Kanika S. Inglett

Temperature sensitivity of greenhouse gas production in wetland soils of different vegetation

Organic matter decomposition regulates rates of carbon loss (CO2 and CH4) in wetlands and has implications for carbon sequestration in the context of changing global temperature. Here we determined the influence of temperature and vegetation type on both aerobic and anaerobic decomposition of organic matter in subtropical wetland soils. As in many other studies, increased temperature resulted in higher rates of respiration and methanogenesis under both aerobic and anaerobic conditions, and the positive effect of temperature depended on vegetation (source of carbon substrate to soil). Under anaerobic incubations, the proportion of gaseous C (CO2 and CH4) lost as CH4 increased with temperature indicating a greater sensitivity of methanogenesis to temperature. This was further supported by a wider range of Q10 values (1.4–3.6) for methane production as compared with anaerobic CO2 (1.3–2.5) or aerobic CO2 (1.4–2.1) production. The increasing strength of positive linear correlation between CO2:CH4 ratio and the soil organic matter ligno-cellulose index at higher temperature indicated that the temperature sensitivity of methanogenesis was likely the result of increased C availability at higher temperature. This information adds to our basic understanding of decomposition in warmer subtropical and tropical wetland systems and has implications for C models in wetlands with different vegetation types.

Land‐Use Effects on Soil Nutrient Cycling and Microbial Community Dynamics in the Everglades Agricultural Area, Florida

Soil subsidence has become a critical problem since the onset of drainage of the organic soils in the Everglades Agricultural Area (EAA), which may impair current land uses in the future. The objectives of this study were to characterize soil microbial community‐level physiology profiles, extracellular enzymatic activities, microbial biomass, and nutrient pools for four land uses: sugarcane, turfgrass, pasture, and forest. Long‐term cultivation and management significantly altered the distribution and cycling of nutrients and microbial community composition and activity in the EAA, especially for sugarcane and turf fields. The least‐managed fields under pasture had the lowest microbial biomass and phosphorus (P) levels. Turf and forest had more microbial metabolic diversity than pasture or the most intensively managed sugarcane fields. Land‐use changes from sugarcane cropping to turf increased microbial activity and organic‐matter decomposition rates, indicating that changes from agricultural to urban land uses may further contribute to soil subsidence.

Restoration of Disturbed Lands: The Hole-in-the-Donut Restoration in the Everglades

The Hole-in-the-Donut (HID) wetland restoration project was established on former agricultural land inside Everglades National Park, where rock plowing and fertilization had altered the hydrology, structure, depth, aeration, and nutrient content of soils. Following the cessation of farming, highly disturbed HID soils were invaded by dense, nearly monospecific stands of Brazilian pepper (Schinus terebinthifolius Raddi). Initial efforts to restore Brazilian pepper-dominated areas failed, and only complete removal of the substrate down to the surface of bedrock was successful. Complete soil removal resulted in the restoration of a plant community dominated by native wetland plants. Following restoration, initially very shallow soils gradually deepened as marl accreted as due to the activities of periphyton. By 15 years postrestoration, an average of 3.7 cm of soil had developed. Initially low nitrogen concentrations increased following restoration, whereas phosphorus was converted to organic forms and diluted by the accumulation of marl. The result of these changes was a gradual switch from nitrogen limitation to phosphorus limitation, eventually mirroring the situation in adjacent undisturbed wetland sites. Complete substrate removal, as used in the HID, could be used to restore other areas of the Everglades degraded by nutrient enrichment.

Clostridium chromiireducens sp. nov., isolated from Cr(VI)-contaminated soil.

