BIOLOGY. Plant Nutrition CAMPBELL. Reece Urry Cain Wasserman Minorsky Jackson 37. Lecture Presentation by Nicole Tunbridge and Kathleen Fitzpatrick

Transcription

1 CAMPBELL BIOLOGY TENTH EDITION Reece Urry Cain Wasserman Minorsky Jackson 37 Plant Nutrition Lecture Presentation by Nicole Tunbridge and Kathleen Fitzpatrick

2 The Corkscrew Carnivore Some plants that live in nutrient poor soils use carnivory to obtain mineral nutrients For example, Genlisea uses modified underground leaves to capture soil organisms as a source of nutrients

3 Figure 37.1

4 Figure 37.1a

5 Figure 37.1b

6 Figure 37.1c

7 Concept 37.1: Soil contains a living, complex ecosystem Plants obtain most of their water and minerals from the upper layers of soil Living organisms play an important role in these soil layers This complex ecosystem is fragile The basic physical properties of soil are Texture Composition

8 Soil Texture Soil particles are classified by size; from largest to smallest they are called sand, silt, and clay Soil is stratified into layers called soil horizons Topsoil consists of mineral particles, living organisms, and humus, the decaying organic material

9 Figure 37.2 The A horizon The B horizon The C horizon

10 Soil solution consists of water and dissolved minerals in the pores between soil particles After a heavy rainfall, water drains from the larger spaces in the soil, but smaller spaces retain water because of its attraction to clay and other particles Loams are the most fertile topsoils and contain equal amounts of sand, silt, and clay Sandy soils don t retain enough water to support plant growth; clayey soils retain too much

11 Topsoil Composition A soil s composition refers to its inorganic (mineral) and organic chemical components

12 Inorganic Components Cations (for example K, Ca 2, Mg 2 ) adhere to negatively charged soil particles; this prevents them from leaching out of the soil through percolating groundwater

13 During cation exchange, cations are displaced from soil particles by other cations, particularly H Displaced cations enter the soil solution and can be taken up by plant roots Negatively charged ions do not bind with soil particles and can be lost from the soil by leaching

14 Figure Mineral cations are released. K Soil particle K 2 CO 2 reacts with H 2 O. Ca 2 K Mg 2 H 2 O CO 2 H 2 CO 3 HCO 3 Ca 2 H H Root hair 1 Roots acidify the soil solution. Cell wall 4 Roots absorb released cations.

15 Animation: How Plants Obtain Minerals from Soil

16 Organic Components Humus builds a crumbly soil that retains water but is still porous It also increases the soil s capacity to exchange cations and serves as a reservoir of mineral nutrients Topsoil contains bacteria, fungi, algae, other protists, insects, earthworms, nematodes, and plant roots These organisms help to decompose organic material and mix the soil

17 Soil Conservation and Sustainable Agriculture Soil management, by fertilization and other practices, allowed for agriculture and cities In contrast with natural ecosystems, agriculture depletes the mineral content of soil, taxes water reserves, and encourages erosion The American Dust Bowl of the 1930s resulted from soil mismanagement

18 Figure 37.4

19 At present, 30% of the world s farmland has reduced productivity because of soil mismanagement The goal of sustainable agriculture is to use farming methods that are conservation-minded, environmentally safe, and profitable

20 Irrigation Irrigation is a huge drain on water resources when used for farming in arid regions For example, 75% of global freshwater use is devoted to agriculture The primary source of irrigation water is underground water reserves called aquifers The depleting of aquifers can result in land subsidence, the settling or sinking of land

21 Figure 37.5

22 Irrigation can lead to salinization, the concentration of salts in soil as water evaporates Drip irrigation requires less water and reduces salinization

23 Fertilization Soils can become depleted of nutrients as plants and the nutrients they contain are harvested Fertilization replaces mineral nutrients that have been lost from the soil Commercial fertilizers are enriched in nitrogen (N), phosphorus (P), and potassium (K) Excess minerals are often leached from the soil and can cause algal blooms in lakes

24 Organic fertilizers are composed of manure, fishmeal, or compost They release N, P, and K as they decompose

25 Adjusting Soil ph Soil ph affects cation exchange and the chemical form of minerals Cations are more available in slightly acidic soil, as H ions displace mineral cations from clay particles The availability of different minerals varies with ph For example, at ph 8 plants can absorb calcium but not iron

