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PLANTS DAY 5 FACTORS THAT AFFECT PLANT GROWTH SUNLIGHT Quantity and quality of light influence a plant’s ability to perform photosynthesis Quantity limited by natural environmental factors like latitude and competition from taller plants Quality of light is influenced by shading by other plants, cloud cover, time of day, and angles of incidence during different seasons – duration of natural light is dictated by the seasons TROPICAL RAIN FOREST – LOTS OF SUNLIGHT YEAR ROUND TEMPERATE RAIN FOREST (B.C.) LOTS OF SUNLIGHT FROM MAY SEPTEMBER Each m2 of ground absorbs only 66% of solar energy Each m2 of ground absorbs 100% solar energy SUNLIGHT Photoperiod, number of daylight hours in a 24 h period, is variable the further away from the equator plants are Northern hemisphere = longer daylight hours in spring and shorter daylight hours in fall and this affects productivity and reproductive life cycle of plants Different plants react differently to photoperiod length SUNLIGHT • Latitudinal variation in the intensity of sunlight results from the Earth's spherical shape; seasonal variation in solar radiation in the Northern and Southern Hemispheres are due to the Earth's tilt of 23.5º relative to its plane of orbit. • Only the tropics receive sunlight from directly overhead year round • The tropics receive the greatest annual input of solar radiation and show the least seasonal variation; only small variations in daylength and temperature occur. • Seasonal variation in light and temperature increases steadily toward the poles PHOTOPERIOD Photoperiod changes dramatically during the year in temperate regions of the world. For many floriculture crops, photoperiod controls growth and flowering, and a small change in photoperiod can mean the difference between vegetative growth and rapid flowering Short-day plants are those that flower, or flower more rapidly, when the photoperiod is shorter Long-day plants are those that flower, or flower more rapidly, when the photoperiod is longer For example, poinsettias and chrysanthemums develop vegetative growth when the photoperiod is long and flowers when the photoperiod is shorter. Growers use blackcloth to provide short days to induce flowering of poinsettias By knowing how daylength affects plant development in photoperiodic species, we can manipulate the natural photoperiod to promote vegetative growth (such as to bulk up plant size or for cutting production) or flowering, whichever is desired. Therefore, successful production of many crops requires an understanding of how plants respond to photoperiod, how photoperiod changes during the year and how to modify the photoperiod to control growth and development. WATER Water is a part of photosynthesis; maintains turgor pressure/firmness of plant tissue and transports nutrients throughout the plant Amount of water regulates opening and closing of stomata = regulates transpiration Is a solvent for minerals moving into the plant (osmosis) and for glucose to move to their site of use/storage (translocation) HUMIDITY Relative = water in air Humidity water air could hold at a given temp. Warm air holds more water vapour than cold air Similar to process of diffusion, water vapour will move from areas of high humidity to areas of low humidity Humidity in air space between cells in plants is almost 100%, so when stomata are open, water vapour rushed out into air that is less humid As water vapour rushed out, cloud of high humidity forms around stomata and this slows down transpiration and helps to cool the leaf = stomata closes tighter so as not to let as much water out NUTRITION Macronutrients: The nutrients that are required by plants in larger quantities are termed as the macronutrients. Micronutrients: The nutrients that are required in smaller quantities by the plants are called as the micronutrients. The eight micronutrients include iron, zinc, molybdenum, manganese, boron, copper, cobalt, and chlorine Macronutrient Nitrogen Potassium phosphorus Calcium Magnesium sulfur Functions Makes up amino acids and thus all proteins and nucleic acids and chlorophyll Leaf growth Involved in water balance to control operation of stomata and water intake in roots; needed to help make proteins Component of DNA, RNA; needed for mitosis and cell division Important in developing and functioning of cell walls Component of chlorophyll Component of most proteins ACIDITY Acidity is measured in pH level, a chemical property that governs how substances interact with each other A wide range of natural acidic properties are present in soils, but some soils may become too acidic for plants to grow healthily They can be treated with alkaline (basic) substances to make them more acidneutral. ACIDITY The acidity inhibits the growth of roots and the absorption of necessary minerals through the root cell walls = weaken plants, causing them to grow very slowly or turn yellowish in color = if acid remains high, plants may wither and die Different plants can survive in different acidity ranges, and hardier plants will be able to deal with high acid levels more easily. Areas with heavy rainfall tend to have more acidic soil, simply because the rain water leeches away alkaline minerals in the soil Soil with high levels of limestone will be more alkaline, while soils with high levels of granite, biomaterial (compost), peat moss or man made acidic fertilizers tend to be more acidic PLANTS AND ACIDITY Plants that thrive in acidic soil: blueberry, gardenia, azalea Plants that thrive in alkaline soil: broccoli, muskmelon, onions TROPISM Plants grow in response to external stimuli; growth responses are called tropisms and are controlled by plant hormones Positive tropisms are growths towards stimulus Negative tropisms are growths away from the stimulus Phototropism: bending and growth of a stem towards a light source – capture more sunlight energy Gravitropism: growth response to gravity. Stems show negative gravitropism and roots show positive gravitropism Thigmotropism: growth in response to touch – vines gain support by growing around a stem or tree trunk