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41.
Diagnostic indicators of elevated nitrogen deposition 总被引:1,自引:0,他引:1
Pitcairn C Fowler D Leith I Sheppard L Tang S Sutton M Famulari D 《Environmental pollution (Barking, Essex : 1987)》2006,144(3):941-950
Tissue N content of mosses, which has been shown to be an indicator of enhanced N, was studied at a range of locations dominated either by wet or dry deposited and oxidised and reduced forms of N. Tissue N responded differently to wet and dry deposited N. For a 1 kg ha(-1) y(-1) increase in N deposition, tissue N increased by 0.01% at wet deposition sites but by 0.03% at sites dominated by dry deposited NH3. Tissue N at wet deposition sites responded more to concentrations of NO3- and NH4+ in precipitation (r(2) 0.63) than to total N deposition (r(2) 0.27), concentration explaining 66% of the variation in tissue N, wet deposition 33%. The study clearly concludes that tissue N concentration in mosses provides a good indication of N deposition at sites where deposition is dominated by NH3, and is also valuable in identifying vegetation exposed to large concentrations of NH4+ or NO3-, in wet deposition dominated areas, such as hilltops and wind exposed woodland edges. 相似文献
42.
J.N. Cape L.J. van der Eerden I.D. Leith 《Environmental pollution (Barking, Essex : 1987)》2009,157(3):1033-1037
The current critical level for ammonia (CLENH3) in Europe is set at 8 μg NH3 m−3 as an annual average concentration. Recent evidence has shown specific effects of ammonia (NH3) on plant community composition (a true ecological effect) at much smaller concentrations. The methods used in setting a CLENH3 are reviewed, and the available evidence collated, in proposing a new CLENH3 for different types of vegetation. For lichens and bryophytes, we propose a new CLENH3 of 1 μg NH3 m−3 as a long-term (several year) average concentration; for higher plants, there is less evidence, but we propose a CLENH3 of 3 ± 1 μg NH3 m−3 for herbaceous species. There is insufficient evidence to provide a separate CLENH3 for forest trees, but the value of 3 ± 1 μg NH3 m−3 is likely to exceed the empirical critical load for N deposition for most forest ecosystems. 相似文献
43.
Direct and indirect effects of ammonia, ammonium and nitrate on phosphatase activity and carbon fluxes from decomposing litter in peatland 总被引:1,自引:0,他引:1
David Johnson Lucy Moore Ian D. Leith 《Environmental pollution (Barking, Essex : 1987)》2010,158(10):3157-3163
Here we investigate the response of soils and litter to 5 years of experimental additions of ammonium (NH4), nitrate (NO3), and ammonia (NH3) to an ombrotrophic peatland. We test the importance of direct (via soil) and indirect (via litter) effects on phosphatase activity and efflux of CO2. We also determined how species representing different functional types responded to the nitrogen treatments. Our results demonstrate that additions of NO3, NH4 and NH3 all stimulated phosphatase activity but the effects were dependent on species of litter and mechanism (direct or indirect). Deposition of NH3 had no effect on efflux of CO2 from Calluna vulgaris litter, despite it showing signs of stress in the field, whereas both NO3 and NH4 reduced CO2 fluxes. Our results show that the collective impacts on peatlands of the three principal forms of nitrogen in atmospheric deposition are a result of differential effects and mechanisms on individual components. 相似文献