Plant adaptations to deserts How to run a Plant webpage...2/10/2015 1 Plant adaptations to deserts...

2/10/2015

1

Plant adaptations to deserts How to run a Plant • A plant is an integrated

system which:

1. Obtains water and nutrients from the soil.

2. Transports them through the roots and stems to leaves.

3. Combines the H2O with CO2

entering the stomata to make sugar.

4. Exports energy rich sugar to where it’s needed for maintenance, growth, and reproduction of the plant.

H2O

CO2

Bananas

Water Transport in Plants

1. Animals have circulatory systems.

2. Vascular plants have one way systems.

Transport in Plants

• Because vascular plants have one way systems, plants need a lot more waterthan same sized animals.

• A sunflower plant “drinks” and “perspires” 17 times as much as a human, per unit of mass.

Oh Yeah?

Good thing we’ve got

roots!

Transpiration and the Stomata• Transpiration (= evaporation of water from

leaves) pulls water and minerals up stems AND provides evaporative cooling, but

• It results in tremendous loss of water, which must be controlled.

• Conflicting leaf needs:1. Avoid

desiccation.2. Get CO2.

• Leaves are covered by a waxy waterproof cuticle.

Good at 1. but not 2.

• Stomata – pores that let CO2 in when there’s not too much water stress.

2/10/2015

2

Stomata• The stoma (or pore) is surrounded

by two specialized cells, called guard cells, which are attached to one another at their ends.

• Stomata typically open in the day(in response to light) and close at night.

This provides CO2 for photosynthesis during the day, but saves water at night.

• A low level of CO2 in the leaf constrains photosynthesis and favors stomatal opening.

• If the leaf is too dry the stomata close.

Regulation of stomatal opening

Photosynthetic Water Use Efficiency • Fundamental plant problem: the pathway for

diffusion of CO2 into leaves is the same as the pathway for diffusion of H2O out.

• A plant’s success in dealing with water loss and CO2 uptake is measured as it’s Photosynthetic Water Use Efficiency (WUE).

• WUE = amount CO2 fixed to sugar by photosynthesis per amount H2O lost by transpiration.

• WUE is extra important in the desert!

Photosynthetic Water Use Efficiency • WUE can be increased by a “cautious” regulation of

stomatal opening.

• But this lowers the rate of photosynthesis.

• Result: a tradeoff between WUE and plant growth rate.

• It’s a little surprising that plants can grow at all in the desert (and the first land plants certainly didn’t).

Adaptations for dealing with heat and water loss• Plants have evolved countless

adaptations for increasing their water use efficiency:

• Low surface to volume ratio• Small leaves• Waxy surfaces to stems and

leaves.

Adaptations for dealing with heat and water loss• Recessed stomata.

• Hairy surfaces• Extensive root systems

2/10/2015

3

3 general plant strategies for coping with heat and lack of water• Store water

• Tolerate drought

• Escape drought

Store Water – Succulent Plants

• Store water in leaves stems or roots

• Examples: Cacti

Store Water – Succulent Plants• Store water in leaves stems or roots

• Examples:


• Boojum (Fouquieria columnaris)


• Agaves


• Succulent plants often have an unusual way of conducting photosynthesis called CAM.

• CAM plants open their stomata at night but keep them closed during the day (backwards!)

• This keeps them from drying out, but they need CO2 to photosynthesize when the sun is out, not at night!

• The CO2 taken in at night is stored as an acid.

• During the day when stomata are closed they convert the acid back to CO2 and photosynthesize.

2/10/2015

4

Store Water – Succulent Plants• CAM plants have about 10 times the

WUE of normal plants (fix 10 X as much CO2 per unit of water lost).

• Tradeoff is that they grow more slowly.

• They usually have reduced surface area to minimize water loss.

• Defend their water with spines and toxic chemicals!

• Often have shallow roots for

rapid water uptake.

Tolerate drought• If a cactus dries out it will usually die.

• But some plants tolerate drying out very well.

• Included in this category:

• Evergreen shrubs like creosote bush that can be active even in very dry times.

Tolerate drought


• Drought deciduous shrubs and trees like bursage and mesquite that tolerate drought by dropping leaves and going dormant.

