Digging for Knowledge … and Nematodes

Hannah Oswalt wrote this post as a part Dr. Stacy Krueger-Hadfield’s Science Communication course at the University of Alabama at Birmingham. Hannah is working towards her PhD in Dr. Chuck Amsler’s lab where she is investigating the effects of ocean acidification on macroalgae and amphipods around the western Antarctic Peninsula.

In early spring, a farmer prepares their field for the season’s planting. They till, then fertilize the soil. It’s easy to imagine how tilling and fertilizing, often referred to as soil management, affects the organisms that can be seen above ground. But, have you ever considered how tillage and fertilizer affect animals beneath the surface? 

One of the many organisms living in the soil of crop fields is the nematode. Nematodes are tiny worms that live nearly everywhere from marine to freshwater to terrestrial and even inside other organisms as parasites. If you can think of a habitat, nematodes probably live there. 

Soil nematodes can be found in all trophic levels and can be divided into functional groups based on their feeding preferences: bacterivores, herbivores, fungivores, carnivores, and omnivores. They are also categorized based on their life history strategy with some settling as opportunistic colonizers and others only arriving after a stable population of nematodes has been established.

While soil nematodes may be hidden from view, they play a vital role in decomposition, nutrient cycling, and pest/pathogen population control. In order to achieve these benefits, nematode populations need to be diverse. However, previous studies have shown that different nematode groups respond differently to soil management. 

Bongiorno et al. (2019) set out to discover how tillage and organic matter addition (e.g., fertilizer) affect soil nematode populations. Most nematode studies have used microscopy, but this method is often time consuming, expensive, and requires specialists. Instead, the authors used amplicon sequencing of the 18S rRNA gene to determine nematode diversity of ten fields across five climatic zones and six soil textual classes (i.e., the ratio of clay, sand, and silt that comprises the soil) across Europe. 

Reducing tillage increased nematode diversity within a field and altered the diversity observed between fields. Reduced tillage increased the total amount of organic carbon, soil aggregation, and microbial biomass. Additionally, lower tillage provided a lower physical pressure on the nematodes when compared to conventional tillage. These factors combined resulted in higher nematode diversity. As a reminder, high nematode diversity is necessary to receive benefits in decomposition, nutrient cycling, and pest/pathogen control. 

Reduced tillage fields were less disturbed and not only had greater stability, but also more food web interactions.  Furthermore, reduced tillage showed an increase in the proportion of fungal feeders. This increase in fungal feeders may have contributed to the retention of nutrients and stored carbon as well as more herbivores.

But why care about nematode communities? It turns out that nematode communities are related to organic carbon and the biological parameters of soil. High diversity among nematodes is positively linked with carbon fractions. From here, carbon is linked to higher microbial biomass, soil respiration, water retention, soil structure, and lower bulk density (an indicator of soil compaction). All of these characteristics combine to result in higher quality soil. Higher soil quality, in turn, results in higher quality crops.

We may be able to improve the overall quality of our soil by using smarter soil management techniques. We can increase soil quality through low effort changes like reducing our amount of tillage and instead allow nature to work its magic through nematodes. The next time you drive by a crop field, instead of focusing on what you can see abovethe surface, spare a thought for the mighty nematodes diligently improving the land beneath the surface. 

References

Bongiorno G., Bodenhausen N., Bunemann E, Brussaard L., Geisen S., Mader P., Quist C., Walser J., Goede R. (2019). “Reduced tillage, but not organic matter input, increased nematode diversity and food web stability in European long-term experiments.” Molecular Ecology 28: 4987-5005.

About Stacy Krueger-Hadfield

I am a marine evolutionary ecologist interested in the impacts of seascapes and complex life cycles on marine population dynamics. I use natural history, manipulative field experiments and population genetic and genomic approaches with algal and invertebrate models in temperate rocky shores,estuaries and the open ocean.
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