Earthworm and arbuscular mycorrhizal communities in agricultural soils : management of key soil organisms for sustainable agriculture

Abstract: Intensive agriculture is detrimental to soil biodiversity and functioning. Promoting communities of key soil organisms, such as earthworms and arbuscular mycorrhizal (AM) fungi, may help improve agricultural sustainability by replacing inputs with ecosystem services. In this thesis, I explore ways to manage earthworm communities for improved soil functioning via adjusted agricultural practices, promotion of source habitats in the landscape, and inoculation. I also explore the effects of soil compaction on AM fungal symbiosis in wheat varieties, and test application of grassland soil as a method to increase AM fungal diversity in agricultural soils. I show that diverse earthworm communities and bioturbation can be promoted by reducing tillage intensity and total earthworm densities can be increased via diversifying crop rotations. Moist and fertile semi-natural grasslands with high small-scale habitat heterogeneity may serve to sustain earthworm diversity in agricultural landscapes. Inoculation with commercially obtained Lumbricus terrestris earthworms may help restore populations of this tillage sensitive species and improve wheat growth but the long-term establishment of these worms is uncertain. Application of grassland soil may increase AM fungal diversity in agricultural soils but this may not be reflected in AM fungal taxa colonizing wheat roots. I also show that soil compaction differently affects AM colonization in wheat varieties. Further research needs to identify which earthworm and AM fungal community properties best result in functional benefits under different conditions. Nevertheless, I show that earthworm and AM fungal communities can be promoted in various ways, individually or in combination, suggesting potential to enhance functional effects of these key organisms in agricultural soils.