Physiological responses of two poplar species to high boron stress

Aims In recent years, international studies have found that poplar species could accumulate high boron with hypertolerance ability. Our objective was to investigate the effect of growth and physiological indicators of Populus russkii and P. bolleca under different boron concentrations, and determine the interspecific difference on boron tolerance, to help explaining and providing certain theoretical basis of phytoremediation technology for boron pollution treatment. Methods Poplar cuttings were grown in potting soil and added boron after three months. Physiological properties tested included plant height, fresh biomass, chlorophyll fluorescence parameters, chlorophyll content, activities of catalase (CAT) and guaiacol peroxidase (Gu-POD), soluble protein (SP) content and soluble carbohydrate (SC) content. Important findings Boron stress seriously inhibited the growth and affected the chlorophyll fluorescence parameters of the two poplar species. Populus russkii was more sensitive than P. bolleca to boron stress, and P. bolleca could stand higher boron level than P. russkii. The boron damage threshold (10%) of P. russkii and P. bolleca were 19 and 35 mg·kg^–1, respectively. The plant height, fresh mass and chlorophyll decreased linearly with the increase of soil boron concentrations. For antioxidant parameters analysis, the activities of CAT and Gu-POD increased at first, and then decreased with increasing concentration of applied boron. Populus bolleca kept higher chlorophyll a/b and non-photochemical quenching than P. russkii under boron stress. Soluble protein and soluble carbohydrate increased with the increasing concentration of applied boron. These results demonstrated that the two poplar species eased the boron toxicity by strengthen the metabolism of protein synthesis but the capacity of clearing up the harmful peroxide was limited, and the CAT and Gu-POD activities were inhibited under high boron concentrations.