Supporting article X: What makes it possible for primary producers to play such a fundamental role in the cycle of life?
Physiology And Growth
Plants have adopted some simple processes that allow them to use the basic elements in the ecosystem, combine them in different ways, and use them to produce food and structures to help them thrive. As a result of this process they have a great impact on the levels of carbon dioxide and oxygen in the atmosphere.
Photosynthesis is the process by which plants make food in their leaves. On the under side of leaves are minute openings called stomata where carbon dioxide from the atmosphere enters the leaf. The cells of the plant absorb energy from the sun and the roots draw water from the soil. All those elements are combined with the help of microscopic green chlorophyll pigment within the cell walls of the leaves.
Food in the form of starches, fats and simple sugars (carbohydrates) is produced through complex chemical processes. Some is used immediately for growth and development of the plant, some combines with other nutrients to create compounds needed for plant health and structure, and some is stored for use at later stages of the plant’s life.
Plants rely on stores of carbohydrates in their roots to maintain the plant over winter and for early stem and root development. Photosynthesis increases as leaves expand providing new stores of food for growth and reproduction in the summer. Extra demand is put on the plants’ carbohydrate stores as they produce flowers and seeds in late summer.
Oxygen is essential to all life. It makes up about 20% of the atmosphere, is a component of the rain and snow that falls from clouds, and, along with carbon, is part of the basic structure of all living organisms. Oxygen is produced as a by-product of photosynthesis, passing out of the plant through the stomata and into the atmosphere.
Water Cycling and Requirements
Water is needed for plants to carry out the process of photosynthesis. An internal “plumbing” system of minute “pipes” links the veins in the leaves to the roots of the plant. A small amount of water is absorbed by the leaves themselves. Xylem cells carry the water from the roots out to the leaves and phloem cells take food back through the plant. Water not needed for photosynthesis evaporates from the stomata in the leaves. This evaporation process is called transpiration.
In hot, dry weather plants may lose more water through transpiration than can be found from the soil by the roots. Plants wilt when there is not enough water to perform photosynthesis and to keep the cells of the plant healthy.
Grassland plants have adapted to the stress of living in hot, dry conditions in many ways: some plants, such as rabbitbrush and arrow-leaved balsamroot, have pale-coloured leaves that reflect the sun and also have fine white hairs all over their surface that reduce windspeed across the leaves and reduce transpiration. Some plants, such as yellow bells, start growing before the snow has completely melted in spring and have completed their life cycle before the hottest and driest weather arrives. Yellow bells is one of many plants in the lily family found in grasslands; they survive through the summer drought and winter cold as an underground bulb. Annual plants such as small-flowered blue-eyed mary survive the drought as seeds. Some bunchgrasses are dormant through the summer months but begin growing again with fall moisture.
The long blades of bluebunch wheatgrass curve gracefully up and away from the centre of the plant and direct rainwater down into the centre of the plant towards the roots. The many long, fine roots fill the surface soils, capturing water before it can penetrate to the lower layers of the soil.
Nutrient Cycling and Requirements
Nutrients are absorbed from the soil through the roots of the plant and taken by the xylem and phloem cells to the parts of the plant that need them.
Three nutrients are especially important: nitrogen, phosphorous, and potassium.
Nitrogen is an important component in the proteins and genetic material of all organisms. It also cycles through the ecosystem. Nitrogen is released when organisms decompose and enters into the soil and the atmosphere. Some nitrogen is also produced by cyanobacteria and by lightning strikes. Plants take up nitrogen through their roots and it is passed to the consumers through the food chain.
In grasslands lichens with cyanobacteria and other free-living cyanobacteria in the cryptogamic crust play an important role in fixing nitrogen.
Phosphorus is an important component of the internal energy system of all organisms. In plants it is an essential part of the processes of photosynthesis, flowering, and root growth.
Potassium is an important component of the water circulation system in plants and of the nervous and circulatory systems of grazing animals.Other important nutrients include: sulphur, iron, calcium and magnesium.