Dissolved Organic Matter (DOM) and the Microbial Loop
What is the main role of bacteria in the microbial loop?
Bacteria consume dissolved organic matter (DOM) and convert part of its carbon into microbial biomass, which can then be transferred to grazers.
What is hydrolysis, and why is it important in organic matter degradation?
Answer: Hydrolysis is the breakdown of chemical bonds through the addition of water. It converts large organic molecules into smaller compounds that microorganisms can absorb.
What is the function of lignin in terrestrial plants, and why does it slow down decomposition?
Answer: Lignin provides structural strength and rigidity to plant tissues. Its complex aromatic structure and resistant chemical bonds make it difficult for microorganisms to degrade.
What are the main sources of dissolved organic matter in aquatic ecosystems?
The main sources are phytoplankton exudation, sloppy grazing and viral lysis of cells.
Why is hydrolysis often the rate-limiting step in microbial degradation?
Answer: Large organic polymers are abundant in nature, but their smaller breakdown products occur at low concentrations. Microorganisms must first produce or use extracellular enzymes to break down these polymers before absorbing the resulting molecules.
How do white-rot fungi differ from brown-rot fungi in lignin degradation?
Answer: White-rot fungi can extensively degrade lignin, often leaving wood bleached. Brown-rot fungi primarily degrade cellulose and hemicellulose, leaving much of the lignin behind.
How does bacterial growth efficiency (BGE) influence the fate of organic carbon in aquatic ecosystems?
BGE determines the proportion of assimilated carbon used for microbial biomass production rather than respiration. A low BGE means that most carbon is released as CO₂, while a smaller fraction becomes biomass available to higher trophic levels.
What happens to organic compounds after they are transported into a microbial cell, and how do catabolism and anabolism differ?
Answer: Inside the cell, compounds can undergo catabolism or anabolism. Catabolism breaks down compounds to release energy, often producing CO₂, whereas anabolism uses compounds to synthesize cellular components and produce new biomass.
What is the priming effect, and how can fresh organic matter accelerate the decomposition of older soil organic matter?
Answer: The priming effect is the acceleration of older organic matter decomposition following the addition of fresh, easily degradable organic matter. Fresh carbon sources, such as root exudates, stimulate microbial activity and may promote the breakdown of previously accumulated organic matter.