Tolerate drought


• Perennial herbs and grasses that die back but live through drought.

Tolerate drought

• Extensive roots - extend 2 to 3 times the diameter of the plant.

• Take up and use water even under quite dry conditions.

• They vary in how long it takes to go from dormancy back to maximal growth: evergreens - fastest,

• drought deciduous -intermediate, • grasses and herbs - slowest.

Escape drought

• Annual plants specialize to favorable weather periods and exist only as seeds in unfavorable periods.

• Winter annuals escape hot summers -germinate in fall and reproduce and die in the spring in areas with winter rain.

• Summer annuals germinate reproduce and die during summer rain.

2/10/2015

5

Some Important Plants• columnar cacti – two defining life forms of

the Sonoran Desert: columnar cacti and legume trees.

• Columnar cacti are found in arid tropical habitats throughout Mexico, Central and South America.

• 41 species in Mexico.

Some Important Plants• 4 big ones in the Sonoran Desert:

• Cardon

• Senita

• Organ pipe

• Saguaro

Some Important Plants• Cardon – Pachycereus

pringlei

• Bigger than saguaro

• Baja California and the coast of Sonora.

Some Important Plants• Flowers open before

dark and remain open after dawn.

• Pollinated mostly by bats

• 3 genders: male, female, hermaphrodite.

Some Important Plants• Organ pipe –

Stenocereus thurberi

• Many unbranched stems from ground level.

• In Arizona, only in and near Organ Pipe Cactus National Monument.

• Throughout Sonora and southern Baja.

Some Important Plants

• More frost sensitive than saguaro.

• Flowers open only in the dark.

• Most pollination and some seed dispersal done by nectar feeding bats.

• Delicious fruits sold commercially in Mexico: pitaya.

2/10/2015

6

Some Important Plants• Senita – Pachycereus schottii

• Grows kind of like organ pipe, but fewer ribs on the stem.

• Very arid habitats, fine textured valley soils.

Some Important Plants• Senita is pollinated by a moth that

deliberately pollinates, then lays eggs in fruits.

• Highly coevolved mutualism.


• Saguaro – Carnegiagigantea

• The only columnar cactus cold hardy enough to grow in the Arizona Upland.

• Largest cactus in USA.

• Best studied plant in Sonoran Desert.


• Pleated ribs enable saguaro (and other cacti) to expand accordion-style to take up water.

• Well watered plants are 90% water.

• Thermal inertia of the massive watery stems keeps saguaros from overheating or freezing.

Snow on Jan 22, 2007

• Saguaros are limited by freezing.

• There are many more saguaros on the south facing wall of Gates Pass than on the north facing wall.

• This snow shot suggest why.

South facing North Facing

Saguaros are limited by freezing.

South facing slope -many North Facing slope - few

2/10/2015

7


• As with most CAM succulents, it has a very shallow but extensive root system.

• Most roots are no more than 4 in. deep and extend as far out as the plant is tall.


• CAM metabolism “idles” during drought.

• With stomata closed, CO2

released from respiration is recycled to CAM photosynthesis.

• The O2 released from photosynthesis is recycled to respiration.

Some Important Plants• Thus it never goes

completely dormant.

• Can resume full growth 24 –48 hrs after rain.

• Most rains in the desert are small with water only percolating down a few inches.

• CAM plants like saguaro can take advantage of these due to shallow roots and idling photosynthesis.


• Flower during the arid foresummer (May – June).

• White flower open late at night and close around mid afternoon the next day.

• Smell like overripe melons.

• Copious nectar

• All this points to bat pollination.

Some Important Plants• Yet bats play a surprisingly small

part in pollination.• Most is done by white-winged

doves and bees during the day.• In the northern part of its range

(Tucson), there are not enough pollen feeding bats to do the job.

• Thus flowers are mysterious.


• Fruits ripen in June and early July.

• >1,000 seeds in juicy red pulp.

• Rind splits in to sections and can be confused for a red flower.

• Important moist food for many animals at a time when not much else is available.

2/10/2015

8

Some Important Plants• Many fruits eaten by white-

wing doves.

• But they spend most of their time on saguaros, so usually drop the seeds around saguaros instead of in nurse plants.

