Where Are Plants?

NASA

The Importance of Abiotic Factors

Dr. Mark McGinleyFulbright Visiting Scholar

Institute of Biological SciencesUniversity of Malaya

Let’s Start By Trying to Understand the Plants

• Because the growth form and species identities of plants are diagnostic characteristics of biomes, ecoregions, and communities we will begin by trying to understand the factors that affect the distrubution and growth form of plants.

Where Are Plants?

NASA

Primary Production

• The rate at which carbon dioxide is turned into sugar by photosynthesis– Typically measured as mass/area/time

• Primary production is important because it is the energy converted from sunlight to sugar by photosynthesis that is available for use by the rest of the food chain.

Primary Production

Units- g C/m2/yrhttp://www.globalcarbonproject.org/science/figures/FIGURE6A.htm

What Limits Primary Production?

• All of the factors that can limit the rate of photosynthesis– Light– Water– Temperature– Nutrients

What Limits Primary Production?

NASA

Effect of Temperature and Precipitation on Biome Type

Patterns We Can Observe

• The rate of photosynthesis varies across the globe

• The number of days per year that plants can conduct photsynthesis varies across the globe

• Primary Productivity varies across the globe• Primary productivity limited by different

factors across the globe

Pattens

• Biome type determined by precipitation and temperature (both factors that affect productivity)

• Biomes often defined by dominant plant type

Dominant Plant Types

• Deserts- shrubs• Prairies- grasses• Forests- trees

• Couple of questions– 1. What are the causes for the differences in

dominant plant types among biomes?– 2. What are the ecological implications of these

differences?

Causes

• All organisms are affected by both abiotic (non-living) and biotic aspects of the environment.

• Abiotic– Temperature, soil moisture, pH, humidity, soil N

content, etc.• Biotic– Competition, predation, mutualism, etc.

Photosynthesis

• I think that it makes the most sense to start with the plants– Plants get useable energy via photosynthesis

• Photosynthetic rates can be limited by light, soil moisture, and soil nutrient content.

• Let’s start focusing on water and light

Water

• Plants pick up water from the soil and lose water to the atmosphere via transpiration– Transpiration occurs when the plants open their

stomata to take up the carbon dioxide they need for photosynthesis

• Water is important to plants because it provides structure (hydrostatic skeleton)– That’s why you know your house plant needs

watering when it starts to wilt

How Does Water Get Into the Soil?

• Precipitation – in the areas we are talking about usually rain (any

snow in Malaysia?)• When precipitation strikes the earth three things

can happen– Evaporates– Runs off into streams, rivers, lakes, and ocean– Infiltrates into the soil

• Water enters the soil as the surface and percolates down• Sometimes there is permanent “ground water”

Desert Plants Live Where There is Very Low Precipitation

• Possible strategies for desert plants to pick up water from the soil– 1. Capture the water as soon as it reaches the soil

and the store the water until it rains again• Shallow, widespread root system• Protect the water while it is stored

– 2. Capture water stored in aquifers– 3. Only live when there is water.

Xerophytes

►Capture water after rainfall– Generally have shallow,

but far spread root system

– Greatly reduced leaf size►Leaves become spine►Reduces transpiration

– Store water►Protected by spines

Prickly pear CactusOptuntia sp.

Barrel CactusFerrocactus sp.

Cactus Root Systems

Store Water in Their Stems

Protect Water- Leaves are modified to spines

Cactus “wood”

Ground Water• Water stored beneath the ground

in “aquifers”• Water infiltrates into the soil until

it hits an impermeable layer– The permeable layers are usually

gravel and sand– The impermeable layers are

usually clay• The top of the saturated zone is

known as the “water table”• Plants with roots deep enough to

reach the water table have access to a permanent water source.

Phreatophytes

►Produce long root systems that reach permanent ground water– often protected by

chemical or physical means

– Also have small leaves to reduce transpiration

CreosoteLarrea tridentata

Mesquite (Prosopis sp.)

Mesquite roots can reach up to 50 m below the surface!!

Ephemerals

►Annual plants that germinate, grow, and reproduce when moisture is available– Seeds may live for many

years in the seed bank until suitable germination conditions occur

– Seeds are an important food source for desert granivores– Rodents, ants, birds

Desert Poppies

Chihuahauan Desert

Desert Annual Blooms

Interesting Points

• The dominant plant types in deserts, the biome type with the lowest primary productivity are woody (cactii and shrubs)

Let’s think about prairies (grasslands)

• Prairies are dominated by grasses– Family Poaceae

• Grasslands in North America are in the central part of the country where precipitation is higher than in deserts but lower than in forests

• Central US falls within the temperate zone– Warm summers, cold winters– Large seasonal changes in temperature and

sometimes precipitation

Climate Graphs for Wichita, Kansas(Kansas was covered with prairie before farming started)

Konza PrairieNear Manhattan, KS

Warm and wet in the summer. Good for plant growth!

