Lect 02 Energy and Biomass

Forms and Conservation of Energy Potential Energy: stored energy chemical bonds  bodies of organisms concentration gradients across a cell membrane Kinetic Energy: energy of motion being used to do ‘work’ Light, heat, motion

First and Second laws of Thermodynamics apply to living things 1st: Energy is neither created nor destroyed 2nd: Energy transfers tend to decrease the ‘quality’ of energy At each transfer some energy is ‘lost’ as heat – or - Entropy (disorder) tends to increase

Energy Flow in Ecosystems: Energy flows through trophic (feeding) levels: Autotrophs: ‘self feeder’ - an organism that can capture light energy … store in organic molecules Photosynthesis – anabolic reaction Plants, algae and certain bacteria Heterotrophs: ‘other feeder’: rely on breakdown of organic molecules produced by an autotroph as an energy source – catabolic Trophic, or feeding level: organisms feeding at the same energy level

Trace in a linear path passage of energy through an ecosystem Food chain Trace in a linear path passage of energy through an ecosystem Arrows indicate direction of energy flow Two types Grazing food chain Detrital food chain Both pathways are important in accounting for the energy budget of the ecosystem.

simplified by isolating a portion of a community food web: branching food chain complex trophic interactions Species may play a role at more than one trophic level simplified by isolating a portion of a community

Sea nettle Juvenile striped bass Fish larvae Fish eggs Zooplankton Figure 54.13 Partial food web for the Chesapeake Bay estuary on the U.S. Atlantic coast Fish larvae Fish eggs Zooplankton

Biomass available at the next trophic level About one order of magnitude of available energy is lost from one trophic level to the next (10% rule) Limits food chains to 3 or 4 steps only Biomass available at the next trophic level How heterotrophs use food energy Energy loss in an ecosystem Cayuga Lake In NY

Ecological or Trophic Pyramids A plant fixes about 1% of the sun’s energy that falls on its green parts Fixed energy is used to build chemical bonds (energy stored) What happens to the other 99% that was not captured to drive photosynthesis? Of the fixed energy only +/-10% is available to organisms that eat the plant (next trophic level) Successive members of a food chain incorporate ~ 10% of energy available in organisms they consume Fewer individuals at higher tropic levels Ecological or trophic pyramid

Heterotrophs Plants= Autotrophs

Photosynthesis: (Chapter 29) Light energy captured by pigments Used to build bonds forming various complex molecules – anabolic processes Carbon dioxide absorbed/oxygen waste product Within PAR specific wavelengths of light are most important in driving photosynthesis

Light-dependent reactions 1. Pigments capture energy from sunlight Water is split, O2 released 2. Using energy to make high energy transfer molecules: ATP and NADPH 3. Using ATP and NADPH to power the synthesis of carbohydrates from CO2 Light-dependent reactions Light-independent reactions The Calvin cycle + 12 H2O water + Light energy + 6 H2O water + 6 O2 oxygen 6 CO2 carbon dioxide C6H12O6 glucose

Absorption spectra of chlorophylls and carotenoids

Primary production (or primary productivity): Overall rate of photosynthesis or total energy captured by photosynthesis Limits to primary productivity: Temperature intensity of PAR Precipitation/availability of water CO2 Nutrients Limiting nutrient

Primary productivity Limits to primary productivity: Gross Primary Productivity (GPP): total amount of photosynthetic energy captured in a given period of time. Limits to primary productivity: Temperature intensity of PAR Precipitation/availability of water CO2 Nutrients Limiting nutrient Net Primary Productivity (NPP): the amount of plant biomass (energy) after cell respiration has occurred in plant tissues. NPP = GPP – Plant respiration plant growth/ total photosynthesis/ unit area/ unit area/unit time unit time

Temperature and precipitation primarily limit terrestrial production. Figure 10 Temperature and precipitation primarily limit terrestrial production. Primary productivity in terrestrial ecosystems. Primary productivity in terrestrial ecosystems is often related to average annual temperature and precipitation. The colored bars represent the ranges for representative high latitude (tundra), middle latitude (temperate forests) and equatorial (rain forests) biomes. Note the overlap between the precipitation of the rain forest and temperate forest. This is likely due to the presence of temperate rain forests and seasonal tropical forests, which are both wetter and drier, respectively, than typical temperate and tropical forests.

Gross primary productivity Gross primary productivity. MODIS image shows the gross primary productivity, or the total amount of chemical energy converted by primary producers from solar energy.

Experimental introduction of iron to the open ocean Figure 8 Experimental introduction of iron to the open ocean Changes in productivity in enriched and control areas. In this graph, open circles and diamonds (◊) represent productivity in control areas where no iron was added, while filled circles and diamonds represent productivity in areas where iron particles were added. Although nitrogen and phosphorus are usually the most important limiting nutrients, sometimes other nutrients become most limiting. In open oceans, iron addition can greatly increase production.

Figure 7 Nutrients play an especially important role in limiting productivity in aquatic ecosystems. Nutrient pollution from agricultural runoff can dramatically alter aquatic ecosystem structure. Phytoplankton bloom in the Bay of Biscay. This satellite image shows the phytoplankton bloom in the Bay of Biscay. The light blue swirls are the phytoplankton.

Secondary Productivity Secondary productivity – the rate at which consumers convert the chemical energy of the food they eat into their own new biomass Involves heterotrophs Essentially reverse of photosynthesis - May occur with or without oxygen Aerobic – most efficient Anaerobic  fermentative pathways (in anoxic environment) ATP immediate cellular energy form

Glycolysis With Oxygen aerobic Fermentation- anaerobic Electron Transport most ATP generated here

Disruptions in Energy Flow/Ecosystem Productivity Eutrophication: Addition of excess nutrients Introduction of non-native species Removal of species -

Nutrient pollution causes eutrophication. Decrease in dissolved O2. Change in species composition. Often reduction in biodiversity. High nutrient inputs Low nutrient inputs Eutrophic versus oligotrophic freshwater. a) A highly eutrophic wetland in Florida, as indicated by greenish-colored water and large amounts of floating algae. b) An oligotrophic wetland in Florida as indicated by relatively clear water with far less floating algae.