• Birds like verdins that feed on saguaro but move to paloverdes and other shrubs to eat and defecate are better dispersers.


• Seeds germinate with the first monsoon rain.

• Seedlings grow very slowly and mostly die from desiccation, freezing, or being eaten.

• nurse plants - shelter from temperature, drought and predators.


• Only survive after several wetter than average years.

• Appropriate conditions only occur several times a century in the Arizona Upland and even less frequently in the Lower Colorado River Valley.

• = Episodic recruitment.

Some Important Plants• “Impending doom”

• Because saguaros establish so seldom but die all the time, there have been several scares about its impending doom.

• Saguaro National Monument East established in 1933 around giant old saguaros born in early 1800s or before.

• Many died in the decade following the 1937 hard freeze.

• Established Saguaro NM West in 1961 partly out of fear of impending doom in Saguaro East.

Some Important Plants• Because Saguaro West did not

have a big cohort of giants, it didn’t suffer as badly from the 1937 freeze.

• Its plants were giants by the 1970s and suffered from the freeze of 1978, generating another scare.

• Saguaros are declining most of the time, but they are not going extinct.

Coda• The newest “eminent disaster”

is the buffelgrass invasion.

• This large African grass can promote fires in the desert that Saguaros and other native desert plants cannot survive.

• We’re in the process of seeing how this will play out.

• You can volunteer at buffelgrass.org

2/10/2015

9


• Creosote – Larrea tridentata

• Most common and widespread shrub in all SW deserts except Great Basis, where it is excluded by cold.


• Vertical leaves covered by a thick layer of resins that are responsible for the “smell of rain”.

• Most drought tolerant perennial in North America.

• The last shrub in the driest parts of the Sonoran Desert.

Some Important Plants• Larrea is an evergreen shrub that

photosynthesizes during the dry season and can grow at any time of year.

• It can maintain a positive balance of photosynthesis to respiration down to very low water potentials.

Some Important Plants• It acclimates to seasonal changes in temperature:

• Optimum temperature for photosynthesis shifts from 20C (68F) in January to 30C (86F) in Sept.

• It doesn’t store carbon or nutrients or go into dormancy.

• It’s moderate growth rate is due to its thin canopy with low leaf area.


• Not eaten by many large animals other than jackrabbits.

• Nurse plant for many other plants.

• Frequent site of rodent burrows.

Some Important Plants• Many insects are specialized

to creosote bush:

• creosote katydid

• creosote grasshopper

• Creosote gall midge (& 11 other different galls).

• 22 species of bees feed only on its flowers.

2/10/2015

10

Some Important Plants• One of the longest lived plants.

• On stable landscapes, it keeps putting out new stems on the outer edge of the root crown.

• Ring forms and keeps growing.

Some Important Plants• Ring forms and keeps growing.

• One in the Mojave is 26 ft. across and several thousand years old.

Some Important Plants• Ambrosia – drab wind pollinated plants that

are a major cause of hay fever.

• Several species very common throughout the Sonoran Desert.

• Critical nurse plants – among the few plants that can colonize exposed ground.

Some Important Plants• They are drought deciduous shrubs.

• They lose their leaves in the hottest and driest seasons.

• They usually have 2 leaf cohorts per year –monsoon and cool winter.

• Since leaves are absent in arid seasons, they can have high photosynthetic ratesat the price of low water use efficiency.

Some Important Plants• Downside: it takes several weeks to

redeploy their photosynthetic machinery (leaves).

• So this strategy works best when there are long predictable wet seasons that are neither too cold nor too hot.

Some Important Plants• The 3 common Ambrosias vary in leaf size

and in drought tolerance.

• Larger leaves have more photosynthesis and can evaporatively cool, if they have plenty of water to keep stomata open.

• But they have a deeper boundary layer of stagnant air at their surface and overheat when stomata are closed.

2/10/2015

11


• Small, dissected, or divided leaves have a smaller boundary layer and lose heat more effectively by convection (transfer of heat by moving air).

• They can stay at ambient temperature.

Some Important Plants• Ambrosia ambrosioides – canyon ragweed.

• A large broadleaf shrub (10-30 cm2 leaves).

• It is confined to washes and canyon bottoms where it can get enough water to evaporatively cool these large leaves.

