Changes in diversity, protein content, and amino acid composition of earthworms from a paddy soil under different long-term fertilizations in the Tai Lake Region, China

Abstract

Abstract Influence of the agricultural management practices on soil quality and the ecosystem functioning has been an increasing concern in soil science and ecology with sustainable agriculture. This study deals with the changes of soil earthworm communityfrom a paddy soil under different long-term fertilizations. The soil earthworms were collected and counted from different fertilizer treated plots in the field after the rape harvest in May 2004, and their taxonomic groups were determined under a binocular stereoscope at the laboratory. The body of the earthworm ( Metaphire californica) was crushed by a cell crusher to collect protein, and the protein molecules with different sizes were analyzed by electrophoresis. Furthermore, the Metaphire californica collected was hydrolyzed and the aliquots were subject to an amino acid auto-analyzer. The results showed that totally seven species of earthworms were recognized in the paddy field with the number varying with different fertilization treatments. The structure of earthworm communities was dramatically affected by the fertilization practice. Under chemical fertilization only, both the number of earthworm species and the quantity of individuals were significantly smaller than those under other treatments, or even than those under no fertilization. Furthermore, there was an obvious decrease in the total amino acid and the contents of most individual amino acids of Metaphire californica under chemical fertilization only, compared with those under the combined fertilization of chemical and organic fertilizers. Although chemical fertilizers in combination with rice straw return increased earthworm amino acid content, long-term pig manure application tended to increase earthworm protein content. As a molecular footprint, long-term chemical fertilization caused a reduction in the content of protein with MW less than 25 kd, but a significant increase in that of protein with molecule size around 33 kd. Our study demonstrated that different fertilizations affected not only earthworm population but also diversity and richness in the paddy soil after 16 years of treatment, and that long-term chemical fertilization may impact the soil animal community and, thus, influence the paddy ecosystem functioning for yield stability. This study implicated that not only the community structure but also the amino acid metabolism for life functioning of earthworms in cropland soils may pose significant responses to the agricultural management practices.