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

The use of C-13 isotope tracer techniques in terrestrial ecology has been r estricted by the technical requirements and high costs associated with the production of (1)3C enriched plant material by (CO2)-C-13 release in labell ing 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 at om% C-13, 2 atom% N-15) by daily misting. Maize was grown in a greenhouse i n 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 t housand delta C-13 (approximate to1.34 atom% C-13) and 434 parts per thousa nd delta N-15 (approximate to0.52 atom% N-15). Enrichments of hot-water ext ractable fractions (289 parts per thousand delta C-13, 469 parts per thousa nd delta N-15) were only slightly higher than those observed in plant bulk material, which suggests that daily urea applications ensured fairly unifor m labelling of different biochemical fractions and plant tissues. Recovery of applied excess C-13 and N-15 in plant shoots was 22% and 42%, respective ly. Roots were less enriched (21 parts per thousand delta C-13 and 277 part s per thousand delta N-15), but no attempts were made to recover roots quan titatively.