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Kurt S. Pregitzer - One of the best experts on this subject based on the ideXlab platform.
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fine roots are the dominant source of recalcitrant plant litter in sugar maple dominated northern Hardwood Forests
New Phytologist, 2015Co-Authors: Alan F Talhelm, Kurt S. PregitzerAbstract:Summary � Most studies of forest litter dynamics examine the biochemical characteristics and decomposition of leaf litter, but fine roots are also a large source of litter in Forests. � We quantified the concentrations of eight biochemical fractions and nitrogen (N) in leaf litter and fine roots at four sugar maple (Acer saccharum)-dominated Hardwood Forests in the north-central United States. We combined these results with litter production data to estimate ecosystem biochemical fluxes to soil. We also compared how leaf litter and fine root biochemistry responded to long-term simulated N deposition. � Compared with leaf litter, fine roots contained 2.9-fold higher acid-insoluble fraction (AIF) and 2.3-fold more condensed tannins; both are relatively difficult to decompose. Comparatively, leaf litter had greater quantities of more labile components: nonstructural carbohydrates, cellulose and soluble phenolics. At an ecosystem scale, fine roots contributed over two-thirds of the fluxes of AIF and condensed tannins to soil. Fine root biochemistry was also less responsive than leaf litter to long-term simulated N deposition. � Fine roots were the dominant source of difficult-to-decompose plant carbon fractions entering the soil at our four study sites. Based on our synthesis of the literature, this pattern appears to be widespread in boreal and temperate Forests.
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chronic n deposition alters root respiration tissue n relationship in northern Hardwood Forests
Global Change Biology, 2012Co-Authors: Andrew J. Burton, Donald R. Zak, Julie C Jarvey, Mickey P Jarvi, Kurt S. PregitzerAbstract:Specific root respiration rates typically increase with increasing tissue N concentration. As a result, it is often assumed that external factors inducing greater root N concentration, such as chronic N deposition, will lead to increased respiration rates. However, enhanced N availability also alters root biomass, making the ecosystem-level consequences on whole-root-system respiration uncertain. The objective of this study was to determine the effects of chronic experimental N deposition on root N concentrations, specific respiration rates, and biomass for four northern Hardwood Forests in Michigan. Three of the six measurement plots at each location have received experimental N deposition (3 g NO 3 -N m 2 yr 1 ) since 1994. We measured specific root respiration rates and N concentrations of roots from four size classes (<0.5, 0.5–1, 1–2, and 2–10 mm) at three soil depths (0–10, 10–30, and 30–50 cm). Root biomass data for the same size classes and soil depths was used in combination with specific respiration rates to assess the response of whole-root-system respiration. Root N and respiration rate were greater for smaller diameter roots and roots at shallow depths. In addition, root N concentrations were significantly greater under chronic N deposition, particularly for larger diameter roots. Specific respiration rates and root biomass were unchanged for all depths and size classes, thus whole-root-system respiration was not altered by chronic N deposition. Higher root N concentrations in combination with equivalent specific respiration rates under experimental N deposition resulted in a lower ratio of respiration to tissue N. These results indicate that relationships between root respiration rate and N concentration do not hold if N availability is altered significantly. For these Forests, use of the ambient respiration to N relationship would over-predict actual root system respiration for the chronic N deposition treatment by 50%.
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simulated nitrogen deposition affects community structure of arbuscular mycorrhizal fungi in northern Hardwood Forests
Molecular Ecology, 2011Co-Authors: Linda T A Van Diepen, Erik A Lilleskov, Kurt S. PregitzerAbstract:Our previous investigation found elevated nitrogen deposition caused declines in abundance of arbuscular mycorrhizal fungi (AMF) associated with forest trees, but little is known about how nitrogen affects the AMF community composition and structure within forest ecosystems. We hypothesized that N deposition would lead to significant changes in the AMF community structure. We studied the diversity and community structure of AMF in northern Hardwood Forests after more than 12 years of simulated nitrogen deposition. We performed molecular analyses on maple (Acer spp.) roots targeting the 18S rDNA region using the fungal-specific primers AM1 and NS31. PCR products were cloned and identified using restriction fragment length polymorphism (RFLP) and sequencing. N addition significantly altered the AMF community structure, and Glomus group A dominated the AMF community. Some Glomus operational taxonomic units (OTUs) responded negatively to N inputs, whereas other Glomus OTUs and an Acaulospora OTU responded positively to N inputs. The observed effect on community structure implies that AMF species associated with maples differ in their response to elevated nitrogen. Given that functional diversity exists among AMF species and that N deposition has been shown to select less beneficial fungi in some ecosystems, this change in community structure could have implications for the functioning of this type of ecosystem.
