Objective The absorption, distribution and re-translocation of foliar boron fertilizer in poplar under different boron conditions were analyzed, in order to provide clues for the cultivation and management of poplar plantation.

Method Populus alba var. pyramidalis Bunge saplings were sand cultured in greenhouse. Different concentrations of boric acid were added to the nutrient solution, and the lower mature leaves were fed with ¹⁰B-rich boric acid (H₃¹⁰BO₃). The growth of poplar was recorded, and the boron content in different parts was determined.

Result (1) Under sand culture condition with low boron concentration, the biomass and boron accumulation of plants decreased significantly, the boron concentration in upper leaves significantly decreased, and the proportion of boron allocated to young leaves significantly decreased also. (2) Application of foliar boron fertilizer (LB + F) could supplement the boron concentration in upper leaves, and reduce the changes of biomass and boron accumulation to a certain extent. Most of boron absorbed from foliar fertilizer was retained in the fertilized leaves, while 31.68%, 5.27% and 1.06% of absorbed foliar boron can be re-translocated to young leaves, roots, and stems. (3) In relative to normal boron concentration, application of foliar boron fertilizer (NB + F) could increase boron concentration in stem, but had no significant effect on boron concentration of roots and leaves and the biomass in different parts. Compared with LB + F, NB + F plant absorbed much less boron from foliar fertilizer, which was only 15.6% of the former.

Conclusion Boron deficiency will result in a reduced boron allocation to young leaves in poplar, thus affects plant growth. The boron fertilizer absorbed by mature leaves could be re-translocated to other parts of the plant, especially the young leaves. The negative effect of rhizosphere boron deficiency on plant growth can be compensated by applying foliar boron fertilizer.