The purpose of this study was (1) to determine the vertical distribution of rare earth element (REE) concentrations, stocks, and geochemical fractions in two different marsh soil profiles and (2) to quantify the relations between REEs and soil properties.
Materials and methods
A sandy Fluvisol recently flooded by tidal water and a clayey Gleysol landward the dike impacted by fluctuating groundwater levels served as reference marsh soils. An aqua regia extraction was used to determine the concentrations of REEs; additionally, a sequential extraction procedure developed by the Commission of the European Communities Bureau of Reference was conducted to assess the geochemical fractions (exchangeable, reducible, oxidisable, residual fraction) of REEs. Both extractions were carried out according to genetic horizons. The stocks of REEs were calculated and the relations between physico-chemical soil properties and concentrations/mobility of REEs were quantified via correlation analysis.
Results and discussion
The aqua regia extractable REE concentrations and stocks of the Gleysol were about two times higher compared to the Fluvisol since the Gleysol was more clayey and REEs might adsorb onto clay minerals. We have detected small differences of REE concentrations and geochemical fractions between the horizons of the single profiles. Rare earth elements existed mainly in residual or reducible fraction, followed by oxidisable, and water soluble/exchangeable/carbonate bound fraction. The most striking difference between the two marsh soil profiles regarding the geochemical fractions was the higher residual fraction in the Fluvisol than in the Gleysol what seemed to be due to the lower aqua regia extractable concentration in the former.
Conclusions
The aqua regia extractable concentration as well as reduction and oxidation processes of (amorphous) iron and manganese complexes seemed to have the most important impact on the geochemical fractions of REEs in the studied marsh soil profiles. In future, those findings should be verified in further marsh soils worldwide. In particular, future studies should elucidate the specific release kinetics of REEs and their determining factors. 相似文献
Novel analogues of mandipropamid have been designed and prepared. The synthetic approach to these stretched and heterocyclic mandelamides is outlined. Biological data demonstrate their high efficacy against important plant diseases like tomato and potato late blight (Phytophthora infestans De Bary) and grape downy mildew (Plasmopara viticola Berliner & de Toni). Structure-activity relationship studies are discussed. 相似文献
According to the classical model of Macevicz and Oster, annual eusocial insects should show a clear dichotomous "bang-bang"
strategy of resource allocation; colony fitness is maximised when a period of pure colony growth (exclusive production of
workers) is followed by a single reproductive period characterised by the exclusive production of sexuals. However, in several
species graded investment strategies with a simultaneous production of workers and sexuals have been observed. Such deviations
from the "bang-bang" strategy are usually interpreted as an adaptive (bet-hedging) response to environmental fluctuations
such as variation in season length or food availability. 相似文献
Summary About 32% of the 99 million ha wheat grown in developing countries experiences varying levels of drought stress. Three major drought types have been identified: Late drought (LD) is common in the Mediterranean region, early drought (ED) is found in Latin America and wheat is produced on residual soil moisture (RM) in the Indian subcontinent and part of Australia. Until 1983, CIMMYT selected all germplasm under near optimum conditions for its yield potential and tested only advanced lines under drought. In spite of many critics, this approach proved to be successful, since in the mid 80's CIMMYT germplasm was grown on 45% of the wheat area in LC with annual rainfall from 300–500 mm and on 21% in areas with less than 300 mm. Since 1983, CIMMYT's drought breeding methodology is to alternate segregating populations between drought stressed and fully irrigated conditions (FI) and to test advanced lines under a line source irrigation system. To compare the efficiency of these approach, yield of four, mostly leading varieties, from each of the regions with LD, ED, RM, and FI and twelve recent CIMMYT cultivars selected for high yield under FI and RM conditions (ALT) were compared under four different moisture regimes (FI, LD, ED, and RM) in 89–90 and 90–91 in Yaqui Valley, Mexico. Genotypic correlation between yield and days to flowering, days to maturity, height, grains m-2, TKW, test weight and grain fill period were calculated.Mean grain yield of the four best lines in the ALT group was highest under all moisture stress regimes, followed by the FI-group. However, the highest yielding cultivar within each moisture regime was from the FI-group under FI, from the LD-group under LD, and from the ALT-group under ED and RM conditions. Estimates for genetic advance suggest that FI is the best environment for increasing grain yield even in all three drought environments. This indicates that yield potential per se is beneficial also in drought environments. The highest yield in drought environments was realized by the CIM cultivars selected under FI and RM. Simultaneous evaluation of the germplasm under near optimum conditions, to utilize high heritabilities and identify lines with high yield potential, and under stress conditions to preserve alleles for drought tolerance seem at present the best strategy. 相似文献
The present study was conducted to investigate the possible interactive effects of rising atmospheric CO2 concentration [CO2] and drought stress on water use of wheat. Spring wheat (Triticum aestivum cv. “Minaret”) was grown either in 1 m diameter lysimeters with 0.4 m soil depth (1998) or in the field (1999) in open-top chambers under two CO2-concentrations (ambient, ambient + 280 ppm) and two watering regimes (well-watered = WW with a plant available water content PAW > 40 mm and drought stressed = DS, 10 mm < PAW < 30 mm) beginning after first node stage. Canopy evapotranspiration (EC) was measured continuously from first the node stage until the beginning of flag leaf senescence using four open-system canopy chambers (0.78 m3). Seasonal changes of the absorption of photosynthetically active radiation (APAR) of the canopy and root growth (1999) were also measured.
