Chap19

CHAPTER 19: NUTRIENT CYCLING AND RETENTION

• Nutrient cycling and retention

  • Grazing speeds up the rate of nutrient cycling.

  • Nutrient spiraling aids retention.

  • Species diversity increases nitrogen storage.

  • Soil microbes control nutrient transformations.

Definitions

• Pool or Reservoir: An entity that contains a nutrient or element.

• Macronutrient versus Micronutrient: Different in abundance and amount needed; often the amount cycled also differs.

• Flux or Flow: Movement of a nutrient or element between pools.

• Nutrient Cycling: The use, transformation, flux, and reuse of nutrients.

• Gaseous Cycle: Characterized by a large gaseous pool of a nutrient or element.

• Sedimentary Cycle: Characterized by a large rock/soil or sediment pool of a nutrient or element.

Earth’s Carbon Cycle

• Pools and Fluxes:

  • Total carbon pool: $10^{15} ext{ g}$

  • Annual carbon flux: $10^{15} ext{ g/yr}$

  • Conversion: $1 imes 10^{15} ext{ g} = 1.0 ext{ GtC}$ (Gigatons of Carbon).

  • C Sink: An area that stores more carbon than it releases.

Earth’s Nitrogen Cycle

• Atmospheric Composition: 80-87% of nitrogen found on Earth is in the atmosphere.

• Annual Flux: $10^{12} ext{ g/yr}$

  • Biological Nitrogen Fixation: Atmospheric nitrogen is converted to ammonia by bacteria using nitrogenase.

  • Question of agriculture: Implications for nitrogen fixation in farming practices.

Earth’s Phosphorus Cycle

• Pools and Fluxes:

  • Total phosphorus pool: $10^{12} ext{ g}$

  • Annual phosphorus flux: $10^{12} ext{ g/yr}$

  • Significant lack of an atmospheric pool.

• Human Impacts: Human movements of phosphorus from terrestrial ecosystems to freshwater ecosystems.

• Phosphorus Movement:

  • From land to atmosphere: $0.025$

  • From oceanic atmosphere to land: $1.0$

  • From soil to freshwater: $90$

  • From soil to oceans: $0.003$

  • From land organisms: $2,600$

• Dissolved phosphorus in oceans: About $1,000$ times the amount in organisms.

• Sediment Pool: Marine sediments hold the largest phosphorus pool at $840,000,000$.

Linking the Carbon Cycle & Energy

• Energy Storage in Ecosystems: Energy is stored in ecosystems as chemical bonds of organic matter.

• Components of Organic Matter: Includes various nutrients and elements that cycle within ecosystems.

• Difference Between Energy and Nutrient Movement: Energy flows through food webs while nutrients cycle through ecosystems.

Decomposition and Nutrient Cycling

• Process of Decomposition: Breakdown of plant and animal detritus by soil animals and microbes, releasing nutrients in inorganic form.

• Processes Involved:

  • Mineralization: Conversion of organic N to inorganic forms such as $NH_4^+$ (ammonium) and release of CO2.

  • Ammonification: Breakdown of organic matter leading to ammonium formation.

  • Importance of Microbes: Bacteria and fungi play critical roles in decomposition, both releasing and immobilizing nutrients.

  Physical Conditions Influencing Decomposition Rates

• Decomposition varies by location and environmental conditions such as precipitation and evapotranspiration.

• Case Study: Less leaf mass loss in areas with lower precipitation (500 mm) compared to higher precipitation (1,600 mm).

• Effect of Soil Moisture: Decomposition is more rapid where actual evapotranspiration is higher.

Detritus Characteristics Influencing Decomposition Rates

• Lignin to Nitrogen Ratio: Higher ratios indicate tougher materials that are harder for microbes to access as an energy source.

• Impact of Nutrient Content: Greater nutrient levels for plants can lower carbon to nutrient ratios; increased nutrients for microbes can stimulate their activity.

Nitrogen Cycle Transformations

• Nitrogen Forms:

  • Organic nitrogen: $R-NH_2$

  • Inorganic forms: $NH<em>4^+, NO</em>2^-, NO_3^-$ (ammonium, nitrite, nitrate).

  • Gaseous forms: $N<em>2, NO, N</em>2O$.

• Many nitrogen fluxes are mediated by microbial activity, including:

  • Denitrification: Conversion of $NO<em>3^-$ to $N</em>2$, typically in anaerobic soils.

• Variations in nitrogen cycling processes in aquatic versus terrestrial ecosystems.

Ecosystem Geophysical Features and Nutrient Transport

• Factors Influencing Transport:

  1. Migratory or highly mobile consumers across ecosystems.

  2. Human systems such as over-fertilization affecting nutrient cycling.

  3. Wind transport of organic materials, such as nutrient-rich loess.

Links to Disturbance and Nutrient Dynamics

• Ecosystems are retentive of nutrients, but disturbances can cause nutrient release.

• Experiments: Studies like the Hubbard Brook Experimental Forest show clearcutting affects nutrient dynamics.

Conclusion

• Nutrient cycling is a complex interaction influenced by physical, biological, and chemical dynamics in ecosystems.

• The retention and transport of nutrients among ecosystems are pivotal for ecological balance and sustainability.

Extra Credit Quiz Topics

• Invasive species.

• Disturbance effects on forest harvesting.

• Soil microbial biomass and carbon pools.

• Net nitrogen mineralization.

• Interacting disturbances and temporal effects.

• Ecology format.

Diagrams and Figures

• Figures on mass loss in forests show variations in tropical versus temperate forests.

• Nitrogen content in plants demonstrates variances among different ecosystem types and conditions.