Review for Exam 1 Flashcards

Question

Properties of Soil: Minerals

Answer 1

**2 ° Minerals = Formed by chemical alteration of 1 °minerals** **Usually smaller particles, clay and some silts** **Vermiculite and Kaolinite**

Answer 2

* More of soil volume is composed of 1° minerals, but more soil functions are controlled by 2° minerals * Clays provide a large surface area and a large "nutrient exchange surface"

Answer 3

* Regulates the supply of N, P, and S to plants * Provides a high surface area for nutrient and retention and exchange * Increases storage and retention of water * Controls soil structure * Serves as an energy source for most microbes * A major source for CO₂to the atmosphere

Answer 4

* The dominant process that determines the composition of soil air is respiration by roots and soil microorganisms * CH₂O → CO₂and O₂→ H₂O * Composition in soil air is important because it can have a large effect on the chemistry of the soil solution * Soil has more CO₂and less O₂than the atmosphere above the soil surface * CO₂in soil air can be as high as 10,000 ppm, O₂as low as a few % * CO₂ combines with water to form H₂CO₃ (carbonic acid) . thus lowering soil-solution pH * Carbonic acid dissolves minerals

Answer 5

* Essential for microorganisms and other soil animals * Many soil microbiota live in water films on the surfaces of mineral particles. * Availability to plants depends on the amount of water in the soil and the adhesion of the water to soil particles * Fine textured soils (clays), because of their high surface area hold water more strongly than coarser-textured soils making water availability lower for plants

Answer 6

* Topography * Orographic Effects = those caused by the presence of mountains * Rain shadows * Altitude * Proximity to water (lakes, oceans) * Prevailing wind directions

Answer 7

Cold air cannot hold moisture, causing precipitation levels to be low

Answer 8

* Cold, average temperature \< 5°C * Rainfall 0.4 – 1 m; but low evapotranspiration too * Strongly seasonal, short growing season * Permafrost in north * Trees – spruce and fir dominant, broad-leaf hardwoods post-disturbance * Frequent fires * LOTS of detritus (11% of Earth’s surface but 40% of world’s soil carbon storage) * Slow decomposition * Acid soils, low fertility

Answer 9

* Warm (avg \>20°C) * But some areas \< 0° in winter * Very low rainfall (\< 25cm/yr) * Low plant density * Shrubs, cacti, grasses * Highly reduced leaves, succulence * Mineral soils, lots of sand, often impermeable (hardpan) * 20% of Earth’s land surface!

Answer 10

* The correlation of NPP with climate is most apparent in the Northern Hemisphere, due to its large land surface area * The highest rate of terrestrial NPP are found in the tropics * NPP declines in arid regions at about 25°N and S * Oceanic NPP peaks at mid-latitudes, where zones of upwelling are found

Answer 11

* Worldwide, terrestrial primary production increases with actual evapotranspiration (AET) * AET is amount of water transpired plus evaporated from land * AET increases with solar energy and precipitation * (Potential ET (PET) increases with solar energy only)

Answer 12

* Proportion of energy transferred from one trophic level to the next * **Trophic Efficiency = (Energy trophic level x+1)/ (Energy trophic level x)** * On average, trophic efficiencies typically 1 - 20% (range is huge)

Answer 13

* Energy or biomass pyramid * Width of the structure indicates the amount of energy contained in that trophic level

Answer 14

**10% is an important value to remember!**

Answer 15

High rates of energy metabolism usually result in low production efficiencies

Answer 16

* **Gross Production Efficiency = (Production / Ingestion) \* 100** * This is the overall energetic efficiency of biomass production within a trophic level * Small terrestrial animals – 5% * Large mammals – 1% * Aquatic animals – 30%

Answer 17

* **Net Production Efficiency = (Production / Assimilation) \*100** * The most active animals have the lowest NPE * Birds - 1% * Small mammals - 6% * Sedentary, aquatic poikilotherms - 70%

Answer 18

* The amount of energy available at each trophic level depends on; * 1) the net primary production at the base of the food chain * 2) the efficiency of energy transfer from one trophic level to the next * The production of each trophic level is approximately only 5% to 20% of the trophic level below it. * ‘Ecological Efficiency’ – the proportion of energy transferred from one trophic level to the next (≈10% per trophic level transfer)

