Productivity and Energy Flow in Communities

Flashcards about Productivity and Energy Flow in Communities

Productivity

Ability of plants to capture energy and incorporate it into organic carbon.

Gross Primary Productivity (GPP)

Grams of carbon fixed per area per unit time; all of the energy captured by photosynthesis.

Net Primary Productivity (NPP)

GPP minus autotroph (plant) respiration, expressed in units of energy, carbon, or biomass.

Biomass/Phytomass/Standing Crop

Dry weight of plant material per area present at a given time.

Exploitation Efficiency

Percentage of total radiation assimilated by a plant; (GPP / total solar radiation) x 100.

Assimilation Efficiency

Percentage of absorbed radiation assimilated; (GPP / absorbed radiation) x 100.

Net Production Efficiency

Percentage of production used for biomass; (NPP / GPP) x 100.

Assimilated Energy (GPP)

May be used for plant respiration or stored in plant tissues (= NPP).

Fate of NPP

Contributes to increase in standing crop, consumed by herbivores, harvested by humans, becomes detritus, or consumed by fire.

Measuring Productivity

Measure changes in biomass over time after accounting for herbivory and loss as detritus.

Accounting for Biomass Losses

Eliminate herbivory using exclosures; use litter traps to estimate total litter fall.

Dimension analysis

Used for large or slow-growing vegetation; involves felling sample trees and measuring biomass.

Measuring Root Productivity

Difficult to measure; use soil core samples, root ingrowth bags, or mini rhizotrons.

Root Productivity

Varies depending on habitat and growth form; can be a high percentage of total NPP.

Annual Plants

More above ground productivity.

Perennials

More below ground productivity.

Plants of Stressful Environments

Higher root biomass, but not necessarily more root productivity.

3 Main fates of Biomass

Remain living, be consumed, become detritus (litter).

Litter

Source of energy and nutrients for decomposers and is highest in tropics, lowest in arctic.

Decomposition Rates

Fastest with moderate moisture and high temperatures (tropical forests); affected by chemical composition of litter.

Terrestrial Vegetation

Occupies only 1/3 of earth’s surface but accounts for roughly 2/3 of world's primary productivity.

Global NPP Distribution

Highest in rainforests and wetlands, lowest in deserts and open water.

High biomass systems (forest--woody habit)

Configuration can achieve a high LAI.

Coniferous forests

Photosynthesis possible when hardwoods are leafless with higher LAI, intercept more light, although photosynthetic rates are lower

Successional Patterns of Productivity & Biomass

Low at pioneer stage, rises during early and mid succession, declines slightly at old growth/climax.

Effects of Herbivory

Reduces photosynthetic area, stimulates regrowth, selects against less vigorous plants, increases nutrient turnover, generates high-quality litter.

Complex relationship

Both inhibits & stimulates production) in grasslands