1. Chapter 29 Soil Bacteria and Mycorrhizal Fungi

2. Concept 29.3: Plants roots absorb essential elements from the soil Water, air, and soil minerals contribute to plant growth. – 80–90% of a plant’s fresh mass is water. – 96% of plant’s dry mass consists of carbohydrates from the CO 2 assimilated during photosynthesis. – 4% of a plant’s dry mass is inorganic substances from soil. © 2014 Pearson Education, Inc.

3. Concept 29.4: Plant nutrition often involves relationships with other organisms Plants and soil microbes have a mutualistic relationship. Microbial activity within a plant’s rhizosphere is 10 to 100 times higher than in nearby soil. Up to 20% of the plants photosynthetic output is secreted into the soil. © 2014 Pearson Education, Inc.

4. Rhizobacteria known as plant-growth-promoting rhizobacteria can play several roles. – Produce hormones that stimulate plant growth – Produce antibiotics that protect roots from disease – Absorb toxic metals or make nutrients more available to roots © 2014 Pearson Education, Inc.

5. 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 nitrate (NO 3 –) or ammonium (NH 4  ) Most usable soil nitrogen comes from actions of soil bacteria. © 2014 Pearson Education, Inc.

6. ATMOSPHERE SOIL Nitrogen-fixing bacteria N2N2 N2N2 NH 3 (ammonia) H  (from soil) Ammonifying bacteria Amino acids NH 4  (ammonium) NO 2 − (nitrite) Nitrifying bacteria NO 3 − (nitrate) Nitrifying bacteria Denitrifying bacteria Microbial decomposition Nitrate and nitrogenous organic compounds exported in xylem to shoot system NH 4  Root Proteins from humus (dead organic material) Plants can only absorb nitrogen as either nitrate (NO 3 –) or ammonium (NH 4  )

7. Roots Nodules Symbiotic relationships with nitrogen-fixing Rhizobium bacteria provide some legumes with a source of fixed nitrogen.

8. Fungi and Plant Nutrition Mycorrhizae are mutualistic associations of fungi and roots. © 2014 Pearson Education, Inc. Epidermal cell (LM) 50  m Fungal hyphae between cortical cells Mantle (fungal sheath) 1.5 mm (Colorized SEM)

9. Figure 29.14 Experiment Results Invaded Uninvaded Sterilized invaded Sterilized uninvaded Soil type Invaded Uninvaded Soil type White ash Sugar maple Seedlings Red maple Mycorrhizal colonization (%) Increase in plant biomass (%) 300 200 100 0 30 20 10 0 40 garlic mustard slows growth of other plants by preventing the growth of mycorrhizal fungi.