Isotopic ecology of earthworms under grassland and arable cropping systems

Changes in the specific diet, habitat and soil organic matter pools assimil ated by earthworms in relation to land use changes were studied using stabl e isotope (C-13 and N-15) techniques. Samples were collected from two sites : Santiago (Northwest Spain) and North Wyke (Southwest England) both consis ting of long term grasslands and recently converted to maize plots. Earthwo rms were hand-sorted in the field at the peak of the maize growth in Spain and after harvesting at both sites. Isotopic analyses of the earthworm tiss ues showed that they were significantly affected by land use changes only a t the Spanish site, with mean delta(13)C values being significantly differe nt between treatments for A. caliginosa and A. rosea, whereas the nitrogen isotope ratios were significantly lower in the grassland plots than in the maize ones for A. trapezoides only. Additionally, at both sites, when the earthworms were grouped according to their ecological categories, delta(13)C values in the maize treatment decre ased in the order epi/anecic > endogeic > epigeic > anecic whereas delta(13 )C values in the grassland treatments and delta(15)N values in both treatme nts decreased in the order endogeic > anecic > epigeic > epi/anecic. The Spanish species showed a higher enrichment in C-13 when compared to Eng lish populations. Further information on the isotopic composition of the so ils is now needed for a better understanding of the feeding ecology of eart hworms under field conditions and different climates.