A simple urea leaf-feeding method for the production of 13C and 15N labelled plant material

The use of C-13 isotope tracer techniques in terrestrial ecology has been restricted by the technical requirements and high costs associated with the production of (1)3C enriched plant material by (CO2)-C-13 release in labelling chambers. We describe a novel, simple and relatively inexpensive method for the small-scale production of (1)3C and N-15 labelled plant material. The method is based on foliar feeding of plants with a urea solution (97 atom% C-13, 2 atom% N-15) by daily misting. Maize was grown in a greenhouse in a compost-soil mixture and enclosed in clear polythene bags between urea applications. Final enrichment in 27 d old maize shoots was 211 parts per thousand delta C-13 (approximate to1.34 atom% C-13) and 434 parts per thousand delta N-15 (approximate to0.52 atom% N-15). Enrichments of hot-water extractable fractions (289 parts per thousand delta C-13, 469 parts per thousand delta N-15) were only slightly higher than those observed in plant bulk material, which suggests that daily urea applications ensured fairly uniform labelling of different biochemical fractions and plant tissues. Recovery of applied excess C-13 and N-15 in plant shoots was 22% and 42%, respectively. Roots were less enriched (21 parts per thousand delta C-13 and 277 parts per thousand delta N-15), but no attempts were made to recover roots quantitatively.