Chemical and biochemical changes in the rhizospheres of wheat and canola

Short-term root processes can influence chemical and biochemical conditions at the soil-plant-root interface. In this study, soil phosphorus forms, pH and biochemical properties within and adjacent to the rhizosphere of hard red spring wheat (Triticum aestivum L. 'Katepwa') and canola (Brassica napus L. 'Westar') seedlings were studied over a 5-wk period. Soils were from the Ap horizon of a Calcareous Dark: Brown Chernozemic soil (Lethbridge, Alta) and an Orthic Gray Luvisolic soil (Breton, Alta) obtained from fertilized and unfertilized long-term continuous-cropped and wheat-fallow rotation plots. Wheat and canola both absorbed more total phosphorus (P), produced more aboveground material and had higher dehydrogenase and alkaline phosphatase activities when grown in Lethbridge soils than when grown in Breton soils. Canola took up more P from both the resin-extractable inorganic P (resin-Pi) and hydrochloric acid extractable (HCl-Pi) fractions than wheat, indicating a greater ability to extract P from soil. Acid phosphatase levels increased over time in the rhizospheres of both wheat and canola. Dehydrogenase activity was greater in the rhizospheres of wheat than of canola, indicating greater microbial activity. Canola roots frequently lowered pH within their rhizosphere which apparently suppressed microbial activity. Dehydrogenase activity in the relatively acidic Luvisolic soils was lower than in the near-neutral Chemozemic soils. The plant-root chemical and biochemical changes in the rhizosphere varied depending on soil chemical characteristics and past soil management history. Results showed canola and wheat utilize different mechanisms to influence their root rhizospheres and obtain their nutritional requirements. Rhizosphere changes were a function of plant species, soil type and previous soil management history.