Functional Redundancy (Part. 3): Taking Concepts to Commercial Agriculture

This is part of our sequence of blogs about “functional redundancy”, a concept from ecology that explains why diverse ecosystems are often more productive and resilient. The following series explores this history of the concept of functional redundancy, why it matters to agriculture, and how we can use it to build better biological products that function consistently across environments.

Why agriculture sometimes runs a "functionality" deficit

We’ve shown that diversity, redundancy, and response diversity matter acutely to ecosystem health. Agricultural fields are still ecosystems even though many of the tools that make them productive also simplify the system: monoculture, tillage, bare periods, and heavy chemical inputs each remove some of the variety that soil communities depend on.

The evidence for the impacts of this are consistent. A study of agricultural regions across Europe found that land-use intensification leaves soil food webs less diverse, with fewer functional groups made up of fewer and more closely related species. Fewer groups with fewer members is a textbook description of lost redundancy and lost response diversity.

When everything goes perfectly, a simplified community can still function well. But as any grower knows, rarely (if ever) has there been such a thing as a perfect growing season. System deficits show up when conditions are hard: a dry spell, a cold spring, a pathogen arriving. And every year throws something new at growers. 

The consistency problem

This is where functional redundancy stops being an academic idea and becomes something a grower feels in the checkbook.

Anyone who has used biological products knows the frustration: strong results in one field or one season, little to show in the next. There are many reasons for that variability, including application, soil chemistry, and weather. But ecology offers one explanation that doesn't get discussed enough.

A single microbial strain, however good, is a single worker with a single set of preferred conditions, usually selected because it performed well under particular circumstances. Put it in soil that is warmer, drier, more acidic, or with different competitors than those circumstances, and it may simply not behave the same way. In ecological terms, a single-strain product carries no response diversity. Performance is only as broad as one organism's comfort zone.

That doesn't necessarily make single-strain products bad. But it does mean that their performance across environments is limited.

What growers and advisors can do

Most practical levers for building diversity and redundancy are familiar to farmers. The ecology in this blog just explains why they work:

• Diversify what's growing. Crop rotation and multispecies cover crops feed wider ranges of soil organisms because the different root exudates support different microbial partners.

• Keep living roots in the ground longer. Roots are the soil community's lifeline. Long bare periods thin out the workforce.

• Reduce disturbance. Tillage and heavy disruption favor fast-recovering generalists over the slower, more specialized organisms.

• Evaluate across conditions. Just like with plant varieties, when comparing biologicals, results across multiple sites and seasons will tell you the most about performance.

Co-culture: building response diversity into products from the start

If response diversity is what buffers ecosystems, a logical next step is to design it into the products themselves. That's the idea behind co-culture: growing multiple microbial species together, rather than separately, so a community is assembled before it ever reaches the field.

There are two parts to this reasoning. The first is the redundancy we have spoken so much about: Several organisms contributing so that outcomes stay consistent. The second reason co-culture matters is subtler, and it has to do with how organisms adjust to each other.

Microbes grown alone are adapted to being alone. Microbes grown together adapt to their neighbors. Experiments show this matters. In a 2015 study, Fiegna et al., cultured artificial microbial communities of 1 to 12 species in three environments for about 60 generations and found that interactions between species evolved to become less negative over time. In that study, community productivity rose only when interactions were part of the community’s evolution. Another experiment with a simple yeast and bacterium pairing found something similar: after many generations, only the bacteria that had been grown in isolation lost the ability to coexist with another partner.

The implication is intuitive once you see it. Organisms that have already learned to live together are more likely to keep living and working together.

Why this is hard, and why it's worth it

If co-culture makes so much ecological sense, why isn't everyone doing it?

Because it's difficult. A single strain is comparatively easy to grow, stabilize, characterize, and reproduce batch after batch. A co-culture is a small ecosystem in a tank: organisms compete, their proportions can drift, and keeping the community consistent from one production run to the next takes real process control and patience. For many companies, the practical choice is to grow each organism separately and blend them at the end, or to stick with single strains.

At Impello, we believe in products that take on that difficulty. But the point here isn't any one product. It's the approach: we think the ecology is clear enough that engaging with the complexity of co-culture is worth it for the capability and consistency it can bring to agriculture.

References

• Fiegna, F. et al. (2015). Evolution of species interactions determines microbial community productivity in new environments. The ISME Journal 9: 1235–1245.

• Tsiafouli, M. A. et al. (2015). Intensive agriculture reduces soil biodiversity across Europe. Global Change Biology 21: 973–985.

• Wei, Z. et al. (2015). Trophic network architecture of root-associated bacterial communities determines pathogen invasion and plant health. Nature Communications 6: 8413.

• (2022). Species interactions constrain adaptation and preserve ecological stability in an experimental microbial community. The ISME Journal.

• Ehrlich, P. & Ehrlich, A. (1981). Extinction: The Causes and Consequences of the Disappearance of Species. Random House.

• Elmqvist, T. et al. (2003). Response diversity, ecosystem change, and resilience. Frontiers in Ecology and the Environment 1: 488–494.

• May, R. M. (1973). Stability and Complexity in Model Ecosystems. Princeton University Press. Tilman, D. & Downing, J. A. (1994). Biodiversity and stability in grasslands. Nature 367: 363–365.

• Walker, B. H. (1992). Biodiversity and ecological redundancy. Conservation Biology 6: 18–23.

• Yachi, S. & Loreau, M. (1999). Biodiversity and ecosystem productivity in a fluctuating environment: the insurance hypothesis. PNAS 96: 1463–1468.

• Allison, S. D. & Martiny, J. B. H. (2008). Resistance, resilience, and redundancy in microbial communities. PNAS 105 (Suppl. 1): 11512–11519.

• Louca, S. et al. (2018). Function and functional redundancy in microbial systems. Nature Ecology & Evolution 2: 936–943.

• Mendes, R. et al. (2011). Deciphering the rhizosphere microbiome for disease-suppressive bacteria. Science 332: 1097–1100.

• Wei, Z. et al. (2015). Trophic network architecture of root-associated bacterial communities determines pathogen invasion and plant health. Nature Communications 6: 8413.