The benefits of added organic matter to the soil have long been known and are usually attributed to increased nitrogen, greater water-holding capacity and an increase in activity of soil earthworms and microbes. But experiments have shown that the increase in carbon dioxide (CO2) release that accompanies added organic matter is certainly one of the main reasons why adding organic matter to the soil increases plant growth.
Greenhouse owners have long understood that plants consume CO2 and release oxygen. In a greenhouse packed full of plants, through the process of photosynthesis, the plants can quickly use up most of the available CO2 and then their growth slows down or stops. To compensate for this, old time growers used to place boxes or flats of fresh manure underneath their greenhouse benches. As the manure decomposed it released CO2 into the greenhouse air and the plants grew faster as a result.
In today's modern greenhouses, especially those with concrete floors, lack of CO2 is always a concern. Most of the newer greenhouse ranges are now equipped with automatic CO2 regulators that monitor the amount of CO2 in the air inside the greenhouse and then release more as needed.
In these greenhouses with their gas growth CO2 generators the plants don't just grow bigger-- they also mature earlier.
So, what has all this to do with global warming and allergies?
As we become more and more reliant on burning petroleum products and as our global temperatures continue to rise, carbon dioxide levels in our air are rising. Before the last election we in the US had assumed, incorrectly, that no matter which candidate won the election, new controls were going to be placed on CO2 emissions.
We know better now.
The US with its huge consumption of fossil fuels, (the U.S. produces nearly 25 percent of man-made carbon dioxide emissions worldwide). also is experiencing the greatest increase in CO2. Actually, CO2 accounts for 80-85 percent of the heat trapping (greenhouse) gases contributing to global warming.
The idea that is now called the "Greening Theory" holds that all this extra CO2 is good. It will result in increased plant growth and thus in resulting increases in food supplies. There is some merit to this theory but there are numerous downsides too.
There are many negative effects from global warming but let's just consider one here, pollen production and it's affect on allergies.
Since 1959 allergies have dramatically increased in the US from 2 to 5 percent of the population affected, to a whopping 38 percent now.
Largely because of the huge horticultural "success" of the much over-simplified theory of "litter-free" landscaping we already have vast urban landscapes that are heavily loaded with wind-pollinated dioecious male cultivars (clones) of trees and shrubs. These modern landscape trees result in surrounding air with unnaturally large amounts of allergenic pollen. Because the "messy" urban female trees are now so rare, almost none of this pollen is now trapped, removed from the air and turned into seed. (Female trees produce no pollen, ever, but they do make seeds, pods, and fruit.)
We have tidy sidewalks but pollen-filled air.
Under normal carbon dioxide levels these male cloned trees will always produce abundant amounts of pollen. Under increased levels of carbon dioxide, they produce considerably more. The increase in temperature itself also results in increased pollen production, and in pollen production that starts earlier in the spring and lasts further into the fall. There is research that shows that under stress conditions male plants are able to take up more water than are females. Under stress conditions, such as drought, male trees are also able to hold onto the water they already have better than are female plants.
Where there are abundant water and soil nutrient sources the increases in carbon dioxide levels in our air will result in larger urban trees, which if they're allergy trees, will be capable of producing ever more pollen.
Increases in carbon dioxide increase plant growth but only if there is enough available extra water and nitrogen in the soil to support this additional growth. When the supplies of water and nutrients are not adequate to support this added CO2-induced growth interesting physiological things happen in plants. Foremost, it is an added stress on the plants and stress often results in an increase in unusual reproduction factors.
A stressed lemon tree, for example, will often produce a huge crop of tiny, very seedy lemons. This is simply the lemon tree's way of preparing for it's own imminent demise and also it's own legacy of possible seedlings.
Another stress example: In daily pollen collections taken by biology professor Dr. Lee Parker and his students from the top of the Fisher Science Building at Cal Poly, San Luis Obispo, California, taken during the middle of a severe seven year drought, all-time record oak pollen count levels were recorded.
In the past twenty years in particular there has been a huge increase in this planting of male cloned street trees. These trees can not produce pollen until they mature but with the increases in CO2 levels, we can predict that they will mature earlier than expected.
Shannon L. LaDeau, a researcher at Duke University found that pine trees grown with elevated levels of CO2 produced three times the normal amount of seeds and also matured prematurely.
Lewis H Ziska, Ph.D., a USDA researcher, recently found that increased CO2 resulted in huge increases in the pollen production of ragweed and other weeds.
David Karowe, a researcher at the University of Michigan, found another interesting factor about increased CO2 levels and plants: their leaves contain fewer nutrients than normal.
Nancy Tuchman, biology professor at Loyola University in Chicago, is also researching the feed value of CO2 enhanced leaves on microorganisms and insects. She found that they all grow slower when fed these "enhanced" leaves. "If all the plants are altered on a global level, then it's certainly going to affect all the organisms on Earth," she said. "No one is going to escape."
Compounding all of this is that excessive burning of fossil fuels and the resulting pollution may well be compromising our very endocrine and immune systems. Theo Colburn explored this well in the very interesting book, "Our Stolen Future."
Great increases in the already excessively high rates of urban pollen, combined with further compromised immune systems, may well be the recipe for allergies of true epidemic proportions in the not too distant future.
Dr. Robert C. Stebbins, renowned biologist from UC Berkeley, told me recently in a phone conversation, that the planting of all these cloned male dioecious and compromised monoecious trees, "is a classic example of how they just didn't think about the ecology involved."
If we don't start paying closer attention to how we landscape our cities, and we don't start getting serious about alternative clean energy sources, rampant allergies and other pollen-related illnesses may well be the end result.
This article first appeared in New Scientist Magazine, in London.