Some Important Plants• Ambrosia deltoidea – Triangleleaf bursage.

• Moderate sized broadleaf shrub with smaller leaves (2-6 cm2).

• Almost identical geographic range as canyon ragweed, but out on plains and bajadas.

• Dominant plant in Arizona Upland with palo verdeand saguaro.

Some Important Plants• Ambrosia dumosa – white bursage.

• Small shrub with small dissected leaves (0.1 – 0.2 cm2).

• Dominant with Larrea over the driest areas of the Lower Colorado River.

• Leaf size in Ambrosias match aridity of habitat.

Some Important Plants• The Sonoran Desert is dominated by

legume trees and columnar cacti.

• The legume trees: Palo verdes(Parkinsonia), Mesquite (Prosopis), Ironwood (Olneya tesota).

Some Important Plants• Palo verde – foothills and

blue

• Blue – needs more water, restricted to washes.

• Flowers for 2 weeks in April.

• Branches droop to the ground.

• Short-lived (< 50yrs?)

2/10/2015

12

Some Important Plants• foothills – more drought

resistant, hillsides

• Flowers for 2 weeks right after blue palo verde.

• Branches droop less.

• Long-lived (100’s of years?).

Some Important Plants• Palo verdes are stem photosynthetic trees.

• One study showed that 72% of annual carbon gain (growth) came from stem photosynthesis.

• Chlorophyll concentration is higher in stems than leaves.

• More photosynthesis with less water loss (higher WUE).

Some Important Plants• Intermediate in function between deciduous shrubs

and evergreens.

• Photosynthetically active all year.

• Produces leaves only in response to heavy rains.

Legume Trees

• Mesquite – Prosopis velutina

• Important plant with an interesting history.

Mesquite – Prosopis velutina

• Wood is hard and attractive

• Popular smoke flavoring for food.

• Major traditional food source for Native Americans

Inner pods sweet

Seeds 35% protein

Meal from seeds is used in native and modern food.

Mesquite – Coevolved with mastodons and other large (extinct) herbivores

• Ate sweet fruits and dispersed seeds widely

• Seeds germinated better after passing through gut.

• Plants lived on hills and valleys.

2/10/2015

13

Mesquite – Coevolved with mastodons and other large

herbivores• Large animals went extinct at

end of Pleistocene.

• Mesquites contracted to flood plains and washes “bosques”

• Cattle 1880’s act like extinct animals – mequites begin to recolonize hillsides.

Mesquite – Coevolved with mastodons and other large herbivores

• If grassland is overgrazed mequites outcompete grasses and take over.

• Since they suppress fire, the conversion is permanent.

Mesquite – Coevolved with mastodons and other large herbivores

• Meanwhile, water tables have dropped dramatically and flood plain mesquites have been cut.

• Few mequite bosques left.

Plants of the Southwest

Some Important Plants• Fouquierias – 11 species from arid Mexico

and SW USA.

• Drought deciduous C3 plants that behave like CAM.

• 5 in the Sonoran desert region: burragei, columnaris, diguetii, macdougalii, splendens

Some Important Plants• Boojum – Fouquieria columnaris

• Name comes from a mythical plant in Lewis Caroll’s The Hunting of the Snark.

• May live > 100 years.

• > 60 ft. tall

• Nearly endemic to Baja California.

2/10/2015

14

Some Important Plants• Ocotillo – Fouquieria splendens

• Widespread in Sonoran and Chihuahuan Deserts

• Leaf blade becomes spine.

Some Important Plants• Short shoots permit deployment of

leaves 3 days from rain.

• Very shallow roots for rapid uptake.

• Behaves like CAM plants, but it is C3.

Some Important Plants• Green parenchyma layer under bark - no stomata.

• Photosynthetically active - recycles CO2 from respiration (no net carbon gain).

• This photosynthetic idling keeps it from using up stored nutrients and lets it respond quickly to short rains like CAM plants.

Some Important Plants• Several hummingbirds migrate

north during the spring and depend on ocotillo as a nectar source – reliable spring flowering.

• Flowers often nectar robbed by verdins and carpenter bees.