A Cr(VI)-resistant, Gram-positive, spore-forming, obligate anaerobe, designated GCAF-1(T), was isolated from chromium-contaminated soil by its ability to reduce Cr(VI) in low concentrations. Mixed acid fermentation during growth on glucose resulted in accumulation of acetate, butyrate, formate and lactate. Morphological studies indicated the presence of peritrichous flagella, pili and an S-layer. The major cellular fatty acids (>5 %) were C(16 : 0), C(14 : 0), summed feature 3 (comprising iso-C(15 : 0) 2-OH and/or C(16 : 1)ω7c), C(18 : 1)ω7c, C(16 : 1)ω9c, summed feature 4 (comprising iso-C(17 : 1) I and/or anteiso-C(17 : 1) B) and C(18 : 1)ω9c. The DNA G+C content of strain GCAF-1(T) was 30.7 mol%. Phylogenetic interference indicated that strain GCAF-1(T) clustered with group I of the genus Clostridium. Of strains within this cluster, strain GCAF-1(T) shared the highest 16S rRNA gene sequence similarities (98.1-98.9 %) with Clostridium beijerinckii DSM 791(T), C. saccharobutylicum NCP 262(T), C. saccharoperbutylacetonicum N1-4(T), C. puniceum DSM 2619(T) and C. roseum DSM 51(T). However, strain GCAF-1(T) could be clearly distinguished from its closest phylogenetic neighbours by low levels of DNA-DNA relatedness (<50 %) and some phenotypic features. Based on the evidence presented here, strain GCAF-1(T) ( = DSM 23318(T) = KCTC 5935(T)) represents a novel species of the genus Clostridium, for which the name Clostridium chromiireducens sp. nov. is proposed.

Microbial Ecology and Everglades Restoration

Much of the activity proposed for Everglades restoration is associated with processes either controlled by or impacting microbial activities. The authors summarize some recent studies related to restoration objectives conducted in a range of Everglades environments, including marsh and tree island soils, and periphyton assemblages. These studies include research related to the development of restoration performance measures based on nutrient status, analysis of controls on organic matter decomposition that may have lead to the development of soil microtopography responsible for water flow paths, microbial drivers of methane production, and analysis of the architecture of periphyton mats and their potential use in nutrient removal treatment strategies. The authors highlight the complexity inherent in microbial control of biogeochemistry, as well as the multitude of approaches that are needed to explain these interactions. Compared to larger ecosystem attributes such as vegetation community structure, the structure and function of microbial communities have remained elusive, and significantly more research into this area is essential to ensure that restoration goals are accomplished.

Seasonal patterns of nitrogen cycling in subtropical short-hydroperiod wetlands: Effects of precipitation and restoration

In the event of increased frequency of extreme wet or dry events resulting from climate change, it becomes more important to understand the temporal dynamics of soil nitrogen (N) processes in ecosystems. Here, seasonal patterns of N cycling were characterized in subtropical wetlands in Everglades National Park, Florida, USA. Two restored sites and one reference site with different nutrient status, soil depth, and vegetation communities, were selected. Soil available N, microbial biomass, potential N mineralization and denitrification rates, enzyme activities of leucine aminopeptidase (LAP) and N-acetyl-β-d-glucosaminidase (NAG) were measured across the wet and dry seasons from 2010 to 2011. In general, most N processes were significantly correlated with soil water contents (P<0.05) which reflected the precipitation regime. The lower elevation and shallower soil (2-3cm depth) at the restored site may contribute to their higher soil water contents compared to the reference site with ~10cm soil depth, which further led to the earlier peaks of microbial biomass at the two restored sites. Potential N mineralization was positively correlated with LAP at the restored sites whereas with NAG at the reference site (P<0.05), implying that different vegetation composition may provide varying substrates for soil microbes. The build-up of nitrate in the dry spring of 2011 induced a pulse of denitrification after rewetting by a sudden rainfall, implying the presence of a hot moment of denitrification during the dry-rewetting transition period. The decrease of MBC:MBN ratio from dry to wet season indicates a possible microbial composition shift from fungi to bacteria, shedding lights on the potential contribution of fugal groups to denitrification in the dry season. Our study highlight that even under the same climate regime, the small-scale variations could affect the seasonal patterns of N cycling.

