Module 6 - Abiotic Threats

Hail damage to a Michigan backyard garden that occurred in July. Image Source: George E. Norkus.

ANNOUNCEMENTS

INTRODUCTION
Plant stress resulting from a variety of non-optimal environmental conditions can produce symptoms that can mirror those resulting from certain types of pest damage. As a horticultural professional it is important that you understand how do differentiate between biotic and abiotic stress.

Simply put biotic stress is caused by living things including those we have covered so far including, fungi, bacteria, insects, snails, mites, slugs, and others. Biotic stress comes from non-living challenges. Biotic stresses include nutrient deficiencies, salt stress, drought, freezing temperatures, excessive heat, excessive light, rapid changes in temperature, hail, lightening, heavy rain, pesticide toxicity, and even damage from mechanical equipment such as lawn mowers.

The exercise this week will be a bit different. I have inundated you with questions up to this point, so I thought it might be a good opportunity for an alternative assignment. You will be building a dichotomous key to cover all the symptoms covered on page 275 and 278 of the textbook. More detail is provided under the study exercise section.

Freezing temperatures can kill tender plants, but if properly acclimated many plants native to temperate regions can survive freezes. Spring freezes tend to be more damaging that those that might occur at other times of the year. New leaf and stem growth, and expanding buds are often very susceptible to freeze injury. Image source: net efekt

LEARNING OBJECTIVES

• Differentiate between abiotic and biotic plant disorder causes.
• List the causes of the common causes of abiotic stress in the landsccape
• Describe corrective landscape management practices for the common types of abiotic plant stress.
  

TERMS TO KNOW

• water deficiency, water excess, flooding, drought
• nutrient deficiency, nutrient toxicity
• chlorotic leaves, interveinal chlorosis, general chlorosis
• salt stress
• herbicide and pesticide phytotoxicity
• mechanical injury
• sunburn, sunscald, light deficiency
• freezing stress, chilling stress, heat stress
• edema
• ozone, sulfur oxide, pollution
  

READING AND MULTIMEDIA ASSIGNMENTS

• Chapter 6. Abiotic or Noninfectious Disorders. pages 273-275.
• Wikipedia entry on Dichotomous keys.
  

STUDY EXERCISE

1. Make sure you read the chapter and the entry on Dichotomous keys thoroughly.
   
   
2. Develop a dichotomous key for the plant stresses summarized on pages 275 and 278 of the text.
   
   
3. Build a Dichotomous key that would a user to start out with a description of symptoms of abiotic stress on a plant and identify the cause of those stress symptoms. For example, the description "Foliage is discolored, pale, or burned" should key out to excess light.
   
   
4. This may seem like a simple exercise at the outset, but let me assure you it is not. Remember that a dichotomous key should allow the user to follow a series of binary decisions to the desired outcome.
   
   
5. After trying this on you own, if you still are having difficulty contact your instructor for an appointment. This thought process if mastered will become a useful tool for many of your learning endeavors.
   

EXTRA CREDIT (+10 possible)
Explain what the cellular common mechanism would be that ties salt, drought, and freezing plant physiological stresses together.

Drought can stress some plants to the point of death, but other plants have adapted anatomical mechanisms such as water storage adaptations or deep root systems. Still others go dormant. Image Source: spoungeworthy