Symbiotic turf/fungi relationships in fine turf

Mycorrhizal fungi and turf health go hand in hand. The study of fungi is called Mycology, and in ecology the area immediately surrounding the roots of plants is called the Rhizosphere. When you see the term mycorrhizal anywhere, it refers to the relationship between fungi and the roots of vascular plants. Mycorrhizal fungi form symbiotic relationships with the roots of at least 90% of all the known plant species. These relationships take several different forms, but all of them can be loosely divided into two main groups. These are endo-mycorrhizal relationships and ecto-mycorrhizal relationships. In endo-mycorrhizal, types the fungal hyphae actually penetrate into the cell cavities in the roots of the plants, whilst in the ecto-mycorrhizal types the fungal hyphae will generally form a sheath around the plant root. It actually gets a lot more complex than this, with many sub types of each main type existing, but this is enough to be going on with for now. Some mycorrhizal fungi are specialists and form relationships with one species of plant, whilst others are generalist. Some plants, mainly trees, can have simultaneous relationships with many different fungi types.
Mycorrhizae and the fine grasses
All of the perennial grasses, including our desired fescue and bent grasses naturally associate with mycorrhizae (mycorrhizal fungi) in symbiotic (mutually beneficial) partnerships. Interestingly, annuals such as poa annua (annual meadow grass) don’t form strong connections like this. Left to their own devices, the roots of our grass plants can access no more than about 3% of the surrounding soil nutrient and water resource. Turf with strong mycorrhizal associations has been shown to require 30% less irrigation in summer and up to 50% less artificial fertiliser for the same results. This is due to the plant being able to access natural resources from a much bigger volume of soil than it would otherwise have access to with its roots alone. From this we can probably deduce that our fine grasses and their symbiotic fungi partners evolved to work together for mutual benefit. And it isn’t hard to see why these useful fungi would want to form lifelong partnerships with our grass plants either. Remember that our grasses are efficient sugar producing factories, using photosynthesis to make high energy food out of thin air and sunlight. The fungal partners of our grass plants are able to benefit from this talent in return for helping the plants to extract more nutrient and water from the soil than they could on their own, which of course allows each grass plant to grow and become an even more efficient food factory and even more attractive partner for the mycorrhizae.
Essential Relationship
All of this can make it sound as if the mycorrhizal relationships between grasses and fungi are optional, nice to have but not essential. Well, such niceties are rare in nature. Non-essential activities are rarely tolerated for long in the natural environment and these relationships have developed over a long period of evolutionary time. They are best considered essential to plant health and successful green management, something we should keep that in mind when deciding on our greenkeeping programmes. It’s hard for us to think of grass and fungi as one thing, but it’s unlikely that we would have fine turf in its current form, or the major success of our crop and food grasses, like rice, wheat and maize if this process wasn’t happening underground. This is why greenkeeping must get away from the symptoms management thinking we discussed last month, where we eradicate problems one by one without thinking about the downstream consequences.
Updating the Circle of Decline
If you are a regular reader here or at Bowls Central, you will know about the Circle of Decline in bowling greens. The mycorrhizal plant/fungi relationship is a key component of the deeper science behind the Circle of Decline phenomenon. Greens slip gradually into the Circle of Decline over many years of inappropriate maintenance. This starts with poor aeration and fertilisation practices, over reliance on fungicides and of course the continued desertification of the top four inches of the rootzone through the application of sand dominated top dressings far beyond the point where they are useful additions. The green gradually and almost imperceptibly becomes unresponsive, thatchy and inert over a period of years. To counteract this effect, the green is subjected to more sand top-dressing in an effort to correct green surface anomalies, actually caused by the constant movement and settlement of the surface due to excessive thatch. Sand is also often considered the answer to flooding and soft turf, again caused by excessive thatch holding water at the surface. More sand makes it worse and makes the green more inert, more anaerobic and more susceptible to localised dry patch. Meantime, a serious consequence of the thatch is the increased fungal disease outbreaks which are treated with fungicides. These fungicides kill off any fungi species they come into contact with, reducing the overall fungal population in the soil, good and bad. The wet thatch and related compaction continue to decrease the oxygen availability in the soil, causing the rootzone to become more frequently anaerobic and increasingly acidic. The beneficial soil microbes essential to the breakdown of thatch and release of nutrients, including the conversion of fertiliser to plant useable forms, are depleted to very low levels. We then need to apply ever bigger loads of artificial fertiliser to get even the minimum result. To get a result in terms of growth and presentation from such turf, we must use increasingly heavy fertiliser applications. The norm is to use inorganic, high salt index fertilisers like Sulphates of Ammonia and Iron. These further acidify the soil and cause black layers and the build-up of noxious soil gasses. All of this can benefit only one grass type and that is the shallow rooted annual meadow grass that frequently exists within the thatch layer only and has no mycorrhizal relationships to call upon for nutrients and moisture. One drought period can leave the green denuded of grass. And so, the Circle of Decline continues – sand-low microbe populations-fertiliser-water-annual meadow grass-thatch-disease-fungicide-flooding-sand-annual meadow grass.
Reaping what we sow
When we maintain our greens in a way that recognises the importance of the eco-system in its entirety, we immediately give ourselves an advantage over the symptoms management approach. The bowling green eco-system is like a million-piece jigsaw puzzle called the Soil Food Web. If one piece of the puzzle is missing, making the green perform at its best can be very difficult. Fungicides kill off mycorrhizal fungi as well as pathogenic ones like fusarium. The truth is that we reap what we sow. If we maintain our greens with inorganic, mineral salt laden fertilisers and fungicides we get inert rootzones with a lot of problems. These problems can be linked to missing pieces of the soil food web. If essential soil fungi groups are missing, then perennial grasses (fescue and bent) will struggle to dominate the sward. If other essential microbe groups are missing or low in population then thatch will continue to build up into thick mat, causing conditions where pathogenic fungi like fusarium will find it easier to thrive. And so, the cycle goes. By maintaining our greens in a more natural way that encourages aerobic microorganisms to thrive, we automatically set them on course to encourage only fine perennial grasses. We can maintain such greens with low to zero pesticides, lower fertiliser inputs, lower irrigation inputs and
set them up for high performance more consistently.
Boosting Mycorrhizal Fungi in your green
High quality soil inoculants containing a range of different species of beneficial mycorrhizae and a range of beneficial bacteria species are available to help to encourage the recovery of inert soil. These can provide many benefits including:
• Faster establishment of new seed
• Promoting the establishment and longevity of fine grasses over annuals
• Stimulating and promoting root growth, increasing root mass
• Enhanced nutrient uptake
• Increased plant tolerance to drought and stress conditions
• Healthy grass is less susceptible to damage and recovers faster from disease and insect damage

Questions: As always, please feel free to drop me a line to: john@bowls-central.co.uk with any questions you have about this or any other greenkeeping issue.

Caption: Turf samples showing mycorrhizae

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