My Green Neighbor’s Ally Seemed to Come Out of Nowhere

Something happened that made me think of a classic scene from Woody Allen’s “Annie Hall”. Woody is waiting for movie tickets and he’s stuck in line with a man behind him pontificating and annoying him.

Well, yesterday morning, life was almost like that for a neighbor of mine. She was trying to convince another neighbor not to use herbicide. Clover for example, she said, makes its own fertilizer. Why kill it?

Now, I’m not the Marshall McLuhan of clover-knowledge, but it is something I’ve dabbled in for many years. And precisely at the moment she said that, by tremendous fluke, I happened to walk by and heard her. I interrupted and said, “well yeah. Rhizobium bacteria have a great mutualism going on with clover plants and the bacteria make ammonium, which plants use to make protein, nucleic acids, etc. ..

“Oh thank you” she said! , as if I had dropped out of the sky to strengthen her argument.

If I had wanted to be rude I would have persisted and pointed out that Rhizobium causes an infection which result in nodules on the roots of clover and other legumes. The bacteria not only get sugars in return for the favor of giving the plants a form of nitrogen that they can use, but from clover and other legumes, Rhizobium bacteria get leghaemoglobins which binds to oxygen, facilitating cellular respiration. Resembling our hemoglobin, leghaemoglobin at the same time prevents excess oxygen from severely slowing down the enzyme (nitrogenase) that the bacteria use to convert relatively inert atmospheric nitrogen to ammonium ion. For over 100 years some scientists have dreamed of inducing such a partnership in other plants, but they have failed to replicate or induce such a complex association.

On the left we see clover roots infected with Rhizobium. The nodules are shaped like ends of Q-tips. On the right a nodule has been dissected to reveal the reddish color of the oxygen-carrying pigment, leghemoglobin. Source: sciencelearn.org.nz/resources/966-the-role-of-clover

Meanwhile, a few years ago, soy leghemoglobin was approved as a color additive, a definitely silly idea. Committed to not eating mammals, why would I— or a vegetarian —want to be reminded of blood while eating a soy product? On a more important note, I learned recently that bacteria known as Rhizobium leguminosarum are too diverse genetically to be considered a single species. It should not come as a shock because— what were the chances that no speciation occurred in bacteria, given that their symbiotic partners, the legume family, consist of 765 known genera and almost 20 000 species that are distributed throughout the world?

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Why so Few Tree Species in Quebec?

The total forested area on Earth is 4.06 billion hectares. 90 million of those hectares, of which 92% are publicly owned, are in a province of Canada called Quebec. It’s a vast area of trees, twice the total area that’s within Sweden’s borders. 1 out of every 45 hectares of the world’s forests are in Quebec, and yet of the ~100 000 species of trees on our planet, only about 50, or 1 in 2000 are native to Quebec. Why is there so little diversity of trees in this province?

According to a recent analysis, climate is the most important factor in determining tree diversity, and the highest number of tree species can be found in the hot, humid tropics. Why? Possibilities include a 365-day growing season which allows ample time to reproduce and recombine genes; higher mutation rates from UV and more isolated niches are my guesses. At latitudes between 45 N and and 63N, there is nothing remotely tropical about Quebec. Its lower latitudes accommodate temperate forests, but north of that is a large area featuring even longer and colder winters. These northern latitudes have the bulk of Quebec’s woodlands: the boreal forest. It is a flat area where genes don’t get isolated easily; the growing seasons are short and speciation of trees suffers. Dominating a vast forest are only five main species. Which one gets the edge partly depends on whether or not the soil retains water: white spruce is found mainly on well-drained upland; black spruce is in the damp lowlands. There is also balsam fir, jack pine and the American larch.

The bulk of Quebec’s forests are of the boreal variety, as is the case throughout the horseshoe-shaped, 2.5-to-4.2- billion-year-old Canadian Shield. (From https://www.the-forest-time.com/en/guides-des-pays-et-regions)

But why do its temperate forests only feature about 40 native deciduous species? The area that is currently temperate was completely covered by ice sheets during ice ages. During periods of glaciation, trees can survive but only in valleys. These are isolated from one another, reducing genetic drift between trees of different valleys, facilitating the formation of different species. But in Quebec, the few mountains existing in the south are too eroded and too low in elevation to block off advancing ice and to shelter the valleys.

Given that we tend to be attached mostly to the trees we grew up with, and since in Quebec’s case, the lack of tree-biodiversity is perfectly natural, I am comforted by the fact that all of its native species are familiar to me.

The genera that have the most Quebec-native species are Acer(maple) with 6; Populus (poplar) with 5; Betula (birch) with 4 and Quercus(oak) with 4. But among the eight genera that have only one lonely representative in Quebec, Rhus typhina, the staghorn sumac is one of my favorites. Elsewhere in the world, there are 200 different species of Rhus ! The staghorn reproduces both sexually and asexually by spreading seeds and rhizomes , respectively. The latter create clones, with older shoots in the middle and younger ones around the mother plant. It’s why sumacs proliferate so easily among the cleared area under hydro towers where they often coexist with wild grapes. It’s only in recent years that I realized that both wild grapes and sumac fruits are edible, although it’s best to use them to make a sweetened drink (red sumac berries) and jam (wild grapes). Sumac belongs to the Anacardiaceae family, which includes interesting warm-climate trees such as the mango (a south Asian native), cashew (of Brazilian origin) and pistachios, originally from Iran.

Staghorn sumac in the autumn.