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simulated nitrogen deposition causes a decline of intra and extraradical abundance of arbuscular mycorrhizal fungi and changes in microbial community structure in northern Hardwood Forests
Ecosystems, 2010Co-Authors: Kurt S. Pregitzer, Linda T A Van Diepen, Erik A Lilleskov, Michael R MillerAbstract:Increased nitrogen (N) deposition caused by human activities has altered ecosystem functioning and biodiversity. To understand the effects of altered N availability, we measured the abundance of arbuscular mycorrhizal fungi (AMF) and the microbial community in northern Hardwood Forests exposed to long-term (12 years) simulated N deposition (30 kg N ha -1 y -1 ) using phospholipid
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characteristics of doc exported from northern Hardwood Forests receiving chronic experimental no 3 deposition
Ecosystems, 2007Co-Authors: Kurt A Smemo, Kurt S. Pregitzer, Donald R. Zak, Andrew J. BurtonAbstract:Sugar maple (Acer saccharum Marsh.)-dominated northern Hardwood Forests of the Great Lakes Region commonly receive elevated levels of atmospheric nitrate (NO 3 − ) deposition, which can alter belowground carbon (C) cycling. Past research has demonstrated that chronic experimental NO 3 − deposition (3 g N m−2 y−1 above ambient) elicits a threefold increase in the leaching loss of dissolved organic carbon (DOC). Here, we used DOC collected from tension-cup lysimeters to test whether increased DOC export under experimental NO 3 − deposition originated from forest floor or mineral soil organic matter (SOM). We used DOC radiocarbon dating to quantify C sources and colorimetric assays to measure DOC aromaticity and soluble polyphenolic content. Our results demonstrated that DOC exports are primarily derived from new C (<50-years-old) in the forest floor under both ambient and experimental NO 3 − deposition. Experimental NO 3 − deposition increased soluble polyphenolic content from 25.03 ± 4.26 to 49.19 ± 4.23 μg phenolic C mg DOC−1, and increased total aromatic content as measured by specific UV absorbance. However, increased aromatic compounds represented a small fraction (<10%) of the total observed increased DOC leaching. In combination, these findings suggest that experimental NO 3 − deposition has altered the production or retention as well as phenolic content of DOC formed in forest floor, however exact mechanisms are uncertain. Further elucidation of the mechanism(s) controlling enhanced DOC leaching is important for understanding long-term responses of Great Lakes Forests to anthropogenic N deposition and the consequences of those responses for aquatic ecosystems.
Andrew J. Burton - One of the best experts on this subject based on the ideXlab platform.
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chronic n deposition alters root respiration tissue n relationship in northern Hardwood Forests
Global Change Biology, 2012Co-Authors: Andrew J. Burton, Donald R. Zak, Julie C Jarvey, Mickey P Jarvi, Kurt S. PregitzerAbstract:Specific root respiration rates typically increase with increasing tissue N concentration. As a result, it is often assumed that external factors inducing greater root N concentration, such as chronic N deposition, will lead to increased respiration rates. However, enhanced N availability also alters root biomass, making the ecosystem-level consequences on whole-root-system respiration uncertain. The objective of this study was to determine the effects of chronic experimental N deposition on root N concentrations, specific respiration rates, and biomass for four northern Hardwood Forests in Michigan. Three of the six measurement plots at each location have received experimental N deposition (3 g NO 3 -N m 2 yr 1 ) since 1994. We measured specific root respiration rates and N concentrations of roots from four size classes (<0.5, 0.5–1, 1–2, and 2–10 mm) at three soil depths (0–10, 10–30, and 30–50 cm). Root biomass data for the same size classes and soil depths was used in combination with specific respiration rates to assess the response of whole-root-system respiration. Root N and respiration rate were greater for smaller diameter roots and roots at shallow depths. In addition, root N concentrations were significantly greater under chronic N deposition, particularly for larger diameter roots. Specific respiration rates and root biomass were unchanged for all depths and size classes, thus whole-root-system respiration was not altered by chronic N deposition. Higher root N concentrations in combination with equivalent specific respiration rates under experimental N deposition resulted in a lower ratio of respiration to tissue N. These results indicate that relationships between root respiration rate and N concentration do not hold if N availability is altered significantly. For these Forests, use of the ambient respiration to N relationship would over-predict actual root system respiration for the chronic N deposition treatment by 50%.
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characteristics of doc exported from northern Hardwood Forests receiving chronic experimental no 3 deposition
Ecosystems, 2007Co-Authors: Kurt A Smemo, Kurt S. Pregitzer, Donald R. Zak, Andrew J. BurtonAbstract:Sugar maple (Acer saccharum Marsh.)-dominated northern Hardwood Forests of the Great Lakes Region commonly receive elevated levels of atmospheric nitrate (NO 3 − ) deposition, which can alter belowground carbon (C) cycling. Past research has demonstrated that chronic experimental NO 3 − deposition (3 g N m−2 y−1 above ambient) elicits a threefold increase in the leaching loss of dissolved organic carbon (DOC). Here, we used DOC collected from tension-cup lysimeters to test whether increased DOC export under experimental NO 3 − deposition originated from forest floor or mineral soil organic matter (SOM). We used DOC radiocarbon dating to quantify C sources and colorimetric assays to measure DOC aromaticity and soluble polyphenolic content. Our results demonstrated that DOC exports are primarily derived from new C (<50-years-old) in the forest floor under both ambient and experimental NO 3 − deposition. Experimental NO 3 − deposition increased soluble polyphenolic content from 25.03 ± 4.26 to 49.19 ± 4.23 μg phenolic C mg DOC−1, and increased total aromatic content as measured by specific UV absorbance. However, increased aromatic compounds represented a small fraction (<10%) of the total observed increased DOC leaching. In combination, these findings suggest that experimental NO 3 − deposition has altered the production or retention as well as phenolic content of DOC formed in forest floor, however exact mechanisms are uncertain. Further elucidation of the mechanism(s) controlling enhanced DOC leaching is important for understanding long-term responses of Great Lakes Forests to anthropogenic N deposition and the consequences of those responses for aquatic ecosystems.
