A simple method for in situ-labelling with 15N and 13C of grassland plant species by foliar brushing

1.Labelling plants with 15N and 13C stable isotopes usually require cultivation of plants in isotopically enriched soil and gas-tight labelling chambers - both approaches are not suitable if one aims to investigate in situ species interactions in real plant communities. 2.In this greenhouse experiment, we tested a labelling method in which dual-labelled (15N, 13C) urea solution is brushed directly onto leaves of twelve temperate grassland species representing grasses, non-leguminous forbs and legumes. 3.Across all plant species, shoots (15N: 0·145; 13C: 0·090 atom percent excess, APE) and roots (15N: 0·051; 13C: 0·023 APE) were significantly enriched after five daily labelling events. Generally, isotopic enrichments were significantly higher in shoots than in roots. No clear pattern of absolute isotopic enrichment was observed between plant functional groups; however, grasses showed a more even allocation between shoots and roots than forbs and legumes. Isotopic enrichment levels after 4 weeks were lower, higher or unchanged compared to those of week one and varied between species or plant parts. 4.Considering the consistent enrichment levels and simplicity of this method, we conclude that it can be applied widely in ecological studies of above-belowground plant-plant or plant-animal interactions even in real plant communities.