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51.
Italy has been used as a country for estimating genetic erosion in crops. It was possible to compare early surveys (from the
1920s to the 1950s), especially on wheats, with results of later missions in the 1980s and 1990s. In the early years, a relatively
high genetic erosion was observed (13.2% p.a.). From the 1950s until the 1980s erosion rates between 0.48 and 4% p.a. were
estimated. In the little island of Favignana there was an erosion rate of 12.2% p.a. leading to the extinction of the last
wheat landraces of this island. There have been no significant differences in erosion rates between field- and garden-crops
though there has been the impression that garden crops are better preserved over the long run. Interestingly extinction rates
of wild plants (0.13% in the Mediterranean) come close to the average erosion rates of crop plants in the area.
1Dedicated to Erna Bennett on the occasion of her 80th birthday
2Lecture presented during the XVIIth Congress of EUCARPIA in Tulln, Austria, 2004 相似文献
52.
In view of the remarkable interest of the flora, vegetation and landscape of Linosa island, a natural reserve should be suggested including protection of the traditional agriculture. Especially for the last aim completely new ways have to be elaborated. An integrated approach of nature protection and on-farm conservation could be the ideal conclusion. 相似文献
53.
New Potentilla synonyms of the Fragaria species names are discussed and considered to be dispensable. Further unnecessary nomenclatural changes based on the argument to recognize monophyletic but not paraphyletic taxa should be avoided to maintain nomenclatural stability for global communication about plant genetic resources. The new combination Fragaria×rosea (Mabb.) K. Hammer et Pistrick is presented for the hybrid Potentilla palustris (L.) Scop. ×Fragaria×ananassa Duchesne ex Rozier. 相似文献
54.
With a world‐wide occurrence on about 560 million hectares, sodic soils are characterized by the occurrence of excess sodium (Na+) to levels that can adversely affect crop growth and yield. Amelioration of such soils needs a source of calcium (Ca2+) to replace excess Na+ from the cation exchange sites. In addition, adequate levels of Ca2+ in ameliorated soils play a vital role in improving the structural and functional integrity of plant cell walls and membranes. As a low‐cost and environmentally feasible strategy, phytoremediation of sodic soils — a plant‐based amelioration — has gained increasing interest among scientists and farmers in recent years. Enhanced CO2 partial pressure (PCO2) in the root zone is considered as the principal mechanism contributing to phytoremediation of sodic soils. Aqueous CO2 produces protons (H+) and bicarbonate (HCO3‐). In a subsequent reaction, H+ reacts with native soil calcite (CaCO3) to provide Ca2+ for Na+ Ca2+ exchange at the cation exchange sites. Another source of H+ may occur in such soils if cropped with N2‐fixing plant species because plants capable of fixing N2 release H+ in the root zone. In a lysimeter experiment on a calcareous sodic soil (pHs = 7.4, electrical conductivity of soil saturated paste extract (ECe) = 3.1 dS m‐1, sodium adsorption ratio (SAR) = 28.4, exchangeable sodium percentage (ESP) = 27.6, CaCO3 = 50 g kg‐1), we investigated the phytoremediation ability of alfalfa (Medicago sativa L.). There were two cropped treatments: Alfalfa relying on N2 fixation and alfalfa receiving NH4NO3 as mineral N source, respectively. Other treatments were non‐cropped, including a control (without an amendment or crop), and soil application of gypsum or sulfuric acid. After two months of cropping, all lysimeters were leached by maintaining a water content at 130% waterholding capacity of the soil after every 24±1 h. The treatment efficiency for Na+ removal in drainage water was in the order: sulfuric acid > gypsum = N2‐fixing alfalfa > NH4NO3‐fed alfalfa > control. Both the alfalfa treatments produced statistically similar root and shoot biomass. We attribute better Na+ removal by the N2‐fixing alfalfa treatment to an additional source of H+ in the rhizosphere, which helped to dissolve additional CaCO3 and soil sodicity amelioration. 相似文献
55.
Jürgen Schultze-Motel Reinhard Fritsch Karl Hammer Peter Hanelt Joachim Kruse Helga I. Maas Harald Ohole Klaus Pistrick 《Genetic Resources and Crop Evolution》1987,35(2):421-439
Summary Important papers on taxonomy and evolution of cultivated plants published in 1985 and 1986 were compiled and briefly discussed.
Taxonomie und Evolution der Kulturpflanzen: Literaturübersicht 1985/1986
Zusammenfassung Wichtige Arbeiten über Taxonomie und Evolution der Kulturpflanzen aus den Jahren 1985 und 1986 wurden zusammengestellt und kurz kommentiert.
¶rt; : 1985–1986
¶rt; , 1985 1986 . .相似文献
56.
