Seasonal and age-related changes in the stable isotope composition (15N/14N and 13C/12C) of millipedes and collembolans in a temperate forest soil

Seasonal changes in environmental conditions and biotic interactions are often ignored when using stable isotope analysis for reconstructing the trophic structure of soil communities in temperate ecosystems. In this study, we estimated seasonal and age-related changes in delta C-13 and delta N-15 values in three epigeic species of collembolans (Pogonognathellus longicornis, Orchesella flavescens and Isotoma viridis) and two litter-dwelling species of millipedes (Polydesmus denticulatus and Leptoiulus proximus) in deciduous and coniferous forest stands in central Russia. Age-related changes in delta C-13 or delta N-15 values were either absent or negligible (within 1 parts per thousand) in L proximus, but adult and subadult specimens of P. denticulatus were enriched in N-15 compared to early larval stages. Since the adults of P. denticulatus were generally more enriched in N-15 than adults of L proximus, they presumably occupy more distinct trophic niches than juveniles do. Age-related changes in isotopic composition were small or absent in collembolans studied. Neither delta C-13 nor delta N-15 values of millipedes changed significantly during the vegetation season. In contrast, consistent seasonal changes in delta C-13 and delta N-15 values were found in collembolans. Increased delta C-13 values coincided with the period of minimum soil moisture and correlated with a decreased C/N ratio in collembolan tissues. These changes can largely be attributed to the depletion of lipid-rich storage tissues. Seasonal changes in delta N-15 values were similar among collembolan species, yet slightly varied between habitats. A general trend of increasing delta N-15 values from June to September October may indicate either a reduced importance of non-vascular plants (algae and lichen) in collembolan diet or variation in the isotopic composition of these plants. Overall, our data show that seasonal variations should be taken into account when estimating the isotopic composition of epigeic collembolans in forest soils. (C) 2014 Elsevier GmbH. All rights reserved.