Lecture 20: Nutrient Supply and Cycling Flashcards
Biogeochemistry
the study of the physical, chemical, and biological factors that influence the movement and transformation of elements
Nutrient Requirements
all organisms have similar nutrient requirements, but amounts and specific nutrients needed vary
Structural Compounds of Plants
- Carbon (C) is the main component
- Nitrogen (N) is largely in enzymes
C:N Ratios
- Reflect biochemistry
- Animals have lower C:N ratios
- Humans have a ratio of 6
- Plants have a ratio of 10-40
- Organic matter with a high ratio will have a low net release of nutrients
plants
- Require a set of essential nutrients
- Some species have specific requirements
- plants that host N-fixing bacteria require cobalt
- plants in selenium-rich soil require colbalt, but it is toxic to most plants
- may resorb as much as 60–70% of the nitrogen and 40–50% of the phosphorus in their leaves before they fall
C4 and CAM Plants
require sodium
Animals
- All require sodium
- mostly get nutrients in food as large, complex molecules
- Some are broken down; others are absorbed intact
Nutrients
- derived from abiotic sources such as minerals in rocks and gases in the atmosphere
- may be cycled within an ecosystem, repeatedly passing through organisms and the soil or water
Minerals
solid substances with characteristic chemical properties
Rocks
collections of different minerals
Weathering
- the process of elements being released from rock minerals
- one of the processes that result in soil formation
Mechanical Weathering
- The physical breakdown of rocks
- Exposes minerals to the processes chemical weathering
Chemical Weathering
- chemical reactions release soluble forms of the mineral elements
Soil
a mix of mineral particles, organic matter, water, and organisms
The Water
contains dissolved organic matter, minerals, and gases
Soil Properties Influence Availibility of Nutrients to Plants
- Texture: determined by particle size
Influences soil water- holding capacity - The Coarest particles: sand
- Clays: the smallest particles
Cation Exchange Capacity
the ability of a soil to hold and exchange cations; it is related to the amount and types of clay particles present
Parent Material
- The rock or mineral material that was broken down by weathering to form a soil
- May be bedrock, or sediment deposited by glaciers, by wind, or by water
- Chemistry and structure determines rate of weathering, amount and type of minerals released, and it influences soil characteristics such as fertility
- exerts an influence on abundance, growth, and diversity of plants in an ecosystem
Climate
influences rate of soil development
Soil Development
- fastest in warm, wet conditions
- In terrestrial ecosystems, the proportion of nutrients in the soil is greater
Most of the Nutrients in these Ecosystems
are in the living tree biomass
What Contributes to Organic Matter in Soils?
- organisms such as plants, bacteria, and fungi
Organic Matter is a Reservoir of Nutrients
- Such as nitrogen and phosphorus
- Organisms also affect weathering
Atmospheric Sources of Nutrients
- Nitrogen Fixation
- Aerosols/Atmospheric Deposition
Nutrient Transformation
- Chemical and biological transformations in ecosystems alter the chemical form and supply of nutrients
Decomposition of Organic Matter
- Releases nutrients back into the ecosystem
Detritus
includes dead plants, animals and microorganisms, and egested waste products
Decomposition
- the breakdown of dead organic molecules, that are released as soluble organic or inorganic compounds for other organisms to take up
Litter
Fresh, undecomposed organic matter on the soil surface
Fragmentation
increases surface area, which facilitates chemical breakdown
Mineralization
Chemical conversion of organic matter into inorganic nutrients
Heterotrophic Microorganisms
release enzymes into the soil that break down organic macromolecules
What Determines Nutrient Availibility to Autotrophs
- Abiotic and biotic controls on decomposition and mineralization
- Decomposition and mineralization rates are faster in warm, moist conditions
Soil Moisture
- influences the availability of water and oxygen to microorganisms
- Wet soils: low oxygen concentrations- which inhibit detritivores
Lignin
- strengthens plant cell walls, and is difficult for soil microbes to degrade
- It decomposes very slowly
- amount of lignin in cell walls varies with plant species
Nitrification
NH3 and NH4 + are converted to NO3 – by chemoautotrophic bacteria, in aerobic conditions
Denitrification
some bacteria use NO3 – as an electron acceptor, converting it into N2 and N2O, in anoxic conditions
Soil Fertility
estimated from the concentration of inorganic forms of nitrogen
Nutrient Cycling
influenced by climate, as temperature and moisture affect metabolic rates of the organisms involved in nutrient transformations
Mean Residence Time (Turnover Rate)
- amount of time on average that a molecule spends in the pool
- Total pool of element/rate of input
Pools
total amount of a nutrient in a component of the ecosystem
Catchment or Watershed
- the land area that is drained by a single stream, is often used
- For terrestrial ecosystems
Measuring Nutrient Inputs and Outputs
- Atmospheric deposition includes elements in precipitation or aerosols and fine dust
- Wet deposition collectors open during precipitation events, then close to prevent evaporation
Early Primary Succession
- little organic matter in the soil, and little nitrogen from decomposition
- Nitrogen availability should limit primary production and community composition
Phosphorus (P)
- originates from weathering of the mineral apatite
- As the supply of P from weathering is exhausted over time, decomposition becomes increasingly important
Occlusion
- Soluble P may combine with iron, calcium, or aluminum to form insoluble compounds that are unavailable as nutrients
