ISSN:1025-6016    

DOI:10.1080/10256019608036303

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

An overview is given about the δ13C- and δ5D-values in the organic material of hemi- and full- parasitic higher plants and of their hosts.

ISSN:1025-6016    

DOI:10.1080/10256019608036304

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

In April 1994 a15N tracer pulse study was started in a 140-year-old spruce stand (Picea abies[L.] Karst.) located at the Fichtelgebirge (NE Bavaria). Highly enriched (98%) [15N]ammonium and [15N]nitrate were applied simulating wet deposition. For two growing seasons the pathways and dynamics of the tracer were followed in all compartments of spruce (needles and twigs of all age classes, stem wood and bark, roots) and understorey vegetation and in soils of the organic (L/Of and Oh) and mineral horizons (A0–5and A5–10). By variations of the application time on different plots within the growing season (spring, summer and autumn) a seasonal effect of labelling on uptake and distribution patterns was tested.

ISSN:1025-6016    

DOI:10.1080/10256019608036305

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A15N tracer-experiment was carried out in a 140-year-old spruce stand (Picea abies(L.) Karst.) in the Fichtelgebirge (NE-Bavaria, Germany). Highly enriched (98 at%) [15N]ammonium and [15N]nitrate were applied as tracers by simulation of a deposition of 41.3 mol N ha−1with 11 water m−2. To examine seasonal variations of uptake by spruce and understorey vegetation, different plots were labelled in spring, summer and autumn 1994.

ISSN:1025-6016    

DOI:10.1080/10256019608036306

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Long-term static fertilizer experiments are important for the soil fertility research, particular for using nitrogen problems. There are several possibilities for15N-traces in such experiments. One example is the International Organic Nitrogen Long-Term Experiment at Berlin-Dahlem in which15N-tracers are used, involving organic and inorganic fertilizers. By analyzing the soil and the plant biomass, it was possible to distinguish between nitrogen originating from the soil and that from the fertilizer. Some results are published.

ISSN:1025-6016    

DOI:10.1080/10256019608036307

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The course of uptake of weed-borne nitrogen by maize was tested with15N in a pot experiment with silty loam after common growth of maize andChenopodium albumL., and mulching the weed in the 5-leaf stage of maize. Harvests 4,8 and 12 weeks after mulching show that the maize took up 35, 63 and 70% of the weed-borne nitrogen, resp., in consequence of a rapid and almost complete mineralization. The portion of weed-borne nitrogen in total N of the maize was 16% at all harvest dates. The differences in yield between weeded and unweeded maize were not significant neither at 5-leaf stage nor at corn maturity.

ISSN:1025-6016    

DOI:10.1080/10256019608036308

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

In pot experiments with15N labelled soil and mineral15N, the influence ofBradyrhizobium (Rhizobium japonicum)inoculation and N fertilization on the symbiotic N2fixation and yield of soybeans [Glycine max(L.) Merill., cv. ‘Fiskeby V‘] was investigated. Symbiotic N2fixation only occured after inoculation withBradyrhizobium.Considerable differences in efficiency of the bacterial preparations were observed. Shortly after flowering, the symbiotic nitrogen fixation was finished and, subsequently, soybeans took up considerable N amounts from the soil. N fertilization at seeding suppressed N2fixation of soybeans. In this case, the dry matter and nitrogen yield increased, because the loss of fixed nitrogen was overcompensated by the mineral N uptake. During flowering of soybeans, the N2fixation was not affected by N supply, because this process was already terminated. The mineral N was additionally available to the plants and led to increased N amounts in plants. It was absorbed to a considerable degree by soybeans. The mineral N was translocated (partly, after intermediate storage in the vegetative organs) into the seeds thus increasing their yields.

ISSN:1025-6016    

DOI:10.1080/10256019608036309

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Young wheat (C3) and maize (C4) plants were exposed to near-ambient concentrations of ozone in open-top chambers in order to investigate the possible effects of ozone on nitrogen metabolism. Nitrogen was supplied to the plants by adding15N-labelled tracer substances via the soil substrate. Enzyme activities (NADH nitrate reductase, nitrite reductase, glutamine synthetase and NADH glutamate dehydrogenase) and the incorporation of15N were determined.

ISSN:1025-6016    

DOI:10.1080/10256019608036310

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Applications of isotopically distinct sulfur compounds have recently been used for tracing the fate of added sulfur in whole catchments or sub-compartments therein. Basic principles, the analytical methodology, and data evaluation for this isotope tracer technique are briefly described. We recommend that δ34S-values of applied and natural sulfur compounds in the investigated ecosystem should differ by more than 20‰ in order to successfully ascertain sulfur fluxes. Where possible, a high ratio of applied sulfur loads versus sulfur pool sizes in the ecosystem should also be realized in order to allow the assessment of sulfur transformations in the study area. Prospects and limitations of this isotope tracer technique are critically discussed by reviewing results from recently or currently conducted lysimeter and field experiments.

ISSN:1025-6016    

DOI:10.1080/10256019608036311

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

In a forested catchment in theFichtelgebirgemountains (NE-Bavaria, Germany) the long term SO42-budget (average 1988–1994) indicated that about 40% of the input with throughfall (16.8 kg SO42-S·ha−1·yr−1) was retained in the catchment. In order to identify processes acting as potential SO42-sinks, δ34S values of SO42-in soil solutions and runoff were measured between May and November 1994. δ34S values of the runoff and the fen were higher (5.8‰) than the δ34S values of the soil solution of the oxic soils in the terrestrial area (3.9‰). Because there is no lithogenic S source within the catchment, it can be assumed that SO42-deposition is the only S source in the catchment. Thus the results were interpreted as a result of SO42-reduction within the catchment, because the uptake of32S is favoured during the dissimilatory SO42-reduction and34S is consequently enriched in the soil solution. To estimate the amount of SO42-reduced isotopic fractionation factors between − 9‰ and −46‰ were considered, resulting in SO42-reduction rates of 1.8–9.3 kg SO42-S·ha−1yr−1. It was concluded that besides dissimilatory SO42-reduction another sink exists in the catchment (e.g. SO42-sorption in deep soil layers).

ISSN:1025-6016    

DOI:10.1080/10256019608036312

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor