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Flashcards in Lecture 1 - Chronosequence Deck (19)
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1

why is fraser isand a model ecological system?

> it has a very distinct soil age sequence (chronosequence)

2

where does fraser island's sand orginate from?

> NSW (Hawkesbury, hunter, clarence river catchments)
> it is at least 350 000 years old (mainland Great Sandy National Park, some of the region 730 000 years old)
> transport of sand still occurs today

3

how does 'time travel' occur on Fraser Island?

> 500 year East Coast young dunes to 700 000 year old dunes form soils
> dune chonosequence spans a short distance
> ecosystems are shaped by, and shape, the soils
> biomass build - up and subsequent decline characterise the ecosystems

4

what are the stages of succession on Fraser?

> earliest succession:
- Pioneer beach vegetation
- low diversity , low biomass
> Early succession:
- Scribbly gum (Eucalyptus racemosa) woodland
- greater species diversity and biomass than pioneer community
> late succession ('climax'):
- Eucalyptus pilularis and Syncarpia hillii
- even higher biodiversity and biomass (?)
> late succession (maybe):
- rainforest
- often not considered strictly part of the chronosequence due to greater water availability, others argue that it is
> retrogression (declining phase):
- Banksia dominated low woodland and heathland
- low biodiversity (?) and biomass

5

what is the concept of ecological (primary) succession?

> in the absence of soil renewal, climax vegetation 'degrades' to form retrogression (declining) vegetation. Nutrient stocks decline (leach), from the soil over geological time spans, resulting in nutrient-impoverished soils.

6

Describe the Fraser island chronosequence

> succession (build up stages)
- coastal pioneers, woodland, tall eucalypt forest, (rainforest)
> retrogression (declining)
- wallum woodland, heathland
> mangroves: marine and terrestrial influences

7

what shapes the vegetation of Fraser Island

> distinct changes in soil and associated nutrient availability.
> nitrogen enters soil, availability increases and then declines
> initial soil phosphorous stocks become available and then decline
> as soils age, nutrients become available (sand to soil) but decline in very old soils due to net loss in the absence of soil renewal (volcano, glaciation)

8

describe the important plant-sol interactions

> plants acquire essential elements from soil (in addition to C, O, H from air and water)
> in most ecosystems, N and P most limit plant growth
> macro-nutrients are essential for plant survival
- >1mg/g of plant dry weight
- N: proteins
- S: proteins
- P: DNA, energy
- K: water relations
- Ca: cell wall
- Mg: Chlorophyll
- Si: Structure

9

describe plant root adaptations and symbiosis

> allow access to nutrients in the depauperate soils
> Early succession: Casuarina, Acacia
- symbiosis with N2 fixing bacteria ("root nodules")
- biological nitrogen fixation is prevalent in low N soils
> climax: Acacia, Eucalyptus
- symbiosis with mycorrhizal fungi
- 80% of plants have mycorrhizas, different types (endo/ecto)
- Ectomycorrhizal fungi shown here occur only in certain woody species
- organic matter breakdown, nutrient acquisition
- higher surface area
> REtrogression: Proteaceae ( banksia, hakea, grevillea)
- cluster roots
- proteaceae, sedges and some other species do not use mycorrhizas but cluster roots
- enhance access to P

10

what are characteristic of the youngest dunes?

> youngest dunes are unstable, exposed to wind and salt, no soil has developed, minimal vegetation and yellow sand
> herbs and grassers are first colonisers, shrubs and trees follow

11

What are characterisitic species from behind the beach? (pioneer communities)

> Casuarina - nitrogen fixing
> acacia sophorae - nitrogen fixing
> Banksia integrifolia
> Pandanus tectorius

12

which species use nitrogen fixation?

> approx. 10% of extant plant species form symbiosis with N-fixing procaryotes (bacteria, cyanobacteria)
> many species in the legume family (Fabaceae) fix N
> also species in Casuarinaceae, other flowering plant families but also ancient plants such as cycads

13

how does nitrogen fixation occur?

> casuarina root nodules house bacteria in genus frankia
> red colour in nodules is indicative of active nodule (leghaemoglobin), low oxygen levels protect nitrogenase enzyme which fixes N2 into N for plants
> Nitrogen enters terrestrial ecosystems via biological N fixation
> only certain bacteria and cynobacteria (symbiotic, associated or free living) possess the enzyme nitrogenase and associates biochemical machinery to convert inert N2 to reactive NH3
> nitrogen accounts for approx. 80% of nutrients acquired by plants from soil, only N-fixing plants can supplement their N demands with N2 derived from air

14

what are some plants represented in the older dunes?

> woodland communities
> Eucalyptus
> Bloodwoods
> Banksia
- cluster roots

15

describe cluster roots

> cluster roots explore a small volume of soil intensively by excluding numerous chemicals and enzymes to release nutrients from soil

16

describe the types of Mycorrhizals

> 80% of terrestrial plants have mycorrhizal (root fungus) symbiosis
> fungus explores soil and exchanges nutrients for photosynthates
>ecto (woody plants)
- outside root
> endo (woody and herbaceous)
- inside root cells
> ericoid (ERicaceae)
- coils inside epidermal cells
- large
- enzymatic capabilities

17

describe the sand and nutrients that start off succession

> Aeolian sand deposition formed Fraser island
> the deposited sand has coating of mineral nutrients
> inside = Quartz grain
> outside = sesquioxide (clay) coating contains essential nutrients, p, Mg, Ca, K for plant growth

18

what are the sstages of soil development?

>plants and microbes strip nutrient coatings from sand grains and incorporate nutrients into biomass
> colour of sand goes from yellow to white (1-> 2)
> accumulation of organic matter results in grey colour
> A1 horizon contains nutrients in organic matter
>A2 horizon is leached (vertical movement of nutrients with water movement)
> B horizon accumulates nutrients as Fe-Al-oxides and other minerals

19

how can the fraser island chronosequence be reset?

> disturbance, such as fire, volcanoes, glaciation etc
> if the disturbance it to great, it can cause collapse of the system
> otherwise, the system can make a partial recovery