Influence of plant communities and soil properties on trace gas fluxes in riparian northern hardwood forests
Introduction
Wetlands are considered to be important sources of the greenhouse gases carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), to the atmosphere. While wetland ecosystems are often net carbon sinks, they can be a net source of CO2 when soils dry and decomposition and total soil respiration rates increase (Armentano and Menges, 1986, Gorham, 1991, Silvola et al., 1996). In addition, wetlands contribute an estimated 110 × 1012 g CH4 year−1 to the atmosphere from anaerobic processes (Matthews and Fung, 1987, Denmen and Brasseur, 2007) and are the second largest natural source of nitrous oxide (N2O) to the atmosphere, behind oceans (Bowden, 1986, Prather et al., 1995). These gases significantly impact atmospheric chemistry; in a 100-year period CH4 is 25 times and N2O is 298 times more potent than CO2 as a greenhouse gas (Solomon et al., 2007). Greenhouse gas emissions from northern temperate wetlands are predicted to increase with temperature, thereby creating a positive feedback loop (Gedney et al., 2004). At the same time, increased temperature may decrease soil moisture, which could result in a decrease of some greenhouse gas emissions. With either response to temperature, there is considerable uncertainty about just what ecosystem variables control greenhouse gas fluxes in these wetlands and how these variables will respond to climate change. These controls are particularly dynamic in riparian wetlands that sit at the interface between terrestrial and aquatic components of the landscape (Naiman and Decamps, 1997).
Much research has investigated how water table position and temperature indirectly influence CO2, N2O, and CH4 production (Davidson and Swank, 1986, Bubier et al., 1993, Dunfield et al., 1993, Willems et al., 1997, Kiese and Butterbach-Bahl, 2002, McLain and Martens, 2006) by controlling the reduction–oxidation (redox) reactions responsible for greenhouse gas flux. Water table position, or water depth, fluctuates regularly in riparian areas with flooding and drying events, and this fluctuation dictates the amount of oxygen in the substrate (i.e., which redox reactions will occur). While CO2 is produced under both aerobic and anaerobic conditions, in aerobic soil zones CH4 is oxidized to CO2 (Altor and Mitsch, 2006), while in anaerobic zones CO2 is reduced to CH4 through the process of methanogenesis (Whalen, 2005). Similarly, N2O can be produced and consumed under both aerobic and anaerobic conditions. Wetlands with variable water levels have been found to have particular potential for high N2O flux (Hernandez and Mitsch, 2006, Hernandez and Mitsch, 2007a).
Few studies have examined the linkages between understory plant communities and greenhouse gas emissions in riparian ecosystems even though plants can influence emissions in several ways. Plant CO2 production by respiration and consumption via photosynthesis vary markedly with species and environmental conditions (Welsch and Yavitt, 2007). Plants influence soil CH4 emissions by plant ventilation and plant-mediated diffusion through aerenchymous tissue (Joabsson et al., 1999), which can be responsible for more than 90% of CH4 flux from a wetland (Holzapfel-Pschorn et al., 1986, MacDonald et al., 1998). Plants also mediate CH4 and CO2 production through the release of oxygen and root exudates (e.g., labile carbon) into the rhizopshere. Exudation of labile carbon may facilitate CH4 and CO2 production, whereas oxygen released from the plant roots can inhibit CH4 production and promote production of CO2 (Frenzel, 2000, Conrad, 2002, Hernandez and Mitsch, 2007b). Plants influence nitrogen availability and N2O flux through variation in root N uptake, and nitrogen content and its subsequent effects on inorganic nitrogen release during decomposition (Reddy and DeBusk, 1987, Welsch and Yavitt, 2007).
Several soil variables can affect greenhouse gas fluxes from riparian systems. In addition to the effects of water table on soil moisture discussed above, soil texture may influence greenhouse gas fluxes by altering the permeability, porosity, and water-holding capacity of soils, which in turn can alter soil moisture (Pinay et al., 2000). There are complex relationships between soil pH and gas fluxes. While some studies have found low soil pH to decrease methane production by inhibiting methanogensis (Dunfield et al., 1993, Valentine et al., 1994), others have found no relationships between pH and CH4 production (Bubier et al., 1993, Chang and Yang, 2003). Low pH can inhibit nitrification, an important source of N2O, but can also increase the N2O yield during denitrification (Robertson and Groffman, 2007). There is great interest in understanding how atmospheric deposition of nitrogen and acid alters soil conditions that influence greenhouse gas fluxes (Venterea et al., 2003a, Venterea et al., 2003b).
