Why the kwongan ecosystem of Australia is so extremely oligotrophic, part 1

Several regions on Earth have senile substrates so exhausted of mineral nutrients - particularly phosphorus and zinc - that virtually the only source of nutrition is aerosols (https://en.wikipedia.org/wiki/Aerosol).

These make for oligotrophic (https://en.wikipedia.org/wiki/Oligotroph) ecosystems, in which efficiency in recycling nutrients is a prime adaptation of plants.

Although oligotrophic lands are effectively nutrient-deserts, they are usually densely vegetated by diverse shrubs possessing extreme adaptations in various organs including photosynthetic, rhizal and reproductive.

An ecosystem that epitomises oligotrophy is that of kwongan (https://en.wikipedia.org/wiki/Kwongan) in southwestern Australia (e.g. https://en.wikipedia.org/wiki/Fitzgerald_River_National_Park and https://en.wikipedia.org/wiki/Badgingarra_National_Park and https://en.wikipedia.org/wiki/Cape_Arid_National_Park and https://en.wikipedia.org/wiki/Little_Desert_National_Park and https://en.wikipedia.org/wiki/Big_Desert_Wilderness_Park).

The plants indigenous to kwongan - totalling at least six thousand species - are so specialised for oligotrophy that even small additions of anthropogenic nutrition, in the form of dust from nearby farms, can rapidly corrupt the ecosystem via encroachment of non-indigenous herbaceous plants.

One of the puzzles of oligotrophic ecosystems in the southern hemisphere is that kwongan seems much nutrient-poorer than its South African counterpart, namely fynbos (https://en.wikipedia.org/wiki/Fynbos).

Both fynbos and kwongan are flammably evergreen with many species featuring cluster roots (https://en.wikipedia.org/wiki/Cluster_root) and/or seed-dispersal by ants
(https://en.wikipedia.org/wiki/Myrmecochory).

However, the former tends to be far poorer in species possessing:

These differences are unexplained by:

  • the concentrations of nutrients in the siliceous, sandy soils, which are minimal in both cases, or
  • the regimes of wildfire, which are similar.

to be continued...

Posted on February 20, 2022 06:11 AM by milewski milewski

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