1. Plant nutrition often involves relationships
37.3
Plant nutrition often involves relationships
with other organisms

2. Rhizobacteria
Rhizosphere: the soil layer that is bound to the plant’s roots.
Rhizobacteria: Soil bacteria with especially large populations in the rhizosphere
Roots of a plant’s rhizosphere secrete nutrients; sugars, amino acids, organic acids
Plant-growth-promoting-rhizobacteria
Have chemicals that induce plant growth
Produce antibiotics that protect against disease
Absorb more nutrients

3. Nitrogen-Fixing Bacteria
Plants cannot use free gaseous nitrogen in Earth’s atmosphere (N2)
Nitrogen Fixation- process of reducing N2 to NH3 so a plant can use it use
N2 + 8e- + 8H+ + 16ATP2NH3 + H2 + 16ADP + 16Pi
N2 reduced to NH3 by adding electrons and H+
Reaction catalyzed by nitrogenase enzyme
Ex. Bacteria Rhizobium and legume plant roots
Rhizobium fixates N2 so it can be processed by the legume root

4. Nitrogen Fixation and Agriculture
Crop rotation- crops rotate each year between a non-legume (ex. maize) and a legume (ex. Alfalfa).
The legume is planted to restore the fixed nitrogen concentration of the soil
Legume seeds get soaked in bacteria culture or dusted with bacterial spores to be sure that they connect to their correct Rhizobium strain.

5. Nitrogen Fixation and Agriculture
Mutualistic nitrogen fixation
Ex. Rice – Azolla
The plant, Azolla is fixes nitrogen. The growing rice kills the Azolla. As Azolla decomposes, the fertility of the crop land is increased for the rice.

6. Fungi and Plant Nutrition
Mycorrhizae: A mutualistic relationship between plants and fungi
Plants offer constant sugar supply for fungus
Fungus increases surface area for the plant to bring in water and nutrients, stimulates root growth, and secretes antibiotics to protect the plant

7. Types of Mycorrhizae Ectomycorrhizae
The fungus surrounds the root and its hyphae extend into the soil to absorb nutrients
Fungus hyphae extends through the root cortex for an increased surface area to exchange nutrients
Hyphae: thread-like extentions of fungi that form the mycelium

8. Types of Mycorrhizae Arbuscular Mycorrhizae
Fungus does not fully surround plant root, but it hyphae still extend into the root cortex to form arbuscules to provide maximum surface area

9. Agricultural and Ecological Importance of Mycorrhizae
Mycorrihzal symbiosis only occurs if the root is exposed to the right fungus speicies.
Fungus is present in the soil of most ecosystems which allows seedlings to develop mycorrhizae.
When seeds are replanted in foreign soil, the plants often become deficient in many nutrients due to the lack of a mycorrhizal partner.

10. Plant nutrition often involves relationships
37.3
Plant nutrition often involves relationships
with other organisms

11. Rhizobacteria
Rhizosphere: the soil layer that is bound to the plant’s roots.
Rhizobacteria: Soil bacteria with especially large populations in the rhizosphere
Roots of a plant’s rhizosphere secrete nutrients; sugars, amino acids, organic acids
Plant-growth-promoting-rhizobacteria
Have chemicals that induce plant growth
Produce antibiotics that protect against disease
Absorb more nutrients

12. Nitrogen-Fixing Bacteria
Plants cannot use free gaseous nitrogen in Earth’s atmosphere (N2)
Nitrogen Fixation- process of reducing N2 to NH3 so a plant can use it use
N2 + 8e- + 8H+ + 16ATP2NH3 + H2 + 16ADP + 16Pi
N2 reduced to NH3 by adding electrons and H+
Reaction catalyzed by nitrogenase enzyme
Ex. Bacteria Rhizobium and legume plant roots
Rhizobium fixates N2 so it can be processed by the legume root

13. Nitrogen Fixation and Agriculture
Crop rotation- crops rotate each year between a non-legume (ex. maize) and a legume (ex. Alfalfa).
The legume is planted to restore the fixed nitrogen concentration of the soil
Legume seeds get soaked in bacteria culture or dusted with bacterial spores to be sure that they connect to their correct Rhizobium strain.

14. Nitrogen Fixation and Agriculture
Mutualistic nitrogen fixation
Ex. Rice – Azolla
The plant, Azolla is fixes nitrogen. The growing rice kills the Azolla. As Azolla decomposes, the fertility of the crop land is increased for the rice.

15. Fungi and Plant Nutrition
Mycorrhizae: A mutualistic relationship between plants and fungi
Plants offer constant sugar supply for fungus
Fungus increases surface area for the plant to bring in water and nutrients, stimulates root growth, and secretes antibiotics to protect the plant

16. Types of Mycorrhizae Ectomycorrhizae
The fungus surrounds the root and its hyphae extend into the soil to absorb nutrients
Fungus hyphae extends through the root cortex for an increased surface area to exchange nutrients
Hyphae: thread-like extentions of fungi that form the mycelium

17. Types of Mycorrhizae Arbuscular Mycorrhizae
Fungus does not fully surround plant root, but it hyphae still extend into the root cortex to form arbuscules to provide maximum surface area

18. Agricultural and Ecological Importance of Mycorrhizae
Mycorrihzal symbiosis only occurs if the root is exposed to the right fungus speicies.
Fungus is present in the soil of most ecosystems which allows seedlings to develop mycorrhizae.
When seeds are replanted in foreign soil, the plants often become deficient in many nutrients due to the lack of a mycorrhizal partner.