“Now the snow can blow,” said Glenn as he came in from doing the last of the chores. He tucked away all the breakable containers and puts plastic bags over some because he uses them to weigh down his pool cover.
It’s a grey November day, the only colour a blaze of orange from the pretty summertime lime Berberis thunbergii ‘Aurea Nana’ in my front yard. This is the beauty that never gets more than a couple of feet tall and can be trimmed, if you are of a mind, into a well-behaved ball that stands out incandescently in the garden. I have three of these barberries. The largest is about seven years old. The other two are at least three years old and still very small, under 12 inches – they seem to take a long time to establish here in Manitoba. I can’t wait until they are all big enough to be showstoppers in the garden in summer and in fall.
It always makes me happy to see them, although I have never seen them bloom or produce berries. But their smiling foliage is enough.
The other morning, as I left the house to go to my office, I noticed a scattering of white marbles all over the lawn. It looked as though we had been visited by a herd of albino bunnies over night, but it was just hard little lumps of hail. It keeps trying to snow, to do its natural thing here, but not just yet.
I read the other day that, before a cloud can produce rain or snow it must produce ice. The ice droplet forms around a nucleator (a particle that becomes the nucleus of a group of water molecules, in this case). Sometimes the nucleator is a speck of dust or a mineral, such as salt, but now it is believed that, more often, the nucleator is biological in origin, often a bacterium called Pseudomonas syringae, a plant pathogen the causes bacterial speck, a nasty disease, on tomato plants. It can also attack canola and other plants.
Dust and salt particles work as nucleators at very cold temperatures whereas the biological catalysts do their job about around or just below 0 degrees C. Nucleation is also what allows a frog to freeze into a “frogcicle” (see Ten Neat Things, November 4, 2011) and it’s the same thing that causes a diet cola to explode when combined with Mentos candies).
Many of the bacterial nucleators are pathogenic in nature and falling to earth can break the walls of the plant cells they feed upon. In addition to tomato speck, Pseudomonas syringae can also cause frost damage to plants. On the other hand, a little scientific manipulation can also make the bacteria useful in protecting citrus crops from frost damage.
Bacteria may be implicated in drought
Without the biological vectors, rain has to get as cold as -40 C before it falls. The bacteria, however, cause ice to form at a much higher temperature so that rain can fall in temperate and even hot regions.
A woman named Cindy Morris, an Agriculture Plant Pathologist at the French National Research Institute, has proven that bacteria are good at making water freeze. She cooled a tube of water to about -6 degrees Celsius, without freezing it. When she dropped some bacterial culture into the tube, the water froze completely in less than two seconds.
Some scientists postulate that a lack of bacteria can create drought. If land is too closely grazed, for example, there is no host for the bacteria and hence no rain.
This hypothesis about bacteria and rain has been around for about 25 years, but it has only recently that there has been a renewal of interest and study on the topic of what is now being called bioprecipitation.
It is part of the wonder of gardening and biological life that never ceases to capture my imagination.
November 6, 2011