Biochar addition improves edaphic conditions and favours root elongation and biomass production of Sarcocornia fruticosa growing in acidic mine wastes

Resumo

Phytomanagement consists on the manipulation of soil-plant systems tocontrol environmental trace metal fluxes. This study aimed to assess theeffects of biochar addition for the phytomanegement of salt marshespolluted by acidic mine wastes. Experimental columns (15x30 cm) werefilled with the acidic mine wastes (pH~4.7), with and without biocharapplication. Two types of biochar were used (from pruning trees -BPTand from sewage sludge -BSS-) at a dose of 6% d.w. Sarcocorniafruticosa (common halophyte species in Mediterranean salt marshes)seedlings were planted in the experimental columns, which were putinside bigger containers. During the first month the containers werefilled with tap water (water level ~5 cm above the column top -thewhole column underwater-), while during the second month half of thewater was removed from the containers (water level ~15 cm below thecolumn top -only the lower 15 cm of the columns underwater-). Thiscycle was repeated four times during one year. The pH and redoxpotential (Eh) were regularly checked and porewater samples extractedfor measuring water soluble organic carbon (WSOC) and water solublemetal concentrations (Cd, Mn, Pb and Zn). The extracted pore water wasused for the performance of germination experiments with Sarcocorniaseeds (seed germination and growth of radicle, hypocotyl andcotyledons). Plant total fresh weight and length were measured at theend of the experiment. Biochar BPT increased the soil pH to ~6.0-6.5while biochar BSS to ~5.5. The presence of vegetation did not have anyeffect on the soil pH. Both types of biochar decreased the Eh values,which was attributable to the estimulation of the soil microbial activitydue to the input of WSOC. Higher pH induced by biochar applicationled to decreasing porewater metal concentrations, regardless of thepresence of vegetation. Both biochars had similar effect on Cd and Pbporewater concentrations, while biochar BPT was more efficientdecreasing Zn and Mn concentrations. Seed germination was notaffected by the different treatments assayed. However, in the absence ofbiochar there was not development of the radicle, hypocotyl andcotyledons in the germinated seeds. Plants grown in the treatmentswithout biochar were the smallest (less fresh weight and shorter). In theamended treatments, plants grown with biochar BSS showed the greatestfresh weigth, althought there were no differences in total lengthcompared to the biochar BPT treatments.