How do leaves change colours

How the colors of leaves will change in autumn.


The factors that influence the leaf colors in the autumn season are :length of night, weather. The Increasing length of night will effect on the leaf color change. The other environmental parameters like temperature, rainfall, food supply will gradually change as the length of night increases during autumn. As night time increases, the day time grow shorter and conditions will become cooler. It effects on the biochemical processes of the leaf and thus it effects on the leaves to change their color.




Where do autumn colors come from?


There are three types of color pigments that are involved in autumn color.

• Chlorophyll: gives green color to the leaves. It is useful for photosynthesis.Trees that are grown in the temperate zones store sugars for the dormant period in the winter.
• Carotenoids: helps in getting yellow, orange, and brown colors to the leaves in such things as corn, carrots etc.
• Anthocyanins: These are the water soluble pigments and appear in the watery liquid of leaf cells.

Throughout the growing season, the leaves contain chlorophyll and carotenoids in the chloroplast and anthocyanin are produced in the autumn season in response to bright light and more amount of sugars within the leaves


During normal growth of the leaf,chlorophyll is continuously produces and utilized for photosynthesis and hence leaves appear green in color. But in the autumn season, as the night length increases,chlorophyll production will be gradually decreased and finally the production is stopped. But the carotenoids and anthocyanins are kept unchanged. So that leaves show other than green color.




Certain colors are characteristic of particular species. Oaks turn red, brown, or russet; hickories, golden bronze; aspen and yellow-poplar, golden yellow; dogwood, purplish red; beech, light tan; and sourwood and black tupelo, crimson. Maples differ species by species-red maple turns brilliant scarlet; sugar maple, orange-red; and black maple, glowing yellow. Striped maple becomes almost colorless. Leaves of some species such as the elms simply shrivel up and fall, exhibiting little color other than drab brown.


The timing of the color change also varies by species. Oaks put on their colors long after other species have already shed their leaves.The differences in these timings is because of genetic inheritance ,weather conditions like temperature and moisture and the latitude at which the plant species is growing.


How does weather affect autumn color? The environment condition like warm, sunny and cool day and not freezing nights gives bright colors to the plants. In such a conditions, lots of sugars are produced in the leaf. But because of cool nights and gradual closing of veins causes obstruction to the sugar flow of the leaves. These conditions make some favour for the production of anthocyanin pigments which gives red, purple and crimson colors. These clogged veins trap sugars in the leaf and promote production of anthocyanins. Once this separation layer is complete and the connecting tissues are sealed off, the leaf is ready to fall.


The autumn colors are also influenced by the moisture in the soil. The moisture content in the soil will change according to the change in the climatic conditions.The warm period is also effect on the autumn colors. A warm wet spring and favourable summer weather and the warm sunny days with cool days will effect on the change in the color of the plant leaves.


What does all this do for the tree?


Perennial plants, including trees, must have some sort of protection to survive freezing temperatures and other harsh wintertime influences. Stems, twigs, and buds are equipped to survive extreme cold so that they can reawaken when spring heralds the start of another growing season. Tender leaf tissues, however, would freeze in winter, so plants must either toughen up and protect their leaves or dispose of them.


The evergreens-pines, spruces, cedars, firs, and so on-are able to survive winter because they have toughened up. Their needle-like or scale-like foliage is covered with a heavy wax coating and the fluid inside their cells contains substances that resist freezing. Thus the foliage of evergreens can safely withstand all but the severest winter conditions, such as those in the Arctic. Evergreen needles survive for some years but eventually fall because of old age.


The leaves of broadleaved plants, on the other hand, are tender and vulnerable to damage. These leaves are typically broad and thin and are not protected by any thick coverings. The fluid in cells of these leaves is usually a thin, watery sap that freezes readily. This means that the cells could not survive winter where temperatures fall below freezing. Tissues unable to overwinter must be sealed off and shed to ensure the plant's continued survival. Thus leaf fall precedes each winter in the temperate zones.


Use of the fallen leaves


The fallen leaves are not wasted at all. They are degraded in the soil by the decomposers and restock the soil with nutrients and forms spongy humus layer of the floor in the forest. This soil has a great hygroscopic capacity and holds rain water. In the forest ecosystem the fallen leaves are used as a food for some micro organisms which are a part of it.


Tags:Fallen leaves, colour changes, leaves changes colour,Perennial plants, Perennial, Carotenoids, chlorophyll, Anthocyanins, colors pigments in autumn, leaves change color in autumn, plants change color in autumn.

Nitrogen Fixation in plants

NITROGEN FIXATION


Nitrogen fixation is a process in which the roots of the leguminous plants (beans, grams ) give shelter to the nitrogen fixing micro organism. These micro organisms helps in the conversion of atmospheric nitrogen into nitrates and nitrites and in return they are getting food and shelter from the plants. To provide shelter to the nitrogen fixing bacteria, leguminous plants produce some nodules in their roots ( root nodules ). Such an inter relationship between two organisms in which both the organisms are benefited by helping each other. This is called SYMBIOSIS.


Why do leguminous plants need nitrates and nitrites ?


All the plants are able to absorb nitrogen in the form of nitrates and nitrites from the soil for their metabolic activities and also for the preparation of proteins and stored food items. Like all other plants, leguminous plants also absorb nitrates and nitrites from the soil by using roots.


But in case of leguminous plants, the plants use more amounts of all these nitrogenous substances for the formation of their seeds like beans and grams. For the formation of these beans and grams there is a requirement of more amounts of proteins. For the formation of the proteins nitrates and nitrites also required. So, these legume plants absorb more nitrogen from the soil but their absorbing capacity is insufficient to absorb sufficient quantity of nitrogen compounds to form seeds. As the plants are unable to absorb nitrogen from the atmosphere they will depend upon the nitrogen fixing micro organisms. For this purpose, they will attract the micro organisms like Rhizobium bacteria to get more amount of nitrogenous substances to prepare their seeds.


Nitrogen fixing bacteria present in the leguminous plants is Rhizobium leguminousarum. It converts atmospheric nitrogen to ammonia.


Ammonia is used by the plants to make amino acids. Some carbohydrates are transported to the root nodules as a food for the rhizobium bacterium. These carbohydrates are prepared by the plants during the process of respiration. In these carbohydrates, rhizobium uses some quantity as a food and the remaining quantity is used for the formation of ammonium ion (NH4+ ) from atmospheric nitrogen.

FLAVONOIDS are the chemicals produced by the legume plants and they are used to signal the rhizobium. In return, the rhizobium responds by producing a lipid-carbohydrates molecules. The lipid carbohydrate molecules stimulates the cells of the roots. The cells of roots divide rapidly to form nodules by pericycle (inner most layer of the root ). Root hairs to which the bacterium attached will curl up , thus enclosing the bacteria. Enzymes produced by the bacteria digest cell walls and enter the cytoplasm. The plant then creates a tube along which bacteria grow and delivers the bacteria to nodules. After few divisions, the bacteria lose their ability to divide and begin producing nitrogenase. The bacteria are now called bacterioid and lose the ability to survive independently.

NITRIFYING BACTERIA : These bacteria breakdown organic matter into nitrate ion ( NO3- ion ) and then to Ammonia (NH3).


Haber – Bosch process : It is the nitrogen fixation reaction. In this reaction, the N2 gas and H2 gas,in the presence of Iron or Ruthenium catalyst,produce Ammonia.


N 2 + 3H 2 ⇔ 2 NH 3


Tags: Nitrogen Fixation, plants, Nitrogen fixation in plants, Nitrifying Bacteria, Haber Bosch process, Flavonoids, leguminous plants, Rhizobium Bacteria, Ammonia