• Opuntias – Chollas and Prickly Pears

Opuntias – Chollas and Prickly Pears

• Chollas (round stem) Now called Cylindopuntia

• Prickly Pears (flat stem)

• Many species (> 300)

2/10/2015

15


• Nasty glochids

• Unique to Opuntias


• Nasty glochids

Opuntias –Prickly Pears• Engelmann Prickly Pear – Opuntia engelmannii

• Most common prickly pear

• It varies so much that scientists aren’t sure if it’s 1 variable species or 2 species that hybridize.

Opuntias –Prickly Pears

• Engelmann Prickly Pear – Opuntia engelmannii

• Fleshy fruits taste good and are eaten by many animals.

• Sold commercially as jelly, syrup, even prickly pear lemonade or margaritas.


• Engelmann Prickly Pear Opuntia engelmannii

• Pads eaten by jackrabbits, packrats, and javelina.

Opuntias –Prickly Pears• And people!

• Some species of prickly pear have been developed commercially in Mexico –nopalitos– good against diabetes and high cholesterol

2/10/2015

16


• Spaniard conquistadors were very interested in prickly pears.

• A little scale insect - cochineal - lives on it that produces a rich red to purple dye.

• Such dye was rare in Europe and worth a lot of money.

Hmm, Prickly pear!, Opuntias – Chollas

• Seven species of chollas around Tucson

• They naturally hybridize and at least 7 natural hybrid forms recognized.

Opuntias – Chollas • Chain fruit Cholla – Opuntia fulgida

• Big tree-like cholla recognized by the chains of fruits.

Opuntias – Chain Fruit Cholla • One of the only plants that produces fruits that

never mature and makes flowers coming out of fruits.

• Seeds seldom germinate.

• Reproduces by falling apart.

• What are those chains for?

Opuntias – Other local chollas

• Christmas cholla – Opuntia leptocaulis

• Name from the red fruits made around Christmas.

• Often grows in with shrubs

• Difficult on the unsuspecting hiker.

Opuntias – Other local chollas

• Pencil cholla – Opuntia arbuscula

• Bigger stems than Christmas cholla

2/10/2015

17

• Cane Cholla – Opuntia spinosior

• Staghorn – Opuntia versicolor

• Buckhorn - Opuntia acanthocarpa

• Thin branched bigger chollas

Opuntias – Other local chollas Opuntias – Other local chollas

• Teddy bear cholla – Opuntia bigelovii

• Try to hug it!

• Asexual clones –seeds usually infertile.

Opuntias – Chollas and Prickly Pears• Wood rats (packrats) make nests under prickly

pears or cover nests with cholla joints

• Cactus wrens build their nests in chollas

Some Important Plants• Desert broom -Baccharis sathoroides

• Grows naturally in desert washes

• “Pioneer” or weed of newly disturbed soil.

• In Nov/Dec its fluffy seeds are everywhere!Male flowers

Female flowers


• Brittlebush - Encelia farinosa

• Hemispherical shrub that paints the desert hillsides yellow when it blooms in the spring.

Brittlebush - Encelia farinosa• Hemispherical shrub that paints the desert

hillsides yellow when it blooms in the spring.

2/10/2015

18

Brittlebush - Encelia farinosa• Tremendous variation in leaves

the green leaf can absorb 85% of solar radiation and photosynthesize more.

the silvery one may reflect more than 60%, including the infrared radiation that causes heating of leaf tissues but they photosynthesize less.


• Ephedra – Ephedra trifurca

Ephedra – Ephedra trifurca

• An ancient relict left over from the age of dinosaurs – seeds but no flowers

Mormon tea – Ephedra trifurca

• Potent herbal tea – caffeine and ephedrine

• Ephedrine is a chemical related to pseudoephedrine, which is Sudafed

Grasses and Grasslands

• Desert Grasslands border the Sonoran desert east of Tucson.

• They are a dry extension of the Great Plains grasslands.


• Going up toward Mt. Lemmon or driving from Phoenix to Flagstaff:

• Oak Juniper Savannah

2/10/2015

19


• There are many native grasses in the desert too.

• Some are annuals (escape)

• Most are perennials (die back to resist drought).

