Nutrient Regeneration

FIELD BIOLOGY & METHODOLOGYFall 2015 Althoff

Lecture

08

Cycling & Nutrient Regeneration

• Elements cycle through ecosystems along paths dictated by their ______________…

a) which determine their chemicalreactions

b) which determine their biologicalreactions

• Processes of nutrient regeneration is different in terrestrial vs. aquatic systems

Terrestrial System: Nutrient

• Nutrients primarily regenerated in the ______• New nutrients source is formation of soil

through weathering of bedrock…in the deep layers of the soil.

• This weathering process is relatively ______, especially in regard to annual uptake of nutrients by vegetation…so where is the bulk of the nutrients made available to plants coming from????

Organic horizon

Horizon generallylacking significant

organic matter

Bedrock

Root penetrationand development

____________________

Hubbard Brook Forest –NH study

• 1960s and 1970s• Evaluated an entire watershed• Examined “inputs” and “outputs”

Rain gauges usedTo measure nutrient inputs

A watershed

Hubbard Brook study

--note the sharp decline in __ in red spruce trees following lowest pH values in precipitation & stream water…and in stream--Ca leached from the watershed--Ca critical to tree growth

Terrestrial System: Nutrient

• Weathering estimates: ~10% of what plants annually take up provided by weathering process in soil

• The bulk (estimated ~90%) nutrients taken up by plants annually are “regenerated” by the breakdown of detritus and small organic molecules within the soil profile

Detritus

• DEFINED: Freshly _______________organic matter• Almost everywhere in terrestrial habitats: a)

parts of plants (dead) not consumed byherbivores b) animal excreta (droppings)

• This “layer” is the location of the breakdown that results in nutrients transforming into forms that can be reused by plants

“Processing” detritus to regenerate nutrients

• Breakdown of this “___________” on the forest floor, for example, occurs in 4 ways:

1) _________ of soluble minerals by ______2) consumption by ____________________

___________ (millipedes, earthworms,wood lice, and other invertebrates)

3) ___________ of woody components of leaves by ________

4) _____________ of about ‘anything’ by ___________

Leaves of different species ……

• Decompose at _________ rates.• Example of first year leaf decomposition rates in

eastern Tennessee forests: Weight loss of decaying leaves for…. mulberry was 64%

oak was 39% sugar maple was 32% beech was 21%

• Decomposition rates also affected by N, P, and other nutrient concentrations required by _______ and ______ for their own growth

Temperate vs. Tropical Ecosystems

• Climate effects weathering

• Climate effects soil properties

• Climate effects the rate of decomposition

Tropical Ecosystems

• Deeply weathered, low in clay content means soils have poor ability to _______________ (low cation exchange capacity)

• Warmer temperatures year-round means decomposition _______________

• Higher productivity associated with ________ ________________ means nutrient uptake by plants results in retention of nutrients in the _____________.

Tropical forest: turnover is __?

• Compared to temperate forest, more nutrients are tied up in living biomass, above ground

• If we harvest rainforest, therefore, what are the consequences?

Soil Fertility is Jeopardized

Carbon Content of Soil (soil organic matter)

Canada Brazil Venezuelan

prairie shrub for. rain forest

Carbon 8.8 kg m-1 3.4 kg m -1 5.1 kg m -1

Activity farming farming farming

Years 65 6 3

Decline 1%/yr 9%/yr 29%

Conclusions

• Cultivated temperate zone soils retain organic matter _____ longer than tropical soils

• Temperate soils provide more _________ store of mineral nutrients that can be released by slower rate of decomposition

Review:

• Distribution of mineral nutrients Ricklefs (1995) (Table 8.1, page 168 – handout)

compare: ash and oak (temperate) vs. tropical

“________________________”

• __________ (“well-nourished”) vs. ___________ (“poorly-nourished”) standing crop & fluxes Ricklefs (1995) (Table 8.2 – handout)

Aquatic Systems

• Nutrients regenerated __________• Mostly regenerated in ______ layers of water

and sediment• Algae and aquatic plants assimilate nutrients

from the water column in the uppermost (sunlight) zones….far removed from sediments at bottom [contrast to plants & soils]

• More ___________ conditions in aquatic sediments than in upper horizons of terrestrial soils

Aquatic Systems

• Thermal stratification hinders vertical mixing in aquatic ecosystems

• Layering created largely by influence of solar radiation warming upper zone(s).

• _____________ can also influence O2 concentration levels…thus, affecting bacteria respiration rates and the water chemistry

p175,Fig. 8.16 (Ricklef’s 5th edition)

Shaded area time of O2 depletion

(________ _________)

Also, note time of “mixing”

Phosphorus & Eutrophication

• Often scare (limiting) in otherwise high-quality (O2) lakes

• Addition of nutrients, particularly P, in sewage and/or runoff & drainage from fertilized agricultural lands can results in nutrient loading…can be negative if BIOLOGICAL OXYGEN DEMAND (BOD) results

BOD (_______________________)

• Oxidative breakdown of the detritus by microorganisms zaps water of dissolved oxygen.

• Serious problem, especially in winter when photosynthesis rates are low and little oxygen in water column…results in fish kill and other organisms negatively impacted

In summary…• Nutrient regeneration in terrestrial ecosystems

takes place in the _____ with nutrients regenerated from leaf litter

• Tropical forest soils differ markedly from temperate forest soils when it comes to nutrient __________ and ________________

• Aquatic sediments are ______________ from sites of nutrient uptake by plants and algae…more so than soil-to-plant distances for terrestrial ecosystems

In summary…

• Vertical mixing in aquatic systems is inhibited by _____________________

• Nutrient regeneration in aquatic sediments is by _______________ decomposition of organic matter—often in highly anaerobic conditions