Organic mulching alters ground-dwelling arthropod communities and promotes key predators in potato agroecosystems

Widespread declines in insect biomass and biodiversity have raised concerns about the sustainability of ecosystem services in agroecosystems. Ground-dwelling generalist predators such as carabids (Carabidae) and spiders (Araneae) are key contributors to natural pest control, yet their populations are threatened by modern farming practices. Organic mulching - a practice that increases within-crop habitat diversity - has been proposed as a means to support beneficial arthropod communities while also delivering agronomic benefits. This study investigated the effects of different organic mulches (triticale/vetch, straw, grass silage) on carabid and spider communities in three large-scale, replicated field trials in potato fields in central Germany. Arthropods were sampled using pitfall traps during and after the growing season, with additional traps used to assess potential sampling biases related to mulch presence. Community composition, species-specific responses, and potential carry-over effects into the following year were analysed using a combination of generalised linear mixed models, diversity indices, ordination methods, and indicator species analysis. Across the trials, 12,076 adult carabids (42 taxa) and 2,399 spiders (38 taxa) were collected, enabling robust analysis of treatment effects on community composition and species-specific responses. The results showed that organic mulching, particularly with triticale/vetch, significantly increased the abundance of several carabid (Bembidion lampros, B. quadrimaculatum, Poecilus cupreus) and Linyphiidae spider (Erigone atra, E. dentipalpis, Agyneta rurestris) species, and altered overall community composition. Species richness tended to be higher in mulched plots, though effects on diversity indices were less consistent. However, positive impacts on predator populations were largely restricted to the potato growing season, with no evidence of persistent carry-over effects into the subsequent year. The study discusses habitat complexity, microclimate moderation, and changes in prey availability as likely mechanisms underlying these patterns.