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  • 1
    Language: English
    In: Proceedings of the National Academy of Sciences of the United States of America, 21 August 2018, Vol.115(34), pp.8587-8590
    Description: Forest soils are a sink for atmospheric methane (CH) and play an important role in modulating the global CH budget. However, whether CH uptake by forest soils is affected by global environmental change is unknown. We measured soil to atmosphere net CH fluxes in temperate forests at two long-term ecological research sites in the northeastern United States from the late 1990s to the mid-2010s. We found that annual soil CH uptake decreased by 62% and 53% in urban and rural forests in Baltimore, Maryland and by 74% and 89% in calcium-fertilized and reference forests at Hubbard Brook, New Hampshire over this period. This decrease occurred despite marked declines in nitrogen deposition and increases in atmospheric CH concentration and temperature, which should lead to increases in CH uptake. This decrease in soil CH uptake appears to be driven by increases in precipitation and soil hydrological flux. Furthermore, an analysis of CH uptake around the globe showed that CH uptake in forest soils has decreased by an average of 77% from 1988 to 2015, particularly in forests located from 0 to 60 °N latitude where precipitation has been increasing. We conclude that the soil CH sink may be declining and overestimated in several regions across the globe.
    Keywords: Greenhouse Gases ; Hydrological Flux ; Increased Precipitation ; Long-Term Ecological Research Sites ; Soil Methane Uptake ; Forests ; Models, Biological ; Soil ; Methane -- Metabolism
    ISSN: 00278424
    E-ISSN: 1091-6490
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  • 2
    In: Ecology, November 2011, Vol.92(11), pp.2035-2042
    Description: Forest ecosystem nitrogen (N) cycling is a critical controller of the ability of forests to prevent the movement of reactive N to receiving waters and the atmosphere and to sequester elevated levels of atmospheric carbon dioxide (CO). Here we show that calcium (Ca) constrains the ability of northern hardwood forest trees to control the availability and loss of nitrogen. We evaluated soil N‐cycling response to Ca additions in the presence and absence of plants and observed that when plants were present, Ca additions “tightened” the ecosystem N cycle, with decreases in inorganic N levels, potential net N mineralization rates, microbial biomass N content, and denitrification potential. In the absence of plants, Ca additions induced marked increases in nitrification (the key process controlling ecosystem N losses) and inorganic N levels. The observed “tightening” of the N cycle when Ca was added in the presence of plants suggests that the capacity of forests to absorb elevated levels of atmospheric N and CO is fundamentally constrained by base cations, which have been depleted in many areas of the globe by acid rain and forest harvesting.
    Keywords: Acid Rain ; Calcium ; Forest Nitrogen Cycling ; Global Environmental Change ; Hubbard Brook Experimental Forest ; New Hampshire ; Usa ; Mineralization ; Nitrification ; Nitrogen ; Plant–Microbe Interactions
    ISSN: 0012-9658
    E-ISSN: 1939-9170
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  • 3
    Language: English
    In: Proceedings of the National Academy of Sciences of the United States, Feb 5, 2013, Vol.110(6), p.2052(6)
    Description: Human mobilization and use of reactive nitrogen (Nr) has been one of the major aspects of global change over the past century. Nowhere has that change been more dramatic than in China, where annual net Nr creation increased from 9.2 to 56 Tg from 1910 to 2010. Since 1956, anthropogenic Nr creation exceeded natural Nr creation, contributing over 80% of total Nr until 2010. There is great interest and uncertainty in the fate and effects of this Nr in China. Here, a comprehensive inventory of Nr in China shows that Nr (including recycled Nr) has continuously and increasingly accumulated on land (from 17 to 45 Tg), accompanied by increasing transfers to the atmosphere (before deposition; from 7.6 to 20 Tg), inland waters (from 2.7 to 9.6 Tg), and coastal waters (from 4.5 to 7.7 Tg) over the past 30 y. If current trends continue, Nr creation from human activities will increase to 63 Tg by 2050, raising concerns about deleterious environmental consequences for land, air, and water at regional and global scales. Tremendous amounts of Nr have accumulated in plants, soils, and waters in China over the past 30 y, but the retention capacity of the terrestrial landscape seems to be declining. There is a possibility that the negative environmental effects of excessive Nr may accelerate in coming decades, increasing the urgency to alter the trajectory of increasing Nr imbalance. Here, a conceptual framework of the relationships between human drivers and Nr cycling in China is oriented and well-targeted to Chinese abatement strategies for Nr environmental impact. national nitrogen budget | biogeochemical cycling | chemical fertilizer | nitrogen use efficiency doi/10.1073/pnas.1221638110
