Bacterial population dynamics after foliar fertilization of almond leaves

Authors: McGarvey, Jeffery - Jeff; HAN, RUYANG - University Of California; TRAN, THAO - University Of California; Hnasko, Robert; BROWN, PATRICK - University Of California

Submitted to: Journal of Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/26/2018
Publication Date: 12/4/2018
Citation: McGarvey, J.A., Han, R., Tran, T., Hnasko, R.M., Brown, P. 2018. Bacterial population dynamics after foliar fertilization of almond leaves. Journal of Applied Microbiology. 126(3):945-953. https://doi.org/10.1111/jam.14169.
DOI: https://doi.org/10.1111/jam.14169

Interpretive Summary: We examined the types of bacteria that live on almond tree leaves after being sprayed with a concentrated foliar fertilizer commonly used in orchards. We observed that the fertilizer reduced some bacteria on the leaves that are involved in nitrogen cycling (dinitrogen fixation and ammonia oxidation) and increased other bacteria, many of which have been shown to be beneficial to the trees because they are able to enhance growth by producing plant growth promoting substances or plant health because they induce the plant’s immune system. It was previously believed that foliar fertilizers only supplied nutrients to the plant but this study showed that they can also alter the bacteria on the plant such that in may also enhance growth and health.

Technical Abstract: Aims: To describe the affects of foliar fertilizer application on the microbiota of almond tree leaves. Methods and Results: We applied a foliar fertilizer onto the leaves of almond trees using a commercial sprayer and collected leaves 1, 7, 14 and 56 days post application and examined their microbiota by 16S rRNA gene sequence analysis. We observed a significant decrease in sequences associated with the bacterial phylum Proteobacteria and significant increases in those associated with the phyla Actinobacteria and Firmicutes after fertilizer application. Significant decreases were also observed in sequences associated with the archaeal phylum Thaumarchaeota after application. Conclusions: Foliar fertilizer application was deleterious to some microorganisms, including many involved in nitrogen cycling; and beneficial to others, many of which have been shown to enhance plant growth and health. The reduction in those that oxidize ammonia or produce plant usable forms of nitrogen (i.e. diazotrophs) would seem to be of little consequence, as ample nitrogen is supplied in the fertilizer. However, the increase in plant growth and health promoting bacteria may be beneficial for plant productivity. Significance and Impact of the Study: This is the first report of the effects of foliar fertilizer application on the microbiota of leaves and provides new insights as to how this process alters the leaf microbiota in ways that may be beneficial to the plant.