DIFFERENTIAL TOLERANCE OF CANOLA TO ARSENIC WHEN GROWN HYDROPONICALLYOR IN SOIL

Separate studies found canola tolerant to arsenic (As) when grown in h ydroponic solutions and generally sensitive to As when grown in soil. Fourteen-day-old canola was transferred to pots containing either soil or nutrient solution and then grown for an additional 14 days in a gr owth chamber at different times for the two different media. Plants we re grown in 0.25-strength Hoagland's solution containing either 0, 0.2 7, 6.67, or 13.3 mu M As or in three soils with As added at rates of 0 , 5, and 10 mg . kg(-1). Soil-solution As concentrations were determin ed via column displacement and were the same or less (0.147 to 4.27 mu M) than the hydroponic As concentrations. Soil-solution phosphorus (P ) concentrations were determined in the same manner and averaged 9.28 mu M P compared to 500 mu M P from the hydroponic solutions. Chlorosis , wilting, and stunted growth-symptoms of As toxicity-occurred in cano la at the highest As rate in two of the three soils used. Dry-matter y ields from the third soil were low from all treatments and a lack of r esponse to As additions was probably due to injury from other soil-rel ated factors. Shoot As concentrations were generally similar from both experiments. Canola did not suffer a yield loss or exhibit As toxicit y symptoms when grown in the hydroponic solutions. Leaf P was 8,000 mg . kg(-1) in the hydroponically-grown canola and 100 mg . kg(-1) for t he soil-grown canola. These values are greater than (hydroponic) and l ower than (soil media) sufficiency levels for plants similar to canola . High solution P concentrations in the hydroponic solution may have d etoxified As by competing with As for uptake in the solution and durin g metabolism. Phosphate should be added to hydroponic solutions in As studies at levels close to normal soil P levels and added daily to rep lenish plant uptake.