A validated analytical procedure for boron isotope analysis in plants by MC-ICP-MS.

Boron (B) is an essential micronutrient for plant growth. Lack of valid methods for pretreatment and measurement of δ11 B in plant restrict applications of it in the biosphere. Dry ashing, one step cation exchange and micro-sublimation were combined to separate and purify boron (B) in plant tissues. The low procedure blank, high B recovery and the accurate δ11 B values of the plant reference materials demonstrate that this method is suitable and valid for B pretreatment and δ11 B measurement in plant samples by MC-ICP-MS. Based on this method, the δ11 B in different plants (Brassica napus, Chenopodium album L, moss, lichen, and Nostoc commune) was analyzed. For Brassica napus, δ11 B increased gradually from root to leaf, and then decreased to rapeseed. For the same parts, the δ11 B increased from the lower parts to the higher parts. This variation may be due to the B(OH)3 transporter of NIP6;1 and the incorporation of B into the cell. The reason for lower δ11 B values in shell and rapeseed compared to those in leaves presumably is to the preferred transport of borate in the phloem. The largest δ11 B fractionation between leaf and root in Brassica napus and Chenopodium album L was + 24.2‰ and + 26.6‰, respectively. The large variation and fractionation of δ11 B within plants indicates that δ11 B is a good tracer to study the B translocation mechanisms and metabolism within plants. The δ11 B in Nostoc commune, lichen, and moss showed variations of -4.1‰ to + 21.5‰, - 9.4‰ to + 7.3‰, and - 18.3‰ to + 11. 9‰, respectively. In the same site, δ11 B in different plants ranked Nostoc commune>moss>lichen and δ11 B in mosses growing in different environment ranked soil>tree>rock. Rain and soil available B are the main B sources for these plants. The δ11 B in Nostoc commune, lichen, and moss may be a useful tracer to study the atmospheric B input. In the future, plants culture experiments under certain environments and studies from molecular level are necessary to decipher the variation of δ11 B and fractionation mechanisms within plants.