June 25, 2019
April 16, 2019
The natural conditions in which plants and trees grow are neither uniform nor controlled. Many changes or fluctuations, even if they are temporary, can have a negative impact on and stress plants. The factors which can lead to stress can be one of two types: abiotic or biotic. Stress can have serious repercussions on various phases of a plant’s growth and, ultimately, crop productivity.
While a few stress factors can be measured in advance and prevented, most have to be dealt with after their occurrence. Thus, it is important to be able to recognize their effects.
Abiotic stress factors stem from the environment in which the plant or tree grows and include light, temperature, moisture, nutrients, and soil conditions.
Stress due to light usually occurs due to a lack of it. Light is necessary for germination, growth, flowering, fruiting, and proper ripening, so it is important that plants receive enough of it. In the case of photoperiodic plants, even the duration of light can be important. The amount of light plants receive can be measured in lux by a lux meter.
Plants are affected if the temperature rises or falls below the optimal range. Trees are more resilient than annuals or biennials to severe temperatures, and seedlings are the most sensitive group. Both proper ambient and soil temperatures are crucial for growing plants and are measured in degrees Celsius or Fahrenheit.
One of the most common stresses that plants will likely experience, especially temporarily, is due to water.
Stress due to nutrients can be one of two types: deficiency, when the essential elements are not present in optimal concentrations, and toxicity, when the elements are in excess.
Both nutrient deficiencies and toxicities can be measured through:
Salinity is one of the main soil factors causing stress in plants. Salinity results when soils have a concentration of soluble salts high enough to affect plant growth. Electrical conductivity (EC) of soil and water samples is used to measure salinity and is expressed as dS/m. Soils are considered saline if the EC is 4 dS/m or more. Nearly 20% of irrigated agricultural lands in the world are saline.
Salinity can occur due to natural causes, such as through the weathering of soil, and due to manmade causes, such as when intensive agriculture replaces perennial vegetation, and irrigation brings up salts stored underground. Salinity inhibits plant growth, because
Biotic stress arises from the other living organisms that the plants coexist and interact with. Biotic stress factors such as pathogens and herbivores can threaten food security and result in heavy monetary loses.
These stressors can be detected by visual field observations of symptoms, and the presence of causal factors can also be detected through field observations or through laboratory examinations.
Pathogens are organisms that cause disease in plants and can be viruses, bacteria, protists, fungi, or nematodes. They can attack all the parts of the plant, affecting plant growth in myriad ways and reducing the productivity of crops. They can be transmitted by insects, wind, water, and even people.
Herbivores can be small pests or mammals which feed on the leaves and other parts of the plant and can even damage entire crops in severe cases.
The effect of stress can influence the physiology of plants, change regulatory networks, and alter gene expression. It is often difficult to pinpoint the exact cause of stress in plants, as more than one factor is usually involved, and they will interact synergistically. For example, saline soils are also likely to be suffering from waterlogging, and this makes it difficult to separate the effects of the various stress factors. Therefore, a fair level of expertise is required to identify stress factors. The availability of field instruments for the detection of some factors makes non-invasive measurement easier, with the purpose of narrowing down stress factors without further stressing the plants.
A number of measurements instruments can be used to detect stress in plants, crops and forests. For example:
Science Writer, CID Bio-Science
Ph.D. Ecology and Environmental Science, B.Sc Agriculture
a. Rhodes D and A Nadolska-Orczyk. 2001. Plant Stress Physiology. 10.1038/npg.els.0001297
g. Ross M. Welch & Dr. Larry Shuman (1995): Micronutrient Nutrition of Plants, Critical Reviews in PlantSciences, 14:1, 49-82. http://dx.doi.org/10.1080/07352689509701922
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