Plant Physiology Forum

1
Plant Physiology Forum

• Co-ordinators Phillip Joy
• Kathy Pickle

2
Endangered Plants Persist Under Phosphorus
Limitation

• MJ Wassen, HO Venterink, ED Lapshina, F
  Tanneberger
• Nature
• 22 September 2005
• 437 547-550

3
Species Diversity

• Human alterations
• Reductions in diversity
• Affects ecosystem functioning
• In order to counteract this we need to
• Uncover the mechanisms responsible

4
Increased Productivity
Major Factor Influencing Species Extinction
5
Grimes Hump-backed Model
6
Nutrient Availability Mechanism

• Low or moderate
• Reduces competitive advantage of fast growing,
  tall species compared to smaller ones.
• Temperate terrestrial ecosystems
• Considered N-limited
• N-enrichment is seen as a major cause of plant
  species loss

7
Authors Report New Findings
The type of nutrient limitation has never been
examined for a large number of sites.
P- rather than N- enrichment is more important in
loss of plant species from some ecosystems
8
What They Did

• Investigated 274 sites with herbaceous vegetation
• Fens, bogs, marshes to grasslands
• Recorded at each site
• Species richness of vascular plants
• Number of endangered species
• Above ground standing crop
• Type of nutrient limitation

9
Netherlands/Belgium to eastern Poland to western
Siberia
Represents a declining gradient of atmospheric N
deposition 40-60 kg N ha-1yr-1 to 5-10 N ha-1yr-1
to lt5 N ha-1yr-1
10
What They Found

• Conformed 2 well established relationships
• The classical hump pattern with highest species
  richness at 200-660 gm-2
• Sites with intermediate tissue NP ratios were
  the most species rich
• Endangered plants species only occurred at low
  productivity sites

11
What Was Not Expected

• In Poland and Siberia, endangered species are
  more frequent at P-limited sites than N-limited
  sites
• Maximum numbers of endangered species are higher
  under P-limitation
• Percentage of endangered species in the
  vegetation increases with P-limitation
• Are better able to persist in P-limited sites
  than other nutrient-limited sites

12

13
(No Transcript)
14

• a, b - Frequency distributions of endangered
  species with preference for a certain type of
  nutrient limitation per region

15
Possible Mechanisms

• 1) wider variation in adaptations to low P than
  to low N
• 2) low productive N-limited systems have become
  P-limited
• 3) human impact has impaired P-limited ecosystems
  to a greater extent

16
Authors Suggest Most Plausible

• First 2 mechanisms discarded
• Third is most likely
• Leads to a larger loss of species
• Various human activities for enhanced
  P-availability in wet and moist ecosystems
• Increased groundwater extraction, eutrophication,
  sulphate pollution

17
Globally

• Estimated that human intervention in the P cycle
  has increased the magnitude of P fluxes by 400
• Much more than N, C, S

18
P - enrichment

• May have caused productivity increase and species
  lost
• Competitive exclusion
• Shift from P- to N- limitation to the
  disadvantage of species adapted to low P

19
Can species richness ever be raised by nutrient
availability???

• Addition of P may increase total species richness
  of P-limited wetlands BUT would promote common
  species at the expanse of rare ones
• These findings support this statement
• Absolute number proportion of endangered
  species greatest in P-limited sites

20
Conclusion

• Conservation requires the preservation and
  restoration of p-limited ecosystems
• Re-establishment often fails
• Policies biased towards reducing N are unlikely
  to protect such species
• Systems approach is needed

21
Questions comments