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microbial cycling of c and n in northern Hardwood Forests receiving chronic atmospheric no 3 deposition
Ecosystems, 2006Co-Authors: Donald R. Zak, Kurt S. Pregitzer, William E Holmes, Matthew J Tomlinson, Andrew J. BurtonAbstract:Sugar maple (Acer saccharum Marsh.)-dominated northern Hardwood Forests in the upper Lakes States region appear to be particularly sensitive to chronic atmospheric NO 3 − deposition. Experimental NO 3 − deposition (3 g NO 3 − N m−2 y−1) has significantly reduced soil respiration and increased the export of DOC/DON and NO 3 − across the region. Here, we evaluate the possibility that diminished microbial activity in mineral soil was responsible for these ecosystem-level responses to NO 3 − deposition. To test this alternative, we measured microbial biomass, respiration, and N transformations in the mineral soil of four northern Hardwood stands that have received 9 years of experimental NO 3 − deposition. Microbial biomass, microbial respiration, and daily rates of gross and net N transformations were not changed by NO 3 − deposition. We also observed no effect of NO 3 − deposition on annual rates of net N mineralization. However, NO 3 − deposition significantly increased (27%) annual net nitrification, a response that resulted from rapid microbial NO 3 − assimilation, the subsequent turnover of NH 4 + , and increased substrate availability for this process. Nonetheless, greater rates of net nitrification were insufficient to produce the 10-fold observed increase in NO 3 − export, suggesting that much of the exported NO 3 − resulted directly from the NO 3 − deposition treatment. Results suggest that declines in soil respiration and increases in DOC/DON export cannot be attributed to NO 3 − -induced physiological changes in mineral soil microbial activity. Given the lack of response we have observed in mineral soil, our results point to the potential importance of microbial communities in forest floor, including both saprotrophs and mycorrhizae, in mediating ecosystem-level responses to chronic NO 3 − deposition in Lake States northern Hardwood Forests.
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simulated chronic no 3 deposition reduces soil respiration in northern Hardwood Forests
Global Change Biology, 2004Co-Authors: Andrew J. Burton, Kurt S. Pregitzer, Gregory P. Zogg, Jeffrey N Crawford, Donald R. ZakAbstract:Chronic N additions to forest ecosystems can enhance soil N availability, potentially leading to reduced C allocation to root systems. This in turn could decrease soil CO2 efflux. We measured soil respiration during the first, fifth, sixth and eighth years of simulated atmospheric NO3 deposition (3gNm � 2 yr � 1 ) to four sugar maple-dominated northern Hardwood Forests in Michigan to assess these possibilities. During the first year, soil respiration rates were slightly, but not significantly, higher in the NO3 amended plots. In all subsequent measurement years, soil respiration rates from NO3 amended soils were significantly depressed. Soil temperature and soil matric potential were measured concurrently with soil respiration and used to develop regression relationships for predicting soil respiration rates. Estimates of growing season and annual soil CO2 efflux made using these relationships indicate that these C fluxes were depressed by 15% in the eighth year of chronic NO3 additions. The decrease in soil respiration was not due to reduced C allocation to roots, as root respiration rates, root biomass, and root turnover were not significantly affected by N additions. Aboveground litter also was unchanged by the 8 years of treatment. Of the remaining potential causes for the decline in soil CO2 efflux, reduced microbial respiration appears to be the most likely possibility. Documented reductions in microbial biomass and the activities of extracellular enzymes used for litter degradation on the NO3 -amended plots are
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simulated chronic no3 deposition reduces soil respiration in northern Hardwood Forests
Global Change Biology, 2004Co-Authors: Andrew J. Burton, Kurt S. Pregitzer, Gregory P. Zogg, Jeffrey N Crawford, Donald R. ZakAbstract:Chronic N additions to forest ecosystems can enhance soil N availability, potentially leading to reduced C allocation to root systems. This in turn could decrease soil CO2 efflux. We measured soil respiration during the first, fifth, sixth and eighth years of simulated atmospheric NO3 deposition (3gNm � 2 yr � 1 ) to four sugar maple-dominated northern Hardwood Forests in Michigan to assess these possibilities. During the first year, soil respiration rates were slightly, but not significantly, higher in the NO3 amended plots. In all subsequent measurement years, soil respiration rates from NO3 amended soils were significantly depressed. Soil temperature and soil matric potential were measured concurrently with soil respiration and used to develop regression relationships for predicting soil respiration rates. Estimates of growing season and annual soil CO2 efflux made using these relationships indicate that these C fluxes were depressed by 15% in the eighth year of chronic NO3 additions. The decrease in soil respiration was not due to reduced C allocation to roots, as root respiration rates, root biomass, and root turnover were not significantly affected by N additions. Aboveground litter also was unchanged by the 8 years of treatment. Of the remaining potential causes for the decline in soil CO2 efflux, reduced microbial respiration appears to be the most likely possibility. Documented reductions in microbial biomass and the activities of extracellular enzymes used for litter degradation on the NO3 -amended plots are
Donald R. Zak - One of the best experts on this subject based on the ideXlab platform.
