Functionality of microbiome in the soil system
May 1, 2017
By Likun Wang
This year CSANR sponsored registration for several WSU students to attend the Tilth Conference. We will be posting reflections written by the students over the next several weeks. Please feel free to comment and give these students your feedback.
As a PhD student in the Department of Plant Pathology, I recently attended the Tilth Conference in Wenatchee, which provided me the opportunity to hear great presentations and spark my thinking on the topic of microbiomes. I am currently working on Brassica seed meal amendments for suppressing apple replant disease under the supervision of Dr. Mark Mazzola. Several presentations, including one by Dr. Mazzola, were inspiring to me at the conference.
“Soil is the living thin skin of our planet,” said Dr. David Granatstein in his presentation. Farmers care a lot about their soils and they are eager to figure out what factors contribute to a healthy soil. It is not an easy question since there is not a single model that fits everything. Soil health can be related to several factors, such as disease suppression, plant access to the water and access to nutrients. Carbon and organic matter are also important elements in the soil system that contribute to the support of a microbiome that is relatively stable and has the capacity to function well, even during low level disturbance. If the microbiome has the capacity to respond to the disturbance, then the plants can probably overcome it.
When we talk about sustainable agriculture, ecologists always highlight the importance of complexity or diversity of the system. Though it is true in some situations, diversity is not everything for the resilience of the soil system. Dr. Mazzola gave us a good example in his presentation during the Tilth Conference Symposium Session. He showed that the diversity of the microbiome in soil amended with canola meal was actually decreased, however this microbiome functioned much better than in non-treated soil, with pathogens decreased in the less diverse, treated system. So, if you have a functional microbiome, it does not matter how diverse the microorganisms are. Reduction in diversity and increase in functionality, like in soil treated with canola meal, is still going to protect the plant against particular pathogen attacks.
Functionality of the microbiome not only prevents pathogen invasion but also supports particular stages of plant growth. For example, plants have a unique rhizosphere microbial community in the flowering stage. During plant growth, many changes occur impacting the overall availability and composition of exudates going into the soil system or rhizosphere. Those exudates make a condition that is conducive for a particular microbiome that supports plant growth. Here is an interesting question: If we study the flowering stage of the model plant Arabidopsis, extract its microbiome from the rhizosphere soil and put the microbiome in the rhizosphere of another plants such as an apple, can we make it flower? Answer: No! Because the exudate expression is not only different from plant to plant but also from genotype to genotype. The interaction of plant host and soil microbiome is more complex than we can imagine, and the interactions are more specialized than universal.
If knowing of the existence of functional microbiome were the first step, then the second step would be determining how to put them into practical use. The Tilth Conference inspired my thinking along these lines and I am eager to integrate what I learned into my research.