Chapter 37 Plant Nutrition

Overview: A Nutritional Network Every organism continually exchanges energy and materials with its environment For a typical plant, water and minerals come from the soil, while carbon dioxide comes from the air The root and shoot systems of a vascular plant ensure extensive networking with both reservoirs of inorganic nutrients

Concept 37.1: Plants require certain chemical elements to complete their life cycle Plants derive most of their organic mass from the CO2 of air, but they also depend on soil nutrients such as water and minerals

LE 37-2 CO2 H2O O2 O2 Minerals CO2 H2O

Macronutrients and Micronutrients More than 50 chemical elements have been identified among the inorganic substances in plants, but not all of these are essential to plants A chemical element is considered essential if it is required for a plant to complete its life cycle Researchers use hydroponic culture to determine which chemicals elements are essential

LE 37-3 Control: Solution containing all minerals Experimental: Solution without potassium

Nine of the essential elements are called macronutrients because plants require them in relatively large amounts The remaining eight are called micronutrients because plants need them in very small amounts

Symptoms of Mineral Deficiency Symptoms of mineral deficiency depend on the nutrient’s function and mobility within the plant Deficiency of a mobile nutrient usually affects older organs more than young ones Deficiency of a less mobile nutrient usually affects younger organs more than older ones The most common deficiencies are those of nitrogen, potassium, and phosphorus

Healthy Phosphate-deficient Potassium-deficient Nitrogen-deficient LE 37-4 Healthy Phosphate-deficient Potassium-deficient Nitrogen-deficient

Concept 37.2: Soil quality is a major determinant of plant distribution and growth Along with climate, soil texture and composition are major factors determining whether a plant can grow well in a certain location Texture is the soil’s general structure Composition is the soil’s organic and inorganic chemical components

Texture and Composition of Soils Topsoil is a mixture of particles of rock, living organisms, and humus (the remains of partially decayed organic material) The topsoil and other distinct soil layers, or horizons, are often visible in vertical profile where there is a road cut or deep hole

LE 37-5 A B C

Animation: How Plants Obtain Minerals from Soil After a heavy rainfall, water drains from the larger spaces of soil, but smaller spaces retain water because of its attraction to clay and other particles The film of loosely bound water is usually available to plants Animation: How Plants Obtain Minerals from Soil

LE 37-6 Soil particle surrounded by film of water Soil particle Root hair Water available to plant Root hair Air space Soil water Cation exchange in soil

Acids derived from roots contribute to a plant’s uptake of minerals when H+ displaces mineral cations from clay particles

Soil Conservation and Sustainable Agriculture In contrast with natural ecosystems, agriculture depletes the mineral content of soil, taxes water reserves, and encourages erosion The goal of soil conservation strategies is to minimize this damage

Fertilizers Commercial fertilizers contain minerals that are mined or prepared by industrial processes Organic fertilizers are composed of manure, fishmeal, or compost

Agricultural researchers are developing ways to maintain crop yields while reducing fertilizer use Genetically engineered “smart” plants inform the grower when a nutrient deficiency is imminent

No phosphorus deficiency Beginning phosphorus deficiency LE 37-7 No phosphorus deficiency Beginning phosphorus deficiency Well-developed phosphorus deficiency

Irrigation Irrigation is a huge drain on water resources when used for farming in arid regions It can change the chemical makeup of soil

Erosion Topsoil from thousands of acres of farmland is lost to water and wind erosion each year in the United States Precautions, such as contour tillage, can prevent loss of topsoil

The goal of soil management is sustainable agriculture, a commitment embracing a variety of farming methods that are conservation-minded

Soil Reclamation Some areas are unfit for agriculture because of contamination of soil or groundwater with toxic pollutants Phytoremediation is a biological, nondestructive technology that reclaims contaminated areas

Concept 37.3: Nitrogen is often the mineral that has the greatest effect on plant growth Plants require nitrogen as a component of proteins, nucleic acids, chlorophyll, and other important organic molecules

