BIOL 4120: Principles of EcologyBIOL 4120: Principles of Ecology

Lecture 20: Nutrient Lecture 20: Nutrient Regeneration in Terrestrial Regeneration in Terrestrial and Aquatic Ecosystemsand Aquatic Ecosystems

Dafeng HuiDafeng Hui

Office: Harned Hall 320Office: Harned Hall 320

Phone: 963-5777Phone: 963-5777

Email: dhui@tnstate.eduEmail: dhui@tnstate.edu

Lodgepole pine

Pinyou pine

Death of trees in 1960s

Acidified precipitation was caused by air pollution from power plants and fossil fuel

burning

Sulfur dioxide (SO2)Sulfuric acid (H2SO4)

Nitrous oxide (N2O)Nitric acid (HNO3)

pH of rainwater fall to as low as 4

In 1970, Clean Air Act passedto reduce emissions of SO2 and particulate matter from factories and power plants.

But forests did not show sign of recovery.

Clear Air Act significantly reduced SO2 and N2O

pH=4

pH=5

First, trees die not because of direct effects of high hydrogen ion concentrations, but because of long- term leaching of nutrients from the soil.

Second, the natural recovery of forests growing on nutrient- poor soils will require restoration of soil nutrients through the slow process of weathering.

Hubbard Brook study held several important lessons for forest ecologists.

Outline (Chapter 24)

20.1 Weathering makes nutrients available in terrestrial ecosystems20.2 Nutrient regeneration in terrestrial ecosystems occurs in the soil20.3 Nutrient regeneration can follow many paths20.4 Mycorrhizal associations of fungi and plant roots promote nutrient uptake20.5 Climate affects pathways and rates of nutrient regeneration20.6 In aquatic ecosystems, nutrients are regenerated slowly in deep water and sediments 20.7 Stratification hinders nutrient cycling in aquatic ecosystems • Oxygen depletion facilitates regeneration of nutrients in deep waters20.8 Nutrient inputs control production in freshwater and shallow- water marine ecosystems 20.9 Nutrients limit production in the oceans

Most essential nutrients are recycled within ecosystem

Internal cycling

Retranslocation or reabsorption

Nitrogen fixation (N2) from atmosphere

Fertilization

Weathering from rocks and sediments

Harvest

Leaching to groundwater and stream runoff

20.1 Weathering makes nutrients available in terrestrial ecosystems

Weathering is the physical breakdown and chemical alteration of rocks and minerals near the earth’s surface.

Important nutrients, such as nitrogen, phosphorus, and sulfur, are typically scarce in parent material.

Igneous rocks such as granite and basalt contain no nitrogen, only 0.3% phosphate, and only 0.1% sulfate by mass. Most sedimentary rocks contain little more. Hence, weathering adds little of these nutrients to soil.

Time: Initial differentiation can be within 30 years. Formation of true soil, 2000 to 20000 years

BIOL 4120: Principles of EcologyBIOL 4120: Principles of Ecology

Lecture 20: Nutrient Lecture 20: Nutrient Regeneration in Terrestrial Regeneration in Terrestrial and Aquatic Ecosystemsand Aquatic Ecosystems

Dafeng HuiDafeng Hui

Office: Harned Hall 320Office: Harned Hall 320

Phone: 963-5777Phone: 963-5777

Email: dhui@tnstate.eduEmail: dhui@tnstate.edu

Element budget in a watershed

Rain gauges are used to measure nutrient inputs.

Stream gauges are used to measure nutrient outputs.

20.2 Nutrient regeneration in terrestrial ecosystems occurs in the soil

Many organisms are involved in decomposition

Decomposition is the breakdown of chemical bonds formed during the construction of plant and animal tissues.

Processes: leaching, fragmentation, changes in physical and chemical structure, ingestion and excretion of waste products.

