Please highlight all the terms in blue. When you are done with the notes: Read and study the chapter in the textbook. Read and review your notes. Come prepared for discussion and activities in class.

Plant nutrition: Obtaining nutrients

Which Nutrients Are Essential? An essential nutrient is an element or compound that is required for normal growth and reproduction. Most vascular plants have 17 essential elements. Three elements make up 96% of the dry mass of the plant: Carbon Hydrogen Oxygen

Macronutrients and Micronutrients Essential nutrients can be obtained from three sources: Water Air Soil

Macronutrients and Micronutrients Macronutrients are elements in the soil that plants require in large quantities. These nutrients are major components of nucleic acids, proteins, and phospholipids. Nitrogen, phosphorus, and potassium often act as limiting nutrients and their availability limits plant growth.

Macronutrients and Micronutrients Micronutrients are required in small quantities. They usually act as cofactors of specific enzymes. Examples include iron, zinc, boron, copper, and nickel. Micronutrients may be vital to plant health, even though they are required in tiny amounts.

When Key Nutrients Are in Short Supply Mobile nutrients such as nitrogen (N), potassium (K), and phosphorous (P) are readily transferred from older leaves to newer leaves when in short supply. Scarcity is reflected in the deterioration of older leaves. Immobile nutrients such as calcium (Ca), iron (Fe), and copper (Cu) remain tied up in older leaves. Scarcity is reflected in deficiency symptoms in newer leaves.

(a) Normal barley (b) N deficiency (c) P deficiency Yellowing Stunted Figure 36.2 (a) Normal barley (b) N deficiency (c) P deficiency Yellowing of leaves Stunted growth, dead spots Figure 36.2 Nutrient Deficiencies Can Produce Distinctive Symptoms. © 2017 Pearson Education, Inc.

Nutrient Uptake Most nutrient uptake occurs just above the growing root tip, in the region called the zone of maturation. Epidermal cells in this region have root hairs that increase the surface area available for nutrient and water absorption. Root hairs create a “zone of nutrient depletion” in the soil surrounding them. Continuous growth of the root tip is vital to a plant’s health.

Zone of maturation Root hairs are extensions of epidermal cells Root Figure 36.9 Zone of maturation Root hairs are extensions of epidermal cells Root hairs Figure 36.9 Root Hairs Provide Tremendous Surface Area for Nutrient Absorption. 1 mm © 2017 Pearson Education, Inc.

Mechanisms of Nutrient Uptake While nutrients pass through plant cell walls freely, plasma membranes are selectively permeable. Root hairs contain membrane proteins that bring nutrients into the cytosol of root cells. Some ions are brought in via proton pumps, which work in tandem with membrane proteins.

Nutrient Uptake via Mycorrhizal Fungi Fungi and plant roots that live in association are called mycorrhizae. Over 80% of all vascular plant species have relationships with mycorrhizal fungi. The symbiotic relationship between plant and fungi is mutualistic. Fungal symbionts obtain sugars from the plant, while plant symbionts receive soil nutrients such as nitrogen from the mycorrhizal fungi.

Nutrient Uptake via Mycorrhizal Fungi Fungi are particularly efficient at acquiring the nutrients required by plants, for two reasons: Networks of filamentous hyphae increase the surface area available for absorbing nutrients by up to 700%. Fungi can acquire nutrients from macromolecules in soil that are unavailable to non-mycorrhizal plants.

Photosynthetic products H2PO4– NH3 Cross section Plants provide Figure 36.11 Photosynthetic products H2PO4– NH3 Plants provide sugars to mycorrhizae Cross section of plant root Mycorrhizae provide nutrients to plants Soil Figure 36.11 Most Mycorrhizal Fungi and Plants Are Mutualists. H2PO4– Hyphae first secrete enzymes that digest macromolecules and then absorb the resulting products Amino acids Macromolecules Fungal hypha Enzymes © 2017 Pearson Education, Inc.

Nutritional Adaptations of Plants 99% of living plants are autotrophs, synthesizing their own sugar through photosynthesis. 95% of vascular plants take up nutrients from soil. 80% of plants obtain soil nutrients from mycorrhizal fungi. However, a few plants don’t follow these rules. Some plants parasitize other plants. Some plants appear to live on air. Some plants catch and digest insects.

Parasitic Plants Parasites live on or in a host, obtaining water or nutrients from the host and reducing the host’s fitness. Some parasitic plants are heterotrophs, producing structures called haustoria that can penetrate the host vascular system to obtain water and nutrients. Most parasitic plants are photosynthetic and use haustoria to extract water and ions from the xylem of the host plant.

Epiphytic Plants Epiphytes grow in the absence of soil, often on the leaves or branches of trees. These plants absorb water and nutrients from rainwater, dust, and particles that collect in their tissues. Some ephiphytic bromeliads have leaves that grow in rosettes to form “tanks” that collect water and organic debris. Nutrients are actually absorbed through the leaves.

(d) Mistletoe on host tree Figure 36.16 (a) Dodder on host stem (b) Haustoria (c) Ghost plant (d) Mistletoe on host tree Dodder Haustoria Figure 36.16 Parasitic Plants Extract Nutrients from Their Hosts. Host stem 1 mm © 2017 Pearson Education, Inc.

Carnivorous Plants Carnivorous plants use modified leaves to trap insects and other animals. These plants kill their prey and absorb the prey’s nutrients. Carnivorous plants make their own carbohydrates via photosynthesis, using carnivory to supplement the nitrogen available in the environment. Most are found in bogs or other habitats where nitrogen is scarce.

Modified Leaves of Carnivorous Plants Pitcher plant leaves form tubes and produce an odor to attract insects. Once inside the leaf, the insect has a difficult time climbing out and eventually drowns in the water at the bottom of the leaf. Sundews have modified leaves containing sticky hairs that trap insects. Venus flytraps capture prey by snapping shut when sensory hairs are triggered by the presence of an insect.

Figure 36.18 Trapped insect Figure 36.18 Sundews Have Modified Leaves with Sticky Surfaces That Catch Insects. © 2017 Pearson Education, Inc.