Soil Bacteria and Nitrogen Availability Nitrogen-fixing bacteria convert atmospheric N2 to nitrogenous minerals that plants can absorb as a nitrogen source for organic synthesis

Improving the Protein Yield of Crops Agriculture research in plant breeding has resulted in new varieties of maize, wheat, and rice that are enriched in protein Such research addresses the most widespread form of human malnutrition: protein deficiency

Concept 37.4: Plant nutritional adaptations often involve relationships with other organisms Two types of relationships plants have with other organisms are mutualistic: Symbiotic nitrogen fixation, involving roots and bacteria Mycorrhizae, involving roots and fungi

The Role of Bacteria in Symbiotic Nitrogen Fixation Symbiotic relationships with nitrogen-fixing bacteria provide some plant species with a built-in source of fixed nitrogen For agriculture, the key symbioses between plants and nitrogen-fixing bacteria occur in the legume family (peas, beans, and other similar plants)

Along a legume’s roots are swellings called nodules, composed of plant cells “infected” by nitrogen-fixing Rhizobium bacteria

Bacteroids in a soybean root nodule. 5 µm Bacteroids within vesicle Nodules Roots Pea plant root. Bacteroids in a soybean root nodule.

Inside the root nodule, Rhizobium bacteria assume a form called bacteroids, which are contained within vesicles formed by the root cell

The bacteria of a root nodule obtain sugar from the plant and supply the plant with fixed nitrogen Each legume species is associated with a particular strain of Rhizobium

LE 37-11 Rhizobium bacteria Dividing cells Infection in root cortex thread Dividing cells in root cortex Bacteroid Dividing cells in pericycle Infected root hair Developing root nodule Bacteroid Nodule vascular tissue Bacteroid

The Molecular Biology of Root Nodule Formation The development of a nitrogen-fixing root nodule depends on chemical dialogue between Rhizobium bacteria and root cells of their specific plant hosts

Symbiotic Nitrogen Fixation and Agriculture Crop rotation takes advantage of the agricultural benefits of symbiotic nitrogen fixation A non-legume such as maize is planted one year, and the next year a legume is planted to restore the concentration of nitrogen in the soil

Mycorrhizae and Plant Nutrition Mycorrhizae are mutualistic associations of fungi and roots The fungus benefits from a steady supply of sugar from the host plant The host plant benefits because the fungus increases the surface area for water uptake and mineral absorption

The Two Main Types of Mycorrhizae In ectomycorrhizae, the mycelium of the fungus forms a dense sheath over the surface of the root

LE 37-12a Epidermis Cortex Mantle (fungal sheath) 100 µm Endodermis hyphae between cortical cells Mantle (fungal sheath) (colorized SEM) Ectomycorrhizae.

In endomycorrhizae, microscopic fungal hyphae extend into the root

LE 37-12b Epidermis Cortex 10 µm Cortical cells Endodermis Fungal hyphae Vesicle Casparian strip Root hair Arbuscules (LM, stained specimen) Endomycorrhizae.

Agricultural Importance of Mycorrhizae Farmers and foresters often inoculate seeds with fungal spores to promote formation of mycorrhizae

Epiphytes, Parasitic Plants, and Carnivorous Plants Some plants have nutritional adaptations that use other organisms in nonmutualistic ways Video: Sun Dew Trapping Prey

LE 37-13a Staghorn fern, and epiphyte. This tropical fern (genus Platycerium) grows on large rocks, cliffs, and trees. It has two types of fronds: branched fronds resembling antlers and circular fronds that form a collar around the base of the fern.

LE 37-13b Host’s phloem Dodder Haustoria Mistletoe, a photosynthetic parasite. Dodder, a nonphotosynthetic parasite. Indian pipe, a nonphotosynthetic parasite.

LE 37-13c Venus’ flytrap. Pitcher plants. Sundews.