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

Evaluation of switchgrass and sainfoin intercropping under 2:1 row-replacement in semiarid region, northwest China

Field experiments were carried out under natural conditions to compare the aboveground biomass, root growth and distribution, and topsoil nutrition contents of switchgrass (Panicum virgatum) and sainfoin (Onobrychis viciaefolia) grown in sole cropping and 2: 1 row-replacement intercropping in semiarid loess region on Loess Plateau of northwest China. The sole and intercropping was compared based on the aboveground biomass, water use efficiency (WUE), soil organic matter (SOM) and total nitrogen (TN), and root biomass and distribution. The aboveground biomass production was measured every year at the end of growth seasons in 2001-2005. Root biomass and vertical distribution were studied only in 2005. Topsoil SOM and TN contents were measured discontinuously during the study period. Results showed that intercropping reduced the aboveground biomass production of sainfoin significantly compared with its pure stand. The WUE of sole switchgrass was significantly the highest in each year among the three stands, while the intercropped stand was significantly higher than sole sainfoin on five-year averaged. The aggressivity of sainfoin to swichgrass decreased along with the growth years. Before 2005, the land equivalent ratio (LER) was bigger than 1.0 and actual yield loss (AYL) was positive. Under intercropping, root biomass input and root: shoot ratio in switchgrass reduced, while sainfoin inputs more photosynthate to root growth. Switchgrass had high root biomass and wide distribution vertically and horizontally indicates a higher belowground competitive ability in the mixture. It indicated a flexible distribution strategy of switchgrass tending to increase soil exploitation and space sequestration efficiency in soil layers. SOM and TN increased significantly for the three stands at the end of the fourth growth year, especially for the mixture. Switchgrass and sainfoin intercropped under 2: 1 row-replacement can be a short-term rotation tillage choice with respect to soil management in the area