    Keywords: Nitrogen (Chemical element) -- Research ; Nitrogen (Chemical element) -- Analysis ; Fertilizers -- Research ; Fertilizers -- Analysis
    ISSN: 0027-8424
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  • 4
    Language: English
    In: Soil Biology and Biochemistry, 2011, Vol.43(12), pp.2441-2449
    Description: High rates of atmospheric nitrogen (N) deposition have raised questions about shifting patterns of nutrient limitation in northern hardwood forests. Of particular interest is the idea that increased supply of N may induce phosphorus (P) limitation of plant and microbial processes, especially in acid soils where P sorption by Al is high. In this study, we established field plots and plant-free laboratory mesocosms with P and Ca additions to test the hypotheses that 1) microbial biomass and activity are limited by P in the northern hardwood forest soils at the Hubbard Brook Experimental Forest in NH USA; 2) elevated Ca increases inherent P availability and therefore reduces any effects of added P and 3) P effects are more marked in the more carbon (C) rich Oie compared to the Oa horizon. Treatments included P addition (50 kg P ha ), Ca addition (850 kg Ca ha ) and Ca + P addition (850 kg Ca ha and 50 kg P ha ). The P treatments increased resin-available P levels and reduced phosphatase activity, but had no effect on microbial biomass C, microbial respiration, C metabolizing enzymes, potential net N mineralization and nitrification in the Oie or Oa horizon of either field plots or plant free mesocosms, in either the presence or absence of Ca. Total, prokaryote, and eukaryote PLFA were reduced by P addition, possibly due to reductions in mycorrhizal fungal biomass. These results suggest that increased N deposition and acidification have not created P limitation of microbial biomass and activity in these soils. ► Atmospheric N deposition may cause P limitation of forest soil microbial processes. ► P or P plus Ca had no effect on microbial parameters in the field or laboratory. ► P limitation is not likely in soils with significant pools of accessible P.
    Keywords: Calcium ; Forest ; Microbial ; Nitrification ; Nitrogen ; Phosphorus ; Agriculture ; Chemistry
    ISSN: 0038-0717
    E-ISSN: 1879-3428
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  • 5
    Language: English
    In: Proceedings of the National Academy of Sciences of the United States of America, 05 February 2013, Vol.110(6), pp.2052-7
    Description: Human mobilization and use of reactive nitrogen (Nr) has been one of the major aspects of global change over the past century. Nowhere has that change been more dramatic than in China, where annual net Nr creation increased from 9.2 to 56 Tg from 1910 to 2010. Since 1956, anthropogenic Nr creation exceeded natural Nr creation, contributing over 80% of total Nr until 2010. There is great interest and uncertainty in the fate and effects of this Nr in China. Here, a comprehensive inventory of Nr in China shows that Nr (including recycled Nr) has continuously and increasingly accumulated on land (from 17 to 45 Tg), accompanied by increasing transfers to the atmosphere (before deposition; from 7.6 to 20 Tg), inland waters (from 2.7 to 9.6 Tg), and coastal waters (from 4.5 to 7.7 Tg) over the past 30 y. If current trends continue, Nr creation from human activities will increase to 63 Tg by 2050, raising concerns about deleterious environmental consequences for land, air, and water at regional and global scales. Tremendous amounts of Nr have accumulated in plants, soils, and waters in China over the past 30 y, but the retention capacity of the terrestrial landscape seems to be declining. There is a possibility that the negative environmental effects of excessive Nr may accelerate in coming decades, increasing the urgency to alter the trajectory of increasing Nr imbalance. Here, a conceptual framework of the relationships between human drivers and Nr cycling in China is oriented and well-targeted to Chinese abatement strategies for Nr environmental impact.
