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| Cellular mechanics are complicated. |
Water transport via xylem is one of the wonders of nature. For starters, it all occurs without the expenditure of any energy by the plant. Imagine how much power would be required to pump water up to the top of a redwood tree. Yet, that tree can bring water to its leaves without using its valuable energy reserves. We would not have tall trees if energy were required to deliver water through them...
This raises two questions. First, why does the water enter the plant? Molecules of water enter the plant root because of root pressure. There is usually a higher concentration of nutrients than water inside root cells. As a result of osmosis, water outside the roots moves across the root cell membranes to dilute these concentrations inside the cells.
The second question is why water inside a root moves toward the xylem system. Here, there are three forces at play: transpiration (the evaporation of water from the surface of the plant), water cohesion, and water adhesion. To understand transpiration, one needs to consider the leaves of the plant. The stomata are leaf pores that open during the day to let in the carbon dioxide needed to make sugars. At the base of these openings are the ends of xylem tubes. Water in the xylem evaporates out into the atmosphere when the stomata are open. Some leaves also have trichomes, tiny hair-like structures that help draw the water that evaporates out, up, and away from the leaf body where there is more air circulating, speeding the evaporative process.
Lowenfels, Jeff; (2013-05-07). Teaming with Nutrients: The Organic Gardener’s Guide to Optimizing Plant Nutrition (Kindle Locations 1232-1235). Timber Press. Kindle Edition.
Water transport is the great issue in gardening and agriculture. We have a dead tree devoted to hanging hoses for the winter, our own Laocoon. Besides that, the soaker hoses remain in the rose garden and on the backyard fence.
Civilizations have risen and fallen based on the availability of water. Some think the mysterious Indian tribe in Phoenix simply ran into a long drought and disappeared. Much later, to change the city's luck, the federal government built a $4 billion water project.
On farms, irrigation is used to dodge the problem of drought, but too much ground water can wreck the soil for growing, as inorganic salts accumulate.
Considering the human problems of water distribution, the natural solutions go far beyond the marvelous. The microscopic engineering of plants assures that water will move up from the roots and evaporate into the atmosphere. Although watermelons can explode from too much water entering after a big rain, plants expertly regulate how much water enters and leaves.
If this were not enough, the other aspect of water movement is nutrition, giving each part of the plant the elements needed while it produces food from solar energy. Some of this is done within the plant itself while key aspects are handled by microscopic life.
Leveraging the Roots
When I learned that trees do most of their feeding in the top 12 inches of soil, something seemed wrong. How could such an enormous plant be so shallow in gathering nutrition? The role of fungus explains this, since fungi multiply the power of the roots
Both types of mycorrhizal fungi can extend the reach as well as the surface area of plant roots; the effective surface area of a tree’s roots, for example, can be increased a fantastic 700 to 1000 times by the association. Mycorrhizal fungi get the carbohydrates they need from the host plant’s exudates and use that energy to extend out into the soil, pumping moisture and mining nutrients from places the plant roots alone could not access.
Jeff; Lowenfels, (2010-09-10). Teaming with Microbes: The Organic Gardener's Guide to the Soil Food Web, Revised Edition (Kindle Locations 976-979). Timber Press. Kindle Edition.
Trees are powerful influences in the yard. We always seem to end with a bedroom on the west side of the house, potentially baked by the setting sun. In Springdale, the afternoon heat is felt with the sun overhead, but the setting sun is filtered by trees evaporating moisture to cool the backyard. Or AC has to be reset as soon as the sun begins to set.
And yet, without fungus, the trees would wither up and die, so which plant is more powerful, the visible one we enjoy or the microscopic one we never see?
