Changes in Tillering, Nutritional Status and Biomass Yield of Panicum maximum Used for Cadmium Phytoextraction

摘要

Although several grasses have been evaluated for cadmium (Cd) phytoextraction, there are few studies assessing how Cd is accumulated and distributed in the tissues of Panicum maximum grown in mildly spiked soils. The evaluation of tillering, nutritional status and biomass yield of this grass, mainly along successive shoot regrowths, is not well studied so far. Thus, P. maximum Jacq. cv. Massai was grown for two periods in an Oxisol presenting bioavailable Cd concentrations varying from 0.04 (control) to 10.91 mg kg~(-1) soil. Biomass yield of leaves and stems' growth has decreased under the highest Cd exposure, but it did not occur in the regrowth period, indicating that Cd-induced toxic-ity is stronger in the early stages of development of P. maximum. The tillering was not compromised even the basal node presenting Cd concentrations higher than 100 mg kg~(-1) DW. We identified a restriction on Cd transport upwards from basal node, which was the main localization of Cd accumulation. Apparently, P, K, Mg, S and Cu are involved in processes that restrict Cd translocation and confer high tolerance to Cd in P. maximum. The Cd-induced nutritional disorders did not negatively correlate with factors used to calculate phytoextraction efficiency. However, the nutritional adjustments of P. maximum to cope with Cd stress restricted the upward Cd transport, which decreased the phytoextraction efficiency from the available Cd concentration of 5.93 mg kg~(-1) soil.