Michel Bertrand

Earthworm services for cropping systems. A review

Intensive agriculture is often criticized for negative impacts on environment and human health. This issue may be solved by a better management of organisms living in crop fields. Here, we review the benefits of earthworms for crops, and we present techniques to increase earthworm abundance. The major points are the following: (1) Earthworms usually improve soil structural stability and soil porosity and reduce runoff. (2) Earthworms modify soil organic matter (SOM) and nutrient cycling. Specifically, earthworms stabilize SOM fractions within their casts, and they also increase the mineralization of organic matter in the short term by altering physical protection within aggregates and enhancing microbial activity. (3) The positive correlation between earthworm abundance and crop production is not systematic, and contrasting effects on yields have been observed. Earthworms induce the production of hormone-like substances that improve plant growth and health. (4) Direct drilling increases earthworm abundance and species diversity, but the beneficial effect of reduced tillage depends upon the species present and tillage intensity. (5) Organic amendments enhance earthworm abundance. (6) Earthworms feeding at soil surface are the most exposed to pesticides and other agrochemicals. Finally, we discuss how to combine management practices, including inoculation, to increase the earthworm services. We conclude that using earthworm services in cropping systems has potential to boost agricultural sustainability.

Transcriptional profiling of wheat in response to take-all disease and mechanisms involved in earthworm's biocontrol effect

Take-all disease caused by the soil-borne fungus Gaeumannomyces graminis var. tritici (Ggt) is the most widespread and well-studied root disease of winter wheat. The absence of plant genetic resistance and efficient fungicide against this disease calls for the development of alternative management strategies such as the use of biological control agents. In a greenhouse experiment, we tested the hypothesis that the earthworm Aporrectodea caliginosa can control this plant pathogen by changing soil pH, inducing plant defence mechanisms or improving plant nutrition. Towards this aim, soil chemical properties, plant production, morphology and transcriptome were assessed in the different treatments to characterize the effects of Ggt, earthworm and the interaction between them. Sixty three days after sowing, Ggt was responsible for a strong reduction in fine root proportion and leaf area, and an 82xa0% decrease in plant total biomass. Earthworms reduced infection rate by 63xa0% and improved plant growth, which was not significantly different from the no-pathogen control. Neither changes in soil pH, plant defence mechanisms or plant nutrition were proved to be involved in this effect. It was concluded that A. caliginosa was a very efficient biocontrol agent against Ggt and that the mechanism responsible for this biocontrol effect could be associated with microbial community modifications or fungal consumption by earthworms.