Modulation of Urochloa brizantha development when phytoremediating lead-contaminated tropical soils: a photosynthetic approach

The accumulation of heavy metals (HMs) in soils is a serious risk to the environment. Lead (Pb) has been a risk to human health and natural resources since the Industrial Revolution. The use of grasses for phytoremediation of HMs is a viable and promising alternative. We evaluated the tolerance of Urochloa brizantha in simulated phytoremediation of Pb in samples of two tropical soils: a clayey Oxisol and a sandy Entisol. To verify how the grass overcomes the stress generated by exposure to Pb, the levels of photosynthetic pigments and chlorophyll a fluorescence were quantified, as well as carbon fixation by CO ₂ assimilation variables and carbo-protein compounds of primary metabolism. The readily available Pb content was higher in Entisol. Oxisol, due to its high Pb adsorption, had less effect on grasses at low Pb concentrations. Only the highest Pb concentration affected photochemistry and C fixation. Biomass was reduced only at higher concentrations, suggesting tolerance at low and medium doses when overall plant development was assessed. In terms of CO ₂ assimilation variables, U. brizantha modulated the photosynthetic apparatus to maintain development and effective biomass accumulation even at high and very high Pb concentrations.