Jim McLain
Special to the Yakima Herald-Republic
There have been incredible findings by researchers in recent years concerning how plants in our landscapes communicate with one another and insects. Would you believe that some plants send out SOS distress calls pleading for help from beneficial predacious insects to come to their rescue? Even more astounding, plants have underground early warning stem internets they use to communicate with one another warning of a possible invasion by harmful insects.
It’s been known for several thousand years that plants communicate with insect pollinators. They communicate with pollinating insects by flaunting colorful flowers and by releasing enticing aromas. But now we know that plants do a lot more communicating than botanists and entomologists once ever dreamed of. It’s also been known for years that plants produce foul-tasting and sometimes toxic chemical compounds in their leaves to discourage insects from devouring them.
Recent discoveries
In recent years, researchers have discovered that some plants emit volatile chemicals (gases) into the air that send out SOS calls to beneficial predacious insects to come to their aid and attack invading bad bugs. For example, it is now known that tiny predacious wasps often answer these calls for help. Upon arrival, they lay their eggs on invading caterpillars (like tomato hornworms). After the eggs hatch, the larvae bore into the caterpillars and devour the caterpillar’s innards. In other cases, predacious insects as large as dragonflies answer the call for help and directly kill and eat the invading munching monsters.
When scientists first observed that plants used volatiles to send out alarms pleading for help, they thought that nearby plants also get a whiff of the volatile chemical and begin preparing for the bug invasion. And possibly they do, but there is a more complex system of inter-plant communication beneath the soil’s surface that works more effectively.
Earlier, researchers had discovered that there were some fascinating things going on down in soil between plant roots and mycorrhizal fungi. These two had a thing going on between each other in which both benefited, sort of like “you scratch my back, and I’ll scratch yours.”
It was found that mycorrhizal fungi, of which there are at least 200 different species, were able to colonize root surfaces with tiny threadlike hyphae. These hyphae are able to grow much further and into smaller spaces than plant roots can to take in water and nutrients that are then delivered to plant roots. In fact, mycorhizae fungal hyphae increases nutrient and water intake as much as 100 to 1,000 times more than plant roots could. In return, plant roots release carbohydrates for mycorrhizal fungi to use for food. Since fungi cannot make their own food because they lack chlorophyll and live underground, it becomes a good deal for both fungi and plants.
But more recently scientists have found that in any one area, sometimes up to thousands of acres, all plants are also linked to one another by a complex connection of plants and mycorrhizae. So when the first plant is attacked, the news of the pending invasion quickly spreads throughout the entire complex via the early warning system so that all connected plants can quickly prepare to meet the invasion by producing toxic compounds in their leaves.
All of this is not to say that nature’s early warning defense system is perfect — far from it. Diseases and bad bugs do get the upper hand and win their share of battles, but in the end it usually balances out — insects are there to fight another day and plant species rarely become extinct. And since plants lack a central nervous system, it would be faulty to think that plants can actually reason; they simply react to various stimuli.
What it means to you
There are at least two kinds of mycorrhizal fungi lurking beneath the soil’s surface in your landscape. One kind cooperates with wood plants, including trees, shrubs and some perennials. The other kind cooperates with vegetable plants and annual flowers. How effective these plant/mycorrhizae mutualistic systems thrive depends to a large degree on how you care for the soil under your lawn, trees, shrubs, flowerbeds and vegetable garden.
The less you disturb the plant/mycorrhizae connection the better. Once you have a healthy lawn established, you probably won’t disturb or compact the soil unless heavy construction equipment is brought to work or you often park your vehicles on your lawn. The soil beneath your tress and shrubs usually is not disturbed.
It’s your flowerbeds and vegetable gardens that most often have their soil disturbed. Hoeing and pulling weeds can disturb the root zones where the mycorrhizae/plant action takes place. If you habitually hoe your flowerbeds and vegetable garden, limit cultivation to the top inch of your soil. Disturbing the soil by deep cultivation, spading or tilling is like cutting your telephone lines. Lack of connection of mycorrhizae with plant roots results in the disconnection of the nutrient and water delivery and the underground early warning system.
What if your soil has been badly disturbed by regularly spading and hoeing? What if your soil has been compacted by heavy construction machinery? In either case much, but not all, of the mycorrhizae/plant connection likely has been destroyed.
You could go on the Internet and type in the word “mycorrhizae” and a plethora of companies will advise you to buy their blend of mycorrhizae inoculants to be spread in the root zone of your soil to almost magically solve your soil problems (they claim). While applying mycorrhizae inoculations to your soil will do no harm, neither will they do much good, according to several university research studies.
So what can you do to build up mycorrhizae in depleted soil? The answer is mulch, mulch, mulch with organic matter, rather than hoe, hoe, hoe. It may take a years for mycorrhizae to make a comeback, but it will.
This is just an additional reason why you would be wise to switch to the no-till method of gardening. (No-till gardening was the topic of a recent On Gardening column.) The less you disturb your soil, the more complex the plant/mycorrhizae mutual benefit system works. It also means that you will need to use fewer fertilizers and insecticide, whether you use either organic or chemical ones.
• Freelance gardening columnist Jim McLain can be reached at 509-697-6112 or ongardening@fairpoint.net.
Source: Plants use fungi to communicate
Photo by A. Jorjadze
