Earthworm Inoculation Improves Upland Rice Crop Yield and Other Agrosystem Services in Madagascar

The effects of earthworm inoculation and cropping systems on upland rice systems were examined over a four-year period in the Highlands of Madagascar. Each year, endogeic earthworms Pontoscolex corethrurus (Rhinodrilidae) were inoculated (EW+) at a density of 75 ind m−2 or were not inoculated (EW0). Inoculation was tested in three cropping systems: conservation agriculture (CA) and traditional tillage with or without residues restitution. Soil and plant properties were measured during the first three years while soil biological properties were assessed at the fourth year. At the end of the experiment, earthworm density was three-fold higher in EW+ than in EW0, demonstrating the success of the inoculation. Earthworm density was more important in CA than in tillage systems. Earthworm inoculation had higher significant effects on soil and plant properties than cropping systems. Earthworm inoculation had positive effects on soil macroaggregation (+43%), aboveground biomass (+27%), rice grain yield (+45%), and N grain amount (+43%). Intensifying earthworm activity in field conditions to meet the challenge of ecological transition is supported by our study.

Bioturbation by endogeic earthworms facilitates entomopathogenic nematode movement toward herbivore-damaged maize roots

Entomopathogenic nematodes (EPNs) have been extensively studied as potential biological control agents against root-feeding crop pests. Maize roots under rootworm attack have been shown to release volatile organic compounds, such as (E)-β-caryophyllene (Eβc) that guide EPNs toward the damaging larvae. As yet, it is unknown how belowground ecosystems engineers, such as earthworms, affect the biological control capacity of EPNs by altering the root Eβc-mediated tritrophic interactions. We here asked whether and how, the presence of endogeic earthworms affects the ability of EPNs to find root-feeding larvae of the beetle Diabrotica balteata. First, we performed a field mesocosm experiment with two diverse cropping systems, and revealed that the presence of earthworms increased the EPN infection potential of larvae near maize roots. Subsequently, using climate-controlled, olfactometer-based bioassays, we confirmed that EPNs response to Eβc alone (released from dispensers) was two-fold higher in earthworm-worked soil than in earthworm-free soil. Together our results indicate that endogeic earthworms, through burrowing and casting activities, not only change soil properties in a way that improves soil fertility but may also enhance the biocontrol potential of EPNs against root feeding pests. For an ecologically-sound pest reduction in crop fields, we advocate agricultural practices that favour earthworm community structure and diversity.

Integrative taxonomy of five astome ciliates (Ciliophora, Astomatia) isolated from earthworms in Central Europe

Four earthworm species, the endogeic Octolasion tyrtaeum (Savigny, 1826), the anecic Lumbricus terrestris Linnaeus, 1758 as well as the epigeic Eisenia fetida (Savigny, 1826) and Dendrobaena veneta (Rosa, 1886), were examined for the presence of astome ciliates. Based on the integrative taxonomic approach, five ciliate species were recognized in their gastrointestinal tracts: Metaradiophrya lumbrici (Dujardin, 1841), M. varians (de Puytorac, 1954), Anoplophrya lumbrici (Schrank, 1803), A. vulgaris de Puytorac, 1954 and A. nodulata (Dujardin, 1841). Their distinctness was assessed using the multivariate morphometric approach and molecular phylogenetic analyses. Although the two species of Metaradiophrya Jankowski, 2007 on the one hand and the two former species of Anoplophrya Stein, 1860 on the other, were not distinctly separated by the multivariate morphometric analyses, they were clearly delimited by the 18S rRNA gene sequences. Species within each genus also differed by their hosts, M. lumbrici and A. lumbrici occurred only in anecic earthworms while M. varians and A. vulgaris occured exclusively in epigeic earthworms. Only a single species, A. nodulata, was detected in endogeic earthworms. It was morphologically distinct from and did not cluster with the two other species of Anoplophrya but was nested within the paraphyletic assemblage containing other astomes from endogeic earthworms. This indicates that the evolution of endosymbiotic ciliates from earthworms has very likely proceeded through a specialization to various ecological groups of their host organisms.

