The Relationship Between Biostimulants And the Growing Environment

Biostimulants are able to increase plant access and efficiency in nutrient use. Photo: Michelle Jones

Editor’s note: This is the first part a monthly three-part series we are launching on the efficacy of biostimulants in the greehouse. Special thanks to Ohio State’s Michelle Jones for compiling the information from a panel she led at Cultivate’21. Part 2 will be posted in late April.

Biostimulants can be used to increase or decrease nutrient uptake, efficiency, tolerance to stress, crop quality, yield, and other plant characteristics. How can biostimulants be used in different greenhouse settings?

Dr. Michelle Jones, The Ohio State University DC Kiplinger Flower Culture Chair, and a panel industry experts addressed these and other questions during a discussion on Cultivate21. Mark Freeman, Matthew Krause (Lallemand Plant Care), Troy Buechel (“Premier Tech”) and Blair Busenbark (“Mycorrhizal Applications”) rounded out the panel.

Continue reading to see highlights of the discussion.

How does the growing environment impact the efficacy and effectiveness of microbial stimulants?

Krause:Living microbial biostimulants have specific nutritional, salinity and pH requirements. They also have limits to their growth and activity. These requirements are not always the same for all biostimulant microbes.

Freeman:The environment, as well as fertilization practices, can affect the effectiveness of microbial microbiostimulants. Mycorrhizae have been used to study the rates and sources of phosphorus and nitrogen. A key consideration is that biostimulants may increase plant access and utilization of nutrients. Numerous studies have shown that different biostimulants can be beneficial for plants. Bacillus, Trichoderma, Penicillium, This is especially true if nutrients are scarce. Many microbes can also be used to help plants cope with abiotic stresses, such as drought or soil salinity. The growing environment can affect how effective a biostimulant is perceived. A biostimulant may not be beneficial if the existing fertilization practices are sufficient to provide the plant with all it needs.

How long do non-mycorrhizal or mycorrhizal mediastimulants last? How long do they last?

Krause:This depends on the microbe at different levels. The product formulation, the strain or combinations of strains of bacteria and fungi in it, the state of the plant, the organic material content and types in its growing media, competition from other microbes and chemical and nutritional factors, as well as temperature, can all affect the plant’s reaction. Mycorrhizal and non-mycorrhizal distributors are well-equipped to advise growers on how to store their microorganism strains in the media and whether or not they need to be reapplied on other crops under different growing conditions.

Busenbark:This is a complicated question as each growing system will give a different answer. Most organisms are number-based or quantity-based. Mycorrhizal fungal fungi have a lower plant productivity benefit because the quantity of the fungi increases with time. While most other organisms decrease over time, it is less about the quantity. The soil or media application of most biostimulants is what provides the benefits and application. There are many factors that can influence longevity. This includes the balance between the microbial biomass from different organisms creating this mutually beneficial environment. The more the system works toward achieving this optimal microbial bio-balance between organisms, the longer it can sustain them. If these are out of balance, there may be differences between organisms or growing systems that can sustain this level for a long time. Fungi, including mycorrhizal mushrooms, play an important role in maintaining balance. They also provide the basis for supporting other organisms.

Freeman:Many products that are not microbial-based include protein hydrolysates. The production system determines the effects. They can be used immediately, or consumed. However, the effects on the plant may last longer. Although the active ingredient (product) may not last in the media, it can still have long-term benefits for the plant’s metabolism.

Buechel:Endomycorrhizal mushrooms inoculum are viable within the products for two years if they are kept at 36F to 80F. Rapid temperature changes are more harmful to its viability than actual temperature changes, up to a certain point. Peat moss, organic components, and endomycorrhizal yeast inoculum are used as an insulation to slow down temperature changes. Our research has shown that viable spores are found in the following: Glomus intraradicesPopulation will be maintained for at least two years in the growing medium, even if temperatures drop to as low as minus 20F and rise to 110F. Populations will decrease if temperatures exceed 110F.

The fertilizer used in pansies was either not applied during production or it was applied as a constant liquid feeding at 75 or 150ppm N rates from 15-5-15 (JR Peters). The 75 ppm rate was lower and plants with growth-promoting microbes like Bacillus or mycorrhizae had better growth and flowering. However, at 150 ppmN, this difference is not observed. Photo: Laura Chapin from The Ohio State University

Is there any data to confirm the colonization by beneficial microorganisms in peat media? What does this all have to do with application timing?

Krause:The activity and longevity of beneficial microorganisms in their growing media depends on the type and amount organic matter present and if they can use that kind of food source. If they can degrade lignin, as many beneficial microorganisms do, TrichodermaFungal strains can survive in media that contain barks, coconut cooir, and sphagnum sphagnum. However, most beneficial bacterial strains can’t use lignin as food source. They can however use cellulose and/or hemicellulose in light sphagnum sphagnum-peat-based media. Some beneficial microbes can also survive on organic matter from the crop, such as root exudates or fragments, or by growing symbiotically within plant tissue. When their food sources become depleted, beneficial microbes die (like Gram-negative bacteria), or go dormant. BacillusThere are many beneficial fungal and bacterial strains. Survival of dormant beneficial microbes is dependent on their survival mechanisms, the energy they have to maintain them, as well as the presence of other microbes who could prey upon them. Biostimulant microbes that remain dormant in a growth medium are unlikely to be of any direct benefit to plants until they become fully active and awake again.

Freeman: Many beneficial microbes are spore-forming and can be found in spores Trichoderma Bacillus For extended periods, species can survive in peat-based media. These organisms’ survival stage, the spores, will continue to exist in the absence or supplementation of organic food sources for some time. How the media is stored will determine how long they survive. The cooler the medium, it will be longer. Some TrichodermaSome fungi can use organic matter to grow, while others (including pathogens), can parasitize other fungi in the medium. Although spores can survive for long periods of time, colonization will be limited if there is no plant host. As long as the spores are viable in the growing medium, spore germination is stimulated once roots are available. Root colonization (protection), will occur.

Timing is critical to ensure that viable inoculum is present in the growing medium at the time plants begin to develop roots (seeds, unrooted cuttings). Some growers apply at the same time as rooting. Others may pre-incorporate the microbe in the growing medium prior to seeding or sticking. There are several studies that highlight the benefits that some organisms have on seed germination and root formation/development in unrooted vegetative cuttings, including woody plants. Use of Trichoderma harzianumThese benefits have been demonstrated, for instance, when sticking or seeding has been done. Even though microbes will continue to grow along with the roots, reapplications are possible after eight to 12 weeks (for T. harzianum) are generally recommended, especially at key times in the crop cycle, when plants are potted up for example, to ensure there is sufficient inoculum in the new growing media to colonize and protect roots as they grow and develop.

Buisenbark: All beneficial relationships between plants or organisms do not depend on the colonization of the plant. Many microbial organisms can cohabitate in the same area, including living on the root, and they can function independently of the plant. Mycorrhizal mushrooms are one example of an organism that can colonize and form a mutually beneficial relationship with the plant. Although the plant is responsible for mycorrhizal fungal relationships, this is not always true for other organisms. Mycorrhizal fungal fungi are a well-known organism in scientific literature. Therefore, there are many references to illustrate plant associations in all types of growing systems. It is well-known that the benefits of this association between plant fungi and mycorrhizae can be different between container-controlled and field-grown systems. These benefits are not comparable. The measured performance of adding inoculum to these systems is dependent on their interactions. This will vary depending on the quantity and the influencers.