Lecture 20

Question 1

Biogeochemistry

Answer 1

• the study of the physical, chemical, and biological factors that influence the movement and transformation of elements

Question 2

Understanding Biogeochemistry is Important In..

Answer 2

• Determining the availability of nutrients - chemical elements required for metabolism and growth
• Nutrients must be in certain forms for uptake by organisms

Question 3

The Rate of Physical and Chemical Transformations

Answer 3

• Determines the supply of nutrients

Question 4

Nutrient Requirements

Answer 4

• all organisms have similar nutrient requirements, but amounts and specific nutrients needed vary

Question 5

Structural Compounds of Plants

Answer 5

• Carbon (C) is the main component
• Nitrogen (N) is largely in enzymes

Question 6

C:N Ratios

Answer 6

• 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

Question 7

Plants

Answer 7

• 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

Question 8

C4 and CAM Plants

Answer 8

• require sodium

Question 9

Animals

Answer 9

• All require sodium
• mostly get nutrients in food as large, complex molecules
• Some are broken down; others are absorbed intact

Question 10

Nutrients

Answer 10

• 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

Question 11

Minerals

Answer 11

• solid substances with characteristic chemical properties

Question 12

Rocks

Answer 12

• collections of dinnerent minerals

Question 13

Weathering

Answer 13

• the process of elements being released from rock minerals
• one of the processes that result in soil formation

Question 14

Mechanical Weathering

Answer 14

• The physical breakdown of rocks
• Exposes minerals to the processes chemical weathering

Question 15

Chemical Weathering

Answer 15

• chemical reactions release soluble forms of the mineral elements

Question 16

Soil

Answer 16

• a mix of mineral particles, organic matter, water, and organisms

Question 17

The Water

Answer 17

• contains dissolved organic matter, minerals, and gases

Question 18

Soil Properties Influence Availibility of Nutrients to Plants

Answer 18

• Texture: determined by particle size
  Influences soil water- holding capacity
• The Coarest particles: sand
• Clays: the smallest particles

Question 19

Cation Exchange Capacity

Answer 19

• the ability of a soil to hold and exchange cations; it is related to the amount and types of clay particles present

Question 20

Parent Material

Answer 20

• 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

Question 21

Climate

Answer 21

• influences rate of soil development

Question 22

Soil Development

Answer 22

• fastest in warm, wet conditions
• In terrestrial ecosystems, the proportion of nutrients in the soil is greater

Question 23

Most of the Nutrients in these Ecosystems

Answer 23

• are in the living tree biomass

Question 24

What Contributes to Organic Matter in Soils?

Answer 24

• organisms such as plants, bacteria, and fungi

Question 25

Organic Matter is a Reservoir of Nutrients

Answer 25

- Such as nitrogen and phosphorus - Organisms also affect weathering

Question 26

Atmospheric Sources of Nutrients

Answer 26

1. Nitrogen Fixation 2. Aerosols/Atmospheric Deposition

Question 27

Nutrient Transformation

Answer 27

- Chemical and biological transformations in ecosystems alter the chemical form and supply of nutrients

Question 28

Decomposition of Organic Matter

Answer 28

- Releases nutrients back into the ecosystem

Question 29

Detritus

Answer 29

- includes dead plants, animals and microorganisms, and egested waste products

Question 30

Decomposition

Answer 30

- the process by which detritivores break down detritus to obtain energy and nutrients - releases nutrients as simple, soluble organic and inorganic compounds that can be taken up by other organisms

Question 31

Litter

Answer 31

- Fresh, undecomposed organic matter on the soil surface

Question 32

Fragmentation

Answer 32

- increases surface area, which facilitates chemical breakdown

Question 33

Mineralization

Answer 33

- Chemical conversion of organic matter into inorganic nutrients

Question 34

Heterotrophic Microorganisms

Answer 34

- release enzymes into the soil that break down organic macromolecules

Question 35

What Determines Nutrient Availibility to Autotrophs

Answer 35

- Abiotic and biotic controls on decomposition and mineralization - Decomposition and mineralization rates are faster in warm, moist conditions

Question 36

Soil Moisture

Answer 36

- influences the availability of water and oxygen to microorganisms - Wet soils: low oxygen concentrations- which inhibit detritivores

Question 37

Lignin

Answer 37

- 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

Question 38

Nitrification

Answer 38

- NH3 and NH4 + are converted to NO3 – by chemoautotrophic bacteria, in aerobic conditions

Question 39

Denitrification

Answer 39

- some bacteria use NO3 – as an electron acceptor, converting it into N2 and N2O, in anoxic conditions

Question 40

Soil Fertility

Answer 40

- estimated from the concentration of inorganic forms of nitrogen

Question 41

Nutrient Cycling

Answer 41

- influenced by climate, as temperature and moisture affect metabolic rates of the organisms involved in nutrient transformations

Question 42

Mean Residence Time (Turnover Rate)

Answer 42

- amount of time on average that a molecule spends in the pool - Total pool of element/rate of input

Question 43

Pools

Answer 43

- total amount of a nutrient in a component of the ecosystem

Question 44

Catchment or Watershed

Answer 44

- the land area that is drained by a single stream, is often used - For terrestrial ecosystems

Question 45

Measuring Nutrient Inputs and Outputs

Answer 45

- Atmospheric deposition includes elements in precipitation or aerosols and fine dust - Wet deposition collectors open during precipitation events, then close to prevent evaporation

Question 46

Early Primary Succession

Answer 46

- little organic matter in the soil, and little nitrogen from decomposition - Nitrogen availability should limit primary production and community composition

Question 47

Phosphorus (P)

Answer 47

- originates from weathering of the mineral apatite - As the supply of P from weathering is exhausted over time, decomposition becomes increasingly important

Question 48

Occlusion

Answer 48

- Soluble P may combine with iron, calcium, or aluminum to form insoluble compounds that are unavailable as nutrients