The relationship between nutrients, bacteria and soil impacts how plants grow
By Craig Allen and Nik Nikolayev
The best grows have been meticulously designed and planned to take all factors into account. Good preparation is the best way to guarantee a successful growing cycle – but the best way to prepare may not necessarily be what you think.
Preparing your medium
This article will take a closer look on what it means to have optimal preparation for good symbiotic relationships in the grow medium. Preparation is crucial here because there is a delay between an action and the consequence — sort of like playing Frisbee with a friend. You have to throw the Frisbee to where the recipient will be rather than where they are. There is a similarity in growing cannabis because you have to know where the plant is going to end up, so be organized and keep your focus ahead of the pace. Soil preparation is much the same; when you act on a plant it can take as little as five minutes or as long as several weeks for a noticeable change to occur.
Some of a plant’s most influential partnerships are in the root zone, where the roots have a symbiotic relationship with bacteria and fungi. Symbiosis can be understood by looking at how plant roots interact with the media in which they are growing. Roots interact with almost all media to obtain carbon, water and nutrients. This interaction speaks to the good as well as the bad, including how the plant canopy interacts with predatory insects, bacteria, fungi, etc. Needless to say, it is a pretty deep topic. However, for the purposes of this article we will stick to beneficial symbiotic relationships which exist between certain types of beneficial bacteria/fungi and plant roots.
Why are symbiotic relationships important? The short answer is nutrient exchange. Plants are highly specialized in that they can utilize energy from the sun to produce energy for themselves — this is photosynthesis, in a nutshell — but this process does not sufficiently meet the needs of the whole plant. As the roots draw nutrients up from the medium and provide the plant with the raw materials necessary to grow more leaves and denser canopies, the plant cannot replenish them faster than it depletes them. Think about your garden. Have you ever noticed that your plants struggle to grow rapidly? If so, the plants are probably not getting enough food. But that doesn’t necessarily mean you haven’t fed them enough nutrients. It usually means they are not effectively able to consume the nutrients they received. Rhizobacteria and fungus are a great place to start when attempting to increase plant health. It seems simple, but it is actually the core of a profound concept.
Rhizobacteria
The faster plants grow, the more nutrients they will demand from the medium. Promoting healthy symbiotic relationships early on in the plant’s life ensures its success as the nutrient demand increases. Plants have become specialized in many ways, such as the ability to turn sunlight into energy, but they are not experts in other chemical processes. Through millions of years of evolution they have come to depend on certain bacteria and fungi to help them obtain critical nutrients. These bacteria and fungi are collectively known as PGPR – plant growth promoting rhizobacteria. This term that was coined in 1978 by two researchers who studied radishes and found certain species of soil bacteria could enhance root growth by a whopping 567% and increase final yields by 200%. This was quite a profound discovery, and ever since then, researchers around the world have been looking at what species of bacteria and fungi can promote plant growth.
PGPR are specialists in many different tasks like changing nitrogen gas into available forms of nitrogen, or converting insoluble phosphates into available forms, and so much more. For example, siderophore proteins secreted by PGPR are unbelievably powerful iron-binding complexes that have been shown to promote plant growth in soils where the availability of iron is so low that plants would otherwise be unable to assimilate iron into a usable form. The gist is that some processes are more difficult for the plant because it is not as specialized in this field – much like a doctor who lacks skill in legal matters compared to an actual lawyer, and vice versa. The earlier the relationships are established, the easier it is for the plant to grow, so plan on introducing some PGPR into your nutrient regimen and your plants will grow well.
How do PGPR work?
Many times, the nutrients required by plants are not available to them because they are either too large to metabolize or in an unavailable form. Think about trying to eat something that is bigger than your whole mouth; you would have to break it down into bite-sized pieces, right? And think about eating a raw egg versus cooking an egg. Sure, it’s an egg in both cases, but cooking it makes all the difference between being edible and potentially dangerous. This is a similar concept to how PGPR can break down insoluble and unavailable forms of nutrients into something the plant can actually absorb and use as nutrition. If you think about it, this also means that when the plant is hungry, the demand for nutrients is felt by the PGPR. They sit along the roots of the plants and constantly exchange broken down bits of food for sugars and amino acids which the plant produces through photosynthesis. Like most bacteria and fungi, PGPR thrive when sugars are available for them to metabolize. They use the energy gained from the breakdown of sugars as fuel for their own growth. Essentially, this process can be summed up by saying that plants help PGPR grow because PGPR help plants grow. It’s almost like they evolved together.
The process of nutrient exchange is not yet fully understood, but it’s evident that both PGPR and plants have mechanisms in place to guard against unwanted interactions. Plant hormones regulate the process by which nutrients become available to PGPR, and vice versa. The whole process is like a secret society handshake – we’re certain they happen, but we just don’t know how.
What has been determined, though, is that plants will regulate nutrient exchange based on their needs. For example, if a plant is in vegetative growth, it needs more nitrogen to make more chlorophyll to grow a larger canopy. To help this occur, nutrients will be exchanged in the root zone with PGPR which provide nitrogen. Alternatively, during flowering, the plant needs more phosphorus so that it can grow large, sticky flowers, and therefore nutrients will be exchanged with PGPR which provide phosphorus.
In truth, these relationships are so complex that they might often sound contradictory until looking at the specific variables. For example, PGPR inhibition of ethylene biosynthesis through ACC-deaminase pathways; that may sound bad until zooming in for a closer look. Significant levels of ethylene in the root zone can decrease root growth and shut down photosynthesis — not good for the PGPR because they need the plant to photosynthesize in order to continue receiving food. It makes sense why they would inhibit this, right?
This is not a Chemistry 420 course though, so let’s keep things relevant to you and your garden. Let’s back up a bit here and review some of the important concepts:
– Plants deplete nutrients from the medium faster than they can replenish them, which creates a bottleneck.
– This bottleneck can be overcome with the help of PGPR. The earlier they colonize the roots, the better.
– The plant is fully aware of this potential, and will strive to maximize its symbiotic relationships.
Wrap-up
There is one last component of symbiotic relationships worthy of mentioning, even if it is not discussed. Preparing your soil with beneficial bacteria and fungi can help provide the plant with a strong immune system. It sounds crazy, but this is actually a very well-documented phenomenon known more recently as “induced systemic resistance.” The idea is similar to nutrient exchange, but rather than the plant asking for nutrition, it will ask the PGPR for help in warding off predatory herbivores or pathogenic bacteria/fungi. This is all the more reason for gardeners to promote healthy symbiotic relationships through preparation and knowledge.
Understanding symbiosis becomes a lot easier from the perspective of personal experiences. Everybody has a relationship with cannabis; in turn, cannabis forms relationships with us. Be mindful about how you grow, and aware that you are a symbiotic component in a relationship – much like a PGPR. Your gardens will flourish as a result.
Craig Allen and Nik Nikolayev are experienced growers and consultants. Allen is the co-owner of Groco Supply in Bellevue, Washington (grocosupply.com). Feedback on this article or any subject regarding nutrients for cannabis plants can be sent to nutrients@grocosupply.com.