In this study, we examined how multiple plant community and soil processes and parameters affect greenhouse gas flux rates in riparian areas in northern hardwood forests in the Adirondack Mountains of New York. The two novel aspects of our study are that we (1) explored links between understory plant communities and trace gas fluxes and (2) in an important and understudied ecosystem type. Understory plant communities are dynamic and very few studies have addressed their effects on trace gas fluxes. While several studies have addressed N2O fluxes in riparian zones in agricultural landscapes, there have been almost no analyses of trace gas fluxes (including methane) in riparian zones in forested landscapes. These zones are particularly important in forested regions subject to high rates of atmospheric deposition of N and S such as our study region. Our specific objectives were to (1) determine if riparian wetlands are significant sources or sinks of CO2, CH4 and N2O in this region and (2) evaluate the plant and soil riparian factors influence these fluxes.
Section snippets
Site description and experimental design
The study area was located in Adirondack Park, near Old Forge, NY, along a 5350 m stretch of Big Moose Road, with a northern terminus at Pancake Hall Creek on the northern edge of Big Moose Lake (43°83′N, 74°87′W) and a southern terminus at Cascade Lake Outlet (Fig. 1). Temperature averages 18 °C in July and −11 °C in January, and mean annual precipitation is 1280 mm (TWC, 2008). The soils in the region are dominated by acidic Spodosols that developed on glacial sediments (R. April, personal
Results
The five riparian sites varied greatly in many plant community and soil variables (Table 1). All four plant community variables (percent cover and number of species per plot and number of stems and species per sampling chamber) were correlated and differed among riparian sites (% plant cover m−2: F = 17.8, P < 0.01). Moss had the highest species richness per plot (10.0 ± 0.6%), and Pancake had the lowest means for all four plant variables. Within the sampling rings, Pancake had the lowest stem count,
Discussion
Our five riparian sites varied greatly in numerous soil and vegetation metrics even though they were in close proximity to one another. This variation led to marked differences in trace gas fluxes, suggesting that evaluating the importance of riparian zones to landscape and regional scale greenhouse gas budgets will be difficult. However, our results show promising relationships between ecosystem-scale variables such as plant cover and soil texture that may be useful for scaling site-specific
Acknowledgements
We sincerely thank Gavin Leighton for his help in the field; Dr. Matt Neatrour for his help in the field and reviewing the manuscript; Dave Lewis and Lisa Martel for their assistance in the laboratory; and Dr. Randy Fuller and Dr. Richard April for sharing their knowledge about the study area and lab equipment. This work was funded by Colgate University and the Andrew Mellon Foundation.
References (80)
- et al.
Methane flux from created wetlands: relationship to intermittent versus continuous inundation and emergent macrophytes
Ecological Engineering
(2006) - et al.
Methane emissions from wetlands in Taiwan
Atmospheric Environment
(2003) Microbial ecology of methanogens and methanotrophs
Advanced Agronomy
(2007)- et al.
Methane production and consumption in temperate and subarctic peat soils: response to temperature and pH
Soil Biology and Biochemistry
(1993) - et al.
CH4 uptake and N availability in forest soils along an urban to rural gradient
Soil Biology and Biochemistry
(1995) - et al.
Denitrification in created riverine wetlands: influence of hydrology and season
Ecological Engineering
(2007) - et al.
Vascular plant controls on methane emissions from northern peatforming wetlands
Trends in Ecology and Evolution
(1999) - et al.
Production, oxidation, emission and consumption of methane by soils: a review
European Journal of Soil Biology
(2001) - et al.
Nitrogen transformations
- et al.
