Wednesday, October 9, 2013

Trees die slowly

There's nothing random about microbes. Each one has, like larger organisms, a specific niche and set of tools to exploit it.

That extends past life into death. When creatures die each one has their own specialized set of organisms designed to feed on its remains. That's true of plants as well as animals.

Let's take the above photograph of leaves as an example. The microbes digesting the two species are feeding on different chemistries; each leaf has its own peculiar mix of nutrients, proteins, and insecticides (natural pesticides) in the form of aromatics. Hence the different patterns of decay on the leaves: the microbes involved may well be different (though perhaps related) strains, even though the leaves fell in close proximity to one another. Each leaf has a particular set of microbes that breaks it down most efficiently; and here, efficiency is everything. The faster a leaf is broken down, the sooner its nutrients become available to the plants that are still growing in the immediate vicinity; and this applies especially to the tree the leaves fell from. So there is an evolutionary dialogue taking place between the tree, its fallen leaves, and its microbes. Microbes that digest its leaves better thrive; leaves with a chemical balance (acidity and nutrient mix) suited to the microbes feed them better; and the faster the leaf nutrients are freed up and leach into the soil (creating new soil in the process) the faster the tree can use them.

There's a principle to be learned here. Efficiency, in an ecosystem, is everything. Ecosystems rely on processing nutrients both before and after the death of organisms in order to thrive. Species that process nutrients faster, in symbiosis with their microbial partners, add efficiency to the system and enhance the ability of those organisms to thrive, reproduce, and hold their own against other species.

When efficiencies are lost— or new efficiencies arise, for example, the arrival of a new flood of nutrients better suited to the efficient growth of alternate species—the dominant species in any ecosystem, microscopic or macroscopic, begin to change.  This is because ecosystems are dynamic entities that respond to changes in efficiency by favoring the organisms, or mix of organisms, best able to use them efficiently. If kudzu, for example, uses an available niche more efficiently than native plants, it grows faster.

This holds true of microbes and fungi as well as larger animals. What it means that an alteration of microbial communities leads to new arrangements in the soil, water, and even air. Residents of North Carolina found this out to their increasing dismay in the 1990's when pfisteria, a dinoflagellate protist you really don't want in your waterways, underwent explosive growth in the tidal areas of North Carolina because of a flood of nutrients entering the watershed from the explosive growth of huge, factory-type hog farming upstream. The microorganisms cause debilitating disease and massive fish kills.

Let's be clear: from the point of view of the microbes, this is not a bad thing. The overall efficiencies of the tidal ecosystems in the Albermarle, Croatan, and other NC sounds haven't deteriorated as a result of this pollution. Odds are the systems are still equally efficient; but they are no longer the same systems.

And this is the lesson: changes in microbial populations can lead to fundamental long term changes in ecosystem efficiency, resulting in drastic changes to the animal and plant communities that depend on them. This phenomenon is still poorly understood, but if the fish kills in North Carolina (and, unfortunately, many other parts of the world)  have taught us one thing, it's that these changes are often unfavorable for man.

Spectacular fish kills are more obvious than slower, long term changes in soil-based microbial populations, but the changes we can't see up front are far more insidious and will, in the long run, be much more difficult to manage. Trees under stress caused by microbial changes may die much more slowly; and the causes may not be identified until well after it's too late.

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