In both growing seasons leaf area index increased in response to elevated [CO2] in both water treatments. The related effects of [CO2] on canopy radiation absorption (APAR) were, however, smaller. EC was linearily related to APAR in both growing seasons. While elevated [CO2] reduced the slope of this relation under WW conditions by ca. 20% in both growing seasons, it was not reduced (1998) and even increased (1999) under drought. Canopy conductance (GC) calculated as EC divided by vapour pressure deficit of air, showed a non-linear relationship to APAR that was best explained by saturation curves. Under WW conditions, elevated [CO2] reduced the initial slope of GC versus APAR as well as GC at saturating light conditions (ca. −30%), while under DS conditions no effect of elevated [CO2] could be detected. Under high light conditions (PAR > 400 μmol m−2 s−1) a critical “threshold value” of PAW (TPAW, ca. 40 mm) could be identified above which GC did not respond to PAW. While in 1998 GC did not respond to elevated [CO2] at PAW < TPAW, it was slightly increased at low PAW values in the field experiments of 1999. The reduction of TPAW by elevated [CO2] may be explained by enhanced root growth (1999) that would have given the plants better access to soil water resources. The present results suggest that below a critical soil water content elevated [CO2] will not reduce canopy water loss of wheat or may even enhance it. 相似文献
The main elements of the international wheat improvement program of the Centro Internacional de Mejoramiento de Maíz y Trigo
(CIMMYT), also known as the International Maize and Wheat Improvement Center, have been shuttle breeding at two contrasting
locations in Mexico, wide adaptation, durable rust and Septoria resistances, international multisite testing, and the appropriate
use of genetic variation to enhance yield gains of subsequently produced lines. Such an approach yielded successes known collectively
as the Green Revolution. However, at the beginning of the 21st century, this “cultivar assembly line” approach needs fine
tuning to address crop needs under increasingly adopted resource conserving practices, as well as those related to nutritional
requirements of the end-users. International wheat improvement will therefore focus on the targeting of traits in respective
mega-environments, and the use of participatory methods, especially in marginal environments. The main features of this wheat
improvement strategy include the introduction of new and novel sources of genetic variation through wild species, landraces,
and, potentially, the use of transgenes for intractable traits. This variation will be combined using international shuttle
breeding, and increased breeding efficiency will be achieved through marker-aided methods, more targeted use of crop physiology,
plant genetics, biostatistics, and bioinformatics. Likewise, CIMMYT will increase its focus on the needs of end-users by emphasizing
regional efforts in participatory research and client-oriented plant breeding. 相似文献
A screening study with 25 common European wild plant species were performed over three consecutive growing seasons to investigate the effects of ozone on plant growth, reproductive development, and resource allocation. Species were grown from seedling stage until the flowering stage or seed maturity, respectively, in open-top chambers in different ozone-enriched atmospheres at environmentally-relevant concentrations. Ozone treatments covered a range of concentrations from 20 to 55 ppb ozone (seasonal 8 h daily mean). The experiments revealed significant differences between species with respect to the sensitivity of different end points toward ozone exposure. Ozone caused a significant reduction in leaf biomass of more than 20% in six species, and a significant increase in leaf biomass in three species. The relative ozone sensitivities of the species in terms of leaf biomass were different from those inferred from total shoot biomass or seed production, indicating that ozone alters resource allocation patterns in wild plants but there was considerable variation between species in effects on the allocation to leaves, stems, flowers/fruits and seeds. Germinability of seeds was affected by ozone such that germination rate was up to 30% lower in ozone-treated plants compared to control plants. Based on the genotypes screened and by combining different sensitivity criteria (vegetative growth, reproductive growth, exposure-growth response relationships) Malva sylvestris must be regarded as the most sensitive species in this study. 相似文献
The construction and operation of a rainfall simulator becomes easier with decreasing plot size. We studied the effect of plot size on the erosion dynamics and whether it is preferable to decrease plot width or plot length. 22 simulated rainfalls were carried out with Veejet 80 100 simulators and on plots of considerably differing dimensions. The plot width has to cover a representative width of the field. With the common 3 m wide farm machinery, a plot width of at least 1.5 m containing one wheel track is necessary. Narrower plots are not suited for erosion experiments on agricultural land. The influence of plot length can be described with the LS factor of the USLE down to a plot length of 4.5 m and with the RUSLE for interrill plots (0.75 m). With decreasing plot size, the runoff started later (up to 20 min) and the afterflow ended earlier. This is not only a result of the plot length (r = 0.78), but mainly of the plot size (r = 0.92). The large time lag on small plots complicates the interpretation of the results. We recommend to disregard the rain erosivity during the time lag for the determination of USLE parameters. This is in accordance with the procedure of Wischmeier & Mannering (1969). Plot sizes have to be selected particularly carefully if the fate of soluble substances is to be studied. 相似文献
European Journal of Forest Research - How drought affects tree and stand growth is an old question, but is getting unprecedented relevance in view of climate change. Stress effects related to... 相似文献