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Plant Growth
Definition
Plant growth is the irreversible, quantitative increase in size, mass, and/or volume of a plant or its parts. It occurs with an expenditure of metabolic energy. Therefore, the events leading to leaf formation and the increase in height of a plant are growth, but the increase in volume of a seed due to uptake of water or imbibition is not growth.
Quantifying Plant Growth
There are various ways of quantifying plant growth. These include cell number, fresh weight, dry weight, plant height, length, width, area, and volume. Each method has its limitations. Generally, growth is a combined effect of cell division and cell enlargement. However, in some instances, growth can occur even without cell division, and the reverse is also true.
Early Growth
Likewise, early growth of the embryo in the flower can be quantified by the increase in cell number, although these cells being small do not increase the size of the embryo.
Plant Development
Definition
Plant development refers to the various changes that occur in a plant during its life cycle. Development consists of both growth and differentiation, involving quantitative and qualitative changes. It is characterized by changes in size, shape, form, degree of differentiation, and state of complexity.
Growth and Differentiation
However, there can be growth without differentiation and likewise there can be differentiation without growth.
Factors Affecting Growth and Development
Overview
Plant growth factors control or influence plant characteristics as well as adaptation. In general, there are two factors affecting plant growth and development: genetic and environmental.
Genetic Factor
The genetic factor is also called an internal factor because the basis of plant expression (the gene) is located within the cell. This factor determines the character of a plant, but the extent to which this is expressed is influenced by the environment.
Environmental Factors
The environmental factors are divided into two main groups: biotic and abiotic factors. The descriptive word "biotic" means living while "abiotic" means non-living or dead.
Climatic Factors
Overview
The climatic factors include rainfall and water, light, temperature, relative humidity, air, and wind. They are abiotic components, including topography and soil, of the environmental factors that influence plant growth and development.
Moisture
In crop agriculture, water is an important climatic factor. It affects or determines plant growth and development. Its availability, or scarcity, can mean a successful harvest, a diminution in yield, or total failure. Most plants are mesophytes, adapted to conditions with a moderate supply of water. However, some plants, called hydrophytes, require watery or water-logged habitats, while others, called xerophytes, are more tolerant to dry conditions.
Light
Light is a climatic factor that is essential in the production of chlorophyll and in photosynthesis, the process by which plants manufacture food in the form of sugar (carbohydrate).
Factors Affecting Growth and Development (Continued)
Temperature
The degree of hotness or coldness of a substance is called temperature. It is commonly expressed in degree Celsius (°C) or Fahrenheit (°F). This climatic factor influences all plant growth processes such as photosynthesis, respiration, transpiration, breaking of seed dormancy, seed germination, protein synthesis, and translocation. At high temperatures, the translocation of photosynthate is faster, causing plants to mature earlier. In general, plants survive within a temperature range of 0 to 50°C.
Air
The oxygen and carbon dioxide in the air are of particular importance to the physiology of plants. Oxygen is essential for respiration, producing energy used in various growth and development processes. Carbon dioxide is a raw material in photosynthesis. The favorable or optimal day and night temperature range for plant growth and maximum yields varies among crop species.
Relative Humidity
Relative humidity affects the opening and closing of the stomata, which regulate water loss from the plant through transpiration and photosynthesis. Understanding this climatic factor is important in plant propagation. Newly collected plant cuttings and bare root seedlings are protected against desiccation by enclosing them in a sealed plastic bag. Propagation chambers and plastic tents are also commonly used in propagating stem and leaf cuttings to ensure high relative humidity conditions.
Wind
Moderate winds favor gas exchanges, but strong winds can cause excessive water loss through transpiration and lead to lodging or toppling of plants. When the transpiration rate exceeds water absorption, partial or complete closure of the stomata may occur, restricting the diffusion of carbon dioxide into the leaves. As a result, the rate of photosynthesis, growth, and yield will decrease.
Growth Analysis Parameters
Leaf Area Index (LAI)
LAI is the ratio of total leaf area to land area, important for assessing photosynthesis.
LAI = Total leaf area / Land area
Crop Growth Rate (CGR)
Indicates crop growth rate based on dry matter produced per day.
CGR = (W2 - W1) / (T2 - T1)
Relative Growth Rate (RGR)
Measures growth per unit dry matter, similar to compound interest.
RGR = [logeW2 - logeW1] / [L2 - L1]
Net Assimilation Rate (NAR)
Indicates net photosynthesis rate per leaf area in a day.
NAR = [(W2 - W1) / (T2 - T1)] * [(logeL2 - logeL1)/(L2 - L1)]
Leaf Area Duration (LAD)
Measures crop’s ability to maintain leaf area over time.
LAD = [L2 - L1] / [logeL2 - logeL1] * (t2 - t1)