Microbial community structure in soilless substrates used for nursery crops

Authors: VALLES-RAMIREZ, SILVIA - THE OHIO STATE UNIVERSITY; Altland, James; Testen, Anna; POELSTRA, JELMER - THE OHIO STATE UNIVERSITY; MICHEL JR, FREDERICK - THE OHIO STATE UNIVERSITY

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/23/2023
Publication Date: 10/4/2023
Citation: Valles-Ramirez, S., Altland, J.E., Testen, A.L., Poelstra, J.W., Michel Jr, F.C. 2023. Microbial community structure in soilless substrates used for nursery crops. HortScience. 58(11):1348-1357. https://doi.org/10.21273/hortsci17275-23.
DOI: https://doi.org/10.21273/hortsci17275-23

Interpretive Summary: Soilless substrates, such as peat, wood fiber, compost, perlite and vermiculite, serve as replacements for soil in the production of nursery, ornamental, and food crops in containers. Little is know about microbial communities of soilless substrates and the impacts of these microbial communities on plant health. This study examined how microbial communities change when compost or peat was added to pine bark and when birch trees are planted. Bacterial and fungal communities in pine bark, compost and peat differed, but with time, microbial communities within different substrate mixtures became more similar. Planting birch trees in the substrates did not greatly influence microbial communities. This study improved our understanding of the microbes present in soilless substrates and will help in future studies on beneficial microbes in soilless substrates to improve specialty crop production.

Technical Abstract: Soilless substrates are widely used for plant cultivation. However, little is known about the dynamics or impacts of media components or plant growth on microbial communities in soilless substrates. The objectives of this study were to analyze microbial communities in a typical pine bark substrate used for nursery crop production and to determine the impacts of compost and plant growth as well as the dynamics of these communities over a production cycle. Three soilless substrate mixes were compared consisting of 80:20:0, 80:10:10, and 80:0:20 (v:v) ratios of pine bark: sphagnum peat and leaf compost. Half of the pots in each substrate treatment were planted with a single birch (Betula nigra 'Cully') liner and the other half were unplanted. Samples were taken from containers maintained in a nursery production setting after 0, 1, 2, 3, and 4 months and DNA was extracted. Bacterial 16s rRNA and fungal ITS primers were used to amplify the DNA and sequenced to identify, quantify and compare individual ribotypes within each sample. Microbial communities in all treatments contained similar phyla and became similar to one another over time. Bacterial communities most resembled those originally in the compost material and least resembled those originally present in the pine bark. Compost amendment influenced the communities primarily during the first two months. Nitrosomonadaceae and Chloroflexi identified in compost were the most abundant communities in mixes containing 10% and 20% compost over time. The influence of planting a birch liner on the bacterial communities was minor. Fungal communities were also affected by compost amendment but were also significantly impacted by planting. Ascomycota and Basidiomycota were the most abundant phyla present in the soilless substrate mixes and resembled those originally in the peat moss and compost, respectively.