also called reabsorption; plant roots reabsorb minerals from the leaves that will be lost from the plant
leaching, fragmentation, changes in physical and chemical structure, ingestion, excretion of waste products
organisms that feed on dead organic matter or detritus (bacteria, fungi, and detritivores); all heterotrophs function to some degree as decomposers
What is the rate of organic decay related to?
plant litter quality, soil properties (texture and pH), and climate (temperature and precipitation)
Net mineralization rate
the difference between the rates of mineralization and immboilization
the transformation of nutrients contained in organic compounds into inorganic forms
the uptake and assimilation of minerals by microbial decomposers
the region of the soil where plant roots function, and active zone of root growth and death with intense microbial and fungal activity
Is decomposition faster in the rhizosphere or in the bulk soil?
rhizosphere because roots alter the chemistry of the rhizosphere by secreting carbohydrates into the soil
What promotes and inhibits bacterial growth in the rhizosphere?
growth is supported by the high-quality root exudates (carbon) and is limited most strongly by nutrient availability (e.g. nitrogen)
What determines the rate of nutrient cycling in the rhizosphere?
the interplay between microbial decomposers and microbivores - strongly enhances the availability of mineral nutrients to plants
Soil microbial loop
plants supplement carbon to microbial decomposers in the rhizosphere, microbes are preyed on by microbivores that release minerals and nutrients back to the soil, enhancement of mineral cycling and an increase in nutrient availability to plants
What links NPP to decomposition?
NPP determines the quantity and quality of organic matter available to decomposers
How does agriculture disrupt NPP and decomposition balance and how is it dealt with?
the balance is disrupted because plants are harvested and the organic matter does not return to the soil, so nutrient supplements (fertilizers) are added
manures, ground animal bones
natural and synthetic sources
Three elements that are necessary in large quantities for plant growth
potassium, phosphorus, and nitrogen
the explosive growth of algae due to excess nitrogen deposited in aquatic ecosystems
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