The Plant Microbiome
Overview
The plant microbiome is the community of bacteria, archaea, fungi, and viruses that lives on, around, and inside of a plant. The plant’s microbiome plays a major role in plant growth and disease prevention. These microbes can help provide nutrients for the plant, promote plant growth, and help the plant fight off potential pathogens.
At Ceragen we are developing plant growth promoting bacterial inoculants that help increase crop yields through nutrient uptake and stress regulation. Our inoculant products are formulated using bacteria that were specifically selected for their ability to survive in hydroponic systems. To maximize yield increases we are developing tailored inoculant products for each commercially relevant crop type grown using hydroponic production.
Designed for Hydroponics
The soilless substrates and constantly moving water present in hydroponic systems is a vastly different environment to the traditional soil based home of most plant growth promoting bacteria. As such, studies have shown that the dominant bacterial species present on the roots of plants in hydroponic systems vary significantly from those found on plants grown in soil. For example, Bacillus bacterial species are a dominant component of the soil grown root microbiome but a very minor player in the root microbiome of hydroponically grown plants. The bacterial species in our inoculant products are selected specifically for their ability to form close interactions with the plant’s roots and thrive in a hydroponic based environment.
Crop Specific Inoculants
The number of bacteria that typically live around the roots of plants is about 10X to 1000X greater than the number found in the surrounding soil. This is caused by the fact that plants excrete chemicals called root exudates that act as a source of food for the microbes. Different plants produce different amounts and different types of root exudates to attract microbes that have beneficial traits and exclude those that are potentially pathogenic. As such, not all microbial products work with every species or variety of plant. To maximize yield increases our company develops inoculant products that are tailored to each crop type by selecting bacterial species that can thrive in the root zone of that specific plant type.
Tips For Using Microbial Inoculants
Microbes are living organisms just like plants, and like plants each microbe has a preferred set of environmental conditions it likes to grow under. As such, the effect of a microbial inoculant will vary between different growing systems. To account for this variability our company recommends conducting a pilot on part of your crop during the first year of an inoculant’s use so you can calculate your return on investment (ROI) when using this product. For inoculants that work by regulating the plant stress response, the expected ROI will vary from year to year depending on environmental conditions.
The Science Behind Increasing Yields
Stress Regulation
In plants the hormone ethylene plays an important role in stress regulation, as well as normal plant growth and development. Under stress conditions (such as flooding, high temperatures, drought, and increased salinity) ethylene is produced by the plant in two peaks. The first, smaller peak is caused by the plant transforming the small quantity of ACC (1-aminocyclopropane-1-carboxylate) that is normally present in the plant tissue into ethylene, which triggers genes related to various plant defense mechanisms.
The second peak of ethylene production occurs (up to several days after the first peak) as the plant produces additional ACC in response to the stress. This second peak is usually much larger and is generally detrimental to the plant. The second peak can cause effects such as leaf loss, leaf yellowing, growth inhibition, or even plant death.
Plant growth promoting bacteria produce an enzyme called ACC deaminase in response to high ACC levels that breaks down the ACC generated by the plant and decreases the magnitude of the secondary ethylene peak (typically by 50-90%). This prevents or reduces the negative effects of the plant stress response caused by the high ethylene levels generated during the second peak.
Nutrient Uptake
Bacteria posses a wide variety of traits that help improve the plant’s ability to uptake nutrients. The majority of these traits function by converting chemical nutrients into a form that is easily absorbed or used by the plant. These nutrients include phosphorus, calcium, potassium, and iron.
Certain bacteria also posses the ability to convert atmospheric nitrogen into a form that is useable by the plant. This process is called nitrogen fixation and is usually carried out by bacteria that live inside the roots of the plants in little lumps called nodules.