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Earthworms can increase nitrous oxide ( N2O) emissions, particularly in no-tillage systems where earthworms are abundant. Here, we study the effect of residue incorporation depth on earthworm-induced N2O emissions. We hypothesized that cumulative N2O emissions decrease with residue incorporation depth, because (i) increased water filled pore space ( WFPS) in deeper soil layers leads to higher denitrification rates as well as more complete denitrification; and (ii) the longer upward diffusion path increases N2O reduction to N2. Two 84-day laboratory mesocosm experiments were conducted. First, we manually incorporated maize ( Z ea mays L.) residue at different soil depths (incorporation experiment). Second, 13C-enriched maize residue was applied to the soil surface and anecic species L umbricus terrestris ( L.) and epigeic species L umbricus rubellus ( Hoffmeister) were confined to different soil depths (earthworm experiment). Residue incorporation depth affected cumulative N2O emissions in both experiments ( P < 0.001). In the incorporation experiment, N2O emissions decreased from 4.91 mg N2O-N kg−1 soil (surface application) to 2.71 mg N2O-N kg−1 soil (40-50 cm incorporation). In the earthworm experiment, N2O emissions from L . terrestris decreased from 3.87 mg N2O-N kg−1 soil (confined to 0-10 cm) to 2.01 mg N2O-N kg−1 soil (confined to 0-30 cm). Both experimental setups resulted in dissimilar WFPS profiles that affected N2O dynamics. We also found significant differences in residue C recovery in soil organic matter between L . terrestris (28-41%) and L . rubellus (56%). We conclude that (i) N2O emissions decrease with residue incorporation depth, although this effect was complicated by dissimilar WFPS profiles; and (ii) larger residue C incorporation by L . rubellus than L . terrestris indicates that earthworm species differ in their C stabilization potential. Our findings underline the importance of studying earthworm diversity in the context of greenhouse gas emissions from agro-ecosystems. [ABSTRACT FROM AUTHOR]

Earthworms have been perceived as benevolent soil engineers since the time of Charles Darwin, but several recent syntheses link earthworm activities to higher greenhouse gas emissions, less soil biodiversity, and inferior plant defense against pests. Our study provides new field-based evidence of the multiple direct and indirect impacts of earthworms on ecosystem functions within an ecological multifunctionality framework (i.e., aggregated measures of the ability of ecosystems to simultaneously provide multiple ecosystem functions). Data from a 13-year field experiment describing 21 ecosystem functions showed that earthworm presence generally enhanced multifunctionality by indirect rather than direct effects. Specifically, earthworms enhanced multifunctionality by shifting the functional composition toward a soil community favoring the bacterial energy channel and strengthening the biotic associations of soil microbial and microfaunal communities. However, earthworm-mediated changes in soil physical structure, pH, and taxonomic diversity were not related to multifunctionality. We conclude that the coordinated actions of earthworms and their associated soil biota were responsible for the maintenance of multifunctionality at high levels in this rice-wheat cropping system. Management of crop residue inputs and reduction of soil physicochemical disturbances should encourage beneficial earthworm effects and support multiple ecosystem services that are vital to sustainable agriculture. • Earthworms enhanced multifunctionality by indirect rather than direct effects • Earthworms shifted functional composition toward bacterial-dominated community • Multifunctionality was unrelated to changes in soil biodiversity, structure, and pH Liu et al. study a 13-year-old field experiment to show that earthworms are beneficial to agroecosystems from a multifunctional perspective. This work incorporates the concerns of negative effects of earthworms in recently published syntheses and highlights the potential pathways in which earthworms contribute to sustainable agriculture. [ABSTRACT FROM AUTHOR]