Lecture 7- Coping with aridity and drought: CAM

Question 1

What happened to Australia in the Tertiary (Paeogene and Neogene) and what were its consequences?

Answer 1

1. Climate changed
   - warm, humid, rainforests initially widespread
   - circumpolar current: cooling of Antarctica
   - reduced wind-bearing rains over Australia and increased aridity from Oligocene (30 my ago)
   - contraction of rainforest
   - evolution and expansion of more arid adapted plants e.g. sclerophylls and animals adapted to them

Question 2

What is a xerophyte?

Answer 2

-a plant that is adapted to living in dry habitat, a desert plant

Question 3

What is unusual about the desert flora of Australia?

Answer 3

• in Australia no cacti in the desert unlike in the US
• in Afrcia, no cacti either but succulent like plants that are capable of storing water
• Sonoran desert: in the US

Question 4

What is the predominant plant in the Sonoran desert (US)?

Answer 4

• Saguaro cactus
• huge, 20 m tall
• can store up to 5 tonnes of water

Question 5

What catus was the major invadoer in Australia?

Answer 5

-Opuntia (prickly pear)

Question 6

Why and how was Opuntia first brought to Australia?

Answer 6

• first imported to support the growth of cochineal insects (and to maintain spiffy red coats on parade), it subsequently, and briefly, lent ambience to early vineyards
• cochineal insects eat the pear and they make dye and that is used in dying army uniforms
• so brought here by the English in the early 1700s

Question 7

What is Carmine?

Answer 7

• the colour of the cochineal insects insides

- used in dying many thing (drinks, food, clothes…)

Question 8

How quickly was Opuntia (prickly pear) invading Australia?

Answer 8

-From a few plants in 1840, it expanded to:
• 4 million ha in 1890
• 6.3 million ha in 1913 • 17.6 million ha in early 1920s
• Nearly 30 million ha by 1930
-300 square meters per second

Question 9

What was the total biomass of Opuntia in Australia?

Answer 9

• Rate of advance = 100 ha per hour!
• Average biomass of 620 tonnes per ha
• total biomass in 1929 of 1.5 gigatonnes

Question 10

What did people try to do to solve the Opuntia invasion?

Answer 10

–people tried to slash and burn them
-tried chemical warfare
-didn’t work very well
-Arsenic can still be detected today from that attempt
- Slash and burn
• 100s of tonnes of arsenic pentoxide were used to kill the prickly pear to no affect.
-the poison used over the years in hundreds of tonnes of arsenic and black= weapons to kill the prickly pears (tanks)

Question 11

What are environmental weeds?

Answer 11

-those species that invade native communities or ecosystems - they are undesirable from an ecological perspective, but not necessarily an economic one.

Question 12

What are serious environmental weeds?

Answer 12

-those that cause major modification to species richness, abundance or ecosystem function.

Question 13

What are very serious environmental weeds?

Answer 13

-those that can totally and permanently destroy an ecosystem.

Question 14

Why do many environmental weeds have a competitive advantage over native plants?

Answer 14

• Better adaptations to the environment
• Resistance to Australian insects, fungi and other
organisms

Question 15

Why was prickly pear so successful?

Answer 15

1. Succulence:plant tissues that have low surface to volume ratio= squichy and full of water
2. Cuticle: the surface of the leaf
   - very good
   - can break it away and keep for half a year, then can put in the grond and it will grow as it could survive on the water it had

Question 16

Why is the low area/volume ratio so good in cacti?

Answer 16

• evaporative surface area is low

- in the barrel cactus it is 1:9

Question 17

What is the root system like in cacti?

Answer 17

• Roots typically 5 - 15 cm below surface
• New “rain roots” form rapidly
• A 15 m saguaro has roots spreading to 20 m
-they don’t have deep roots
-can collect the water when it rains in a big area
-light rain so it is better to tap in to the water when it rains, as opposed to having deep roots where there is more water
-store lot of water to deal with the aridity

Question 18

How can cacti survive such long droughts?

Answer 18

-store lot of water
• Cortex and pith - water storage
• Water undrinkable in most cacti
• Photosynthesis in the outer cortex
-can expand and contract a lot depending on how much water is available

-sunken stomata and the layers above are resistant to water loss

Question 19

What is CAM?

Answer 19

• CAM - Crassulacean Acid Metabolism
• First identified in members of the family Crassulaceae
• Generally grow where water is scarce, with some exceptions
• CAM is not wide- spread in Australia
• crassulaceae= family of succulent plants

Question 20

What are some common CAM plants?

Answer 20

• Pineapple •A loe • Orchids • 26 Angiosperm families
–C actaceae, Orchidaceae, Bromeliaceae, Liliaceae
• Some Ferns and at least one gymnosperm • About 7% of vascular plant species are CAM
-tequila is made from agave
CAMs grow in amazing places, can grow on powerlines= problem in Venezuela

Question 21

How did the cacti not die after the arsenic spraying?

Answer 21

-Jean White-Haney working at the isolated Dulacca field station in Queensland, reported that the kill was more effective if (arsenic) spraying was done at night.