Answer 19

1. Leaching of soluble compounds 2. Consumption and fragmentation by soil organisms 3. Breakdown of cellulose 4. Breakdown of lignin

Answer 20

* 10-30% of mass – * Rapid - days rather than weeks * salts, sugars, amino acids * Left over? Macromolecules, lipid-soluble, some more labile contents still trapped inside cells

Answer 21

* Organisms remove the easily-digested macromolecules (e.g. lipids, starch, proteins) * Cannot digest the cellulose or lignin * “Macrofauna” (1-50 mm length) * Earthworms, millipedes, wood lice * “Macrofauna” (1-50 mm length) * Earthworms, millipedes, wood lice * “Mesofauna” (0.1 – 1 mm) * Mites, springtails (collembolans) * “Microfauna” (\<1 mm) * Ciliate and flagellate protozoans, nematodes

Answer 22

* Some fungi * Some bacteria

Answer 23

* Few organisms can break down * Some fungi and bacteria

Answer 24

* Temperature * Moisture * Chemistry of substrate * Cellulose, lignin slow decomposition * Secondary compounds (plant chemical defences) slow decomposition

Answer 25

Seasonality! Growing seasons heavily influence the fluctuations on this graph. During plant dormancy plants release CO₂, but during growing season, plants take it in

Answer 26

* N₂makes up 79% of atmospheric gases, but N limits productivity in many biological systems across Earth * Earth’s crust \<\< 0.01% N, soils 0.02-0.5% N, plants 0.5-3% N * Adequate N supply  higher biomass plants and higher crop yields

Answer 27

1) **Interception** – root growth into pockets of high nutrient availability (Minor importance for most nutrients) ## Footnote 2) **Mass flow** – movement of nutrients dissolved in flowing water (Most important for ions with low diffusion rates, e.g., NH4 + ) 3) **Diffusion** – movements of nutrients down a concentration gradient (Most important for mobile nutrients, especially anions such as NO3^- )

Answer 28

* Early succession: Advective N supply through mass flow accounts for over twice the N supply of microbially-mediated N flux * Mid-succession: Nitrogen mineralization during shoulder seasons and winter accounts for nearly half of the annual N flux * Late succession: Ecosystem nitrogen flux is dominated by organic forms (N turnover and N uptake)

Answer 29

* Organic N -\> NH₃ is part of decomposition process * No change in oxidation state * Microbes - mineralize NH₄ ⁺ to get at the C in organic molecules * Animals – mineralize N during normal protein turnover and when diet is high in protein * Once mineralized, available to plants again * In soil, NH₃generally present as NH₄ ⁺, clings to clay (remember cation exchange capacity?), does not readily leach

Answer 30

* Oxidation of NH₄ ⁺ to NO₃^- primarily by specialized groups of autotrophic bacteria * Importance of nitrification * Dominant process in agricultural soils * A key pathway for N loss from terrestrial systems, because nitrate is very soluble (also it is not held on soil well) * \*Nitrate can be a major groundwater pollutant

Answer 31

* NH₃ -\> amino acids, nucleic acids * In soil, NH₃ generally present as NH₄ ⁺ * Assimilated by plants, bacteria, fungi * No change in N’s oxidation state * Plants, bacteria, fungi can assimilate NH₄ ⁺ and NO₃^- * But must transform NO₃ ^- to NH₃ before they can use it * The ability to convert NH₄ ⁺ -\> amino acids is why plants don’t urinate! * Some plants in far north can assimilate amino acids * Animals must assimilate organic forms of N (amino acids, nucleic acids)

Answer 32

* Conversion of NO₃ ^-or NO₂ ^- to N gas * Carried out by bacteria in the absence of oxygen * (water-logged soils, freshwater and ocean sediments) * Wide diversity of denitrifying bacteria * Use NO3 as terminal electron acceptor * Denitrification is an important source of N₂O (nitrous oxide), a greenhouse gas that also catalyses the breakdown of ozone.

Answer 33

* North Facing Slope * Less solar energy * Less evaporation * Wetter, thicker soils * Later plant flowering * Shorter day length * Fairbanks - permafrost

Answer 34

* More solar energy & greater diurnal temperature changes * More evaporation * Drier, thinner soils * More drought-tolerant species * Earlier plant flowering * In Fairbanks no continuous permafrost * Mesic (cool, wet) conditions at toe slope