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To determine the dominant processes controlling nitrogen (N) dynamics in soils and increase insights into soil N cycling from nitrogen isotope (?15N) data, patterns of 15N enrichment in soil profiles were compiled from studies on tropical, temperate, and boreal systems. The maximum 15N enrichment between litter and deeper soil layers varied strongly with mycorrhizal fungal association, averaging 9.6 � 0.4? in ectomycorrhizal systems and 4.6 � 0.5? in arbuscular mycorrhizal systems. The 15N enrichment varied little with mean annual temperature, precipitation, or nitrification rates. One main factor controlling 15N in soil profiles, fractionation against 15N during N transfer by mycorrhizal fungi to host plants, leads...
The five major reductive degradation products of TNT-4ADNT (4-amino-2,6-dinitrotoluene), 2ADNT (2-amino-4,6-dinitrotoluene), 2,4DANT (2,4-diamino-6-nitrotoluene), 2,6DANT (2,6-diamino-4-nitrotoluene), and TAT (2,4,6-triaminotoluene)-labeled with 15N in the amine positions, were reacted with the IHSS soil humic acid and analyzed by 15N NMR spectrometry. In the absence of catalysts, all five amines underwent nucleophilic addition reactions with quinone and other carbonyl groups in the soil humic acid to form both heterocyclic and nonheterocyclic condensation products. Imine formation via 1,2-addition of the amines to quinone groups in the soil humic acid was significant with the diamines and TAT but not the monoamines....
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Recent sediments from two alpine lakes (> 3300 m asl) in the Colorado Front Range (USA) register marked and near-synchronous changes that are believed to represent ecological responses to enhanced atmospheric deposition of fixed nitrogen from anthropogenic sources. Directional shifts in sediment proxies include greater representations of mesotrophic diatoms and increasingly depleted d15N values. These trends are particularly pronounced since ~ 1950, and appear to chronicle lake responses to excess N derived from agricultural and industrial sources to the east. The rate and magnitude of recent ecological changes far exceed the context of natural variability, as inferred from comparative analyses of a long core capturingthe...
The nonnative annual grass Bromus tectorum has successfully replaced native vegetation in many arid and semiarid ecosystems. Initial introductions accompanied grazing and agriculture, making it difficult to separate the effects of invasion from physical disturbance. This study examined N dynamics in two recently invaded, undisturbed vegetation associations (C₃ and C₄). The response of these communities was compared to an invaded/disturbed grassland. The invaded/disturbed communities had higher surface NH₄� input in spring, whereas there were no differences for surface input of NO₃�. Soil inorganic N was dominated by NH₄�, but invaded sites had greater subsurface soil NO₃�. Invaded sites had greater...
We used carbon and nitrogen isotopes to investigate changes in the diet of California condors from the Pleistocene to the recent. During the Pleistocene, condors from California fed on both terrestrial megafauna and marine mammals. Early accounts reported condors feeding on the carcasses of marine mammals, but by the late 1700s, condor diets had shifted predominantly to terrestrial animals, following the commercial harvesting of marine mammals and the development of cattle ranching on land. At present, dairy calves provided by humans significantly augment condor diet, constituting an artificial support of the current population. Reestablishing a marine mammal component in the condor diet may be an effective strategy...


    map background search result map search result map Anthropogenic nitrogen deposition induces rapid ecological changes in alpine lakes of the Colorado Front Range (USA) Length, Weight, Energy Density, and Isotopic Values of Fish from Rivers in Northwest Alaska, 2015-2019 Nearshore Fish Isotope Values, Beaufort Sea, Alaska, 2017-2019 Anthropogenic nitrogen deposition induces rapid ecological changes in alpine lakes of the Colorado Front Range (USA) Nearshore Fish Isotope Values, Beaufort Sea, Alaska, 2017-2019 Length, Weight, Energy Density, and Isotopic Values of Fish from Rivers in Northwest Alaska, 2015-2019