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 delta B-11 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 delta B-11 values of the plant reference materials demonstrate that this method is suitable and valid for B pretreatment and delta B-11 measurement in plant samples by MC-ICP-MS. Based on this method, the delta B-11 in different plants (Brassica napes, Chenopodium album L, moss, lichen, and Nostoc commune) was analyzed. For Brassica napus, delta B-11 increased gradually from root to leaf, and then decreased to rapeseed. For the same parts, the delta B-11 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 delta B-11 values in shell and rapeseed compared to those in leaves presumably is to the preferred transport of borate in the phloem. The largest delta B-11 fractionation between leaf and root in Brassica napus and Chenopodium album L was + 24.2 parts per thousand and + 26.6 parts per thousand, respectively. The large variation and fractionation of delta B-11 within plants indicates that 81113 is a good tracer to study the B translocation mechanisms and metabolism within plants. The delta B-11 in Nostoc commune, lichen, and moss showed variations of -4.1 parts per thousand to + 21.5 parts per thousand, - 9.4 parts per thousand to + 7.3 parts per thousand, and - 18.3 parts per thousand to + 11. 9 parts per thousand, respectively. In the same site, delta B-11 in different plants ranked Nostoc commune > moss > lichen and delta B-11 in mosses growing in different environment ranked soil > tree > rock. Rain and soil available B are the main B sources for these plants. The delta B-11 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 delta B-11 and fractionation mechanisms within plants