Twenty years after the Chernobyl accident, root uptake from the surface layers of contaminated forest soils plays a major role in radiocaesium ((137)Cs) transfer to the trees and accumulation in perennial compartments, including stemwood. Trustworthy long-term predictions (modelling) of stemwood contamination with (137)Cs should accordingly be based on a reliable picture of this source-sink relationship. Considering the complexity of the processes involved in (137)Cs cycling in forest stands, elementary ratios like transfer factors (TF) were shown to be not very relevant for that purpose. At the tree level, alternatives like the wood immobilisation potential (WIP) have therefore been proposed in order to quantify the current net (137)Cs accumulation in stemwood. Our objective was here to compare WIP values determined for a series of contaminated forest stands in Belarus with the corresponding pools of (137)Cs available in the soil for root uptake. The comparison reveals that both indices are quite proportional, whatever the forest ecosystem features. This corroborates the relevancy of WIP as an indicator of the current (137)Cs root uptake by the trees, which could accordingly help to improve the existing models of (137)Cs cycling and the long-term management of contaminated forest ecosystems. 相似文献
Rhizospheres can promote self-transmissible plasmid transfer, however, the corresponding mechanism has not received much attention. Plant-microbe remediation is an effective way to promote pollutant biodegradation; however, some pollutants, such as naphthalene, are harmful to plants and result in inefficient plant-microbe remediation. In this study, transfer of a TOL-like plasmid, a self-transmissible plasmid loaded with genetic determinants for pollutant degradation, among different bacteria was examined in bulk and rhizosphere soils as well as addition of maize root exudate and its artificial root exudate (ARE). The results showed that the numbers of transconjugants and recipients as well as bacterial metabolic activities, such as xylE mRNA expression levels and catechol 2,3-dioxygenase (C23O) activities of bacteria, remained high in rhizosphere soils, when compared with bulk soils. The number of transconjugants and bacterial metabolic activities increased with the increasing exudate and ARE concentrations, whereas the populations of donor and recipient bacteria were substantially unaltered at all concentrations. All the experiments consistently showed that a certain number of bacteria is required for self-transmissible plasmid transfer, and that the increased plasmid transfer might predominantly be owing to bacterial metabolic activity stimulated by root exudates and ARE. Furthermore, ARE addition increased naphthalene degradation by transconjugants in both culture medium and soil. Thus, the combined action of a wide variety of components in ARE might contribute to the increased plasmid transfer and naphthalene degradation. These findings suggest that ARE could be an effectively alternative for plant-microbe remediation of pollutants in environments where plants cannot survive. 相似文献
The residues from the extraction of lead/zinc (Pb/Zn) ores of most Pb/Zn mines are permanently stored in tailings ponds, which require revegetation to reduce their environmental impact. This can only be done if the main constraints on plant establishment are evaluated. This can readily be done by field and greenhouse studies.
To test this, the properties of different tailings from Lechang Pb/Zn mine located at the north of Guangdong Province in southern China have been studied. Physical and chemical properties including concentrations of metals (Pb, Zn, Cd and Cu) in the tailings and soils collected from different sites have been measured. The results showed that tailings contain low nitrogen (0.016–0.075%), low-organic matter (0.58–1.78%), high salt (3.55–13.85 dS/m), and high total and diethylene–tetramine–pentaacetic acid (DTPA)-extractable metal concentrations (total: 1019–1642 μg g−1 Pb, 3078–6773 μg g−1 Zn, 8–23 μg g−1 Cd, and 85–192 μg g−1 Cu; DTPA-extractable: 59–178 μg g−1 Pb, 21–200 μg g−1 Zn, 0.30–1.5 μg g−1 Cd, and 4.3–12 μg g−1 Cu). Aqueous extracts of tailings/soils (10%, 20% and 30%, w/v) from different sites were prepared for testing their effects on seed germination and root elongation of a vegetable crop Brassica chinensis and a grass species Cynodon dactylon. It was found that root elongation provided a better evaluation of toxicity than seed germination. The ranking of toxicity using root elongation was: high-sulfur tailings>tailingdam>sparsely vegetated tailings>densely vegetated tailings>mountain soil for both plants. This order was consistent with DTPA-extractable Pb contents in the tailings and soils. B. chinensis seedlings were then grown in the mixtures of different proportions of tailings and farm soil for 4 weeks, and the results (dry weights of seedlings) were in line with the root elongation test. All these demonstrated that heavy metal toxicity, especially available Pb, low content of nutrient, and poor physical structure were major constraints on plant establishment and colonization on the Pb/Zn mine tailings. 相似文献
