Breaking good: Soil nematodes as important players for plant performance

Dr. Olivera Topalović, Postdoctoral Fellow at University of Copenhagen, Denmark & Wageningen University and Research, The Netherlands

Dr. Stefan Geisen, Assistant Professor at Wageningen University and Research, The Netherlands

Nematodes are among the most abundant soil organisms, occupying four-fifths of all animals on Earth. Their trophic abilities place them at all levels of the soil food web – from microbivores to predators to insect killers to plant parasites. This wide range of interactions make nematodes important players in soil multifunctionality, including nutrient cycling. Their vast biodiversity of many thousands of species with distinct niches makes nematodes excellent bioindicators of soil health. In agroecosystems, nematodes are mostly considered to be negative, resulting in a huge gap in understanding of the positive roles of nematodes in plant performance.

This is not surprising as plant-parasitic nematodes are important plant pests leading to global yield losses of billions of US $ annually. Damage to plants is caused by direct feeding on belowground and aboveground plant parts. For instance, the infective juveniles of root-knot nematodes, one of the most notorious groups of plant pests, release a cocktail of enzymes at feeding sites in roots that cause proliferation and enlargement of highly nutritious cells – so-called “giant cells”. As a result, numerous galls are formed on the roots, which disrupt normal plant growth and crop yield. In addition to direct feeding, plant-parasitic nematodes form disease complexes with various plant pathogenic bacteria and fungi and support their transport into the roots.

Figure: Contribution of free-living nematodes in microbial regulation of plant parasitic nematodes (Topalović & Geisen, 2023)

In our review “Nematodes as suppressors and facilitators of plant performance”, recently published in the journal New Phytologist, we address these negative aspects of plant-nematode interactions, but also fill some important knowledge gaps in understanding the positive role of nematodes on plant performance. We show that even plant-parasitic nematodes, when present in soil in numbers below damage thresholds, can improve plant performance through the release of root exudates and increased microbial activity in the rhizosphere. We also highlight the more numerous, but certainly less explored, benefits of free-living nematodes in promoting plant performance. This positive contribution is entirely indirect through interactions between free-living nematodes and other soil biodiversity, especially bacteria and fungi. In fact, several studies show increased abundances of some groups of free-living nematodes linked to improved plant growth and reduced disease symptoms under organic and conservation agriculture.

Considering that the majority of bioproducts that are based on microbial isolates usually have low efficiency when applied in the field, we propose to finally address the many questions related to the potential of free-living nematodes themselves as novel bioproducts for application in agroecosystems. We think that a more precise understanding of the importance of free-living nematodes in plant performance and in regulating plant pests and pathogens requires a multidisciplinary approach. This effort will require integrative laboratory and greenhouse studies to investigate nematode interactions with other soil biodiversity and field studies on testing the possibility and efficiency of free-living nematodes as bioproducts. To get a more complete overview on the positive side of soil nematodes and how these might help in more sustainable soils, read the full article here.

Reference:

Topalović, O. & Geisen, S. Nematodes as suppressors and facilitators of plant performance. New Phytologist (2023). https://nph.onlinelibrary.wiley.com/doi/abs/10.1111/nph.18925

O. T. was funded by Novo Nordisk Foundation (grant no. NNF21OC0071015)