| Dry
rainforest species have gained increasing
attention in recent years among horticulturists
and local councils for use as amenity
trees. The hard man-made surfaces
of urban environments make cities
significantly warmer than surrounding
areas. This results in discomfort
for the inhabitants and increased
power consumption due to higher demand
for air conditioning. Plants ameliorate
the urban heat island effect as water
evaporates from their leaves (transpiration)
and they cast shade beneath their
canopies.
The drought tolerance of dry rainforest
species has been linked to leaf morphologies
and growth habits that confer reductions
in water stress and heat loads. However,
surprisingly little scientific research
has been done on the drought tolerance
of rainforest species.
Some epiphytic species have embraced
a special form of photosynthetic carbon
fixation known as Crassulacean Acid
Metabolism (CAM). CAM allows plants
to accumulate carbon dioxide from
the air at night rather than during
the day like most other plant species.
By opening their stomata at night
and temporarily trapping the carbon
dioxide in an organic acid form, CAM
plants maximise their water use efficiency.
Thus, compared to normal plants, far
less water is lost relative to the
amount of carbon dioxide absorbed.
As might be expected, desert dwelling
succulents like cacti are typically
CAM plants. Perhaps surprisingly,
in terms of numbers of species, CAM
plants inhabiting rainforests far
outnumber desert species.
The article delves into the research
with Deep Yellow Wood (Rhodosphaera
rhodanthema) as an example of
CAM.
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