Relationship between earthworm abundance, ecological diversity and soil function in pastures

Abstract

Earthworms contribute to a wide range of process that underpin soil function and ecosystem services and are an important component of a soil’s natural capital stocks. With increasing interest in soil health, it is important to better understand the type of earthworm community required to enhance soil functions. This is of particular interest in New Zealand where pasture systems are dominated by exotic earthworm species and low ecological diversity. Two separate mesocosm experiments were established to explore the interaction between earthworm abundance and ecological diversity as it influences soil functions. Experimental increases in earthworm abundance increased soil macroporosity and water infiltration, increased plant nitrogen (N) and plant growth. Although some benefits were observed at the lowest earthworm abundances, the greatest benefits were seen at the higher abundances. Earthworm ecological diversity is also critical to ensure soil functions are optimised. For example, the single species of Aporrectodea caliginosa alone was not able to improve water infiltration or pasture production. However, when this species was found in combination with Aporrectodea longa, there was positive influence on soil functions despite the abundance of A. longa itself not increasing. This study highlights the importance of including a measure of ecological diversity alongside a measure of abundance to assess soil biological health.