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Research article - Peer-reviewed, 2024

Soil moisture and fertility drive earthworm diversity in north temperate semi-natural grasslands

Torppa, Kaisa A.; Castano, Carles; Glimskar, Anders; Skanes, Helle; Klinth, Marten; Roslin, Tomas; Taylor, Astrid R.; Viketoft, Maria; Clemmensen, Karina E.; Maaroufi, Nadia I.

Abstract

Intensive management of arable land reduces earthworm density and diversity. This may impair earthwormmediated soil functions, such as nutrient mineralization and soil structure formation. To sustain earthworm source populations for re-colonization of cultivated soils, it is therefore important to preserve habitats with high earthworm diversity. Semi-natural grasslands, with a long continuity without soil disturbance, could serve as such earthworm diversity reservoirs. This is particularly important in mixed agricultural landscapes with elements of multiple land uses. Nonetheless, earthworm density and diversity vary greatly among grasslands. To preserve and optimally manage the most suitable grasslands, knowledge about which grassland characteristics best explain earthworm diversity is needed. Additionally, we have a limited picture of earthworm diversity in general, because previous studies have neglected juvenile earthworms and cryptic species. The juvenile fraction commonly comprises the main part of earthworm samples, whereas morphologically inseparable cryptic species account for an unknown fraction. This fraction is of particular importance, as juveniles reflect the local reproductive and regeneration potential of earthworm populations and communities. To determine the full species composition of earthworm communities, we sampled earthworms from 28 semi-natural grasslands in southcentral Sweden and identified them to species by DNA barcoding. To test how grassland characteristics explain earthworm density, diversity, and community composition, we measured several characteristics of soils, vegetation, and management of the grasslands, and descriptors of the surrounding landscape. DNA barcoding revealed nearly twice as many species as were identified morphologically. Earthworm densities were higher in grasslands with higher Ellenberg moisture indicator values and lower soil C:N ratios. The diversity and occurrence of many earthworm species was also higher in grasslands with higher soil moisture indicator values and lower C:N ratios, and further increased with habitat heterogeneity. Certain species occurred more likely in grasslands with higher grazing intensity. Epigeic earthworms, which live in and feed on surface litter, were more common in grasslands with higher moisture indicator values and SOM content. Thus, dry and relatively unproductive semi-natural grasslands, which are common in Sweden, are unlikely to sustain high earthworm diversity - a pattern contrasting to previously reported plant diversity responses. Instead, earthworm diversity seems concentrated to more productive grazed grasslands, with large within-grassland heterogeneity. Therefore, we highlight the importance of considering soil animals in conservation policies for semi-natural grasslands.

Keywords

Lumbricidae; Pasture; Land-use change; Soil biodiversity; Soil conservation

Published in

Agriculture, Ecosystems and Environment
2024, Volume: 362, article number: 108836