Substantial nutritional contribution of bacterial amino acids to earthworms and enchytraeids: A case study from organic grasslands

摘要

Many aspects of the feeding ecology of terrestrial oligochaetes are poorly understood despite the essential role of these soil and detritus feeders for maintaining soil fertility. To investigate dietary contributions of various soil components to two ecological groups of worms, anecic and endogeic species, we employed delta C-13 fingerprinting of essential amino acids (EAA) for distinguishing between bacterial, fungal, and plant derived food sources. We collected earthworms and enchytraeids from organic grasslands with grass, clover, and mixtures of these two plants. Our results showed that the worms either relied on plants or bacteria as their primary EM source, but not on fungi, and that EM targets were unaffected by crop type. Two anecic species received 60-75% of their EAA from plant sources with bacterial contributions ranging from 18 to 23%. In contrast, both enchytraeids and an endogeic worms relied equally on bacterial and plant derived EAA. Our study provides answers to some of the long-standing questions in regards to the role of bacteria for earthworm nutrition. While bacterial EM contribution to anecic worms was relatively modest, less than one-quarter, bacterial contribution to endogeic and enchytraeid worms was substantial comprising almost half of their EM. Our findings are important for understanding how different ecological groups of terrestrial oligochaetes meet nutritional needs and partition food resources. (C) 2016 Elsevier Ltd. All rights reserved.