ecology lecture 20 - nutrient cycling

How do nutrient requirements vary between bacteria, plants, and animals?

Animals require much more nutrients comparend to bacteria and plants

What is carbon's role as a nutrient?

The main component of structural compounds in plants

What is nitrogen's role as a nutrient?

It is largely tied up in enzymes

How do C:N ratios compare between plants and animals?

Animals have lower C:N ratios

How do C:N ratios impact herbivore feeding?

Since plants have high ratios (low nitrogen), herbivores must eat much more in order to get enough nutrients

Where are all nutirents derived from?

Minerals in rocks and gasses in the atmosphere

How is soil classified?

Its relative composition of clay, silt, and sand

What determines the soil's porosity?

The size of the soil particles

How do clay, silt, and sand compare in terms of size?

Clay is smallest, then silt, then sand.

What type of charge do the ions in clay and humus (organic matter) have?

Negative

What type of charge do plant nutrients have?

Positive

What is the cation exchange capacity?

The ability of a soil to hold and exchange cations. It is related to the amount and types of clay particles present

Why does the london-area see a lot of puddles after rain?

There is high silt and silver clay in our soil, making it harder for water to pass through.

What is parent material?

The rock or mineral that was broken down by weathering to form soil

What is till?

Sediment deposited by glaciers

What is loess?

Sediment deposited by wind (from bedrock)

What conditions help soil to develop fastest?

Warm, wet conditions

How nutrient-dense is the soil in tropical environments?

They are nutrient-poor as they have experienced high rates of weathering and leaching for a long time

What is decomposition?

Breaking up nutrients into small soluble compounds so they are available to organisms

What is litter?

Fresh, undecomposed matter on the soil surface

What is fragmentation?

Breaking up litter into progressively finer particles. This is done by earthworms, termites, and nematodes. It increases surface area which facilitates chemical breakdown.

What is mineralization?

Chemical conversion of organic matter into inorganic nutrients

How do heterotrophic organisms break down organic molecules?

Releasing enzymes

What type of environment has fast rates of decomposition and mineralization?

Warm, moist conditions (wet soils have low O2 which inhibits detritivores)

How does lignin impact decomposition?

It strengthens plant cell walls, and is difficult to degrade, so it slows decomposition.

What is nitrification?

When NH3 and NH4 is converted to NO3 by chemoautotrophic bacteria in aerobic conditions

What is denitrification?

When bacteria uses NO3 as an electron acceptor to convert it into N2 and N2O in anoxic conditions

How is soil fertility estimated?

Using the concentrations of inorganic forms of nitrogen (NO3 and NH4)

What pigment is broken down in leaves to recover nutrients in fall?

Chlorophyll

How much nitrogen and phosphorus do plants reabsorb before they fall?

60-70% of nitrogen and 40-50% of phosphorus

What is nutrient cycling?

Movement of nutrients in ecosystems as they undergo biological, chemical, and physical transformations

What can be used to quantify nutrient cycling?

Pools and mean residence time (turnover rate)

What are pools?

The total amount of a nutrient in a compartment of the ecosystem

What is the mean residence time?

The amount of tim eon average that a molecule spends in a pool (turnover rate)

How does the mean residence time vary between tropical and boreal forest soils?

Tropical soils are over 100x faster since their pools are much smaller

How are nutrients lost?

Leaching out of the root zone into groundwater and streams, or as gases, or if they are converted into chemcial forms that cannot be used by organisims

What is a catchment/watershed?

The land area that is drained by a single stream, often used to define boundaries

Where do most nutrient losses from a catchment come from? How are they quantified?

Most is lost in stream water, it can be quantified by measuring dissolved and particulate matter in that stream water.

How could salmon (oceanic nutrients) be deposited in terrestrial ecosystems?

When salmon travel to spawn in rivers, they die, and then bears carry them on land where they will decompose.

What are the two components of atmospheric deposition?

Wet deposition and dry deposition

What is wet deposition?

Elements in precipitation

What is dry deposition?

Aerosols and fine dust

How is wet deposition quantified?

[element] x volume of precipitation received = amount of element entering the catchment

How is dry deposition quantified?

Atmospheric samples are analyzed and combined with wind speed and direction to estimate deposition on surfaces (difficult and done less often)

How is volume of stream water estimated (for nutrient losses)?

Placing a v-shaped weird across the stream to gauge flow

What is nutrient availability like in primary production?

It is very low, and it limits primary production in early stages. Primary production can increase as nitrogen increases.

When is phosphorus concentration important in soil?

Later succession since it takes so long to weather (often unavailable)

What is occlusion?

When soluble phosphorus combines with iron, calcium, or aluminum to form insoluble compounds that are unavailable as nutrients