U6115: Populations & Land UseTuesday, June 24 2003

Biogeochemical Cycling on LandBiogeochemical Cycling on Land

A)A) Systems Analysis and Biotic ControlSystems Analysis and Biotic ControlB)B) Components of Terrestrial EcosystemsComponents of Terrestrial EcosystemsC)C) Structure of Terrestrial EcosystemsStructure of Terrestrial Ecosystems

U6115: Populations & Land UseTuesday, June 24 2003

Biogeochemical Cycling on LandBiogeochemical Cycling on Land

A)A) Readings:Readings:Chapin et al (1997), Science, Vol. 277, p.500-503 (pdf)“Biogeochemistry” – Chaps. 5-6“Terrestrial Ecosystems” – Chaps. 1-2, 4 (not 9)

Systems Analysis Turnover rate: The fraction of material in a

component that enters or leaves the reservoir in a specified time interval Or:

r = O/M (or I/M)

0 = 1/r = M/O

Systems Analysis Resistance/Resilience: The degree to which systems

respond to disturbances Resilience is the opposite of Resistance

Biotic Control over EcosystemsChapin et al (1997), Science, Vol. 277, p.500-503

Ecosysts Processes: productivity and nutrient cycling Regional Processes: trace gases and nutrient fluxes Community Processes: competition and predation Ecosyst Services: benefits to humans from above processes

Biotic Control over EcosystemsChapin et al (1997), Science, Vol. 277, p.500-503

““Changes in species composition are likely to alter Changes in species composition are likely to alter ecosystem processes through changes in functional ecosystem processes through changes in functional traits of biota”traits of biota”

1)1) The number of species in a community is a measure of the The number of species in a community is a measure of the probability of the presence of species with particularly probability of the presence of species with particularly important traitsimportant traits

2)2) Greater diversity allows a greater range of traits to be Greater diversity allows a greater range of traits to be represented in the ecosystem providing opportunities for represented in the ecosystem providing opportunities for more efficient resource use in a more efficient resource use in a variable environmentvariable environment

No two species are ecologically redundant, even if they No two species are ecologically redundant, even if they appear similar in their ecosystem effects under one appear similar in their ecosystem effects under one particular set of environmental conditions.particular set of environmental conditions.

Biotic Control over EcosystemsResistance/Resilience vs. Vulnerability

Changes in the abundance of species that differ in Changes in the abundance of species that differ in ecosystem consequences should affect process rates or ecosystem consequences should affect process rates or patterns,patterns,

Abundance of species with similar ecological effects Abundance of species with similar ecological effects should give stability (resistance and resilience)should give stability (resistance and resilience)

Defining the EcosystemBiology is not the sole subject of ecosystem studies Biology is not the sole subject of ecosystem studies The The flow flow of energy and materialsof energy and materials (i.e. water, chemicals) into and out of (i.e. water, chemicals) into and out of biological communities biological communities definesdefines the main theme of ecosystem the main theme of ecosystem studiesstudies

Defining the EcosystemThere exists an inseparable relationship between the flow of There exists an inseparable relationship between the flow of energy and the flow of nutrient elements (i.e. N, P, K, Ca, etc)energy and the flow of nutrient elements (i.e. N, P, K, Ca, etc)

Chemical Elements (the Periodic Table) and those essential for life

Of the 103 elements in the Periodic Table, only 24 are required by organisms

Required elt Required for some life forms

Toxic elt

Macronutrients: Macronutrients: Required in large Required in large amountamount (“Big Six”: (“Big Six”: C, N, P, S, O, H)C, N, P, S, O, H)

Micronutrients: Micronutrients: small or moderate small or moderate amountamount

Chemical Elements - Essential for lifeCarbon

Carbon forms three-dimensional molecules of large size and complexity in organic (carbon-containing) compounds that form large molecules (amino acids, sugars, enzymes, DNA), and other chemicals vital to life on Earth.

Chemical Elements - Essential for lifeNitrogen

Nitrogen (along with carbon) is the essential element that allows formation of amino acids ( proteins) and DNA.

Proteins contain up to 16% N

Chemical Elements - Essential for lifePhosphorus

Phosphorus is the “Phosphorus is the “energy elementenergy element” occurring in ” occurring in compounds called ATP and ADP important for compounds called ATP and ADP important for energy transfer processes and DNA.energy transfer processes and DNA.

