PL SC 324 Lecture 2: Plant Growth Requirements and Resource Allocation

Where do plants get there resources?

1. Atmosphere

2. Hydrosphere

3. Lithosphere & Soil

4. Biological Interactions (Legumes)

Atmosphere contains _% Nitrogen, _% Oxygen, _% Rare gases, _% Carbon Dioxide

78% Nitrogen, 21% Oxygen, 0.95% Rare gases, 0.035% Carbon Dioxide

What % of ground water is accessible to plants?

About 1% of ground water is accessible to plants.

Some important soil properties for plants to get their resources

Soil organic content, soil texture, soil depth, soil pH, biological activity

Biotic components from where plants get their resources

Rhizosphere (influenced by plant roots), Soil microorganisms, Trophic interactions (herbivores, pollinators), Plant-plant interactions: Facilitation, competition, allelopathy.

What do plants do with their resources? (in order of importance)

1. Maintenance (respiration and basic repair)

2. Initiation and growth of new roots (to bring in new resources)

3. Initiation of new leaf area (Bring in new energy)

4. Stem elongation, flowering and seed production

5. CHO storage (ONLY with net positive photosynthesis)

When does a plant start to allocate carbohydrates to other parts besides leaves?

Once the plant has a net positive increase in carbohydrates

What is storage in plants?

Storage is the build up of resources that can be mobilized in the future to support synthesis and growth

Accumulation

-Interim deposition, occurs when the rate of resource acquisition exceeds demands for growth and maintenance

-Responsible for the short-term flux of plant chemical composition:

-This allows for a relatively constant flow of carbohydrates from leaves to the rest of the plant over a 24-hr cycle (starch accumulates when sunny, is depleted when dark).

               -Storage of Nitrogen, a luxury, occurs when pulses of available Nitrogen exceed the capacity of the plant to use it.

Reserve formation

Diversion of acquired Carbon and Nutrients into storage

-These reserves allow the plant to be less dependent on current photosynthesis or nutrient acquisition.

-Advantageous in early Spring

-Enable recovery after major disturbance

-Allow for reproduction

Name some storage organs in plants

Rhizomes, tuber, bulb, taproot

Variation across species in how they prioritize storage Carbohydrates

Soluble sugars, starch, fructans

How is Nitrogen stored?

In petioles and shoots as nitrate (in plants)

Amino acids, amides, protein in lower fertility soils

How is phosphorus stored

inorganic phosphate and in compounds that contain phosphate

Nutrient Recycling in Plants

-Some material in senescing leaves is recovered.

               -Especially N & P

               -Not a major source of C

               -Ca is highly recalcitrant

In what type of habitats are biennials found?

often found in habitats with intermittent resource availability

Storage and Remobilization: Annuals

-Annuals don’t store much carbon or nutrients, allocation is to seeds.

-During senescence nutrients and carbon from leaves is recycled to seeds

Storage and Remobilization: Perennials

-Perennials have the largest capacity for storage

               -This limits early growth potential

               -However, once C and nutrients are stored, it allows early season growth or survival of unfavorable conditions.

               -In cold climates, storage as proteins also reduces the risk of freezing damage

               -Short days often induce increased storage (light or temperature response).

Opportunity cost of storage

Reduced growth due to allocation to storage

Storage and Remobilization: Biennials

-Biennials are often found in habitats with intermittent resource availability

               -Store C and N

               -Nitrogen is typically the limiting nutrient

Stress

is any process that limits plant growth