Mixing of different mineral soil layers by endogeic earthworms affects carbon and nitrogen mineralization 总被引:1,自引:0,他引:1
The effect of the endogeic earthworm species Octolasion tyrtaeum (Savigny) on decomposition of uniformly 14C-labelled lignin (lignocellulose) was studied in microcosms with upper mineral soil (Ah-horizon) from two forests on limestone,
representing different stages of succession, a beech- and an ash-tree-dominated forest. Microcosms with and without lower
mineral soil (Bw-horizon) were set-up; one O. tyrtaeum was added to half of them. It was hypothesised that endogeic earthworms stabilise lignin and the organic matter of the upper
mineral soil by mixing with lower mineral soil of low C content. Cumulative C mineralization was increased by earthworms and
by the addition of lower mineral soil. Effects of the lower mineral soil were more pronounced in the beech than in the ash
forest. Cumulative mineralization of lignin was strongly increased by earthworms, but only in the beech soil (+24.6%). Earthworms
predominantly colonized the upper mineral soil; mixing of the upper and lower mineral soils was low. The presence of lower
mineral soil did not reduce the rates of decomposition of organic matter and lignin; however, the earthworm-mediated increase
in mineralization was less pronounced in treatments with (+8.6%) than in those without (+14.1%) lower mineral soil. These
results indicate that the mixing of organic matter with C-unsaturated lower mineral soil by endogeic earthworms reduced microbial
decomposition of organic matter in earthworm casts. 相似文献
57.
The increase of rhizosphere pH in the course of nitrate nutrition results from H+ consumption in the external medium during uptake of NO3? in a H+ co-transport and from internal OH? production during nitrate reduction. Synthesis of organic acids for NH4+ assimilation as well as strong partial depolarization of membrane potential with NH4+ uptake are the important reasons for rhizosphere acidification during ammonium nutrition. Despite differences in proton balance depending on N form, cytoplasmic pH changes are small due to physico-chemical buffering, biochemical pH regulation, H+ inclusion in vacuoles, and H+ release into the rhizosphere. Because of the large capacity for proton excretion the plasmalemma H+ ATPase of root cells plays an essential role during ammonium nutrition. An increase of the kinetic parameter Vmax after ammonium nutrition relative to nitrate nutrition suggests that the capacity of H+ release may be adjusted to the particular requirements of ammonium nutrition. Moreover, H+ ATPase is adjusted not only quantitatively but also qualitatively. The increase of the kinetic parameter km as well as the capability of the plasmalemma vesicles in vitro to establish a steeper pH gradient favours the supposition that H+ ATPase isoforms are formed which allow H+ release into the rhizosphere under conditions of low pH or poor H+ buffering of the soil. In this respect species differences exist, e.g. between maize (efficient adaptation) and faba bean (poor adaptation). 相似文献
58.
A survey was undertaken in two valleys of the Bumthang area in Central Bhutan to study the morphological diversity, farmers’
knowledge, management practices, yield and income generation potential of the neglected Himalayan Pear (Pyrus pashia Hamilton ex D. Don). For this study a total of 148 Pyrus pashia accessions were collected and 103 households interviewed. Three quantitative and 14 qualitative traits such as colour, size,
shape and texture of fruits and tree habit were used for morphological characterization of the accessions. The results demonstrated
a high morphological diversity within the P. pashia trees. Fruit shape varied widely from globose to pyriform, fruit skin colour from light yellow and glossy to brown and dull.
The observed diversity is likely due to the fact that under farmers’ conditions trees are propagated through seedlings rather
than by grafting. None of the characters were specific and correlated with region or altitude. Distinct local cultivars with
specific characters were absent making it impossible to group the pears morphologically. Interviews revealed low numbers of
trees per farmers, lacking marketability of the fruits and farmers’ subsequent preference for improved varieties as major
obstacles for the in situ preservation of biodiversity in P. pashia in this area. 相似文献
59.
60.
Shallow soil A horizon (topsoil) caused by soil erosion and soil movement from cultivation is known to reduce soil and crop productivity. The reduction may be related to limitation of root growth. A field study was conducted to investigate the effects of topsoil thickness on distributions of root density and growth. Soybeans [Glycine max (L.) Merr.] were grown on plots of Mexico silt loam (fine, montmorillonitic, mesic Mollic Endoaqualfs) with topsoil thicknesses of 0, 12.5, 25.0, and 37.5 cm above the Bt horizons. Root density was measured 60 and 90 days after planting using a minirhizotron video‐camera system. Root density was significantly reduced as topsoil thickness decreased from 37.5 to 0 cm. Mean density and net change of the density across profile between 30 and 60 days of growth had a linear function of topsoil thickness. The reduction and lower activity induced by shallow topsoil were attributed to detrimental properties in the Bt horizons. Root distribution pattern and rooting depth were not significantly affected by topsoil thickness. The roots appeared to be accumulated on the upper layers of the Bt horizons. Roots growing in thicker topsoil were more active than roots growing without topsoil. High soil moisture content during the growing season may mitigate the detrimental effects of shallow topsoil, inhibit root penetration, and enhance root activity. 相似文献