Field photosynthesis
measurements and CAM
plants
In the interest of making difficult
measurements
What is CAM
again?
Why so
difficult?
Field
photosynthesis
A tale of two
Tillandsias
What is CAM
again?
Why so
difficult?
Field
photosynthesis
A tale of two
Tillandsias
Crassulacean
Acid
Metabolism
Water-saving adaptation
Approximately 7% of all
vascular plants have CAM
Evolved independently in
over 33 families
C3
CO2 uptake (carbon fixation) and photosynthesis
(Calvin cycle) is concurrent with light absorption
(“light reactions”) = all in the daytime.
C4
CO2 uptake and photosynthesis occur in different
cells, but both are still concurrent with light
absorption
CAM
CO2 uptake and photosynthesis occur in the same
cell, separated temporally; CO2 uptake occurs at
night and photosynthesis during the day.
PEP Carboxylase
Rubisco
CAM cycle
Typical
Las plantas
CAM, como
Agave tequilana,
Presentan una
mayor actividad
durante la noche
Pineapple Ananas comosus
Opuntia ficus-indica
Epiphytic Acmea
Epiphytic Tillandsia
Terrestrial Acmea
Many orchids
A CAM orchid
with no stems or
leaves… just
photosynthetic
roots.
Opuntia species
Clusia species
What is CAM
again?
Why so
difficult?
Field
photosynthesis
A tale of two
Tillandsias
Field
photosynthesis
Gas exchange
Acid accumulation
Biomass production
Field
photosynthesis
Gas exchange
Field
photosynthesis
Gas exchange
Field
photosynthesis
Acid accumulation
Field
photosynthesis
Acid accumulation:
dawn - dusk
1. Freeze tissue
samples.
2. Grind or boil for
5 min.
3. Titrate with
0.01N NaOH to
pH7.0.
4. Each 0.5 mol
protons is equal
1 mol CO2.
Field
photosynthesis
Biomass production
Most productive CAM plants:
Agave salmiana: 42 tons hectar-1 year-1
Opuntia ficus-indica: 47-50
C3 crop: Beta vulgaris: 30-34
C3 tree: Cryptomeria japonica: 44
C4 crop: Saccharum officinarum: 50-67
Productivity can be high for tended CAM plants.
What is CAM
again?
Why so
difficult?
Field
photosynthesis
A tale of two
Tillandsias
Why so
difficult?
Physical
problems
Why so
difficult?
Physiological
problems
Why so
difficult?
Physiological
problems
dark day
decarboxylation
is low
Why so
difficult?
Physiological
problems
dawn minus dusk
acid is affected
by previous day
dark day
decarboxylation
is low
Why so
difficult?
24-hour
gas exchange!
Difficult to
repeatedly
seal against
surfaces,
leaks are
common.
With cuvettes always sealed against plant surfaces, 24-h gas
exchange structures become more apparent.
What is CAM
again?
Why so
difficult?
Field
photosynthesis
A tale of two
Tillandsias
Tillandsia elongata
Tillandsia brachycaulos
Tillandsia brachycaulos – succulent leaves
Tillandsia elongata – tank forming
Vertical
Stratification
results in
different light
regimes.
T. elongata is
more exposed
than T.
brachycaulos.
Both species tend to accumulate similar photodamage
when they occur in similar light environments in the field.
Plants taken from the field are transferred to five
shade treatments near the laboratory .
Both species saturate at low light. Tillandsia
brachycaulos seems to suffer some photoinhibition at
moderate light levels.
The portable gas
exchange system is
adapted to measure
24-hour, whole-plant
gas exchange in the
lab.
Measurements are
made automatically
every 10 minutes.
NO 24-h gas exchange
in the field.
T. elongata has higher rates per kg fresh mass than T.
brachycaulos under similar conditions.
During drought, T. elongata dropped to a daily
negative carbon gain after 8 days; T. brachycaulos
after 28 days.
Plants were re-watered at arrows and gas exchange
recovered quickly for both species.
C3 gas exchange
disappeared
quickly.
T. elongata had
a lower drought
tolerance
compared to T.
brachycaulos,
even though it is
in more exposed
locations.
Gas exchange
during rewetting
after drought
was similar:
T. elongata had
a higher gas
exchange rate
after 1 day than
T. brachycaulos.
Still no C3
photosynthesis
after 3 days
rewetting.
Conclusions:
Tillandsia elongata is a “drought avoider” and occurs in
more exposed locations to take advantage of direct
rainfall and dew formation (a common occurrence even
in the dry season).
Tillandsia brachycaulos is a “drought tolerator” and
relies on leaf succulence to maintain gas exchange
during drought.
Differences in drought strategies,
rather than photoprotection
probably affect the vertical
locations of each species in the
canopy.