Switchgrass tolerance to cadmium: uptake and translocation
Recent efforts have been initiated to develop switchgrass (Panicum virgatum L.) as a bioenergy crop. Switchgrass requires input of nitrogen (N) to be productive. Alternatives to inorganic fertilizers are needed to reduce input costs and maintain a positive energy balance. Municipal sludge may be an economical source of N and other nutrients for biomass production; however, the response of switchgrass to heavy metals in the sludge is not known. Two greenhouse studies and a 2-yr field study were conducted to determine the interaction of (1) cultivar and cadmium (Cd)application, (2) soil pH and Cd application, and (3) soil moisture and Cd application on biomass accumulation and Cd allocation of switchgrass. In the first experiment, 'Alamo', 'Blackweir, 'Cave-in-Rock', and 'Trailblazer' switchgrass were grown in sand culture and were watered twice weekly with nutrient solution containing 0, 1,2, 4, 8, or 16 mg Cd L^-1. Cultivars differed (P<0.05) by less than 15% for biomass accumulation and allocation. Cadmium levels of 16 mg L' reduced biomass yields by 31% for roots, 39% for leaf blades, and 47% for shoots (culm + leaf sheath) as compared to no added Cd. At 16 mg Cd L', Cd concentration in leaf blades was 9.9 mg kg"'. The highest levels of Cd (329 mg kg^-1) were found in roots of Blackwell and Trailblazer grown at the high Cd level. In the second experiment. Alamo switchgrass was grovm in pots at five soil pH levels (4.0, 5.1, 5.8, 6.6, and 7.3) and four soil Cd levels (0, 50, 100, and 200 mg Cd kg^-1). Two hundred mg Cd kg^-1 decreased biomass accumulation of all plant components by 95%. Cadmium concentrations of 900 mg kg' were found in root tissue of plants grown in soil with 200 mg Cd L ' and a pH of 4.0. In the third experiment. Alamo switchgrass was grown in the field at three irrigation levels (0, 50, and 100%) of weekly pan evaporation) and four soil Cd levels (0, 25, 50, and 100 kg ha^-1). Biomass yield, tiller mass, and mass of tiller components were not significantly (P>0.05) affected by either irrigation or Cd level in 1995 or 1996. Concentrations of Cd in aboveground tissue ranged from 0.36 to 0.87 mg kg"'. Alamo switchgrass translocated little Cd to the aboveground portion of the plant at all Cd application levels and tolerated 100 kg ha^-1 of applied Cd. However, in different environments and management systems, Cd concentrations in aboveground tissue may increase to levels above suggested maximum tolerance levels. Producers should maintain soil pH near neutral to minimize Cd accumulation by switchgrass.
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