Can Fire Residues (Ash and Char) Affect Microbial Decomposition in Wetland Soils

With increasing fire frequency expected with climate change, understanding the direct and indirect effect of fire on the global carbon budget is critical. While many studies focus on carbon loss through biomass removal and shifts in greenhouse gas (GHG) emission, minimal studies have taken a mechanistic approach to determine the indirect effect of fire residues on GHG production post-fire. The study objective was to isolate the effect of vegetation-derived fire residues (char and ash) on microbial decomposition in wetland soils of varying phosphorus concentrations. Carbon GHG production was influenced by residue type and oxygen availability and results varied by soil phosphorus concentrations. Aerobic decomposition decreased following ash addition in low-phosphorus soil initially; however, there were no additional effects of residues on aerobic decomposition. Under anaerobic conditions, residues had no effect on decomposition in high-phosphorus soil. In contrast, char stimulated CO2 production; and regardless of residue, CH4 production was stimulated in low-phosphorus soil. While char contained higher available phosphorus and carbon relative to ash, ash still provided phosphorus suggesting variable gas production in situ may be dependent on fire residue proportion and associated nutrient input. Taken together, increased fire frequency associated with climate change may stimulate CH4 production in low-phosphorus wetlands.

Greenhouse Gas Emissions Under Different Drainage and Flooding Regimes of Cultivated Peatlands

Globally, approximately 10–20 % of peatlands have been drained for agricultural purposes. A strategy to protect peatlands and mitigate carbon dioxide (CO2) emissions, while continuing agricultural production, is the use of intermittent flooding and drainage. A potential drawback of this strategy could be increases in methane (CH4) and nitrous oxide (N2O) emissions. The objective of this study was to compare greenhouse gas (GHG) emissions from peatlands under various flooding-drainage cycles. A laboratory study was performed using intact soil cores subjected to different durations of flooding and drainage for 6 months. Average daily emissions of CO2 and N2O were significantly higher (P < 0.001) under drained (667 ± 37 mg CO2-C m-2 d-1 and 135 ± 19 μg N2O-N m-2 d-1) than flooded conditions (86 ± 6 mg CO2-C m-2 d-1 and 48 ± 2 μg N2O-N m-2 d-1). Methane emissions were not influenced by drained/flooded conditions, with an average rate of 116 ± 11 μg CH4-C m-2 d-1. Peaks of CH4 and N2O emissions were observed after flooding events and lasted less than 24 h. The peak emissions were approximately 8 and 19 times higher than the mean CH4 and N2O emissions, respectively. Carbon dioxide was the dominant component of GHGs, irrespective of hydrologic regime, accounting for more than 92% of overall global warming potential (GWP). Global warming potential was inversely proportional to the flooding period, indicating that prolonging the flooding period of peatlands would help mitigate soil oxidation and GHG emissions, and enhance sustainability of these agricultural peatlands.

Biogeochemical Indicators of Nutrient Enrichments in Wetlands: The Microbial Response as a Sensitive Indicator of Wetland Eutrophication

In wetlands it is still usual to use the same indicators of eutrophication which were developed to study the effects of nutrient enrichment in lakes; however, since hydroecology and biogeochemistry of wetlands is significantly different from lakes, monitoring of these indicators does not allow a good diagnosis of the changes undergone by the wetland ecosystem under nutrient enrichment scenarios. Microbial activities and their respective community responses have been considered as a measure of ecosystem stability and an indicator of ecosystem perturbation through changes on functional properties associated with nutrient cycling. As in most aquatic ecosystems, the addition of a limiting nutrient to wetland ecosystems promotes primary productivity and stimulates microbial processes. As nutrient loading increase, biogeochemical processes in wetlands are altered, changing their concentrations in water and soil, and therefore, nutrient fluxes and cycling. Nutrient enrichment induces changes in soil physicochemical and microbiological characteristics that may then serve as indicators of nutrient enrichment. In this review, a set of microbial community measurements known to be sensitive to nutrient enrichment in aquatic systems, such as extracellular enzyme activities, respiratory activities, microbial biomass C, N, and P, and microbially mediated N and P turnover rates have been used to characterize physiological response of the microbial community to wetland eutrophication. Some indicators as metabolic efficiency and phosphatase activity clearly reflect the main shifts on wetland ecosystem processes induced by nutrient enrichment and may be considered better than those that are currently used to assess the effects of eutrophication. Moreover, the combined use of different ecophysiological measurements such as extracellular enzymatic ratios and microbial biomass under resource allocation models and ecological stoichiometry demonstrates that ecophysiological measures are sensitive indicators of wetland eutrophication. Further studies are needed refining this approach to get the complex biogeochemical variability of the different wetland types, and to move from a site-based heuristic model to a holistic approach, describing eutrophication patterns in wetlands.