Microbial decomposers: Bacteria are dominant decomposer (to animal)

Fungi (to plant)

Aided by detritivores

4 major groups

Microfauna, mesofauna, macrofauna, and megafauna

Breakdown of leaf litter occurs in four ways

1. Leaching of soluble minerals

2. Consumption by detritivores

3. Breakdown by fungi

4. Breakdown by bacteria

Proteins and soluble C are decomposed very fast, then the cellulose and hemicellulose, lignin is very difficult to decompose

Proteins etc. 15%

Cellulose etc. 60%

Lignin: 20%

Decomposition rate measurement

Litterbag method

Mesh bag (1-2mm)

Mass of remaining in the bag includes both original plant matter as well as bacteria and fungi that have colonized and grown on the plant litter.

Carbon is lost to the atmosphere as CO2 in the process of respiration

Smith 2002

Based on the data, the decomposition rate can be calculated

Decomposition rate calculated as k=0.0097 wk-1 and 0.0167 wk-1 for two tree species

Lignin contents influence litter decomposition

Terrestrial environment Aquatic environment

20.3 Rates of Decomposition and influencing factors

Rate at which nutrients are made available to primary producers is determined largely by rate of decomposition.

influenced by:• temperature, • moisture, • chemical compositions of leaves• Decomposers

Physical conditions influence litter decomposition

O2 concentration

Decomposition of Spartina litter is more efficient in aerobic than anaerobic conditions

Lack of fungi, which require oxygen for respiration, hinders the decomposition of lignin component, slow the decomposition rate.

Valiela 1984Litter bags on the marsh surface or buried 5-10 cm below surface

Changes in climate influence litter decomposition

Decomposition of red maple litter at three sites (litter quality similar for three sites). Warm and wet conditions, decompose fast (3 studies)

7.2oC, 621 mm

12.2oC, 720 mm

14.4oC, 806 mm

Temperature influence on decomposition

Diurnal changes in air temperature and decomposition in a temperature deciduous forest (Whitkamp and Frank 1969)

20.4 Nutrient regeneration can follow many paths

Monomers: monomeric subunit of large organic polymers such as amino acids, nucleic acids.

Depolymerization is accomplished by microorganisms secreting enzymes and other reactive substances.

Mineralization, immobilization and net mineralization rate

Mineralization: a process that microbial decomposers –bacterial and fungi- transform nitrogen and other elements contained in organic matter compounds into inorganic (or mineral) forms. • Organic N ammonia (waste product of

microbial metabolism) Immobilization: uptake and assimilation of

mineral nitrogen by microbial decomposer.• N used by microbes to grow

Net mineralization rate: different between the rate of mineralization and immobilization

Nitrogen remaining in the litter during decomposition

Initial phase (A) leaching soluble N, then immobilized by microbes, then net N release from litter.

Chemical compositions of leaves in response to nutrients

C:N ratio• low C:N ratio – high protein level • High C:N ratio – low in proteins, high in

lignin and secondary metabolites Leaf C:N ratio is influenced by nutrients

availability in the environment Leaf C:N ratio influences decomposition

rate and interactions with herbivores• Nutrient requirements for compensatory

growth

N content influence the decomposition

Under high N, the initial N can exceed the rate of immobilization from onset of experiment, N concentration will not increase

Patterns of immobilization and mineralization of sulfur (S), calcium (Ca), and manganese (Mn) in decomposing needles of Scots pine

Five year litterbag experiment

20.5 Mycorrhizal associations of fungi and plant roots promote nutrient uptake

Symbiotic association of fungus and root is called a Mycorrhiza: Arbuscular Mycorrhizae ( AM) penetrate cell walls in root tissue and form vesicles or branched structures in intimate contact with root cell membranes. Ectomychorrhizae ( EcM): form a dense sheath around the outsides of small roots and penetrate the spaces between the cells of the root cortical layer

Function: promote plant growth, increase a plant’s uptake of minerals by penetrating a greater volume of soil than the roots.

