Abundant and functionally diverse earthworm communities in perennials deliver ecosystem services like increasing nutrient availability by incorporating organic matter. This study aimed to analyse the decomposition of annual and perennial energy crop residues, and the subsequent nutrient release, depending on earthworm functional diversity. In a laboratory experiment, two ecological earthworm groups—anecics (detritivorous Lumbricus terrestris (L.)) and endogeics (geophagous Aporrectodea caliginosa and A. rosea)—were incubated with wilted cup plant (Silphium perfoliatum) and maize (Zea mays) litter for 4 or 8 weeks. Decomposition and consumption rates were calculated. The C, N and P in litter and casts were analysed. Mineralisation was a function of earthworm biomass and the number of individuals. Functional diversity had no beneficial effect. Decomposition was found to be highest in treatments with detritivorous earthworms, i.e., higher earthworm biomass, yet consumption and nutrient turnover in relation to earthworm biomass were higher in treatments with geophages indicating enhanced competition. N limitation became apparent in both litter treatments and was predominant with cup plant litter. N limitation and recalcitrant cell wall compounds affected consumption rates and the egestion of total C and P. While N in casts was lower than expected, P was increased. We observed that the effects manifested at different stages of decomposition of maize and cup plant, highlighting differences in temporal development of decomposition and nutrient turnover between litter types. Our results indicate that earthworms promote decomposition of recalcitrant litter and nutrient turnover, but N limitation may hamper nutrient release. Cup plant systems offer a suitable habitat for soil-dwelling organisms, but management approaches must consider the adequate input of organic matter as an energy and nutrient source to enhance ecosystem service provision.

Aims: Cup plant ( Silphium perfoliatum ) contributes to sustainable bioenergy production. However, little is known about the role of intensive litter fall and increased soil biodiversity on respiration and denitrification in its cultivation. This study aimed to assess CO ₂ , N ₂ O and N ₂ emissions of annual and perennial energy cropping systems affected by earthworms when supplied with senescent cup plant or maize litter. Methods: In a 32-day laboratory incubation, the ¹⁵ N gas flux method was applied in an N ₂ -reduced atmosphere to a repacked silt loam soil, inoculated with Lumbricus terrestris L., and amended with senescent maize and cup plant litter. During incubation, CO ₂ , N ₂ O and N ₂ emissions were measured. After incubation, NO ₃ ⁻ , NH ₄ ⁺ , total C, and total N was analysed in soil and casts. Litter removal from the soil surface and net nitrification rates were calculated. Results: Earthworms caused a fivefold increase in maize litter removal and a threefold increase regarding cup plant litter. Highest N ₂ O + N ₂ fluxes were observed in treatments with earthworms and cup plant litter, although the high CN ratio of senescent cup plant litter implied higher N immobilisation than the CN ratio of senescent maize litter. Earthworms increased CO ₂ , N ₂ O, and especially N ₂ emissions lowering the product ratio of denitrification ( N ₂ Oi ). Conclusions: Earthworm-controlled litter incorporation increased labile C from decomposition of recalcitrant litter as substrate for denitrification. Mineralisation patterns of senescent litter cannot be explained by CN ratio alone. The combination of both mechanisms affected denitrification, lead to elevated N ₂ O and N ₂ emissions and N loss from the soil.

Perennial energy cropping systems are hailed as a sustainable way of mitigating and potentially adapting to climate change. As a result of the absence of tillage, soils cropped with perennials like cup plant ( Silphium perfoliatum ) promote abundant and functionally diverse earthworm communities. Hence, ecosystem service provision because of earthworm activity and functional redundancy, for example, litter decomposition, water infiltration and nutrient turnover, is considerably enhanced in perennial cropping systems. We studied the abundance and functional role of earthworms in non‐tilled perennial systems and reduced‐tilled annual systems to assess their relationship with the respective above‐ground organic residues and their implications for the soil water dynamic. We sampled earthworms and simultaneously measured the saturated infiltration rate for two consecutive years in cup plant and maize ( Zea mays ) fields. Furthermore, we sampled above‐ground litter each trimester in both systems and analysed the total C and N content and CN ratios. Our field investigations revealed significantly higher earthworm abundance, species diversity and richness in cup plant systems likely because of the absence of tillage and the formation of a litter layer. High abundances of juveniles in both maize and cup plant systems pointed to harsh habitat conditions likely because of temperature variations, waterlogging and bulk density. The respective field litter was of minor importance as a food source in both systems because of poor quality, but may positively affect the soil water balance in cup plant systems. Earthworm populations in maize may have been supported by organic fertilizer while earthworm populations in cup plants may have additionally benefitted from the extensive root network and a higher on‐site plant diversity. Reduced tillage regimes in maize systems may have enhanced saturated infiltration rates. A direct link between earthworms and infiltration was not validated, but may not be excluded in the future, as earthworm populations may develop slowly because of adverse habitat conditions. Our results show that perennials support abundant and diverse earthworm populations and indicate the importance of functional redundancy and the diversity of food sources. The combination of both earthworm abundance and perennial cropping systems is capable of increasing on‐site ecosystem stability and supporting adaptation to climate change by increasing functional redundancy and, ultimately, providing ecosystem services. The noticeable occurrence of the latter, however, may be delayed because of the slow establishment of earthworm communities and delayed build‐up of ecosystems stability. Hence, a transitional phase is inevitable to reap the benefits of perennial energy cropping systems and must be accounted for.