Soil 10 - Dillon Guest Lec Flashcards
When was the rhizosphere first described?
1904 by Hiltner
What are some examples of plant exudates?
- sugars
- amino acids
- growth factors
- enzymes
What cells do most exudates come from?
cells involved in elongation and root cell formation
What is the R:S ration?
ratio of microbes in root:soil (bulk soil)
What are 3 traits of soil actinomycetes and proteobacteria?
- most numerous
- smallest biomass (small cell size)
- large R:S ratio
What are PGPR and PGPBE?
Plant Growth-Promoting Rhizobacteria and Endophytes
What do PGPR and PGPBE do?
- enhance germination and plant growth
- colonize and outcompete other bacteria in the rhizosphere
What 2 methods do PGPR and PGPBE use?
- Biofertilization (increase accessiblity of major nutrients)
- Phytostimulation (producing plant hormones)
What are two types of plant growth inhibiting microorganisms?
- traditional pathogens
- parasitic plant pathogens (parasitize cells, don’t directly cause disease)
What is antibiosis?
inhibition or cell death of pathogens
- enzymes
- lytic agents
- volatile compounds
What do soil organisms compete for?
- nutrients
- oxygen
- space
Why is P different from N and C
- not mobile in soil
- no large flux with atmosphere
- not a primary source for oxidation
- limiting factor for plants since it is quickly lost
How does phosphate become fixed in soil?
- P reacts with Al and Fe at edges of clay minerals
- forms a single, weak bond, then a second, stronger one over time
How much of soil phosphorous is organic?
usually 30-50%
(ranges from 3-90%)
In what 4 ways do organic compounds increase P availability?
- formation of organophosphates
- replacing H2PO4- on absorption sites
- coating Fe/Al oxides
- increasing quantity of organic P
What is the primary transport of P in soil?
diffusion
What are some functions of P in plants?
- usually concentrated in seeds
- developing healthy roots
- seed development
- crop maturation
- photosynthesis, respiration
- ATP
- DNA, RNA etc
What is a visual sign of P deficiency?
purple leaves
What are the 2 main kinds of mycorrhizae?
- arbuscular
- ectomycorrhizal
What are some traits of arbuscular mycorrhizae?
- on mosses, ferns, seed plants
- ancient and ubiquitous
- hyphae penetrate plant cell walls, form arbuscules for P transfer
What are the two types of arbuscular mycorrhizae?
- Arum type (highly branched)
- Paris-type (highly coiled)
What are some features of ectomycorrhizae?
- on woody seed plants
- form sheath outside of plant
What 4 benefits do fungi provide to plants?
- N uptake
- P uptake
- drought resistance
- pathogen protection