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chronic n deposition alters root respiration tissue n relationship in northern Hardwood Forests
Global Change Biology, 2012Co-Authors: Andrew J. Burton, Donald R. Zak, Julie C Jarvey, Mickey P Jarvi, Kurt S. PregitzerAbstract:Specific root respiration rates typically increase with increasing tissue N concentration. As a result, it is often assumed that external factors inducing greater root N concentration, such as chronic N deposition, will lead to increased respiration rates. However, enhanced N availability also alters root biomass, making the ecosystem-level consequences on whole-root-system respiration uncertain. The objective of this study was to determine the effects of chronic experimental N deposition on root N concentrations, specific respiration rates, and biomass for four northern Hardwood Forests in Michigan. Three of the six measurement plots at each location have received experimental N deposition (3 g NO 3 -N m 2 yr 1 ) since 1994. We measured specific root respiration rates and N concentrations of roots from four size classes (<0.5, 0.5–1, 1–2, and 2–10 mm) at three soil depths (0–10, 10–30, and 30–50 cm). Root biomass data for the same size classes and soil depths was used in combination with specific respiration rates to assess the response of whole-root-system respiration. Root N and respiration rate were greater for smaller diameter roots and roots at shallow depths. In addition, root N concentrations were significantly greater under chronic N deposition, particularly for larger diameter roots. Specific respiration rates and root biomass were unchanged for all depths and size classes, thus whole-root-system respiration was not altered by chronic N deposition. Higher root N concentrations in combination with equivalent specific respiration rates under experimental N deposition resulted in a lower ratio of respiration to tissue N. These results indicate that relationships between root respiration rate and N concentration do not hold if N availability is altered significantly. For these Forests, use of the ambient respiration to N relationship would over-predict actual root system respiration for the chronic N deposition treatment by 50%.
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characteristics of doc exported from northern Hardwood Forests receiving chronic experimental no 3 deposition
Ecosystems, 2007Co-Authors: Kurt A Smemo, Kurt S. Pregitzer, Donald R. Zak, Andrew J. BurtonAbstract:Sugar maple (Acer saccharum Marsh.)-dominated northern Hardwood Forests of the Great Lakes Region commonly receive elevated levels of atmospheric nitrate (NO 3 − ) deposition, which can alter belowground carbon (C) cycling. Past research has demonstrated that chronic experimental NO 3 − deposition (3 g N m−2 y−1 above ambient) elicits a threefold increase in the leaching loss of dissolved organic carbon (DOC). Here, we used DOC collected from tension-cup lysimeters to test whether increased DOC export under experimental NO 3 − deposition originated from forest floor or mineral soil organic matter (SOM). We used DOC radiocarbon dating to quantify C sources and colorimetric assays to measure DOC aromaticity and soluble polyphenolic content. Our results demonstrated that DOC exports are primarily derived from new C (<50-years-old) in the forest floor under both ambient and experimental NO 3 − deposition. Experimental NO 3 − deposition increased soluble polyphenolic content from 25.03 ± 4.26 to 49.19 ± 4.23 μg phenolic C mg DOC−1, and increased total aromatic content as measured by specific UV absorbance. However, increased aromatic compounds represented a small fraction (<10%) of the total observed increased DOC leaching. In combination, these findings suggest that experimental NO 3 − deposition has altered the production or retention as well as phenolic content of DOC formed in forest floor, however exact mechanisms are uncertain. Further elucidation of the mechanism(s) controlling enhanced DOC leaching is important for understanding long-term responses of Great Lakes Forests to anthropogenic N deposition and the consequences of those responses for aquatic ecosystems.
