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  • 1
    Electronic Resource
    Electronic Resource
    Do Forests Receive Occult Inputs of Nitrogen? (2000)
    Springer
    Ecosystems 3 (2000), S. 321-331 
    Details
    ISSN: 1435-0629
    Keywords: Key words: nitrogen input; forest biogeochemistry; long-term studies.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The nitrogen (N) cycle of forest ecosystems is understood relatively well, and few scientists expect that major revisions will be necessary; most current work on N cycling focuses on improving the precision estimates of pools and fluxes, or measuring the magnitudes of well-known pools in response to management or disturbances. However, in the past few decades more than a dozen articles in refereed journals have claimed very high rates of N input, far beyond the rates expected for known sources of N. In this review, we summarize the literature on N accretion rates in forests that lack substantial contributions from symbiotic N-fixing plants. We critique each study for the strength of the experimental design behind the estimate of N accretion and consider whether unexpectedly large inputs of N really occur in forests. Only 6 of 24 estimates of N accretion had strong experimental designs, and only 2 of these 6 yielded estimates of 〉5 kgN ha-1 y-1. The high accretion estimates with a strong experimental design come from repeated sampling at the Walker Branch watersheds in Tennessee, where N accretion rates ranged from 50 to 80 kg N ha-1 y-1 over 15 years after harvesting. At the same location, an unharvested stand showed no significant change. We conclude that there is no widespread evidence of high rates of occult N input in forests. Too few studies have carefully tested for balanced N budgets in forests (inputs minus outputs plus change in storage), and we recommend that at least a few of these studies be undertaken on soils that permit high precision sampling.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100210000029
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  • 2
    Electronic Resource
    Electronic Resource
    Resin-core and buried-bag estimates of nitrogen transformations in Costa Rican lowland rainforests (1992)
    Springer
    Plant and soil 139 (1992), S. 275-283 
    Details
    ISSN: 1573-5036
    Keywords: early-successional forest ; gross N mineralization ; moist tropics ; N immobilization ; 15N ; nutrification ; nutrient cycling ; old-growth forest
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract We compared the resin-core and buried-bag incubation methods for estimating nitrogen (N) transformation rates using the 15N pool dilution technique in alluvial soils of an early successional forest (ESF) and an old-growth forest (OGF) at the La Selva Biological Station in Costa Rica. Soil cores (38×100-mm) from both forests were incubated in situ for 7 days. The two methods gave generally similar estimates of net N mineralization rates for the two forests. Estimates of ammonium production by the resin-core method were higher than those by the buried-bag method in ESF, but did not differ significantly in OGF (p〈0.05). Estimates of nitrate production by the two methods did not differ significantly. Nitrate averaged 74% and 81% of the total inorganic N production in ESF and OGF, respectively. Net N mineralization in ESF (6.6 mmol m-2d-1) did not differ significantly from that in OGF (5.0 mmol m-2d-1). Fluxes of ammonium and nitrate were high for both forests, but the OGF tended to have higher gross mineralization and nitrification rates than ESF. Approximately 60% of the gross nitrate production and less than 30% of the ammonium were immobilized by microorganisms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00009319
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
    Fulltext
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