Sulfur, chromium, and selenium accumulated in Chinese cabbage under direct covers.

Currently, pollution of our agricultural soils and waters is increasing and is often associated with many human health ailments. Soils contaminated with low levels of heavy metals and other trace elements are frequently used for growing vegetable crops and in such a situation, these toxic contaminants often accumulate in the edible portions of these agricultural plants and thereby enter the human food chain. In 3 consecutive years of field experiments (1994-1996), two different crop-covering treatments--T (50 microm perforated polyethylene), and T2 (17 gm(-2) non-woven polypropylene)--were used to modify the environmental conditions for the growth of Chinese cabbage 'Nagaoka 50' [Brassica rapa L. (Pekinensis group)]. Open-air plots (T(0)) were used as controls. Analytical determinations of chromium (Cr), selenium (Se), two forms of sulfur (total-S and sulfate-S), and amino acids (Isoleucine, leucine, lysine, methionine, serine, threonine, and valine) were performed utilizing plant shoots for analysis. The T1 and T2 treated plants contained concentrations of lysine, methionine, serine, and threonine higher than in T(0). Under T1, the extent of Cr and Se removal in the field was more favorable. Direct covers could be used in contaminated agricultural zones for a variety of plant species, not just for use with those plants previously reported to be efficient at bio-accumulating toxic elements because the thermal effect created by the covers favors phytoextraction processes. However, it is clear that the accumulation of these toxic substances in the plants (Cr) would deem the plant material unsuitable for human consumption and use as animal fodder.

Growth conditions, elemental accumulation and induced physiological changes in Chinese cabbage.

Soils contaminated with low levels of heavy metals and other trace elements are now frequently used for vegetable growing. In this situation, heavy metals and trace elements from these polluted soils may accumulate in the agricultural plants being grown in them and thereby enter the human food chain. The objectives of this study are to elucidate the effects of growth conditions, manipulated by the crop covers, on the phytoaccumulation of elements, and to investigate the conceivable influences of these conditions on the plant biochemistry. In three consecutive years of field experiments, open air (T(0)), and floating rowcover treatments (T(1): perforated polyethylene 50 micrometers; T(2): polypropylene 17 gm(-2)) were used to produce different environmental conditions for the growth of Chinese cabbage [Brassica rapa L. (Pekinensis group) cv. 'Nagaoka 50']. Five samplings (whole tops) were carried out from transplanting to harvest and measurements of B, Al, Ag, Si and Ca concentration as well as phenolics (orto-diphenols, total phenols and anthocyanins), pectic fractions, amino acids (histidine, phenylalanine and tyrosine) and polyphenol oxidase activity, were carried out in samples. The T(1) (perforated polyethylene sheet) gave greater B, Al, Ag and Si concentration and phytoextraction (in weight units) than the open-air control. These findings can help to develop new cost-effective techniques for phytoremediation as the application of plastic covers in the field. The build-up of heavy metals in those crops would make the product less suitable for human consumption.

Accumulation of Zn, Cd, Cu, and Pb in Chinese cabbage as influenced by climatic conditions under protected cultivation.

Accumulation of heavy metals from agricultural soils contaminated by low levels heavy metals has important implications in the understanding of heavy metal contamination in the food chain. Through field experiments (1994-1996), the influence of thermal regime under different treatments on the accumulation of zinc, cadmium, copper, and lead in Chinese cabbage [Brassica pekinensis (Lour) Rupr. cv. Nagaoka 50] grown in a Calcareous Fluvisol (Xerofluvent) in Granada (southern Spain) was examined. Two floating row covers were used: T(1) (perforated polyethylene, 50 microm thick) and T(2) (17 g m(-2) polypropylene nonwoven fleece). An uncovered cultivation (T(0)) served as control. Zn, Cd, Cu, and Pb levels in the whole tops of experimental plants were analyzed. Treatments T(1) and T(2) gave rise to differences in environmental conditions with respect to T(0). The influence of environmental factors manipulated by floating row covers (particularly under T(1)) increased total heavy metal accumulation in the above ground plant biomass with respect to the open-air crop. The total contents of Zn, Cd, Cu, and Pb were 30, 50, 90, and 40% higher in T(1), respectively, than in T(0). This technique could be used in contaminated zones for different plant species because the thermal effect favors the process of phytoextraction and thus reduces the contamination.