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microbial cycling of c and n in northern Hardwood Forests receiving chronic atmospheric no 3 deposition
Ecosystems, 2006Co-Authors: Donald R. Zak, Kurt S. Pregitzer, William E Holmes, Matthew J Tomlinson, Andrew J. BurtonAbstract:Sugar maple (Acer saccharum Marsh.)-dominated northern Hardwood Forests in the upper Lakes States region appear to be particularly sensitive to chronic atmospheric NO 3 − deposition. Experimental NO 3 − deposition (3 g NO 3 − N m−2 y−1) has significantly reduced soil respiration and increased the export of DOC/DON and NO 3 − across the region. Here, we evaluate the possibility that diminished microbial activity in mineral soil was responsible for these ecosystem-level responses to NO 3 − deposition. To test this alternative, we measured microbial biomass, respiration, and N transformations in the mineral soil of four northern Hardwood stands that have received 9 years of experimental NO 3 − deposition. Microbial biomass, microbial respiration, and daily rates of gross and net N transformations were not changed by NO 3 − deposition. We also observed no effect of NO 3 − deposition on annual rates of net N mineralization. However, NO 3 − deposition significantly increased (27%) annual net nitrification, a response that resulted from rapid microbial NO 3 − assimilation, the subsequent turnover of NH 4 + , and increased substrate availability for this process. Nonetheless, greater rates of net nitrification were insufficient to produce the 10-fold observed increase in NO 3 − export, suggesting that much of the exported NO 3 − resulted directly from the NO 3 − deposition treatment. Results suggest that declines in soil respiration and increases in DOC/DON export cannot be attributed to NO 3 − -induced physiological changes in mineral soil microbial activity. Given the lack of response we have observed in mineral soil, our results point to the potential importance of microbial communities in forest floor, including both saprotrophs and mycorrhizae, in mediating ecosystem-level responses to chronic NO 3 − deposition in Lake States northern Hardwood Forests.
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simulated chronic no 3 deposition reduces soil respiration in northern Hardwood Forests
Global Change Biology, 2004Co-Authors: Andrew J. Burton, Kurt S. Pregitzer, Gregory P. Zogg, Jeffrey N Crawford, Donald R. ZakAbstract:Chronic N additions to forest ecosystems can enhance soil N availability, potentially leading to reduced C allocation to root systems. This in turn could decrease soil CO2 efflux. We measured soil respiration during the first, fifth, sixth and eighth years of simulated atmospheric NO3 deposition (3gNm � 2 yr � 1 ) to four sugar maple-dominated northern Hardwood Forests in Michigan to assess these possibilities. During the first year, soil respiration rates were slightly, but not significantly, higher in the NO3 amended plots. In all subsequent measurement years, soil respiration rates from NO3 amended soils were significantly depressed. Soil temperature and soil matric potential were measured concurrently with soil respiration and used to develop regression relationships for predicting soil respiration rates. Estimates of growing season and annual soil CO2 efflux made using these relationships indicate that these C fluxes were depressed by 15% in the eighth year of chronic NO3 additions. The decrease in soil respiration was not due to reduced C allocation to roots, as root respiration rates, root biomass, and root turnover were not significantly affected by N additions. Aboveground litter also was unchanged by the 8 years of treatment. Of the remaining potential causes for the decline in soil CO2 efflux, reduced microbial respiration appears to be the most likely possibility. Documented reductions in microbial biomass and the activities of extracellular enzymes used for litter degradation on the NO3 -amended plots are
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simulated chronic no3 deposition reduces soil respiration in northern Hardwood Forests
Global Change Biology, 2004Co-Authors: Andrew J. Burton, Kurt S. Pregitzer, Gregory P. Zogg, Jeffrey N Crawford, Donald R. ZakAbstract:Chronic N additions to forest ecosystems can enhance soil N availability, potentially leading to reduced C allocation to root systems. This in turn could decrease soil CO2 efflux. We measured soil respiration during the first, fifth, sixth and eighth years of simulated atmospheric NO3 deposition (3gNm � 2 yr � 1 ) to four sugar maple-dominated northern Hardwood Forests in Michigan to assess these possibilities. During the first year, soil respiration rates were slightly, but not significantly, higher in the NO3 amended plots. In all subsequent measurement years, soil respiration rates from NO3 amended soils were significantly depressed. Soil temperature and soil matric potential were measured concurrently with soil respiration and used to develop regression relationships for predicting soil respiration rates. Estimates of growing season and annual soil CO2 efflux made using these relationships indicate that these C fluxes were depressed by 15% in the eighth year of chronic NO3 additions. The decrease in soil respiration was not due to reduced C allocation to roots, as root respiration rates, root biomass, and root turnover were not significantly affected by N additions. Aboveground litter also was unchanged by the 8 years of treatment. Of the remaining potential causes for the decline in soil CO2 efflux, reduced microbial respiration appears to be the most likely possibility. Documented reductions in microbial biomass and the activities of extracellular enzymes used for litter degradation on the NO3 -amended plots are
Melany C. Fisk - One of the best experts on this subject based on the ideXlab platform.
