A problem in the ecological restoration of closed landfills is the producti
on of potentially toxic gases by decomposition of refuse that affects the r
oot system and physiology of plants growing on these sites. The aim of the
present study was to assess the effects induced by landfill biogas contamin
ation on gas-exchanges of soybean [Glycine mnu (L,) Merr.]. Simulated landf
ill and control gases were supplied to soybean plants under laboratory cond
itions for 10 d. The composition of the simulated landfill gas used was: 16
% O-2, 8% CO2, 3% CH4, and 73% N-2; a control gas was also tested (21% O-2,
0.035% CO2, and 78% N-2). Photosynthesis and stomatal conductance were sig
nificantly affected by the gas treatment after 3 d; in the course of the ex
periment, biogas treatment progressively reduced A(max) in light-saturation
curves. The fresh and dry weight, leaf area and leaf chlorophyll content w
ere not affected by the treatment. A metabolic adaptation to the biogas in
the roots of treated plants was related to the disappearance of a fraction
of the protein pool.