By Peter Baas, PhD; Colin Bell, PhD and Matt Wallenstein, PhD
When we get asked by cannabis growers why they should use microbes in their cannabis cultivation, we answer: because they work to naturally increase plant health, crop quality and yield. Over the last few decades, scientists have unveiled the critical role microbes play to support plant growth. Our research team at Growcentia has spent years exploring the specific ways in which plant-microbe interactions affect plant development and yield. In a previous article in Grow Magazine (July 2017), we discussed several mechanisms by which microbes can affect plant success. In this article, we will focus specifically on how microbial consortia (i.e. groups of different microbial species) work together, just like in nature, to support plant growth more effectively than any single microbial species can alone.
Microbial consortia make up the foundation of all ecosystems. More than 700 million years ago, plants evolved into a microbial world as their roots extended into soils teeming with microbial life. To this day, no plant in nature exists without help from soil microbial consortia supporting plant success by converting macronutrients into plant-available forms. There are several reasons why microbial consortia are more effective at supporting plant growth over single microbial species or non-synergistic microbial mixtures. The main reason is because nutrient cycling often requires several different metabolic pathways–and no one microbial species can carry out all the pathways alone.
Microbial nutrient cycling often requires multiple processes or “steps.” These steps are somewhat equivalent to an assembly line in a factory. However, in this case, the final product is bioavailable nutrients for plants to uptake. No single microbial species has the genetic ability to conduct all the steps in cycling nutrients–they need to work together as consortia to get the job done. For example, cycling nitrogen into bioavailable forms for plant uptake (typically ammonium and nitrate) require specialized microbial functions to complete different steps of nitrogen cycling. Liberating phosphorus for plant uptake requires a wide range of chelating, solubilizing, and catalyzing processes that can only be facilitated by different microbial species interacting within the consortia. Microbial consortia are also important for cycling potassium into bioavailable forms for plant uptake. Overall, microbial consortia cycle nutrients much more effectively than any single microbial strain.
Microbial consortia also form complex networks using biochemical and even electrical signaling to coordinate many processes. This type of communication within a microbial consortium is called quorum sensing. For example, intricate microbial networks can produce a specific compound that signals their density and activity in an environment. When enough of these microbes are present, they are able to trigger a physiological change for the initiation of the “next step” of nutrient cycling. These physiological triggers are often useless for single organisms acting along, but essential when microbial consortia work together.
We are now able to use modern technology to analyze and learn from microbial consortia in action–recording their activities, specific functions, and communication networks. One approach uses DNA genetic markers as unique identifiers to collect a census of the tens of thousands of different microbial species in an environment. This tool gives us a great idea of what microbes are working together within the consortia. Likewise, by utilizing DNA metagenomic tools, we are now able to identify the expression of specific microbial functional genes and unravel the functions performed by microbial consortia.
Over the last century, the agriculture “green revolution” focused on intensive use of chemical fertilizers to maximize crop productivity. However, these intensive farming practices also resulted in soil degradation and negative environmental consequences. To address some of these issues, microbial technologies are now being widely adopted to support soil and plant health. Our ability to harness the natural power of soil microbes is now being considered one of the next most important agriculture innovations to support plant development and yield across many crops.
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