Plant roots and mycorrhizal fungiPlant roots and mycorrhizal fungiFungi assist the plant with the uptake of nutrient Fungi assist the plant with the uptake of nutrient

from the soil (from the soil (extended water and nutrients absorption)

Plant provides the fungi with carbon, a source of Plant provides the fungi with carbon, a source of energy.energy.

Endomycorrhizae (a)

Ectomycorrhizae (b)

Mycorrhizal fungi work well under poor nutrient conditions

20.6 Key ecosystem processes influence the rate of nutrient cycling Primary productivity determines rate

of nutrient transform from inorganic form to organic form (nutrient uptake)

Decomposition determines the rate of transformation of organic to inorganic form (N mineralization)

Rates of these two determine the internal cycling

Feedback between nutrient availability, NPP and N release

20.7 Climate affects pathways and rate of nutrient retention

Climate affects weathering, soil properties, and rate of decomposition of detritus.

Tropical soils: Deeply weathered, less clay (can’t hold nutrients)Leach out if not uptake by plants, nutrient-poor soils

Why productivity is high? 1) rapid decomposition of detritus under warm, humid conditions; 2) rapid uptake by plants and other organisms from upper-most layer of soils 3) effective retention of nutrients by plants and mycorrhizal fungal associationsLitter on the forest floor constitutes only 1-2% of total biomass of vegetation and detritus; <25% of carbon stored in soils

Temperate forests: 1) Litter on the forest floor constitutes 20% in needle-leaved forests, 5% in hardwood forests. 2) 50% carbon stored in soils and litter.

Tropical forest ecosystems hold most of their nutrients in living vegetation

In an ash-oak forest in Belgium, most of the P and N stored in the soil as detritus, decomposed organic or inorganic nutrients.

But in a tropical deciduous forest in Ghana, soil:biomass ratios are much lower.

Eutrophic and oligotrophic soils

Two type of soils in tropics

Eutrophic soil: well-nourished soils.developed in geological active areas where erosion is high

and soils are relative young. bedrock closer to soil surface, weathering adds nutrients

more rapidly and soil retain nutrients more effectively Occur: Neotropics -- Andes, Center America, West Indies

Oligotrophic soil: nutrient-poor soildevelop in old, geologocally stable areas, intense

weathering over long periods removes clay and reduce the capacity of soils to retain nutrients.

Occur: Amazon Basin

In oligotrophic tropical soils, plants retain nutrients by keeping leaves for long periods and by withdrawing nutrients from them before they are dropped.

Dense mats of root (and fungi) to help nutrient uptake.

RecapNutrient regeneration in terrestrial ecosystems occurs in the soil:

Litter and soil organic carbon decompositionInfluence factors on litter decomposition

Nutrient regeneration can follow many pathsMineralization, immbilization and net

minerlization

Mycorrhizal associations of fungi and plant roots promote nutrient uptake

Function of AM and ECM

Climate affects pathways and rate of nutrient retention Tropic

Habitat conversion and soil nutrient

Habitat conversion changes soil nutrient conditions

Deforestation (cutting) and burning

Habitat conversion and soil nutrient

Deforestration and convert from forests to crops in the tropics

1.Cutting and burning loss nutrients directly 2.Without plants, nutrients leach out quickly3.Upward movement of water draws ion and Al3+ to the surface and form laterite (bricklike substance), as soil dries out4.Surface runoff without plants will cause soil erosion.

A study compared soil nutrient changes in three places

Canada prairie site C: 8.8 kg/m2; after 65 yrs, reduced by 51%, 1% per year

Brazil Forest site C: 3.4 kg/m2; after 6 yrs, decreased by 40%, 9% per year

Venezuelan rain forest C: 5.1 kg/m2; after 3 yrs, decreased by 29%, 11% per

year

Global warming and boreal forest

Boreal forests hold 200-500 Gt of C, 80% of total C in the atmosphere

Annual change from a loss of 0.7 metric Ton C to a gain of 0.1 T per ha over four years. Four year total, a slightly loss

In terrestrial ecosystem (shallow water), plants bridge the physical separation between the zones. In deep ocean, there is no direct link. Need a transport system.