26 Controlling Erosion Topsoil from thousands of acres of farmland is lost to water and wind erosion each year in the United States Erosion of soil causes loss of nutrients

27 Erosion can be reduced by Planting trees as windbreaks Terracing hillside crops Cultivating in a contour pattern Practicing no-till agriculture

28 Figure 37.6

29 Phytoremediation 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 Plants capable of extracting soil pollutants are grown and are then disposed of safely

30 Concept 37.2: Plants require essential elements to complete their life cycle Soil, water, and air all contribute to plant growth 80 90% of a plant s fresh mass is water 96% of a plant s dry mass is from CO 2 assimilated into carbohydrates during photosynthesis 4% of a plant s dry mass is inorganic substances from soil

31 Essential Elements More than 50 chemical elements have been identified among the inorganic substances in plants, but not all of these are essential to plants There are 17 essential elements, chemical elements required for a plant to complete its life cycle and reproduce Researchers use hydroponic culture to determine which chemical elements are essential

32 Figure 37.7 Control: Solution containing all minerals Experimental: Solution without potassium

33 Table 37.1

34 Table 37.1a

35 Table 37.1b

36 Nine of the essential elements are called macronutrients because plants require them in relatively large amounts The macronutrients are carbon, oxygen, hydrogen, nitrogen, phosphorus, sulfur, potassium, calcium, and magnesium

37 The remaining eight are called micronutrients because plants need them in very small amounts The micronutrients are chlorine, iron, manganese, boron, zinc, copper, nickel, and molybdenum Plants with C 4 and CAM photosynthetic pathways also need sodium Micronutrients function as cofactors, nonprotein helpers in enzymatic reactions

38 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

39 Improving Plant Nutrition by Genetic Modification Plants can be genetically engineered to better fit the soil

40 Resistance to Aluminum Toxicity Aluminum in acidic soils damages roots and greatly reduces crop yields The introduction of bacterial genes into plant genomes can cause plants to secrete acids that bind to and tie up aluminum

41 Smart Plants Smart plants inform the grower of a nutrient deficiency before damage has occurred A blue tinge indicates when these plants need phosphate-containing fertilizer

42 Figure 37.8 No phosphorus deficiency Beginning phosphorus deficiency Well-developed phosphorus deficiency

43 Figure 37.8a No phosphorus deficiency

44 Figure 37.8b Beginning phosphorus deficiency

45 Figure 37.8c Well-developed phosphorus deficiency

46 Concept 37.3: Plant nutrition often involves relationships with other organisms Plants and soil microbes have a mutualistic relationship Dead plants provide energy needed by soil-dwelling microorganisms Secretions from living roots support a wide variety of microbes in the near-root environment

47 Bacteria and Plant Nutrition The layer of soil closely surrounding the plant s roots is the rhizosphere Rhizobacteria are free-living bacteria that occupy the rhizosphere Endophytes are nonpathogenic bacteria that live between the cells of host plant tissues

48 Endophytes and rhizobacteria depend on nutrients secreted by plant cells and, in return, help to enhance plant growth by Producing chemicals that stimulate plant growth Producing antibiotics that protect roots from disease Absorbing toxic metals or increasing nutrient availability

49 The species composition of bacterial communities living endophytically and in the rhizosphere vary markedly

50 Figure % similar Endophytes Clayey soil Endophytes Porous soil Outside rhizosphere Clayey soil Inside rhizosphere Clayey soil Inside rhizosphere Porous soil 80% similar Outside rhizosphere Porous soil Bacteria (green) on surface of root (fluorescent LM) Percent similarity of the species composition of communities Younger roots Older roots

51 Figure 37.9a Bacteria (green) on surface of root (fluorescent LM)

52 Figure 37.9b 34% similar Endophytes Clayey soil Endophytes Porous soil Outside rhizosphere Clayey soil Inside rhizosphere Clayey soil Inside rhizosphere Porous soil 80% similar Outside rhizosphere Porous soil Percent similarity of the species composition of communities Younger roots Older roots

