Soil and earthworm-derived enzymatic activities in soil microcosms following addition of a N- and P-enriched polysaccharide-based vs a conventional starch-based mulching film

Abstract

Bio-based mulching films are gaining increasing attention in contemporary agriculture as feasible and environmentally friendly alternatives to polyethylene films whose use causes the undesirable release of plastic debris into the environment, thus contributing to pollution and negatively affecting soil quality. Being a source of readily available C, following soil incorporation bio-based mulches can stimulate the biological activity and benefit soil fertility and health.

This work aims to evaluate short-term impacts of an innovative N- and P-enriched carboxymethylcellulose, sodium alginate and chitosan-based biodegradable mulch film on physical (aggregate stability index), chemical (pH, electrical conductivity, total organic C, total N, P-Olsen, water soluble anions) and enzymatic soil activities using soil microcosms added or not with an epigeic earthworm (Lumbricus terrestris L.) over a 30-d incubation period. Mater-Bi was used as reference. Analysis of earthworm casts, tissues, digestive enzymes and oxidative stress biomarkers was also included since earthworms can play a role both as indicators of pollution and as drivers of bio-based mulch degradation with their borrowing lifestyle and release of hydrolytic enzymes. The C/N ratio of incorporated mulches differently primed C mineralization.

Mulching films addition did not significantly alter soil enzymatic activities, whereas their combination with earthworms markedly those activities involved in nutrient-cycling. Earthworms exposed to all types of films showed oxidative stress, evidenced by increased glutathione oxidation and carboxylesterase inhibition. This work suggests that biodegradable films can replace conventional plastic films in a more environmentally sustainable way, but their environmental effects still disturb soil biological activity and earthworm activity. Moreover, this study showed that carboxylesterase could be an appropriate biomarker to study the effects of mulching films on earthworms.