The Mycelium Connection

When man first began to settle out of the hunter-gatherer phase of our evolution we did so in fertile areas. We would perhaps stop where there was a constant source of water, and fair enough weather to allow us a safe and permanent homestead. But, as the world’s population increased those ideal spots became competitive and not everybody had access to things like constant supplies of water to manage crops with.

Enter irrigation: the best agricultural idea since somebody first dropped a seed in a hole.
In essence irrigation is simply transporting water from a source to a place where it is needed. Now, this has been going on a long time, evidence suggests the 6^th Millennium BCE, and we have developed a whole host of styles. But in the end they all do the same thing; take water from here to there.

Developing irrigation techniques allowed us to thrive in places without an immediate source of water, which opened the world up to us. It also led to a massive population boom (see everybody alive today).

And that is where we run into problems. You see as we grow more populous, we use more water, and leave more waste. So we are left with this transition: More access to water= more crops= more people= more waste= less clean water.

But worry not! People are the ones who ingeniously developed irrigation in the first place, and now all we needed were ways to take the waters we contaminated and use them instead of freshwater. And we have. The use of treated wastewater is one of the most used alternatives to freshwater for irrigation in areas of limited natural resources.

So, we have found ways to deal with dirty water: to take it and try to make it clean and reuse it. But the question is, at what cost? Now for most people here is where we would turn to crop yield, or potential health effects of eating foods grown with wastewater, but we both know that isn’t what I am concerned with.
And a study recently published in PLOS One helps shed light on another impact of irrigating with wastewater: the effect on fungal diversity.

Long-Term Effects of Irrigation with Waste Water on Soil AM Fungi Diversity and Microbial Activities: The Implications for Agro-Ecosystem Resilience

This study from Southeast Spain measured the effects of irrigating an experimental orange grove with treated urban wastewater over the course of 43 years. The study included isolating and measuring Arbuscular Mycorrhizal Fungi (AMF) diversity in order to better understand techniques for management, sustainability, and productivity of the soils.

They researchers sequenced 145 AMF samples that were grouped into 19 types, all from the Glomeraceae family. They sequenced multiple times to ensure full coverage of fungal diversity in both the wastewater irrigates as well as samples from a control plot of land that has been irrigated with freshwater.
And there results demonstrated a significantly greater diversity of fungal species in the freshwater treated soils. With 15 different AMF types compared to only 10 from the Wastewater irrigated soils.

The team speculated that the addition of nutrients to the soil could be a cause of lower AMF diversity, an observation backed up by evidence that shifts in community composition in nutrient-rich areas leads to a reduced AMF diversity.

In this study they found a significant increase in enzymatic activities of alkaline phosphatase, urease, dehydrogenase, protease and β-glucosidase in the soils treated with wastewater. Previous long term studies measuring irrigation with municipal wastewater concur with this result on the activity of soil enzymes.

The enzymes in the soil, and the introduction of readily available organics in the wastewater allows for a significant increase in microorganism populations. That actually has a beneficial effect on the total microbial biomass in treated soils, but the increased microorganisms don’t help with the Mycorrhizal diversity. It leads to the conclusion that while treatment with wastewater does have several benefits, it selects for the AMF’s that are most able to tolerate higher levels of enzyme activity in the soil.

Using the results from this study could help us define methods to balance the soil microbiota to ensure the best yield per acre of healthy robust crops. See how I went back to crop yields there? And you thought I didn’t care about that.

Awesome Researchers:
del Mar Alguacil, M., Torrecillas, E., Torres, P., García-Orenes, F., & Roldán, A. (2012). Long-Term Effects of Irrigation with Waste Water on Soil AM Fungi Diversity and Microbial Activities: The Implications for Agro-Ecosystem Resilience PLoS ONE, 7 (10) DOI: 10.1371/journal.pone.0047680

Photo Cred:
Wikipedia contributor Paulkondratuk3194