Reverchon Threeawn (Aristidapurpurea Nutt. var. nealleyi)

purple threeawn (Aristida purpureaNutt. var. purpurea)

Six Weeks Needle Grama (Bouteloua aristidoides)

Sprucetop grama (Boutelouachondrosioides) Sideoats Grama (Bouteloua

curtipendula)

2/10/2015

20

Black Grama (Bouteloua eriopoda)Tanglehead (Heteropogon contortus)

feather fingergrass (Chloris virgata) Arizona cottontop (Digitariacalifornica)

Fluff grass (Erioneuron pulchellum)

Bush muhly (Muhlenbergia porteri) –

2/10/2015

21

Some Important Plants• Invasive grasses are threatening the Sonoran Desert.

• Mediterranean grass, buffelgrass.

Some Important Plants• Mediterranean grass (Schismus barbatus) has been

around since at least 1926.

• Widespread and common even in the

driest deserts.

Some Important Plants• Buffelgrass (Pennisetum ciliare) has been extensively

introduced to Arizona and Sonora for livestock forage since the 1960s.

• It is rapidly expanding along highways and invading the desert.

• It is all over Tucson and expanding in the foothills and mts around Tucson.

Some Important Plants• It is big and burns easily.

• In Sonora more than 1,000,000 hectares (500,000 acres) of desert have been purposely converted to buffelgrass.

• Results in drastically reduction of habitat and reduced species diversity.

• It may destroy large hunks of the saguaro/palo verde desert here.

Quercus oblongifolia

• Mexican Blue Oak – Quercus oblongifolia

• the dominant species in lower open oak woodland.

• It is an important constituent of pinyon-juniper communities.

• Silverleaf Oak, Quercus hypoleucoides

• lanceolate leaves - dark green on top

• silver white on bottom

• commonly found in moist canyons and on ridges and with conifers in S AZ mountains

• deciduous

2/10/2015

22

Quercus arizonica

• Arizona White Oak

• one of the largest southwestern oaks

• Found on sky islands in AZ, NM, Sonora, Chihuahua

• Sprouts from stumps after moderate fires

• evergreen

Quercus emoryi

• Emory Oak

• grows in dry hills at moderate altitudes

• evergreen

Quercus rugosa

• Netleaf Oak

• Deep leaf veins

Quercus gambelii

• Gambel Oak

• deciduous

• small tree or large shrub

• widespread in the foothills and lower mountain elevations

• More widespread and goes further north

Platanus wrightii

• Arizona Sycamore or Alamo

• Riparian – desert and sky islands

Pinus ponderosa

• Rocky Mt Ponderosa Pine

• All over the west, up to Canada

• Widespread in mts of SW and along Mogollon Rim and around Grand Canyon in AZ

• Fire adapted, but doesn’t do well with hot fires

2/10/2015

23

Pinus strobiformis

• Southwestern (or Chihuahua) White Pine

• Mexico – Sierra Madre

• high-elevation pine – growing with other pines

• Likes cool moist places but very drought tolerant

• Huge cone!

Pinus discolor

• Border Pinyon Pine

• Grassy pinyon juniper woodlands

• Makes pine nuts

• sky islands - a layer cake of biomes each with its own plants and animals

Pinusengelmannii

• Apache pine

• Mainly Mexican

• AZ: south & east of Tucson

• Needles up to 15 in. long!!

Abiesconcolor

• White Fir

• Long narrow tapering tree

• Distintive gray bark

• High altitude in AZ, widespread in W US

Abieslasiocarpavar. arizonica

• Corkbark Fir

• Looks like white fir, but thick corky bark

• Straight leaves in two rows

• Grows at treeline in NM and AZ

2/10/2015

24

Pseudotsugamenziesii

• Douglas Fir

• Higher mountains throughout West

• One of the tallest trees in USA

• Cones have funny brackssticking out

• Not a true fir.

Populus tremuloides

• Quaking Aspen

• Most massive living organism?

• Huge geographic range?

• Great beauty?

• A “phoenix” species?

• One is ~80,000 yo with 47,000 trees (in Utah)

• Grows in gaps after fire

Plant adaptations to deserts How to run a Plant webpage...2/10/2015 1 Plant adaptations to deserts...

Documents

Transcript of Plant adaptations to deserts How to run a Plant webpage...2/10/2015 1 Plant adaptations to deserts...