Removal of boron from wastewater: Evaluation of seven poplar clones for B accumulation and tolerance

Boron (B) contamination of wastewater is a serious environmental and health problem, which has proved difficult to remediate. One potential approach is phytoremediation, i.e., the use of plants to extract B into the shoot systems, which can then be harvested and removed. The purpose of this study was to investigate the ability of seven hybrid poplar clones to accumulate and tolerate B at different levels of B and salinity. The clones were grown in quarter strength Hoagland's nutrient solution and exposed to four B treatments: 0.25, 25, 75 and 125 mg B L−1 in factorial combination with three salinity treatments: 0, 0.5 and 5 g L−1. Measurements were made of biomass (dry weight) and B concentrations (analyzed by inductively coupled plasma-optical emission spectroscopy) of plant tissues. The results showed that, with increasing level of B supply, the B concentrations in the shoot tissue of the poplar clones increased, while shoot biomass decreased. Comparison of the seven different poplar clones revealed that the clone designated 195-529 exhibited the greatest ability for B accumulation and tolerance. Generally, the 0.5 g L−1 level of salinity was beneficial for poplar growth and B removal, while the high salinity level of 5 g L−1 significantly inhibited poplar growth and B translocation from roots to shoots. Based on the results obtained with this hydroponic system, the clone 195-529 (P. trichocarpa × P. deltoides) is likely to be the most useful for the removal of B from B contaminated wastewater.