The effect of pH on boron toxicity and nutrient uptake by wheat and rapeseed

Although boron (B) is essential micronutrient, higher soil B concentrations become toxic to the plants in arid and semi-arid regions of the world. Very little is known about the pH related nutrient solubility, including transpiration-mediated B uptake by plants. The effects of high B (200 μM) and low to high pH (3.0–10.0) on B toxicity, transpiration and nutrient uptake by wheat and rapeseed were studied. Plants were grown for 5 weeks under greenhouse conditions and analyzed for elements concentrations. Regardless of high B or not, low pH favored in the higher B accumulation in roots and shoots of both plant species. However, both plant species exhibited a differential B uptake pattern in roots and shoots. Both low and high pH levels in combination with high B decreased the plant biomass, transpiration, N and Mg concentrations, whereas increased the K, Ca, S, Cu, Fe, Mn and Zn concentrations. With the increase in pH 3.0–10.0, excess B decreased the Cl concentrations in wheat and rapeseed. In conclusion, low pH and high B supply enhanced the transpiration-assisted B uptake by plants although pH alone had little effects on B concentrations. Furthermore, nutritional disorder caused by high B in conjunction with low to high pH (3.0–10.0) inhibited the plant growth and transpiration.