Lecture 10- Coping with aridity and drought IV

Question 1

What are the strategies plants employ ti survive in dry and hot environments? (3)

Answer 1

1. Reduce radiation load
2. Maximize water supply/Buffer water supply
3. Water use efficiency

Question 2

What is the radiation load on a horizontal leaf like?

Answer 2

• if horizontal (wet areas) there the sun at noon will hit the leaf the most, suffers ,most at noon
• highest amount

(• horizontal leaf absorbs most light

• vertical east-west almost as much
• vertical N-S much less)

Question 3

What is an azimuth?

Answer 3

-orientation in 3D space

Question 4

How can plants optimize their leaf angle and azimuth depending on their radiation circumstances?

Answer 4

• leaf can have various orientations, if horizontal (wet areas) there the sun at noon will hit the leaf the most, suffers most at noon
• eucalyptus= leaves are pendulous (vertical) blade can be east west/ south-north or anything in between
• if pointing east west, not long after sunrise= get max load, at noon= minimal, and in the afternoon then get more
• the integral is about the same (same amount of light just not in the hottest part of the day)

Question 5

What does parahelitrophic mean?

Answer 5

-leaves always parallel to sun’s rays -always keep the leaf parallel to the source of the radiation, not that common in xerophytes however as it is difficult to engineer ( what xerophytes often do-if have a vertical leaf with east to west direction it is then very similar with how much radiation it captures)

Question 6

What does diaheliotrophic mean?

Answer 6

-maximizes the radiation interception -leaves always perpendicular to sun’s rays

Question 7

How can plants reduce radiation load by leaf shape?

Answer 7

reduce radiation load by leaf shape - acacia peuce= in the desert, -the leaves are like a needle= low surface to volume ratio -so not much light is intercepted

Question 8

How do grasses reduce their radiation load?

Answer 8

-leaf shape - xerophytic grasses can roll them up in a cylinder shape (minimizes surface area/volume ratio) -sunken stomata= cannot lose water as quickly as they are on the inner side

Question 9

What are the ways of reducing the radiation load on a plant?

Answer 9

1. Leaf orientation: azimuth, angle, heliotropism 2. Leaf shape: succulents, cylinders 3. Leaf amount: drought deciduous, low leafiness 4. Leaf optics: high reflectance – wax, salt

Question 10

How can plants reduce their radiation load with leaf amount?

Answer 10

-if less than won’t have as many surfaces to intercept the radiation -have low leaf weight ratio (M of leaves over M of plant) drought deciduous plants -can be drought deciduous= when water stressed drop their leaves

Question 11

How can plants use leaf optics to reduce radiation load?

Answer 11

-whiteish = reduce radiation as it reflects, high reflectance (wax and salt)

Question 12

How does the salt bush change its leaf optics?

Answer 12

• All Atriplex species(59 in Australia) are covered with unique bladder hairs • Hairs have a hugh balloon-like terminal bladder cell supported by a stalk cell • Bladders accumulate high concentrations of salt -the salt in bladders crystalizes (as they dry up and have spontaneous crystalization)

Question 13

How is photosynthesis affected in the salt bush depending on leaf orientation?

Answer 13

• lower photosynthesis when horizontal as opposed to vertical
• if high temp persist the greenish leaf becomes white
• that reflects well and photosynthesis goes up

Question 14

What are the three ways of maximizing water supply (strategy 2)?

Answer 14

1. Water spenders 2. Drought escapers 3. Water collectors

Question 15

What do water spenders do?

Answer 15

e.g.-river red gum= most widely distributed eucalyptus in australia -send their roots deep down into the soil and tap into water source so they never experience water stress (unless in extreme conditions)

Question 16

What do drought escapers do?

Answer 16

• annuals in deserts, go through the entire life cycle when it is wet and never encounter the really hot and dry environment

Question 17

What do the water collectors do?

Answer 17

can collect lot of water in their stalks -baobab tree

Question 18

What are the characteristics of the baobab tree?

Answer 18

-surpass the sarano cactus in water holding ability -100 tonnes of water in one tree -baobab fruits can be eaten -Adansonia gregorii • One species in Australia • some very old • up to 15 m diam. • up to 100 kL water • fruit can be eaten

Question 19

How is water use efficiency distributed across australia?

Answer 19

strategy 3: C4 photosynthesis is good, C3 worst, CAM best

• C4 distributed along the dry areas
• water efficiency

Question 20

How does C3 photosynthesis do with water efficiency?

Answer 20

normal C3 - CO2 diffuses in via stomata into the chloroplasts, the more you open them the more water you lose, so stomatal aperture is dangerous in dry areas -C3 not very water efficient as has to open stomata

Question 21

How does C4 do in water efficiency?

Answer 21

it can suck CO2 in rather than diffuse it in -so don’t have to open the stomata as much -less water is evaporated -why don’t all plants do it? need energy to run the pump, so when not as hot not worth it

Question 22

What are the common grass species in Australia?

Answer 22

triodia species grasses that are common -2 types= triodia pungens (dominant in tropics) -triodia basedowii (southern region) -spitifex as well grass= archetypal grass, C4 grass, superficial roots to get to the water when it rains

Question 23

What is the Mulga?

Answer 23

Mulga= tree (Accacia species) -refers to a set of acacia species -grow in the driest parts of the country -10 species are refered to as Mulga

Question 24

What are the survival tricks of the Mulga?

Answer 24

• Deep rooted • Drought deciduous • Water-catcher • Pays protection (nectar) • Seeds dispersed by ants -have deep roots, can find better water supply -drought decidious= under extreme drought stress the leaves will drop -vertical orientation of phyllodes directs water to the bottom of the tree so it can use it -seed dispersal is good as you cannot have trees next to one another, would be too much competition for water= good xerophytic advantage

Question 25

What is the ant-Mulga mutualism like?

Answer 25

• Most ants prefer nectar with sucrose • Acacia nectaries contain invertase • Acacia ants have little invertase in guts – prefer low sucrose nectar -mutualism= ants and acacias (Mulgas) -the parrots drop the seed, ants then take the seeds and disperse them (seeds are antproof, but capsules are edible= elaisomes) put the seeds into a waste chamber -mulga ants get nectar with invertase (enzyme= splits sucrose, into glucose and fructose) -the mulga ants have little of the invertase in their guts so this way they can eat the sucrose -specialist on the mulga trees

Question 26

Why is the way mulga ants discard the seeds important?

Answer 26

-elaisomes= fat rich -discarding seeds= important, in chamber in the nest -chamber depth= protected from fire but stil get the temperature -acacias need 100 C temp to germinate - Mulga seeds - shielded from fire “ Chamber depth - 100 C during fire “ Perfect pre-treatment for germination

Question 27

What are the water saving strategies of Xerophytes? (6)

Answer 27

1. Schlerophylly 2. Sunken, closed and partially closed stomata 3. Drought deciduous behavior 4. Leaf orientation and optics 5. Osmoregulation (roots making osmotically active molecules= causes the water to be dragged into the plant) 6. High root: shoot ratio