Technical Yearbook 2023

TABLE 1. Effects of different categories of plants on microbial communities. 28 Cover crop type Microbial effects

Species studied

System type

Increases diversity of AM fungi.

Lotus corniculatus , Trifolium repens , Ononis repens.

Annual, natural.

Increases persistence of entomopathogenic fungi. T. repens.

Perennial.

Legumes

Lathyrus pratensis , Lotus corniculatus , Medicago lupulina , Medicago varia , Onobrychis viciifolia , Trifolium spp. , Vicia cracca.

Decreases abundance of DAPG and PRN-producing bacteria. Increases abundance of DAPG and PRN-producing bacteria. Cultivar-specific disease-suppressive bacterial community. Low mycorrhizal response (less AM fungi?).

Experimental.

Lolium perenne.

Experimental.

C3 grasses

Perennial.

Triticum (different cultivars).

Koeleria cristata, Bromus inermis, Festuca arundinacea, Lolium perenne, Agropyron smithii, Elymus cinereus. Andropogon gerardi, Panicum virgatum, Sorghastrum nutans, Bouteloua curtipendula. Brassica napus/mustard green manure, B. napus seed meal. B. napus (living plant or seed meal). B. juncea, B. napus (crop rotation) seed meal.

Natural.

C4 grasses High mycorrhizal response (more AM fungi?).

Natural.

Decreases fungal pathogens.

Annual, perennial.

Increases disease-suppressive bacteria.

Annual. Annual.

Favors Trichoderma and other disease-protective fungi.

Alters microbial community.

Perennial.

B. napus seed meal.

Inhibits AM spore germination, decreases AM fungal diversity.

Experimental, perennial. Experimental, annual/natural. Perennial/natural. Experimental. Annual/natural Perennial/natural, experimental.

B. kaber, B. nigra, B. napus seed meal.

Brassicas

Increased plant diversity, increases disease suppressive bacteria.

N/A N/A N/A N/A

Increases AM fungal diversity.

Decreases overall negative feedback. Increases diversity and abundance of entomopathogenic fungi.

Native species Improved AM fungal diversity and plant benefit.

N/A

as in and out of the roots, each time wounding the root. This feeding and migration cause necrosis of the root tissue, as well as allow other soil-borne pathogens to enter through the wounds. The last group of nematodes is the ectoparasitic nematodes. These are usually large nematodes, with large stylets able to feed on nutrient-rich areas deep within the roots. Damage due to these nematodes is usually due to large numbers of nematodes feeding on the roots. Nematodes also play an important role in essential soil processes with their direct contribution to nitrogen mineralisation being the most important one. Studies have shown that the presence of free-living nematodes increases the available nitrogen in the form of ammonia 25 and it can increase plant biomass. 11 Nematodes contribute directly to nitrogen mineralisation by consuming excess nutrients and excreting the excess in a form that can readily be taken up by plants. 2, 7, 11, 15 They have been shown to contribute up to 19% of nitrogen mineralisation. 2, 15 Omnivorous and predatory nematodes do not contribute to nutrient recycling as much as bacterial and fungal-feeding nematodes. Their

role within the soil food web, much like other predators, is population control. In 1999 13 it was found that predatory nematodes could become important regulators of bacterial feeding nematodes, while omnivorous nematodes did not have a strong effect on fungal-feeding nematodes. Plant parasitic nematodes can also be regulated through predatory and omnivorous nematodes. 18, 19 Predatory nematodes, however, do play a central role as indicators within the soil food web. Their presence and abundance may be correlated with predaceous microarthropods. 20 By further classifying nematodes according to their c-p values, nematodes can also be indicators of organic enrichment. cp-1 organisms or enrichment opportunists are most responsive to organic enrichment. cp-2 organisms are general opportunists. These organisms may already be present, but are exploiting a new food source. 8 Greater dominance of cp-1 organisms indicates enrichment, an increase in cp-2 organisms with a decrease in cp-1 and cp-3-5 indicates stress, while an increase in cp-3-5 represents natural succession mediated by environmental stability. 5

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TECHNICAL YEARBOOK 2023