The simplest way to tell if lichen is dormant or growing is by looking at its color. The darker black or brighter green lichen is, chances are that it is photosynthesizing.
Of course, if it is wet and pliable, that is a good indication too. If lichen looks pale and is dry and brittle, then it is dormant and waiting for the next rain or fog event before it starts photosynthesizing.
Lichens need clean, fresh air to survive. They absorb everything through their cortex. From beneficial nutrients to harmful toxins, lichens absorb it all. They also absorb water in the air, which is why so many are found in fog belts along oceans and big lakes. Look around the big cities of the world. What do you see? Very few lichens can survive near factories, next to highways, and other sources of pollution.
The ones that do survive have a higher tolerance to the pollutants in the air, like heavy metals and acid rain. Just like all living things, lichens need nutrients to survive and grow. The main nutrients include nitrogen, carbon, and oxygen. Nitrogen is especially important since it is necessary for the production of proteins and organic acids, and not just for lichens, but for life on this planet.
Lichens, like plants, have difficulty retrieving nitrogen for their use. That is why cyanobacteria are so useful. Like plants, lichens use cyanobacteria to "fix" nitrogen so it can be used. Fixing nitrogen is the process of changing unusable nitrogen into a usable form of nitrogen. Plants like legumes and rye grass use cyanobacteria to fix nitrogen from the soil.
Lichens use cyanobacteria to fix nitrogen from the air. Similar to plants, all lichens photosynthesize. They need light to provide energy to make their own food.
More specifically, the algae in the lichen produce carbohydrates and the fungi take those carbohydrates to grow and reproduce. Different lichens need different amounts of light.
That is why you will find lichens on exposed rock and desert soils, as well as on a leafy tree or in its shadow on the mossy ground below. The color of lichen is also dependent on the amount of light it receives. It is not algal or fungal. So why are lichens found on mainly dead or dying trees? They need sunlight for photosynthesis to provide food for themselves. During the summer the leaves of deciduous trees, which drop their leaves in winter, provide shade to help retain moisture.
During the winter leaf drop allows more sunlight through. Lichens will attach and grow where moisture and sunlight are appropriate for photosynthesis to manufacture carbohydrates for sustenance. When they are found on dead or dying branches, particularly when accompanied by thinning of the tree crown, they have located themselves because of the geater availability of light from leaf drop. A resident brought in some branches of a redbud Cercis spp. All of the leaves had visible signs of downy mildew.
The resident noted that the top of the tree was losing leaves. The conditions described are a good example of the presence of lichen providing an alert that trouble may be arising and should be evaluated.
Redbud should not be dropping canopy leaves right now. Canopy die-back is a warning of a potential disease for the species. The presence of downy mildew indicates another stressor, a moisture excess, that allowed a fungal infection to advance but not from the lichen. We provided a list of certified arborists with the recommendation that the tree be evaluated on site for stressors including insect, disease, or environmental. Removal of dead branches to encourage new growth, or cultural change in watering or fertilizing might help the tree, but a tree expert needs to assess the cause.
You may have heard that lichens indicate good air quality. It has a pale green, granulose thallus and brown, convex apothecia. Some people believe that lichens that grow on trees are killing the trees. While there is still much to be learnt about the interactions between trees and lichens a century of investigation has produced no evidence to show lichens to be a major problem on trees. Of course there's more than trees to the plant kingdom and you can find lichens associating with a great variety of plants - trees, shrubs, herbs, grasses, ferns, bryophytes.
The word bryophytes is the collective term for mosses, liverworts and hornworts. Looking at the plant kingdom as a whole the only general comment that can be made is that lichens may have adverse or beneficial effects on plants.
In this section we'll look at some of those effects. The lichen hyphae block lenticels, split cork layers horizontally, and by increasing air exchange in the bark indirectly cause the cork cells to thicken and become more permeable to water. Small shrubs and trees densely covered with lichens could clearly be stunted and damaged. There is also no doubt that epiphytic lichens can have deleterious effects on the host plants.
A study that compared oak twigs heavily covered by the fruticose species Evernia prunastri with lichen-free oak twigs found that leaves growing from the former had a lower chlorophyll content than leaves growing from the latter.
Another study found that hyphae of Evernia prunastri could grow into the xylem vessels of host trees, so providing an entry point for lichen metabolites into the host plant. Pseudocyphellaria sp. These observations could initially give the impression that lichens are terribly destructive. However, the records of any lichen-induced death or severe debility seems to be rare.
Moreover, if you think for a minute you'd probably be able to recall having seen many healthy, lichen-covered trees. It is difficult to generalize about lichen penetration of bark since many factors will influence the depth of penetration. Thus far relatively few lichens have been shown to be deeply penetrating.
0コメント