A core microbiota of the plant-earthworm interaction conserved across soils

Microorganisms participate in most crucial soil functions and services benefiting human activities, such as biogeochemical cycles, bioremediation and food production. Their activity happens essentially in hotspots created by major soil macroorganisms, like rhizosphere and cast shaped by plants and earthworms respectively1. While effects of individual macroorganism on soil microbes are documented, no studies attempted to decipher how the mosaic of microhabitats built by multiple macroorganisms and their interaction determine the structure of microbial communities. Here we show a joint shaping of soil bacterial communities by these two macroorganisms, with a prevalent role of plants over earthworms. In a controlled microcosm experiment with three contrasted soils and meticulous microhabitat sampling, we found that the simultaneous presence of barley and endogeic earthworms resulted in non-additive effects on cast and rhizosphere bacterial communities. Using a source-sink approach derived from the meta-community theory2,3, we found specific cast and rhizospherecore microbiota4,5of the plant-eartworm interaction, detected in all soils only when both macroorganisms are present. We also evidenced acore networkof the plant-earthworm interaction, with cosmopolitan OTUs correlated both in cast and rhizosphere of all soils. Our study provides a new framework to explore aboveground-belowground interactions through the prism of microbial communities. This multiple-macroorganisms shaping of bacterial communities also affects fungi and archaea, while being strongly influenced by soil type. Further functional investigations are needed to understand how thesecore microbiotaandcore networkcontribute to the modulation of plant adaptive response to local abiotic and biotic conditions.

Improving Complementarity Effect of Legume Intercrop by Earthworm Facilitation for Wheat Performance

Intercrops and crop mixtures are considered to be a way to increase nitrogen use efficiency by promoting niche complementarity and facilitation, reducing the input of fertilizers and herbicides, which are important factors when considering the effects of climate change. However, interactions between crop communities and soil functional diversity also have major effects on crop cover function. Our study aimed to investigate the simultaneous effects of plant composition and presence of earthworms on the growth (roots and shoots) of wheat (Triticum aestivum L.). Mesocosms filled with soil were sown with either 6 wheat plants of the same cultivar, or 6 plants of 3 different wheat cultivars, or 3 wheat plants of 3 different cultivars with 3 clover plants (Trifolium hybridum L.). A part of the mesocosms was inoculated with either endogeic earthworms (Aporrectodea caliginosa S.) or a mixture of endogeic and anecic earthworms (Lumbricus terrestris S.). A relative interaction index was calculated to highlight competition strength between plants with or without earthworms. The presence of different cultivars had no influence on wheat performance, but with clover, plant competition decreased to the benefit of wheat biomass and N accumulation. Earthworms also reduced the competitive strength between wheat plants in mixed-cultivar mesocosms and in intercropping. In intercrops with clover, wheat performance was improved as a result of niche complementarity and earthworm facilitation for N resource. Our results suggest that the plant functional group, such as legumes, and earthworm communities work synergistically to improve wheat yields.

Diversité Et Dynamique Des Communautés De Vers De Terre De Trois Formations Végétales Dans Une Savane Humide De l’Afrique De l’Ouest (Lamto, Côte d’Ivoire)

The maintenance and stability of many terrestrial ecosystems are in part related to the ecosystem functions and services of soil organisms. The present study aims to evaluate the influence of litter biomass produced by three types of vegetation in the Lamto reserve on the dynamics of earthworm community. Each vegetation formations has been subdivided into 3 parcels. These parcels were geo-referenced using a GPS and mapped using QGIS software. For each plot, 25 points were randomly selected using their GPS coordinates. The litters were collected by manual collection to evaluate their biomass. Monoliths of the TSBF (Tropical Soil Biology) type were dug in order to collect the earthworms by direct manual sorting. Also, soil clumps were collected to determine the organic matter levels by the method of lossto-fire. In total, 12 species of earthworms belonging to 3 ecological categories were collected. The forest block had the highest density of earthworms with a predominance of epigeic earthworms followed by grassy savannah with a predominance of endogeic earthworms. The wooded savannah has the lowest density of earthworms with a predominance of anecic earthworms. In terms of species richness, the grassy savannah contained the greatest number of earthworm species followed by the wooded savannah and the forest block that had the same number of species. In the three vegetations formations, it was found that earthworm densities were correlated with litter biomass as well as organic matter levels (correlation between earthworm density and litter biomass: r 2 =0, 75; correlation between density of earthworms and the rate of organic matter: r 2 =0, 93).