20.6 In aquatic ecosystems, nutrients are regenerated slowly in deep water and sediments

Primary productivity in aquatic ecosystems is highest where nutrients regenerated in sediments can reach the photic zone

20.7 Stratification hinders nutrient cycling in aquatic ecosystems

Vertical mixing of water

Energy input and wind

Turbulent mixing in shallow water and upwelling along coasts

Thermocline

Density and temperature

Turnover of water and nutrient link two zones together

Change in T, light and nutrient influence NPP, and photosynthesis also influences nutrient availability

Vertical mixing can stimulate productivity, and can also reduce productivity, as mixing bring phytoplakton far below photic zone.

20.8 Oxygen depletion facilitates regeneration of nutrients in deep waters

During prolonged periods of stratification in freshwater lakes, bacteria respiration in the carbon-rich bottom sediments tend to deplete O2 supply in the hypolimnion.

Bacteria switch to sulfate as an oxidizer and produce H2S (hydrogen sulfide)

In O2 depleted environments, bacteria have insufficient O2 to nitrify NH4+;Iron and Mg shift to reduced forms (increase solubility). Thus, nutrients accumulate under these reducing conditions.

20.9 Nutrient inputs control production in freshwater and shallow-water marine ecosystems

Phosphorus is critical to the productivity of freshwater lakes.

Two parts separated, one side added carbon and nitrogen (near), another side added C, N and P (far).

With P, photosynthesis cyanobacteria were developed within 2 monthsP caused eutrophication in a Canadian Lake

experiment

Productivity depends on external inputs from rainfall and streams and regeneration of nutrients in the lake.

Fertilization and eutrophication

Overfertilizaiton

Runoff

Eutrophication: overproduction of organic matter within a lake or river

Consequences:More food source for fishBut if too productivity, can lead to imbalance

when decomposers of this excess organic matter consume O2 faster than it can regenerated by photosynthesis.

O2 depletion

Estuaries and salt marshes

High productivity

Due to plentiful supplies of nutrients

Inputs from rivers and tidal flow and regenerated within ecosystem.

Where does the primary production go?

Energy flow diagram shows energy flow in a Georgia salt marsh

Hypoxic zones in Estuaries and Shallow Marine Ecosystems

Hypoxia: the depletion of O2 to the extent that acquatic organisms can no longer survive

Defined as: <2 mg O2/liter of water (normal, >10)

Reason: high nutrient concentrations

20.10 Nutrients limit production in the oceans

Productivity in the open ocean is typically low

Lack of nutrients (nitrogen and phosphorus)

Ion and silicon are important and in shortage

Temperature and climate factors also influence productivity

Does iron limit marine productivity?

Iron addition

Increased productivity in the South patch

The Redfiled ratio and nutrient limitation in the open ocean

Nutrient concentrations in the ocean need to match the requirements of photosynthetic organisms; otherwise, production would be reduced and abundant nutrients go unused.

Alfred Redfield

In phytoplankton, N:P is approximately 16:1 (Redfield ratio)

Phytoplankton incorporate 16 times as much as nitrogen as phosphorus into their biomass and release the same ratio as they decompose after death.

Adding C, C:N:P =106:16:1

Stoichiometry

20.10 Water flow influences nutrient cycling in streams and rivers

Nutrient spiraling

Jack Webster (Virginia Tech)

Because nutrients are continuously being transported downstream, a spiral rather than a cycle better represents the cycling of nutrients.

One cycle in the spiral: uptake of one nutrient atom, its passage through food chain, and its return to water, where it is available for re-use.

The longer the distance required, the more open the spiral.

Newbold et al. from ORNLPhosphorus

at Walker Branch watershed

Phosphorus movement: 10.4 m per dayCycled once every 18.4 days

One spiral: 190 m

The End