Root-zone temperature influences the distribution of Cu and Zn in potato-plant organs.

Root-zone temperatures (RZT) in relation to Cu and Zn uptake and tissue accumulation, and to total biomass, in potato plants (Solanum tuberosum L. var. Spunta) were studied. Using five different plastic mulches (no cover, transparent polyethylene, white polyethylene, coextruded white-black polyethylene, and black polyethylene) resulted in significantly different RZT (16, 20, 23, 27, and 30 degrees C, respectively). These RZT significantly influenced Cu and Zn content (concentrated) and the biomass in various potato organs. Root-zone temperature at 20 degrees C resulted in significantly high Cu content in leaflets, and soluble Cu content in leaflets and stems, whereas 23 and 27 degrees C resulted in significantly high Cu content in roots. However, RZT had no effect on Cu content in tubers or stems or on soluble Cu in roots or tubers. The RZT at 20 degrees C resulted in significantly high Zn and soluble Zn in stems, roots, and tubers; whereas, at 27 degrees C Zn and soluble Zn content were significantly highest in leaflets. The most biomass occurred in roots and tubers at 27 degrees C; whereas in leaves and stems, the RZT influence was highly variable. Total accumulation of both Cu forms was affected by RZT at 20 degrees C, with roots and tubers having significantly the least Cu and stems and leaflets having the most. Total accumulation of both Zn forms by RZT in potato organs was highly variable, but tubers consistently accumulated the most.

Floating row covers affect the molybdenum and nitrogen status of Chinese cabbage grown under field conditions.

In three consecutive years of field experiments, an uncovered control (T0), and floating row covers treatment (T1: perforated polyethylene, 50 µm; T2: polypropylene, 17 g m-2) were used to produce different growth conditions for Chinese cabbage [Brassica pekinensis (Lour) Rupr. cv. Nagaoka 50]. Five samplings (whole tops) were made between transplant and harvest, and measurements were made of NO3-, NH4+. organic N, and Mo concentrations, as well as nitrate reductase (NR) activity, and amino acids in the whole shoots. The microclimatic conditions in T0 resulted in plants with higher Mo accumulation, as well as the highest basal NR activity and the lowest NO3- concentrations. The thermal environment under the T1 treatment induced the highest mean temperature values and resulted in plants with the highest amino acid level, whereas the plants in the T2 treatment with its intermediate thermal conditions, had the lowest levels of Mo and the highest NO3- concentrations. The floating row covers influenced the Mo status, which in turn affected NR activity. In addition, T1-polyethylene sheet and T2fleece favoured an increase in the levels of NO3- by the limitation in the NR activity, with the consequent risk of a high NO 3- level in vegetables for human consumption.

Corrigendum to: Floating row covers affect the molybdenum and nitrogen status of Chinese cabbage grown under field conditions.

In three consecutive years of field experiments, an uncovered control (T0), and floating row covers treatment (T1: perforated polyethylene, 50 µm; T2: polypropylene, 17 g m-2) were used to produce different growth conditions for Chinese cabbage [Brassica pekinensis (Lour) Rupr. cv. Nagaoka 50]. Five samplings (whole tops) were made between transplant and harvest, and measurements were made of NO3-, NH4+. organic N, and Mo concentrations, as well as nitrate reductase (NR) activity, and amino acids in the whole shoots. The microclimatic conditions in T0 resulted in plants with higher Mo accumulation, as well as the highest basal NR activity and the lowest NO3- concentrations. The thermal environment under the T1 treatment induced the highest mean temperature values and resulted in plants with the highest amino acid level, whereas the plants in the T2 treatment with its intermediate thermal conditions, had the lowest levels of Mo and the highest NO3- concentrations. The floating row covers influenced the Mo status, which in turn affected NR activity. In addition, T1-polyethylene sheet and T2fleece favoured an increase in the levels of NO3- by the limitation in the NR activity, with the consequent risk of a high NO 3- level in vegetables for human consumption.