53 Bacteria in the Nitrogen Cycle Nitrogen can be an important limiting nutrient for plant growth Plants can absorb nitrogen as either NO 3 or NH 4 Most soil nitrogen comes from actions of soil bacteria The nitrogen cycle transforms nitrogen and nitrogen-containing compounds

54 Figure ATMOSPHERE N 2 ATMOSPHERE N 2 N 2 SOIL NH 3 (ammonia) H (from soil) SOIL Nitrogen-fixing bacteria NH 4 (ammonium) Amino acids Proteins from humus (dead organic material) Ammonifying bacteria Nitrifying bacteria Microbial decomposition NO 2 (nitrate) Denitrifying bacteria Nitrifying bacteria NO 3 (nitrate) Nitrate and nitrogenous organic compounds exported in xylem to shoot system NH 4 Root

55 Figure 37.10a N 2 ATMOSPHERE N 2 NH 3 (ammonia) SOIL Nitrogen-fixing bacteria H (from soil) NH 4 (ammonium) Amino acids Proteins from humus (dead organic material) Ammonifying bacteria Nitrifying bacteria Microbial decomposition NO 2 (nitrate) Denitrifying bacteria Nitrifying bacteria NO 3 (nitrate) Nitrate and nitrogenous organic compounds exported in xylem to shoot system NH 4 Root

56 Figure 37.10aa N 2 ATMOSPHERE NH 3 (ammonia) SOIL Nitrogen-fixing bacteria H (from soil) NH 4 (ammonium) Proteins from humus (dead organic material) Amino acids Ammonifying bacteria Nitrifying bacteria Microbial decomposition NO 2 (nitrate)

57 Figure 37.10ab N 2 Denitrifying bacteria Nitrate and nitrogenous organic compounds exported in xylem to shoot system NH 4 NO 2 (nitrate) Nitrifying bacteria NO 3 (nitrate) Root

58 Conversion to NH 4 Ammonifying bacteria break down organic compounds and release ammonia (NH 3 ) Nitrogen-fixing bacteria convert N 2 into NH 3 NH 3 is converted to NH 4 Conversion to NO 3 Nitrifying bacteria oxidize NH 3 to nitrite (NO 2 ) then nitrite to nitrate (NO 3 )

59 Nitrogen is lost to the atmosphere when denitrifying bacteria convert NO 3 to N 2

60 Nitrogen-Fixing Bacteria: A Closer Look Nitrogen is abundant in the atmosphere, but unavailable to plants because of the triple bond between atoms in N 2 Nitrogen fixation is the conversion of nitrogen from N 2 to NH 3 Symbiotic relationships with nitrogen-fixing Rhizobium bacteria provide some plant species (e.g., legumes) with a source of fixed nitrogen

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

62 Figure Nodules Roots

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

64 The plant obtains fixed nitrogen from Rhizobium, and Rhizobium obtains sugar and an anaerobic environment Each legume species is associated with a particular strain of Rhizobium The development of a nitrogen-fixing root nodule depends on chemical dialogue between Rhizobium bacteria and root cells of their specific plant hosts

65 Figure Chemical signals attract bacteria and an infection thread forms. Nodule vascular tissue Bacteroids Infected root hair Infection thread Rhizobium bacteria Dividing cells in root cortex 2 Bacteroids form. Bacteroid Dividing cells in pericycle Bacteroid Root hair sloughed off Developing root nodule 5 Sclerenchyma cells The mature nodule grows to be many times the diameter of the root. Bacteroid Nodule vascular tissue 4 3 Growth continues and a root nodule forms. The nodule develops vascular tissue.

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

67 Instead of being harvested, the legume crop is often plowed under to decompose as green manure Nonlegumes such as alder trees and certain tropical grasses benefit from nitrogen-fixing bacteria Rice paddies often contain an aquatic fern that has mutualistic cyanobacteria that fix nitrogen

68 Fungi 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 Mycorrhizal fungi also secrete growth factors that stimulate root growth and branching

69 Mycorrhizae and Plant Evolution Early land plants would have encountered harsh conditions 400 to 500 million years ago These plants lacked the ability to extract essential nutrients from the soil, while fungi were unable to produce carbohydrates Mycorrhizal fungi may have helped plants overcome the challenges of life on land

