Turfgrass management has traditionally focused on the quality and characteristics of the green plant shoot. In the several years, this focus has shifted to the root system. According to Dr. F. B Holl, a plant ecosystem can be compared to an iceberg, with the foundation composed of the root system. To avoid subsequent collapse of the ecosystem, the root system must remain strong. To do this, turfgrass managers need to understand the characteristics and benefits of the root zone, otherwise known as the rhizosphere.
What is the rhizosphere? The word rhizosphere is derived from Greek – rhiza meaning “root” and shaira meaning “world” or “globe” – thus, “root world.” The German scientist Hiltner is credited with first using the word to describe the volume of soil surrounding roots in which bacterial growth is stimulated. Rhizoshpere is now seen as the soil under the influence of plant roots. Rhizosphere is not used to refer to soil without vegetation of with soil that is outside the influence of a plant’s root system.
The rhizosphere is made up of plants, animals and microbes. The plant portion of the rhizosphererefers to the root system of a the plant. Roots provide several functions for the plant. Rootsanchor the turfgrass providing stability; they are the primary source for water and nutrientabsorption; a well-developed root system can reduce plant stress (especially in droughtconditions) and roots add to the organic matter found in the soil.
Animals found in the rhizosphere range from nematodes and protozoans to insects, earthworms and mammals, such as moles, mice or even squirrels. Microbes are represented by algae, fungi, Actinomycetes and bacteria. Animals and microbes either contribute to the vitality of the rhizosphere or to the detriment of the rhizosphere. Most fungi and bacteria are associated with different turfgrass diseases. But, there are always exceptions.
Mycorrhizal fungi are fungi which can penetrate into the root and develop a symbioticrelationship with the plant. The plant supplies the mycorrhizal fungi with Carbon and the fungi,with their massive network of mycelia, will extend the plant’s root system. Since surface area isincreased considerably, the fungi enable the plant to increase its water and nutrient uptake.According to Dr. Holl, this increase can be as much as ten fold.
Actinomycetes are bacteria which exhibit characteristics of both fungus and bacteria. Actinomycetes are important to the rhizosphere for their ability to degrade complex organic compounds such as cellulose and chitin. Actinomycetes also produce their own antibiotic which will inhibit or kill other microbes. This is significant to keeping the populations of the “bad”microbes down.
Bacteria are essential in the breakdown of organic matter into usable nutrients for the plant. Increased amounts of organic matter lead to increased bacterial populations which ultimately lead to more plant nutrients. All microbial populations require and energy source to thrive. Research done by Parent showed that supplementing with a fertilizer containing a carbohydrate (such as Nature Safe) will vastly improve the microbial populations with no apparent disproportionate stimulation of plant pathogens. Bacteria prefer simple sugar compounds for energy, such as what was used in this study, while pathogenic fungi prefer complex organic compounds for energy. Thus, bacterial populations thrive and through their ability to decompose organic matter and then later, through their demise, a beneficial nutrient cycle is implemented for the plant.