FTIR-Spectroscopy for Root Discrimination in Multi-Species Mixtures

Various methods can be used to study species-specific rooting patterns in multi-species mixtures. Fourier Transform Infrared (FTIR) spectroscopy in combination with attenuated total reflection (ATR) was successfully applied to discriminate roots of different species and in some cases, cultivar separation was possible.

Dry rootlets, ground roots and even fresh rootlets are suitable to record absorbance by FTIR spectroscopy. Thus, minimal preparation of root material is necessary and only few roots or single rootlets are required.

We recorded FTIR absorbance spectra of roots of the following crop species: pea, faba bean, oat, wheat, barley, maize, sugar beet, oilseed rape, the following grassland species: white clover, ryegrass, chicory, and the following weed species: barnyard grass, black grass, common lambsquarters, wild oat, loose silky bentgrass, hedge mustard.

FTIR absorbance spectra of roots of different crop, grassland and weed species revealed a species-specific peak distribution. On that basis, species discrimination of roots was possible by FTIR spectroscopy. Root spectra could be discriminated by cluster analysis and root spectra heterogeneity reflected the degree of kinship between species. Quantification models including two or three species could estimate species proportion in mixtures showing low standard errors of prediction and high residual predictive deviation values. Single rootlet identification by FTIR spectroscopy on a soil profile wall enabled a detailed analysis of root distribution in a legume-cereal intercropping.

A separation of dry rootlets and ground roots was possible with all tested species. Using fresh roots, species discrimination was possible with far related species (e.g. pea and oat), but closely related species could not be separated. We conclude that FTIR spectroscopy offers successful species discrimination of crop, grassland and weed roots in multi-species mixtures using dry rootlets or ground roots.