Prairies

• Conditions are good for plant growth during the summer when it is warm and wet.

• What happens during the winter when it is cold and potentially freezing?

How do plants deal with cold weather?

• Stay alive and active during the winter– Evergreens– In the US, most evergreen trees are Gymnosperms

• Go dormant during the cold season– These plants typically lose their leaves before the

winter comes - deciduous• That’s why we call the season that comes between

summer and winter fall

– Many angiosperms are deciduous

Winter-Deciduous Trees

• If leaves die in the winter, the plants lose all of the resources in the leaves

• Thus, in the fall many species of plants translocate nutrients from the leaves to the roots where it is stored during the winter

• Because chlorophyll, the pigment that makes leaves green, is broken down leaves change color in the fall before they are dropped by the tree.

“Fall colors” in the Eastern Deciduous Forest

Deciduous trees have no leaves during the winter.

Back to Prairies

Prairie grasses die during the winter. Here is summer…

Here is Konza Prairie in the Winter!

Grasses are Not Deciduous

• In the fall, grasses translocate nutrients to the roots and eventually the leaves die

• In the spring, new leaves are formed

• Dead leaves (litter) can build up in the prairie!!!!

Prairie Fires!!

Some Basic Botany

• Not all plant cells are capable of cell division.• Once cells have differentiated into a certain

cell type the can not divide.• Areas of plants with cells that are capable of

active cell division are called “meristems”

Apical Meristems

• “Apical meristems” are located at the end of branches and roots.

• If an apical meristem is damaged in some way then that branch or root can no longer grow.

Intercalary Meristems• Intercalary meristems

are areas of actively dividing cells located within the stems

• Only found in monocots• Thus, if the tip of a

branch is damaged a plant with an intercalary meristem can still grow.

Important Adaptation for Prairie Plants

• Intercalary meristems are very important adaptations to allow plants to survive in the grassland biome. – Suggest that dicot plants with only apical

meristems could not survive well in the prairie environment.

• To understand why we need to think about what can damage the tips of plants in the prairie/grassland?

What Can Damage the Tips of Branches in Grasslands/Prairies?

• Abiotic factors• Biotic factors

Abiotic Factors- Fire

• Prairie fires commonly occur in the summer when plants are actively growing– Warm temperatures– Windy– Fires started by

lightning strikes from summer thunderstorms

Biotic Factors- GrazersAmerican Prairies used to be covered with huge bison herds!

African Grazers

Fire and Grazers Can Damage the End of Branches

• How do grasses survive?

• Intercalary meristems are located near or below ground level– Not damaged by fire

or grazing– Simply regrow after

burned our eaten

Intercalary meristem

Grasses appear to be best adapted to living in conditions found in “prairie” biomes

• In slightly more productive environments grasses are the dominant growth form

Can’t see the forest for the trees

• As precipitation increases, then it becomes less likely that soil moisture will become the major factor limiting the rate of photosynthesis.

• In these cases, light might become a limiting factor.

Light• Light energy is part of the electromagnetic

spectrum that is released by fusion reactions on the sun.

Light

• For our purpose, a very important thing to know about light is the seemingly trivial fact that light “shines down”.

Competition for Light

• Because light shines “down”, if two plants are competing for light, then the taller plant will win.

• However, there is a limit to how tall a plant can grow without adaptations to help it grow taller.

How to plants get “taller”?

• Produce tissues that support tall growth– Wood => trees

• Grow on top of other plants– ephiphytes

Wood expensive and non photosyntheitic

• Carbon that is invested in cellulose in wood can not be used to make leaves or roots

• Therefore, in order for natural selection to favor large investment in wood, there must be a big advantage to growing taller.

Forests

• Competition for light selections for large investment in wood

• Tall trees• Canopy layers

Tropical ForestsLots of Opportunities for Epiphytes

Tropical Rainforests

• Wet and Warm– Some of the highest productivity of any terrestrial

ecosystems.

Patterns

• Possible interesting relationship between productivity and dominant plant type

• Lowest- deserts-shrubs (little trees)• Next lowest- prairies- grasses• Next highest- forests- trees• Highest-marshes- grasses (????)