Researchers are figuring out the mechanisms by which bacteria survive on leaf surfaces through the hot, dry days of the growing season.
We’ve always known that bacteria and fungi can – and always should – coat the surfaces of any plant. We commonly apply microbes to foliage (an aerated “tea” being the best delivery vehicle), and we can gauge progress by staining leaf samples and measuring microbe coverage using epifluorescence microscopy.
Evidence going back a decade or two has suggested that microscopic films of water allow microbes to survive on leaf surfaces, but it remained mysterious just how it all worked. (the 20th Century unfortunately didn’t contribute much to our understanding of the microbiome).
As reported in October by four researchers at Isreal’s Hebrew University, it all starts with the microscopic bits of organic and mineral matter littering the surfaces of plant foliage. These materials contain salts, which make them “deliquescent” – they can absorb moisture straight out of the air, until they accumulate a big-enough droplet to dissolve into solution. This effect, combined with the wicking properties that exist within the canyons, mountains and towering structures that compose the microscopic leaf landscape, allow tiny films of moisture to persist through the midday heat.
Droplets persist the longest in the space surrounding objects. Observations showed that physical structures, including individual bacteria, serve as anchors for the last lingering bits of moisture on a hot afternoon. Bacteria further capitalize on this phenomenon by forming aggregates, producing oozy, glue-like substances that allow them to adhere to surfaces and to one another. The larger the aggregate, the larger the moisture film it can maintain.
The researchers conducted their study mostly in the lab, using about a dozen lab-culturable species. They surmise that some among the vast number of species adapted to the phyllosphere (the above-ground portion of the plant) are adapted to the high salinity in those micro-droplets, and likely possess many other mechanisms that rely on complimentary qualities among the species that share their habitat.
This all points back, therefore, to the importance of microbial diversity in any plant-production system. Our understanding of the microbiome may still be limited, but we can see clearly that we can’t sustain maximized plant health without the diversity of microorganisms nature intended.
We here at FoothillBio are thankful for publications like the nonprofit eLife (which published this study). For decades, public research has operated under the heavy influence of industry, and has therefore focused largely on development of marketable products. This has made it all the more difficult to advance our understanding of the ecological principals at work in our farm fields.
Check it out. Good reading.