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Perennial Plant Response to Defoliation - An Overview

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Perennial Plants

It is early spring. You are driving west on Highway 2 through the native grasslands of the Nebraska Sandhills. The perennial plants that are an important part of life in this region of the world have been dormant since fall, making the countryside look desolate. However, things are about to change, not only for the plants but also for the people and cattle who depend on these plants. To truly appreciate this change, a little insight into the life of perennial plants is necessary.


Perennial plants live for three or more years, and usually produce seed or vegetative forms of reproduction each year. In Nebraska and surrounding areas, perennial herbaceous plants die back to ground level at the end of the growing season, remain dormant during the winter, and resume growth in the spring. Perennial grasses and broadleaves (also known as forbs) are herbaceous plants that are common in a diversity of landscapes including wildlands and intensively cultivated crop fields and gardens. Grasses have a hollow or pithy stem and slender leaves with parallel venation. Grass stems are also jointed, meaning there are nodes located along the stem. An example of a perennial grass is little bluestem (Schizachrium scoparium), Nebraska’s state grass. Forbs are herbaceous, broad-leaf plants that have solid or pithy stems and relatively broad leaves. An example of a perennial forb is Missouri goldenrod (Solidago missouriensis), Nebraska’s state flower.

The position and composition of leaves, stems, roots, and other parts of perennial plants are specific to an individual plant’s needs in order to survive. The following list details the plant parts of both grasses and forbs.

Figure 1: Examples of grass (left) and broadleaf (right).



 

  • Leaf: Leaves are the energy production centers of the plant. They are responsible for performing photosynthesis (discussed later) which in turn produces the carbohydrates needed for plant growth. Leaves can also act as temporary storage organs for carbohydrates during maximum production phases of the growing season.
     
  • Inflorescence: An inflorescence is a clustered flower system that produces the seed head of a grass plant.
     
  • Node: A node is the point along the stem where the leaf is attached
     
  • Internode: An internode is the space along the stem in between nodes, present in both grasses and broadleaves.
     
  • Tiller: A tiller is specific to grass plants. Also known as the shoot, it is composed of a growing point, stem, leaves, nodes, and buds.
     
  • Branch: A branch, specific to forbs, is a lateral shoot composed of stem, leaves, nodes, buds, and lateral meristem.
     
  • Rhizomes and Stolons: Rhizomes and stolons are both stem structures that grow parallel to the soil surface and are present in many different grasses and forbs. Rhizomes grow below ground while stolons grow above the soil surface. Both contain nodes that have the ability to develop into new plants.
     
  • Apical meristem (growing point): Apical meristem is involved in the primary growth of plants including root and shoot development. The apical meristem is composed of undifferentiated cells capable of developing into many different tissues. Apical meristem tissues are located at the tips of roots and the base of shoots in grasses during vegetative growth. As grass shoots begin to elongate the growing point moves from the base of the plant to a higher position along the main shoot. Apical meristem is found at the root tips and tip of the main shoot in forbs. These areas of plants are where new growth is initiated.
     
  • Intercalary Meristem: The intercalary meristem is directly involved in secondary growth such as internode and leaf growth in grasses and branch development in forbs. Intercalary meristem is located at the base of leaf blades, leaf sheaths, and internodes in grasses.
     
  • Roots: The root structure of plants can be taproot or fibrous. Both types of systems contain apical meristem tissue. The main functions of roots include absorbing nutrients and water from the soil, storing carbohydrates, and anchoring the plant in the soil. The root system of perennial plants stays intact from year to year with the potential to initiate new growth each season.
     
  • Axillary buds: Buds are described as undeveloped shoots, leaves, or flowers. The axillary buds, also known as lateral buds, are located in the leaf axil (the area created between the stem and leaf) of forbs.

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