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nitrogen oligotrophication in northern Hardwood Forests
Biogeochemistry, 2018Co-Authors: Melany C. Fisk, Timothy J Fahey, Peter M Groffman, Colin B Fuss, Jorge Duran, John Campbell, Lynn M Christenson, Charles T Driscoll, Gene E LikensAbstract:While much research over the past 30 years has focused on the deleterious effects of excess N on Forests and associated aquatic ecosystems, recent declines in atmospheric N deposition and unexplained declines in N export from these ecosystems have raised new concerns about N oligotrophication, limitations of forest productivity, and the capacity for Forests to respond dynamically to disturbance and environmental change. Here we show multiple data streams from long-term ecological research at the Hubbard Brook Experimental Forest in New Hampshire, USA suggesting that N oligotrophication in forest soils is driven by increased carbon flow from the atmosphere through soils that stimulates microbial immobilization of N and decreases available N for plants. Decreased available N in soils can result in increased N resorption by trees, which reduces litterfall N input to soils, further limiting available N supply and leading to further declines in soil N availability. Moreover, N oligotrophication has been likely exacerbated by changes in climate that increase the length of the growing season and decrease production of available N by mineralization during both winter and spring. These results suggest a need to re-evaluate the nature and extent of N cycling in temperate Forests and assess how changing conditions will influence forest ecosystem response to multiple, dynamic stresses of global environmental change.
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climate change decreases nitrogen pools and mineralization rates in northern Hardwood Forests
Ecosphere, 2016Co-Authors: Melany C. Fisk, Timothy J Fahey, Peter M Groffman, Jorge Duran, Jennifer L Morse, John Campbell, Lynn M Christenson, Charles T Driscoll, Gene E LikensAbstract:Nitrogen (N) supply often limits the productivity of temperate Forests and is regulated by a complex mix of biological and climatic drivers. In excess, N is linked to a variety of soil, water, and air pollution issues. Here, we use results from an elevation gradient study and historical data from the long-term Hubbard Brook Ecosystem Study (New Hampshire, USA) to examine relationships between changes in climate, especially during winter, and N supply to northern Hardwood forest ecosystems. Low elevation plots with less snow, more soil freezing, and more freeze/thaw cycles supported lower rates of N mineralization than high elevation plots, despite having higher soil temperatures and no consistent differences in soil moisture during the growing season. These results are consistent with historical analyses showing decreases in rates of soil N mineralization and inorganic N concentrations since 1973 that are correlated with long-term increases in mean annual temperature, decreases in annual snow accumulation, and a increases in the number of winter thawing degree days. This evidence suggests that changing climate may be driving decreases in the availability of a key nutrient in northern Hardwood Forests, which could decrease ecosystem production but have positive effects on environmental consequences of excess N.
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earthworms increase soil microbial biomass carrying capacity and nitrogen retention in northern Hardwood Forests
Soil Biology & Biochemistry, 2015Co-Authors: Peter M Groffman, Patrick J. Bohlen, Melany C. Fisk, Timothy J Fahey, Joseph B Yavitt, Ruth E Sherman, John C MaerzAbstract:Abstract Earthworms have been shown to produce contrasting effects on soil carbon (C) and nitrogen (N) pools and dynamics. We measured soil C and N pools and processes and traced the flow of 13C and 15N from sugar maple (Acer saccharum Marsh.) litter into soil microbial biomass and respirable C and mineralizable and inorganic N pools in mature northern Hardwood forest plots with variable earthworm communities. Previous studies have shown that plots dominated by either Lumbricus rubellus or Lumbricus terrestris have markedly lower total soil C than uncolonized plots. Here we show that total soil N pools in earthworm colonized plots were reduced much less than C, but significantly so in plots dominated by contain L. rubellus. Pools of microbial biomass C and N were higher in earthworm-colonized (especially those dominated by L. rubellus) plots and more 13C and 15N were recovered in microbial biomass and less was recovered in mineralizable and inorganic N pools in these plots. These plots also had lower rates of potential net N mineralization and nitrification than uncolonized reference plots. These results suggest that earthworm stimulation of microbial biomass and activity underlie depletion of soil C and retention and maintenance of soil N pools, at least in northern Hardwood Forests. Earthworms increase the carrying capacity of soil for microbial biomass and facilitate the flow of N from litter into stable soil organic matter. However, declines in soil C and C:N ratio may increase the potential for hydrologic and gaseous losses in earthworm-colonized sites under changing environmental conditions.
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soil nitrogen availability affects belowground carbon allocation and soil respiration in northern Hardwood Forests of new hampshire
Ecosystems, 2015Co-Authors: Ruth D Yanai, Timothy J Fahey, Kikang Bae, Melany C. FiskAbstract:Plant nutrient acquisition in Forests requires respiration by roots and mycorrhizae. Belowground carbon allocation and soil respiration should thus reflect plant effort allocated to nutrient uptake, for example in conditions of different nutrient availabilities controlled by site quality or stand history. Soil respiration, belowground C allocation, and fine root biomass were measured in three sites differing in nutrient availability in the northern Hardwood Forests of the White Mountains of New Hampshire. Annual soil respiration and belowground C allocation measured in two stands at each site were lowest at Jeffers Brook, the site with highest nutrient availability, and higher at Hubbard Brook and Bartlett Experimental Forests. Neither soil respiration nor belowground C allocation differed significantly between mid-aged (31–41 year old) and older stands (>80 year old) within the sites, despite higher fine root (<1 mm) biomass in old stands than mid-aged stands. During the growing season, soil respiration was low where net nitrogen mineralization and net nitrification were high across an extensive sample of thirteen stands and annual belowground C allocation decreased with increasing nitrification across the six intensively studied stands. Available P was not related to soil respiration. The relationships among N availability, belowground C allocation, and soil respiration support the claim that Forests allocate more C belowground in ecosystems with low availability of a limiting nutrient.