Soil fertility levels, climate, aboveground interaction for light in plant canopies, and belowground interactions of the root systems for nutrients and water have an important influence on the performance of cropping systems. This study aims at identifying the impact of agroforestry treatments and fertilizer application on the root development of cassava-based cropping systems. At three sites in southern Bénin, the root development of intercropped maize (Zea mays) and cassava (Manihot esculenta) vs. sole-cropped cassava was monitored in an NPK fertilizer treatment and a no-fertilizer and no-mulch treatment. The latter represented local farmers’ practice. In addition, root development of sole-cropped cassava in three agroforestry systems was recorded at the same sites consisting of: (i) annually planted Cajanus cajan, (ii) perennial alleys, and (iii) a tree block of a Gliricidia sepium, Flemingia macrophylla, Parkia biglobosa, Millettia thonningii mixture. Soil monolith sampling was used to extract roots and generate data on the morphological development of root systems and their interactions. In general, intercropping reduced cassava root length density (RLD). Fertilizer applications significantly increased (P≤0.05) the RLD of intercropped maize and intercropped cassava at all sites. Annual alleys of C. cajan developed smaller RLD and root weight densities (RWD) than the perennial tree mixture, leading to less interference with cassava. Block arrangement of the tree mixture had detrimental effects on the cassava growth in the adjacent rows, indicated by high RLD and RWD of the tree mixture. However, the overall effect on cassava yield was positive, when the crop yield is calculated on an entire field basis. 相似文献
Exogenous application of plant-growth promoting substances may potentially improve phytoremediation of metal-polluted substrates by increasing shoot and root growth. In a pot-based study, fodder radish (Raphanus sativus L. var. oleiformis Pers.) was grown in As-Zn-Cu-Co-Pb-contaminated pyrite waste, and treated with indolebutyric acid (IBA) either by foliar spraying (10 mg L−1), or by direct application of IBA to the substrate (0.1 and 1 mg kg−1) in association, or not, with foliar spraying. With the exception of foliar spraying, IBA reduced above-ground biomass, whilst direct application of IBA to the substrate surface reduced root biomass (−59%). Trace element concentrations were generally increased, but removals (mg per plant) greatly reduced with IBA application, together with greater metal leaching from the substrate. It is concluded that, in our case, IBA had a negative effect on plant growth and phytoextraction of trace elements, possibly due to unsuitable root indoleacetic acid concentration following soil IBA application, the direct chelating effect of IBA and the low microbial activity in the pyrite waste affecting its breakdown. 相似文献
In winter wheat (Triticum aestivum L.)-summer maize (Zea mays L.) rotation system in the North China Plain, maize roots do not extend beyond 1.2 m in the vertical soil profile, but wheat roots can reach up to 2.0 m. Increases in soil nitrate content at maize harvest and significant reductions after winter wheat harvest were observed in the 1.4-2.0 m depth under field conditions. The recovery of 15N isotope (calcium nitrate) from various (1.0, 1.2, 1.4, 1.6, 1.8 and 2.0 m) soil depths showed that deep-rooting winter wheat could use soil nitrate up to the 2.0 m depth. This accounted partially, for the reduced nitrate in the 1.4-2.0 m depth of the soil after harvest of wheat in the rotation system. 相似文献
In Europe more than 2,500 lysimeters operated by research institutes and industry (Lanthaler 2005). Originally lysimeters
were built for investigations of soil water and solutes, nutrient leaching and pesticide degradation (see e.g. Winton and
Weber 1996). Currently lysimeters additionally used as a tool for investigations on biological processes, and structural changes
of plants, including root distribution, and enzyme activities etc. (see e.g. Dizer et al. 2002; Schloter et al. 2005). 相似文献