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

Abstract

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.