    Keywords: Reactive Nitrogen Species -- Analysis
    ISSN: 00278424
    E-ISSN: 1091-6490
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  • 6
    In: Global Change Biology, September 2013, Vol.19(9), pp.2826-2837
    Description: Despite growing recognition of the role that cities have in global biogeochemical cycles, urban systems are among the least understood of all ecosystems. Urban grasslands are expanding rapidly along with urbanization, which is expected to increase at unprecedented rates in upcoming decades. The large and increasing area of urban grasslands and their impact on water and air quality justify the need for a better understanding of their biogeochemical cycles. There is also great uncertainty about the effect that climate change, especially changes in winter snow cover, will have on nutrient cycles in urban grasslands. We aimed to evaluate how reduced snow accumulation directly affects winter soil frost dynamics, and indirectly greenhouse gas fluxes and the processing of carbon (C) and nitrogen (N) during the subsequent growing season in northern urban grasslands. Both artificial and natural snow reduction increased winter soil frost, affecting winter microbial C and N processing, accelerating C and N cycles and increasing soil : atmosphere greenhouse gas exchange during the subsequent growing season. With lower snow accumulations that are predicted with climate change, we found decreases in N retention in these ecosystems, and increases in and flux to the atmosphere, significantly increasing the global warming potential of urban grasslands. Our results suggest that the environmental impacts of these rapidly expanding ecosystems are likely to increase as climate change brings milder winters and more extensive soil frost.
    Keywords: Carbon ; Carbon Dioxide ; Global Change ; Methane ; Nitrogen ; Nitrous Oxide ; Nutrient Cycling ; Trace Gases ; Urban Lawns
    ISSN: 1354-1013
    E-ISSN: 1365-2486
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  • 7
    Language: English
    In: Soil Biology and Biochemistry, February 2011, Vol.43(2), pp.271-279
    Description: Acid deposition can deplete soil calcium (Ca) and be detrimental to the health of some forests. We examined effects of soil Ca and phosphorus (P) availability on microbial activity and nitrogen (N) transformations in a plot-scale nutrient addition experiment at the Hubbard Brook Experimental Forest in New Hampshire, USA. We tested the hypotheses that (1) microbial activity and N transformations respond to large but not small changes in soil Ca, (2) soil Ca availability influences net N mineralization via the immobilization of N, rather than via changes in microbial activity, and (3) the response to Ca is constrained by P availability. Seasonality was a primary influence on the microbial response to treatments; N cycling processes varied from May to October and treatment effects were only detectable in the mid-growing season, in July. Neither microbial activity (C mineralization) nor gross N mineralization responded to Ca or to P, in either horizon. In the Oa horizon in July net N mineralization was reduced by high Ca and by Ca + P, and gross nitrification was increased by P addition. In the Oe horizon in July net N mineralization was reduced by Ca + P. These results partially supported our hypotheses, suggesting that soil Ca depletion has the potential to increase mid-growing season N availability via subtle changes in N immobilization, and that this effect is sensitive to soil P chemistry. The horizon-specific nature of the responses that we detected suggests that the proportions of Oe and Oa horizons comprising the surface organic layer will influence the relative importance of these processes at the ecosystem scale. Our results highlight the need for further attention to seasonal changes in controls of microbial mineralization/immobilization processes, to functional differences between organic horizons, and to interactions between Ca and P in soils, in order to learn the specific mechanisms underlying the influence of Ca status on nutrient recycling in these northern hardwood ecosystems. ► Calcium addition reduced net N mineralization in the Oa horizon, by increasing N immobilization. ► Phosphorus availability interacted with Ca to reduce net N mineralization in Oe and Oa horizons. ► Soil acidification may be increasing net N mineralization in forests of the northeastern USA. ► These effects are likely sensitive to soil P and proportions of Oe and Oa in the forest floor.