Chemical Elements - Essential for lifeCarbon:Nitrogen:Phosphorus Ratios

Organisms actively concentrate certain elements essential for life: Algae concentrate Iron (Fe) 100,000 times vs. its concentration in the Ocean

• Most organisms keep a rather constant chemical composition

Algae and plankton C:N:P ratio of 106:16:1 (Redfield Ratio)

Soil microbes maintain a relatively constant proportion of nutrients in their biomass (and at higher levels than the OM they decompose)

Chemical Elements - Essential for life• Availability of some elements (particularly N & P) is often limited and the supply of these elements may control the rate (or type) of primary production in terrestrial ecosystems.

• External sources of nutrients are varied and depend of nutrient Annual circulation dominates most inputs of limiting elements (N, P, K)

Chemical Elements - Essential for life• Plants obtain essential elements from soils (i.e. N from NO3

-)

• Soil chemical reaction (ion exchange, precipitation, chemical solubility) set initial constraints on availability of nutrients.

• Plants may increase the solubility (and thus transfer) of nutrients through active uptake (low solution) or release of active molecules/compounds that increase nutrient solubility

• Plant uptake is enhanced by enzymes that carry ions across root membranes using active transport leads to adaptability

Delimiting the Ecosystem

““The boundaries of a systems are determined by The boundaries of a systems are determined by the purposes of the study or the questions posed”the purposes of the study or the questions posed”

Terrestrial systems:Terrestrial systems:

1)1) WatershedWatershed

2)2) Stand (sufficientStand (sufficient

homogeneity…)homogeneity…)

Component of Terrestrial Ecosystems

For the flow of energy For the flow of energy components can be separated components can be separated according to their source of energy:according to their source of energy:

Autotrophs and heterotrophsAutotrophs and heterotrophs

Component of Terrestrial EcosystemsA more complex picture…A more complex picture…

(complete but not detailed!)(complete but not detailed!)

Distribution and Characteristics of Terrestrial Ecosystems

On a global scale, climate plays the On a global scale, climate plays the largestlargest role in determining the structure of both vegetation and soils in terrestrial role in determining the structure of both vegetation and soils in terrestrial ecosystems.ecosystems.Specifically:Specifically: Temperature, and Temperature, and Balance betweenBalance betweenprecipitation and evaporationprecipitation and evaporation

Distribution and Characteristics of Terrestrial Ecosystems

On a global scale, climate plays the On a global scale, climate plays the largestlargest role in determining the role in determining the structure of both vegetation and soils in terrestrial ecosystems.structure of both vegetation and soils in terrestrial ecosystems.

Distribution and Characteristics of Terrestrial Ecosystems

Distribution and Characteristics of Soils Podzolization: leaching of Podzolization: leaching of elements (Fe, Al) elements (Fe, Al) Cool, Cool, moist and acidic conditionsmoist and acidic conditions Laterization: leaching of Si Laterization: leaching of Si (not Fe, Al) (not Fe, Al) Hot and moist Hot and moist conditionsconditions Melanization: Mixed and Melanization: Mixed and addition of OM addition of OM Temperate Temperate conditionsconditions Calcification/Salinization: low Calcification/Salinization: low water and preservation of salts water and preservation of salts Arid conditions Arid conditions

Distribution and Characteristics of Terrestrial Ecosystems

Biotic Control over EcosystemsResistance/Resilience vs. Vulnerability

Changes in the abundance of species that differ in Changes in the abundance of species that differ in ecosystem consequences should affect process rates or ecosystem consequences should affect process rates or patterns,patterns,

Abundance of species with similar ecological effects Abundance of species with similar ecological effects should give stability (resistance and resilience)should give stability (resistance and resilience)

Biotic Control over Ecosystems

Biotic Control over EcosystemsResistance/Resilience vs. Vulnerability

U6115: Populations & Land UseNext week…

A)A) Photosynthesis and Primary ProductionPhotosynthesis and Primary ProductionB)B) Nutrient and Water Use EfficiencyNutrient and Water Use EfficiencyC)C) Production Fate and DetritusProduction Fate and DetritusD)D) Mass Balances of Soil OM and NutrientsMass Balances of Soil OM and Nutrients