial biomass carbon (MBC), and microbial biomass nitrogen-were measured in surface soil samples to assess soil environmental conditions. Analyses were performed to determine the effects of soil traits and lignin degradation on changes in stable isotope abundances. This study revealed that stable isotope abundances were significantly lower at high groundwater levels than at low groundwater levels. Lignin degradation was associated with a decrease in both δ¹³C and δ¹⁵N abundances. These two stable isotopes were positively related with soil N and bulk density, but negatively with pH and microbial quotient (MBC/TOC). Variation partitioning analysis (VPA) showed that soil variables and lignin decay rates explained 80.1% of the δ¹³C variation and 42.8% of the δ¹⁵N variation. Soil chemical and biological variables exhibited significant interactions with lignin decay rates, indicating they may affect stable isotope abundances via complex mechanisms. Our results indicate that the change in stable isotope abundances during decomposition may be affected directly by soil variables or indirectly through lignin degradation. Our results provide useful insight for understanding the roles of litter decomposition and soil traits in changing environmental conditions of seasonal floodplain wetlands.

Nitrous oxide production and consumption by denitrification in a grassland: Effects of grazing and hydrology

Denitrification is generally recognized as a major mechanism contributing to nitrous oxide (N2O) production, and is the only known biological process for N2O consumption. Understanding factors controlling N2O production and consumption during denitrification will provide insights into N2O emission variability, and potentially predict capacity of soils to serve as sinks or sources of N2O. This study investigated the effects of hydrology and grazing on N2O production and consumption in a grassland based agricultural watershed. A batch incubation study was conducted on soils (0-10 cm) collected along a hydrological gradient representing isolated wetland (Center), transient zone (Edge) and pasture upland (Upland), from both grazed and ungrazed areas. Production and consumption potentials of N2O were quantified on soils under four treatments, including (i) ambient condition, and amended with (ii) NO3(-), (iii) glucose-C, and (iv) NO3(-) +glucose-C. The impacts of grazing on N2O production and consumption were not observed. Soils in hydrologically distinct zones responded differently to N2O production and consumption. Under ambient conditions, both production and consumption rates of Edge soils were higher than those observed for Center and Upland soils. Results of amended incubations suggested NO3(-) was a key factor limiting N2O production and consumption rates in all hydrological zones. Over 5-d incubation with NO3(-) amendment, cumulative production and consumption of N2O for Center soils were 1.6 and 3.3 times higher than Edge soils, and 3.6 and 7.6 times higher than Upland soils, respectively. However, cumulative N2O net production for Edge soils was the highest, with 2 to 3 times higher than Upland and Center soils. Our results suggest that the transient areas between wetland and upland are likely to be "hot spots" of N2O emissions in this ecosystem. Wetlands within agricultural landscapes can potentially function to reduce both NO3(-) leaching and N2O emissions.

A comprehensive study of the impact of polycyclic aromatic hydrocarbons (PAHs) contamination on salt marsh plants Spartina alterniflora: implication for plant-microbe interactions in phytoremediation

These pot experiments aimed to investigate the effects of polycyclic aromatic hydrocarbons (PAHs) on plant uptake, rhizophere, endophytic bacteria, and phytoremediation potentials of contaminated sediments. Salt marsh plant Spartina alterniflora was selected and cultivated in phenanthrene (PHE)- and pyrene (PYR)-contaminated sediments (for 70 days). The results indicated that the amount of PHE removed from the sediments ranged from 13 to 36 %, while PYR ranged from 11 to 30 %. In rhizophere sediment, dehydrogenase activities were significantly (P < 0.05) enhanced by higher concentration of PHE treatments, while polyphenol oxidase activities were prohibited more than 10 % in non-rhizophere sediment. Compared with the control, PHE treatments had also significantly (P < 0.05) lower total microbial biomass; especially for gram-negative bacteria, this decrease was more than 24 %. However, the PYR treatments had little effect on the dehydrogenase, polyphenol oxidase, and total phospholipid fatty acid analysis (PLFA) biomass. The greatest abundance of PAH-ring hydroxylating dioxygenases isolated from gram-negative bacteria (PAH-RHDα-GN) of rhizoplane and endophyte in roots were found at high concentration of PHE treatments and increased by more than 100- and 3-fold, respectively. These results suggested that PAH pollution would result in the comprehensive effect on S. alterniflora, whose endophytic bacteria might play important roles in the phytoremediation potential of PAH-contaminated sediments.