Answer Internal Staff
The most obvious factors influencing plant growth are those that are necessary for plant survival and photosynthesis, known as limiting factors; sunlight, water, carbon dioxide and oxygen. During photosynthesis, atmospheric carbon dioxide is fixed into more complex, energy-rich compounds used in metabolism or as raw materials in the synthesis of cellular components that the plant needs. To ensure efficient gaseous exchange, the inner surfaces of the leaf (the spongy mesophyll) need to be kept moist, and constantly lose water to the atmosphere, which needs to be replaced. Water is also therefore an important limiting factor in plant growth and survival.
Plants also require small amounts of many different elements, including phosphorus, potassium, sodium and calcium. These form important components of enzymes and other biological molecules. Plants also require a constant supply of nitrogen in order to construct their proteins, and its lack results in severely stunted plants. Although the atmosphere contains 78% nitrogen, most plants cannot absorb this directly. Some plants (such as clover and legumes) form symbiotic relationships with nitrogen-fixing bacteria in their roots to ensure a constant supply. Other plants can benefit from the increased nitrogen concentration these plants leave in the soil; this is part of the basis of crop rotation.
Other factors which can influence the growth of plants include plant hormones. These have a wide variety of effects, and can be used to influence crop growth to suit human needs, such as producing seedless fruit, and influencing crops’ growth patterns. Some plant parasites can also influence plant hormones to suit their needs; Phytoplasma bacteria are parasites of the phloem spread by insects such as leafhoppers. Phytoplasma cause plants to become more bushy and densely branching (phyllody), and reduce their chemical defences to make them more appealing these insects.