Mineralization and nitrification patterns at eight northeastern USA forested research sites
Forest Ecology and Management
(2004)
Emission of N2O, N2, CH4, and CO2 from constructed wetlands for wastewater treatment and from riparian buffer zones
Ecological Engineering
C-13/C-12 fractionation of methane during oxidation in a temperate forested soil
Geochimica et Cosmochimica Acta
Nitrate removal in riparian wetland soils: effects of flow rate, temperature, nitrate concentration and soil depth
Water Research
Methane fluxes in a northern hardwood forest ecosystem in relation to acid precipitation
Chemosphere
Standard Methods for the Examination of Water and Wastewater
Patterns of change in the carbon balance of organic soil-wetlands of the temperate zone
Journal of Ecology
Global change, nitrification, and denitrification: a review
Global Biogeochemical Cycles
Gaseous nitrogen emissions from undisturbed terrestrial ecosystems: an assessment of their impacts on local and global nitrogen budgets
Biogeochemsitry
Annual nitrous oxide fluxes from temperate forest soils in the northeastern United States
Journal of Geophysical Research Atmospheres
Effects of nitrogen additions on annual nitrous oxide fluxes from temperate forest soils in the northeastern United States
Journal of Geophysical Research Atmospheres
Pflanzensoziologie
Site variation in methane oxidation as affected by atmospheric deposition and type of temperate forest ecosystem
Global Biogeochemical Cycles
Hierarchical control on nitrous oxide emission in forest ecosystems
Global Biogeochemical Cycles
Methane emissions from wetlands in the midboreal region of northern Ontario, Canada
Ecology
Exchange of N2O and CH4 between the atmosphere and soils in spruce-fir forests in the northeastern United States
Biogeochemistry
Soils, a sink for N2O? A review
Global Change Biology
Control of microbial methane production in wetland rice fields
Nutrient Cycling in Agroecosystems
Seasonal patterns of methane uptake and carbon dioxide release by a temperate woodland soil
Global Biogeochemical Cycles
Environmental parameters regulating gaseous nitrogen losses from two forested ecosystems via nitrification and denitrification
Applied Environmental Micorbiology
Effects of Phragmites australis removal on marsh nutrient cycling
Wetland Ecology and Management
Plant-associated methane oxidation in ricefields and wetlands
Advanced Microbial Ecology
Climate feedback from wetland methane emissions
Geophysical Research Letters
Particle-size analysis
Northern peatlands: role in the carbon cycle and probable responses to climatic warming
Ecological Applications
Denitrification
Evaluating annual nitrous oxide fluxes at the ecosystem scale
Global Biogeochemical Cycles
Snow depth, soil freezing, and fluxes of carbon dioxide, nitrous oxide and methane in a northern hardwood forest
Global Change Biology
Landscape and regional scale studies of nitrogen gas fluxes
The full greenhouse gas balance of an abandoned peat meadow
Biogeosciences
Cited by (26)
Methane and nitrous oxide production and their driving factors in Phragmites riparian wetlands of Dianchi Lake, China
2022, Ecological IndicatorsCitation Excerpt :However, how these abnormally high nutrient inputs regulate CH4 and N2O production in eutrophic lake riparian areas is still unknown. Meanwhile, there are limited investigations focusing on CH4 and N2O in the riparian zone around lakes (Hopfensperger et al. 2009; Mander et al. 2022; Schindler et al. 2020). Therefore, a systematic and comprehensive study of CH4 and N2O production and their driving factors in riparian wetlands around eutrophic lakes is needed.
Carbon dioxide emissions: Spatiotemporal variation in a young and mature riparian forest
2019, Ecological EngineeringCitation Excerpt :The greater CO2 emissions from the RH compared to the UNF site were also observed in an earlier study by Oelbermann et al. (2015). Similarly, Hopfensperger et al. (2009) reported considerable differences in CO2 emissions among five northern hardwood riparian sites (Adirondack Park, New York) in close proximity to each other. This was due to differences in soil temperature and moisture, micro-topography, vegetation patterns and structure, and the availability and quality of soil C substrates that influenced microbial activity and the emission of CO2 (Mori et al., 2017).
Nitrogen cycling players and processes in green roof ecosystems
2018, Applied Soil EcologyHydrologic conditions drive denitrification and greenhouse gas emissions in stormwater detention basins
2015, Ecological EngineeringCitation Excerpt :Grover et al. (2013) also observed pulses of N2O as high as 1100 μg N m−2 h−1 after simulated precipitation events. Compared to forested riparian wetlands in upstate New York, mean N2O emissions for all basins (4.6 μg N m−2 h−1) were higher than the mean wetland emissions of 0.9 μg N m−2 h−1 (Hopfensperger et al., 2009) though emissions from wet basins only (0.5 μg N m−2 h−1) were lower. Several studies of N2O fluxes in grass lawns provide additional context.