The most important problem in the restoration of closed landfills is the production of toxic gases by decomposition of refuse. Such gases affect the root system of plants growing on these sites. The aim of the present study was to assess the effects induced by landfill biogas contamination on germination and initial root growth of Vicia villosa (hairy vetch), Lotus corniculatus (birdsfoot trefoil), Trifolium pratense (red clover), and Trifolium repens (white clover). In laboratory conditions, simulated landfill and control gas were supplied to the seedlings. The composition of the simulated landfill gas used was: 16% O2, 8% CO2, 3% CH4, and 73% N2; a control gas was also tested (21% O2, 0. 035% CO2, and 78% N2). Percentage of germinated seeds was determined after 6 and 12 days from the starting date; at the same time qualitative assays of metabolic root functionality were also performed by using an agar technique in order to visualize changes in rhizosphere pH. At the end of the experiment, the length of the primary and secondary root was measured. Germination after 6 days was affected by the gas treatment; the landfill biogas caused a delay in germination with respect to the control in seeds of V. villosa and L. corniculatus. Root fresh weight and dry weight were significantly decreased by biogas treatment in V. villosa and T. repens. In contrast, root dry weight was higher in gas treated L. corniculatus and T. pratense compared to control seedlings. Total root system was significantly higher in treated T. pratense. The qualitative assay suggests, with the exception of T. pratense, a metabolic adjustment of the treated seedlings.

Key words: restoration, landfill biogas, legumes.