Chapter 29 Part 2

© 2016 Pearson Education, Inc. Concept 29.4: 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 © 2016 Pearson Education, Inc. 2

Many mutually beneficial relationships occur between species from different kingdoms or domains © 2016 Pearson Education, Inc.

© 2016 Pearson Education, Inc. Figure 29.10 MAKE CONNECTIONS: Mutualism Across Kingdoms and Domains Animal–Fungus Animal–Bacterium Plant–Fungus Leaf-cutter ants tending a fungal garden Puffer fish (fugu) Fungus on a sorghum root (SEM) Fungus–Bacterium Plant–Bacterium Plant–Animal Figure 29.10 Make connections: mutualism across kingdoms and domains The lichen Peltigera The floating fern Azolla Ants on an Acacia plant © 2016 Pearson Education, Inc.

Bacteria and Plant Nutrition Soil bacteria can benefit plants by Exchanging beneficial chemicals with plant roots Increasing nutrient availability by decomposing dead organic materials Converting nitrogen © 2016 Pearson Education, Inc.

© 2016 Pearson Education, Inc. Rhizobacteria The soil layer surrounding the plant’s roots is the rhizosphere Nonpathogenic bacteria (or fungi) called endophytes live between cells within the plant; free-living rhizobacteria inhabit the rhizosphere Rhizobacteria and endophytes depend on sugars, amino acids, and organic acids secreted by roots © 2016 Pearson Education, Inc.

Rhizobacteria and endophytes enhance plant growth by Producing growth-stimulating chemicals Producing antibiotics that protect roots from disease Absorbing toxic metals Making nutrients more available to roots © 2016 Pearson Education, Inc.

Bacteria in the Nitrogen Cycle Nitrogen can be an important limiting nutrient for plant growth The nitrogen cycle transforms atmospheric nitrogen and nitrogen- containing compounds Plants can only absorb nitrogen as either NO3– or NH4+ Most usable soil nitrogen comes from actions of soil bacteria © 2016 Pearson Education, Inc. 8

© 2016 Pearson Education, Inc. ATMOSPHERE Figure 29.12 N2 SOIL N2 ATMOSPHERE N2 Nitrate and nitrogenous organic compounds exported in xylem to shoot system SOIL Proteins from humus (dead organic material) Nitrogen-fixing bacteria Microbial decomposition Figure 29.12 The roles of soil bacteria in the nitrogen nutrition of plants Amino acids Denitrifying bacteria NH3 (ammonia) Ammonifying bacteria Weathering of rock NH4+ H+ (from soil) NH4+ (ammonium) NO2- (nitrite) NO3- (nitrate) Nitrifying bacteria Nitrifying bacteria © 2016 Pearson Education, Inc. Root

© 2016 Pearson Education, Inc. Figure 29.12-1 N2 ATMOSPHERE Proteins from humus (dead organic material) SOIL Nitrogen-fixing bacteria Microbial decomposition Amino acids NH3 (ammonia) Ammonifying bacteria H+ (from soil) Figure 29.12-1 The roles of soil bacteria in the nitrogen nutrition of plants (part 1) NH4+ (ammonium) NO2- (nitrite) Nitrifying bacteria © 2016 Pearson Education, Inc.

© 2016 Pearson Education, Inc. Figure 29.12-2 N2 Nitrate and nitrogenous organic compounds exported in xylem to shoot system Denitrifying bacteria Weathering of rock NH4+ Figure 29.12-2 The roles of soil bacteria in the nitrogen nutrition of plants (part 2) NO2- (nitrite) NO3- (nitrate) Nitrifying bacteria NH4+ Root © 2016 Pearson Education, Inc.

Conversion to NH4+ Conversion to NO3– Ammonifying bacteria break down organic compounds and release ammonium (NH4+) Nitrogen-fixing bacteria convert N2 gas into NH3 NH3 combines with H+ from soil to form NH4+ Conversion to NO3– Nitrifying bacteria oxidize NH4+ to nitrite (NO2–) then nitrite to nitrate (NO3–) Different nitrifying bacteria mediate each step © 2016 Pearson Education, Inc.

Nitrogen is lost to the atmosphere when denitrifying bacteria convert NO3– to N2 © 2016 Pearson Education, Inc.

Nitrogen-Fixing Bacteria: A Closer Look Nitrogen is abundant in the atmosphere but unavailable to plants due to the triple bond between atoms in N2 Nitrogen fixation is the conversion of nitrogen from N2 to NH3: Some nitrogen-fixing bacteria are free-living; others form intimate associations with plant roots N2 + 8 e– + 8 H+ + 16 ATP → 2 NH3 + H2 + 16 ADP + 16 © 2016 Pearson Education, Inc.

Symbiotic relationships with nitrogen-fixing Rhizobium bacteria provide some legumes with a source of fixed nitrogen Along a legume’s roots are swellings called nodules, composed of plant cells “infected” by nitrogen-fixing Rhizobium bacteria © 2016 Pearson Education, Inc. 15

© 2016 Pearson Education, Inc. Figure 29.13 Nodules Figure 29.13 Soybean root nodules Roots © 2016 Pearson Education, Inc.

© 2016 Pearson Education, Inc. Crop Rotation Alternate crops planted in the same field every other year; one depletes nitrogen, the other fixes nitrogen © 2016 Pearson Education, Inc.

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 © 2016 Pearson Education, Inc. 18

Mycorrhizae and Plant Evolution Neither early land plants nor fungi were fully equipped to exploit the terrestrial environment Fossil evidence indicates that mycorrhizae were an early adaptation that helped plants and fungi colonize the land © 2016 Pearson Education, Inc. 19

Agricultural and Ecological Importance of Mycorrhizae Seeds can be inoculated 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 © 2016 Pearson Education, Inc. 20

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 © 2016 Pearson Education, Inc. 21

Epiphytes grow on other plants and obtain water and minerals from rain, rather than tapping their hosts for sustenance © 2016 Pearson Education, Inc.

© 2016 Pearson Education, Inc. Figure 29.15-1 Epiphytes Figure 29.15-1 Exploring unusual nutritional adaptations in plants (part 1: epiphytes) Staghorn fern, an epiphyte © 2016 Pearson Education, Inc.

© 2016 Pearson Education, Inc. Figure 29.15-1 Epiphytes Figure 29.15-1 Exploring unusual nutritional adaptations in plants (part 1: epiphytes) Drynaria fern, an epiphyte © 2016 Pearson Education, Inc.

© 2016 Pearson Education, Inc. Figure 29.15-1 Epiphytes Figure 29.15-1 Exploring unusual nutritional adaptations in plants (part 1: epiphytes) Orchid, an epiphyte © 2016 Pearson Education, Inc.

Some species parasitize the mycorrhizal hyphae of other plants Parasitic plants absorb water, sugars, and minerals from their living host plant Some species also photosynthesize, but others rely entirely on the host plant for sustenance Some species parasitize the mycorrhizal hyphae of other plants © 2016 Pearson Education, Inc. 26