Effects of high chromium applications on miscanthus during the period of maximum growth

Chromium levels comprised between 50 and 200 mg L−1 Cr were toxic to miscanthus and growth was completely stopped with concentrations equal or higher than 150 mg L−1 Cr. Root growth was less affected than shoot growth, but root morphology changed drastically. Up to 100 mg L−1 Cr, total length of roots increased and their average diameter decreased, whereas the opposite occurred with higher Cr levels. The net uptake rate of nitrogen, its net translocation rate from the hypogeal to the aerial plant part, and the N content of all plant parts decreased in parallel to growth reduction. The Cr concentration of the hypogeal part was approximately 18 times higher than that of the aerial part up to 100 mg L−1 Cr, and only eight times higher with higher Cr levels. Green leaves always showed the lowest Cr concentration, but a consistent translocation of Cr to dead leaves was observed. These patterns suggest the existence of different active mechanisms restricting Cr accumulation in green leaves. The hypogeal plant part retained between 90% and 95% of the Cr accumulated by the plant. The highest Cr content of the entire plant was achieved with 100 mg L−1 Cr, but that of the aerial part was highest with 150 and 200 mg L−1 Cr. Thus, in our experiment, Cr accumulation in the aerial part of miscanthus was higher with extreme toxic levels, whereas the overall ability of this species to remove Cr from solution was higher with moderate toxicity.