    Keywords: Acid Deposition ; Calcium ; Gross Nitrogen Transformations ; Microbial Activity ; Nutrient Limitation ; Phosphorus ; Soil Acidification ; Agriculture ; Chemistry
    ISSN: 0038-0717
    E-ISSN: 1879-3428
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  • 8
    Language: English
    In: Soil Biology and Biochemistry, March, 2012, Vol.46, p.145(3)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.soilbio.2011.12.005 Byline: Jorge Duran, Jennifer L. Morse, Peter M. Groffman Abstract: Nitrogen mineralization is a critical ecosystem process that is difficult to measure. Among several in situ methods used to estimate N mineralization rates in soils, the buried bag and covered-cylinder methods are two of the most common. Few studies have compared N mineralization rates from these two in situ methods, and it is still unclear if they provide analogous results. We compared both techniques, and two different core diameters, to determine if the different methods produce comparable results. Contrary to our expectations, larger cores were not more representative than smaller due to the importance of site-specific soil characteristics, especially rockiness. Dissimilarities in means, and weak and inconsistent correlations between methods, suggested that the different methods may not be equivalent. Our results suggest that the method optimization depends on specific site conditions, at least in forest soils, and that comparison among studies using different in situ methods should be made with caution until more standardization is achieved. Author Affiliation: Cary Institute of Ecosystem Studies, Box AB, 2801 Sharon Turnpike, Millbrook, NY 12545, USA Article History: Received 11 October 2011; Revised 5 December 2011; Accepted 6 December 2011
    Keywords: Forest Soils -- Comparative Analysis ; Forest Soils -- Methods
    ISSN: 0038-0717
    Source: Cengage Learning, Inc.
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  • 9
    In: Journal of Geophysical Research: Biogeosciences, March 2012, Vol.117(G1), pp.n/a-n/a
    Description: Wetland soil oxygen (O) is rarely measured, which limits our understanding of a key regulator of nitrogen loss through denitrification. We asked: (1) How does soil [O] vary in riparian wetlands? (2) How does this [O] variation affect denitrification rates and end products? and (3) How does [O] variation and previous exposure to Oaffect trace gas fluxes? We collected a continuous seven‐month record of [O] dynamics in a “wet” and “dry” riparian zone. In April 2009, soil [O] ranged from 0 to 13% and consistently increased with increasing distance from the stream. [O] gradually declined in all sensors until all sensors went anoxic in early September 2009. In mid‐fall, a dropping water table increased soil [O] to 15–20% within a 2–3 day period. We measured denitrification using the Nitrogen‐Free Air Recirculation Method (N‐FARM), a direct measurement of N production against a helium background. Denitrification rates were significantly higher in the wetter areas, which correlated to lower O conditions. Denitrification rates in the drier areas correlated with [O] in the early spring and summer, but significantly decreased in late summer despite decreasing O concentrations. Increasing [O] significantly increased core NO production, and therefore may be an important control on nitrous oxide yield. Field NO fluxes, however, were highly variable, ranging from 0 to 800 ug N m hr with no differences between the wet and dry sites. Future research should focus on understanding the biotic and abiotic controls on O dynamics, and O dynamics should be included in models of soil N cycling and trace gas fluxes. Soil oxygen is rarely measured but highly dynamic in riparian wetlands Soil O2 controls the rates and end products of denitrification Increased exposure to soil O2 selects for microbes that produce more N2O
    Keywords: N 2 O Yield ; Denitrification ; Nitrous Oxide
    ISSN: 0148-0227
    E-ISSN: 2156-2202
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  • 10
    Language: English
    In: Proceedings of the National Academy of Sciences of the United States of America, 18 November 2014, Vol.111(46), pp.16413-8
    Description: Despite decades of measurements, the nitrogen balance of temperate forest catchments remains poorly understood. Atmospheric nitrogen deposition often greatly exceeds streamwater nitrogen losses; the fate of the remaining nitrogen is highly uncertain. Gaseous losses of nitrogen to denitrification are especially poorly documented and are often ignored. Here, we provide isotopic evidence (δ(15)NNO3 and δ(18)ONO3) from shallow groundwater at the Hubbard Brook Experimental Forest indicating extensive denitrification during midsummer, when transient, perched patches of saturation developed in hillslopes, with poor hydrological connectivity to the stream, while streamwater showed no isotopic evidence of denitrification. During small rain events, precipitation directly contributed up to 34% of streamwater nitrate, which was otherwise produced by nitrification. Together, these measurements reveal the importance of denitrification in hydrologically disconnected patches of shallow groundwater during midsummer as largely overlooked control points for nitrogen loss from temperate forest catchments.
    Keywords: Denitrification ; Forested Watershed ; Nitrogen Cycle ; Stable Isotopes ; Streamwater Chemistry ; Denitrification ; Forests ; Seasons ; Nitrogen Isotopes -- Metabolism ; Oxygen Isotopes -- Metabolism ; Trees -- Metabolism
    ISSN: 00278424
    E-ISSN: 1091-6490
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