The effect of high CO2 and low O-2 concentrations in simulated landfill gas on the growth and nodule activity of Leucaena leucocephala

When roots of Leucaena leucocephala seedlings (White Popinac, a tropical legume tree belongs to the Family Mimosaceae) were fumigated with simulated landfill gas (CO2 above 10% and O-2 from 10% to atmospheric level), the stem elongation rate and stomatal conductance were inhibited at the absence of any apparent leaf water deficit. When compared with a treatment where root system was flooded, the effect of gas fumigation on the shoot physiology was relatively mild and appeared later. On the other hand, nodule activity (measured as rate of acetylene reduction activity, ARA) was much more severely inhibited by gas fumigation. Although nodule dry weight and carbohydrate storage in nodules were reduced, the inhibition was not likely a result of the shortage of carbohydrate reserve in the nodules. This was because the ARA of untreated fresh nodules was also inhibited immediately following exposure to the simulated landfill gas. In further experiments where CO2 and O-2 were manipulated separately, although a reduction of O-2 concentration to half of the atmospheric level might account for up to 30% loss of ARA with considerable variation, the high CO2 alone showed a much more severe inhibition. This CO2-induced inhibition was not reversible one hour after the high CO2 gas was removed. There was some recovery of activity 5 day after plants were fumigated, suggesting that the legume plant can maintain some nitrogen-fixation activity under the influence of landfill gas.