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earthworms reduce biotic 15 nitrogen retention in northern Hardwood Forests
Ecosystems, 2015Co-Authors: Holly A Ewing, Patrick J. Bohlen, Melany C. Fisk, Timothy J Fahey, Peter M Groffman, Amy R Tuininga, Kathleen C Weathers, Esteban SuarezAbstract:Invasive exotic earthworms are significantly influencing understory community composition, soil, and ecosystem processes in northern Hardwood Forests in North America, but their effect on the retention of nitrogen (N) has been inconclusive. We examined this in two northern Hardwood forest sites in New York state, USA through a tracer study. In both spring and fall, we added tracer amounts of 15N as nitrate—to simulate atmospheric deposition—with the biologically less active tracer bromide (Br−) to areas both with and without large populations of invasive earthworms. Total recovery of 15N was lower in earthworm-invaded plots, largely due to less retention in litter and upper soil horizons. Although the strong relationship between retention in the upper soil horizons and total 15N recovery suggests that earthworm destruction of the forest floor may be one mechanism reducing the capacity for N retention, in some cases the mineral soil in earthworm-invaded plots retained substantial N. Biotic pools, particularly litter and microbial biomass, retained significantly less 15N in earthworm-invaded plots than in their uninvaded counterparts. In plots invaded by earthworms, negative effects of earthworms on trees were revealed through root-uptake assays suggesting somewhat greater plant demand for ammonium in the spring and in lower 15N recovery in maple seedlings the year following tracer addition. Although similar patterns of Br− movement across treatments suggested that earthworms had smaller effects on hydrologic tracer movement than expected, they appear to have significant effects on the biological processes that underlie N retention.
Timothy J Fahey - One of the best experts on this subject based on the ideXlab platform.
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nitrogen oligotrophication in northern Hardwood Forests
Biogeochemistry, 2018Co-Authors: Melany C. Fisk, Timothy J Fahey, Peter M Groffman, Colin B Fuss, Jorge Duran, John Campbell, Lynn M Christenson, Charles T Driscoll, Gene E LikensAbstract:While much research over the past 30 years has focused on the deleterious effects of excess N on Forests and associated aquatic ecosystems, recent declines in atmospheric N deposition and unexplained declines in N export from these ecosystems have raised new concerns about N oligotrophication, limitations of forest productivity, and the capacity for Forests to respond dynamically to disturbance and environmental change. Here we show multiple data streams from long-term ecological research at the Hubbard Brook Experimental Forest in New Hampshire, USA suggesting that N oligotrophication in forest soils is driven by increased carbon flow from the atmosphere through soils that stimulates microbial immobilization of N and decreases available N for plants. Decreased available N in soils can result in increased N resorption by trees, which reduces litterfall N input to soils, further limiting available N supply and leading to further declines in soil N availability. Moreover, N oligotrophication has been likely exacerbated by changes in climate that increase the length of the growing season and decrease production of available N by mineralization during both winter and spring. These results suggest a need to re-evaluate the nature and extent of N cycling in temperate Forests and assess how changing conditions will influence forest ecosystem response to multiple, dynamic stresses of global environmental change.
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climate change decreases nitrogen pools and mineralization rates in northern Hardwood Forests
Ecosphere, 2016Co-Authors: Melany C. Fisk, Timothy J Fahey, Peter M Groffman, Jorge Duran, Jennifer L Morse, John Campbell, Lynn M Christenson, Charles T Driscoll, Gene E LikensAbstract:Nitrogen (N) supply often limits the productivity of temperate Forests and is regulated by a complex mix of biological and climatic drivers. In excess, N is linked to a variety of soil, water, and air pollution issues. Here, we use results from an elevation gradient study and historical data from the long-term Hubbard Brook Ecosystem Study (New Hampshire, USA) to examine relationships between changes in climate, especially during winter, and N supply to northern Hardwood forest ecosystems. Low elevation plots with less snow, more soil freezing, and more freeze/thaw cycles supported lower rates of N mineralization than high elevation plots, despite having higher soil temperatures and no consistent differences in soil moisture during the growing season. These results are consistent with historical analyses showing decreases in rates of soil N mineralization and inorganic N concentrations since 1973 that are correlated with long-term increases in mean annual temperature, decreases in annual snow accumulation, and a increases in the number of winter thawing degree days. This evidence suggests that changing climate may be driving decreases in the availability of a key nutrient in northern Hardwood Forests, which could decrease ecosystem production but have positive effects on environmental consequences of excess N.
