Abstract
Previous studies have shown that low soil water supply depresses boron (B) uptake and may induce B deficiency in crops at low soil B. The present study was conducted to assess the possibility that increases in root/shoot ratio induced by water stress might offset the negative effect of water stress on B absorption in low B soil. Oilseed rape (Brassica napus cv. Eureka) plants were subject to a factorial combination of two levels of B: +B (0.45 mg B kg- 1 air dry soil) and -B (without added B); and three levels of water supply: adequate (Wet), subsoil dry (Wet-Dry) and surface soil dry (Dry). In -B soil, the water stress treatments significantly increased root dry weights, but decreased shoot dry weights, resulting in a decrease in shoot/root ratio. By contrast, water stress had no effect on shoot/root ratios of plants in +B soil. Decreasing water supply in the soil significantly decreased B absorption per unit root mass in -B soil but not in +B soil. The increase in root/shoot ratio was unable to significantly offset the decrease in B uptake induced by dry soil conditions and water stress still strongly depressed B concentrations in young leaves.