U6115: Populations & Land Use Tuesday, June Biogeochemical Cycling on Land A)Systems Analysis and Biotic Control B)Components of Terrestrial Ecosystems C)Structure of Terrestrial Ecosystems

U6115: Populations & Land Use Tuesday, June Biogeochemical Cycling on Land A)Readings: Chapin et al (1997), Science, Vol. 277, p (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 Ecosystems Chapin et al (1997), Science, Vol. 277, p 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 Ecosystems Chapin et al (1997), Science, Vol. 277, p “Changes in species composition are likely to alter ecosystem processes through changes in functional traits of biota” 1)The number of species in a community is a measure of the probability of the presence of species with particularly important traits 2)Greater diversity allows a greater range of traits to be represented in the ecosystem providing opportunities for more efficient resource use in a variable environment  No two species are ecologically redundant, even if they appear similar in their ecosystem effects under one particular set of environmental conditions.

Biotic Control over Ecosystems Resistance/Resilience vs. Vulnerability Changes in the abundance of species that differ in ecosystem consequences should affect process rates or patterns, Changes in the abundance of species that differ in ecosystem consequences should affect process rates or patterns, Abundance of species with similar ecological effects should give stability (resistance and resilience) Abundance of species with similar ecological effects should give stability (resistance and resilience)

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

Defining the Ecosystem There exists an inseparable relationship between the flow of 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: Required in large amount (“Big Six”: C, N, P, S, O, H)  Micronutrients: small or moderate amount

Chemical Elements - Essential for life Carbon  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 life Nitrogen  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 life Phosphorus  Phosphorus is the “energy element” occurring in compounds called ATP and ADP important for energy transfer processes and DNA.

Chemical Elements - Essential for life Carbon: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 NO 3 - ) 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 purposes of the study or the questions posed” Terrestrial systems: 1) Watershed 2) Stand (sufficient homogeneity…) homogeneity…)

Component of Terrestrial Ecosystems For the flow of energy  components can be separated according to their source of energy: Autotrophs and heterotrophs

Component of Terrestrial Ecosystems A more complex picture… (complete but not detailed!)

Distribution and Characteristics of Terrestrial Ecosystems On a global scale, climate plays the largest role in determining the structure of both vegetation and soils in terrestrial ecosystems. Specifically:  Temperature, and  Balance between precipitation and evaporation

Distribution and Characteristics of Terrestrial Ecosystems On a global scale, climate plays the largest role in determining the structure of both vegetation and soils in terrestrial ecosystems.

Distribution and Characteristics of Terrestrial Ecosystems

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

Distribution and Characteristics of Terrestrial Ecosystems

Biotic Control over Ecosystems Resistance/Resilience vs. Vulnerability Changes in the abundance of species that differ in ecosystem consequences should affect process rates or patterns, Changes in the abundance of species that differ in ecosystem consequences should affect process rates or patterns, Abundance of species with similar ecological effects should give stability (resistance and resilience) Abundance of species with similar ecological effects should give stability (resistance and resilience)

Biotic Control over Ecosystems

Resistance/Resilience vs. Vulnerability

U6115: Populations & Land Use Next week… A)Photosynthesis and Primary Production B)Nutrient and Water Use Efficiency C)Production Fate and Detritus D)Mass Balances of Soil OM and Nutrients