The use of higher plants to remediate contaminated land is known as phytoremediation, a term coined 15 years ago. Among green technologies addressed to metal pollution, phytoextraction has received increasing attention starting from the discovery of hyperaccumulator plants, which are able to concentrate high levels of specific metals in the above-ground harvestable biomass. The small shoot and root growth of these plants and the absence of their commercially available seeds have stimulated study on biomass species, including herbaceous field crops. We review here the results of a bibliographical survey from 1995 to 2009 in CAB abstracts on phytoremediation and heavy metals for crop species, citations of which have greatly increased, especially after 2001. Apart from the most frequently cited Brassica juncea ( L.) Czern., which is often referred to as an hyperaccumulator of various metals, studies mainly focus on Helianthus annuus L., Zea mays L. and Brassica napus L., the last also having the greatest annual increase in number of citations. Field crops may compensate their low metal concentration by a greater biomass yield, but available data from in situ experiments are currently very few. The use of amendments or chelators is often tested in the field to improve metal recovery, allowing above-normal concentrations to be reached. Values for Zn exceeding 1,000 mg kg(-1) are found in Brassica spp., Phaseolus vulgaris L. and Zea mays, and Cu higher than 500 mg kg(-1) in Zea mays, Phaseolus vulgaris and Sorghum bicolor (L.) Moench. Lead greater than 1,000 mg kg(-1) is measured in Festuca spp. and various Fabaceae. Arsenic has values higher than 200 mg kg(-1) in sorghum and soybean, whereas Cd concentrations are generally lower than 50 mg kg(-1). Assisted phytoextraction is currently facilitated by the availability of low-toxic and highly degradable chelators, such as EDDS and nitrilotriacetate. Currently, several experimental attempts are being made to improve plant growth and metal uptake, and results are being achieved from the application of organic acids, auxins, humic acids and mycorrhization. The phytoremediation efficiency of field crops is rarely high, but their greater growth potential compared with hyperaccumulators should be considered positively, in that they can establish a dense green canopy in polluted soil, improving the landscape and reducing the mobility of pollutants through water, wind erosion and water percolation

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In recent years, minirhizotrons have received increasing interest in field studies for characterising several biological processes, such as fine root production, root longevity, mycorrhization and parasitism, as collecting repeated video or digital images allows the fate of individual roots to be followed in time.This review summarises recent technical improvements in root observation and imaging, comparing results from various construction materials and installation angles. Both glass and transparent acrylic or polycarbonate tubes have shown a relatively low influence on root behaviour; tilted tubes are preferred to vertically oriented ones, in order to avoid artefacts, and to horizontal ones, which involve considerable soil disturbance during positioning in their surroundings in the open field. Precise camera positioning systems and new high-resolution (600 DPI and more) digital sensors are currently replacing external-tracked tubes and analog sensors, enhancing image capturing and quality. This allows for frequent root observation throughout the plant cycle and seasons, required for accurate estimation of root dynamics.Although manual and semi-automatic image analysis requires timing and tedious work, in the last few years minirhizotron systems have been increasingly used, thanks to fundamental advances in image analysis. The development of new algorithms for root detection and measurement in minirhizotron images has speeded up processing and research. The most interesting results in image analysis derive from the integration of luminance intensity-and geometry-based root vs. non-root classifiers. Discrepancies still remain between minirhizotron data and

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