70 The Two Main Types of Mycorrhizae Mycorrhizal associations consist of two major types Ectomycorrhizae Arbuscular mycorrhizae

71 Figure Epidermis Cortex Mantle (fungal sheath) 1.5 mm Mantle (fungal sheath) (Colorized SEM) Epidermal cell Endodermis Fungal hyphae between cortical cells (LM) 50 μm (a) Ectomycorrhizae Epidermis Cortex Cortical cell Endodermis Fungal hyphae Root hair (b) Arbuscular mycorrhizae Fungal vesicle Casparian strip Arbuscules Plasma membrane (LM) 10 μm

72 Figure 37.13a Epidermis Cortex Mantle (fungal sheath) (Colorized SEM) 1.5 mm Mantle (fungal sheath) (a) Ectomycorrhizae Epidermal cell Endodermis Fungal hyphae between cortical cells (LM) 50 μm

73 Figure 37.13aa (Colorized SEM) 1.5 mm Mantle (fungal sheath)

74 Figure 37.13ab Epidermal cell Fungal hyphae between cortical cells (LM) 50 μm

75 Figure 37.13b Epidermis Cortex Cortical cell Endodermis Fungal hyphae Root hair (b) Arbuscular mycorrhizae Fungal vesicle Casparian strip Arbuscules Plasma membrane (LM) 10 μm

76 Figure 37.13ba Cortical cell Arbuscules 10 μm (LM)

77 In ectomycorrhizae, the mycelium of the fungus forms a dense sheath over the surface of the root These hyphae form a network in the apoplast, but do not penetrate the root cells Ectomycorrhizae occur in about 10% of plant families including pine, oak, birch, and eucalyptus

78 In arbuscular mycorrhizae, microscopic fungal hyphae extend into the root These mycorrhizae penetrate the cell wall but not the plasma membrane Hyphae form branched arbuscules within cells; these are important sites of nutrient transfer Arbuscular mycorrhizae occur in about 85% of plant species, including grains and legumes

79 Agricultural and Ecological Importance of Mycorrhizae Farmers and foresters often inoculate seeds with fungal spores to promote formation of mycorrhizae Some invasive exotic plants disrupt interactions between native plants and their mycorrhizal fungi For example, garlic mustard slows growth of other plants by preventing the growth of mycorrhizal fungi

80 Epiphytes, Parasitic Plants, and Carnivorous Plants Some plants have nutritional adaptations that use other organisms in nonmutualistic ways Three unusual adaptations are Epiphytes Parasitic plants Carnivorous plants An epiphyte grows on another plant and obtains water and minerals from rain

81 Figure 37.14a Staghorn fern, an epiphyte

82 Figure 37.14b Parasitic plants Rafflesia, a nonphotosynthetic parasite Indian pipe, a nonphotosynthetic parasite of mycorrhizae Mistletoe, a photosynthetic parasite

83 Figure 37.14ba Mistletoe, a photosynthetic parasite

84 Figure 37.14bb Rafflesia, a nonphotosynthetic parasite

85 Figure 37.14bc Indian pipe, a nonphotosythetic parasite of mycorrhizae

86 Figure 37.14c Carnivorous plants Sundew Pitcher plants Venus flytraps

87 Figure 37.14ca Pitcher plants

88 Figure 37.14cb Pitcher plants

89 Figure 37.14cc Sundew

90 Figure 37.14cd Venus flytrap

91 Figure 37.14ce Venus flytrap

92 Video: Sundew Trapping Prey

93 Parasitic plants absorb sugars and minerals from their living host plant Carnivorous plants are photosynthetic but obtain nitrogen by killing and digesting mostly insects

94 Figure 37.UN01 Older leaf Young leaf

95 Figure 37.UN02 (from atmosphere) Proteins from humus (to atmosphere) N 2 (dead organic material) N 2 NH 3 (ammonia) H Nitrogen-fixing bacteria NH 4 (from soil) (ammonium) Amino acids Nitrifying bacteria Microbial decomposition Ammonifying bacteria NO 2 (nitrate) Denitrifying bacteria Nitrifying bacteria NO 3 (nitrate) NH 4 Root

96 Figure 37.UN03