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earthworms increase soil microbial biomass carrying capacity and nitrogen retention in northern Hardwood Forests
Soil Biology & Biochemistry, 2015Co-Authors: Peter M Groffman, Patrick J. Bohlen, Melany C. Fisk, Timothy J Fahey, Joseph B Yavitt, Ruth E Sherman, John C MaerzAbstract:Abstract Earthworms have been shown to produce contrasting effects on soil carbon (C) and nitrogen (N) pools and dynamics. We measured soil C and N pools and processes and traced the flow of 13C and 15N from sugar maple (Acer saccharum Marsh.) litter into soil microbial biomass and respirable C and mineralizable and inorganic N pools in mature northern Hardwood forest plots with variable earthworm communities. Previous studies have shown that plots dominated by either Lumbricus rubellus or Lumbricus terrestris have markedly lower total soil C than uncolonized plots. Here we show that total soil N pools in earthworm colonized plots were reduced much less than C, but significantly so in plots dominated by contain L. rubellus. Pools of microbial biomass C and N were higher in earthworm-colonized (especially those dominated by L. rubellus) plots and more 13C and 15N were recovered in microbial biomass and less was recovered in mineralizable and inorganic N pools in these plots. These plots also had lower rates of potential net N mineralization and nitrification than uncolonized reference plots. These results suggest that earthworm stimulation of microbial biomass and activity underlie depletion of soil C and retention and maintenance of soil N pools, at least in northern Hardwood Forests. Earthworms increase the carrying capacity of soil for microbial biomass and facilitate the flow of N from litter into stable soil organic matter. However, declines in soil C and C:N ratio may increase the potential for hydrologic and gaseous losses in earthworm-colonized sites under changing environmental conditions.
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soil nitrogen availability affects belowground carbon allocation and soil respiration in northern Hardwood Forests of new hampshire
Ecosystems, 2015Co-Authors: Ruth D Yanai, Timothy J Fahey, Kikang Bae, Melany C. FiskAbstract:Plant nutrient acquisition in Forests requires respiration by roots and mycorrhizae. Belowground carbon allocation and soil respiration should thus reflect plant effort allocated to nutrient uptake, for example in conditions of different nutrient availabilities controlled by site quality or stand history. Soil respiration, belowground C allocation, and fine root biomass were measured in three sites differing in nutrient availability in the northern Hardwood Forests of the White Mountains of New Hampshire. Annual soil respiration and belowground C allocation measured in two stands at each site were lowest at Jeffers Brook, the site with highest nutrient availability, and higher at Hubbard Brook and Bartlett Experimental Forests. Neither soil respiration nor belowground C allocation differed significantly between mid-aged (31–41 year old) and older stands (>80 year old) within the sites, despite higher fine root (<1 mm) biomass in old stands than mid-aged stands. During the growing season, soil respiration was low where net nitrogen mineralization and net nitrification were high across an extensive sample of thirteen stands and annual belowground C allocation decreased with increasing nitrification across the six intensively studied stands. Available P was not related to soil respiration. The relationships among N availability, belowground C allocation, and soil respiration support the claim that Forests allocate more C belowground in ecosystems with low availability of a limiting nutrient.
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earthworms reduce biotic 15 nitrogen retention in northern Hardwood Forests
Ecosystems, 2015Co-Authors: Holly A Ewing, Patrick J. Bohlen, Melany C. Fisk, Timothy J Fahey, Peter M Groffman, Amy R Tuininga, Kathleen C Weathers, Esteban SuarezAbstract:Invasive exotic earthworms are significantly influencing understory community composition, soil, and ecosystem processes in northern Hardwood Forests in North America, but their effect on the retention of nitrogen (N) has been inconclusive. We examined this in two northern Hardwood forest sites in New York state, USA through a tracer study. In both spring and fall, we added tracer amounts of 15N as nitrate—to simulate atmospheric deposition—with the biologically less active tracer bromide (Br−) to areas both with and without large populations of invasive earthworms. Total recovery of 15N was lower in earthworm-invaded plots, largely due to less retention in litter and upper soil horizons. Although the strong relationship between retention in the upper soil horizons and total 15N recovery suggests that earthworm destruction of the forest floor may be one mechanism reducing the capacity for N retention, in some cases the mineral soil in earthworm-invaded plots retained substantial N. Biotic pools, particularly litter and microbial biomass, retained significantly less 15N in earthworm-invaded plots than in their uninvaded counterparts. In plots invaded by earthworms, negative effects of earthworms on trees were revealed through root-uptake assays suggesting somewhat greater plant demand for ammonium in the spring and in lower 15N recovery in maple seedlings the year following tracer addition. Although similar patterns of Br− movement across treatments suggested that earthworms had smaller effects on hydrologic tracer movement than expected, they appear to have significant effects on the biological processes that underlie N retention.
