Germination and initial root growth of four legumes as affected by landfill biogas atmosphere

The most important problem in the restoration of closed landfills is the pr oduction of toxic gases by decomposition of refuse. Such gases affect the r oot system of plants growing on these sites. The aim of the present study w as to assess the effects induced by landfill biogas contamination on germin ation and initial root growth of Vicia villosa (hairy vetch), Lotus cornicu latus (birdsfoot trefoil), Trifolium pratense (red clover), and Trifolium r epens (white clover). In laboratory conditions, simulated landfill and cont rol gas were supplied to the seedlings. The composition of the simulated la ndfill gas used was: 16% O-2, 8% CO2, 3% CH4, and 73% N-2; a control gas wa s also tested (21% O-2, 0. 035% CO2, and 78% N-2). Percentage of germinated seeds was determined after 6 and 12 days from the starting date; at the sa me time qualitative assays of metabolic root functionality were also perfor med 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 treatme nt; the landfill biogas caused a delay in germination with respect to the c ontrol in seeds of V. villosa and L. corniculatus. Root fresh weight and dr y weight were significantly decreased by biogas treatment in V. villosa and T. repens. In contrast, root dry weight was higher in gas treated L. corni culatus and T. pratense compared to control seedlings. Total root system wa s significantly higher in treated T. pratense. The qualitative assay sugges ts, with the exception of T. pratense, a metabolic adjustment of the treate d seedlings.