silvics

Cavitation

The rupture of the water column in xylem

causes cavitation 3

• Water stress

• Excessive transpiration

• Freeze-thaw cycles

effects of cavitation? 3

• Air bubbles form (embolism)

• Water transport is disrupted

• Hydraulic capacity decreases

embolism

Air bubbles in xylem that block water transport.

P50 represent?

The water potential at which 50% of hydraulic conductivity is lost.

PLC Curves

the relationship between water stress and loss of xylem function.

embolisms reversal?

Freeze-Thaw Embolism

Ice formation forces gases out → bubbles form when thawed.

Why do plants respire?

To release energy from sugars for maintenance and growth.

Where does plant respiration happen?

In mitochondria of all living cells.

Temperature Effects

Higher temperature → higher respiration.

Sun vs Shade Leaves

Which leaves respire more?

Sun leaves (more photosynthetic machinery).

age affect respiration?

Older plants → more non-photosynthetic tissue → higher respiration cost.

Respiration

carbon cost of living

GPP curve is above Reco

sink

If Reco exceeds GPP

source

Positive NEP

carbon uptake

Negative NEP

carbon loss

What happens to NEP during drought

It decreases and can become negative → ecosystem becomes a CO₂ source.

How does drought affect forest carbon sink strength

It weakens the sink or can turn forests into carbon sources.

Why does drought often turn ecosystems into CO₂ sources?

Because GPP decreases more than respiration.

What is the main component of phloem sap?

Sucrose (transport sugar)

Angiosperms Anatomy

• Sieve tube elements

• Companion cells

Gymnosperms Anatomy

• Sieve cells

• Albuminous cells

Are phloem cells alive?

Yes

Which way does phloem sap move?

source → sink

What Drives Movement?

Pressure gradient

What happens when sugar is added to phloem?

• ↓ Water potential (Ψ becomes more negative)

• Water enters via osmosis

What happens when water enters?

• ↑ Pressure (turgor pressure increases

How does drought affect phloem transport? 3

• Less water available

• Reduced pressure buildup

• Slower or impaired sugar movement

Xylem cells alive?

no

Are young leaves sources or sinks?

sink

What is SPAC?

Soil–Plant–Atmosphere Continuum
→ Continuous water movement from soil → plant → atmosphere

Why is stored water important?

It buffers trees during drought.

Foliar Uptake

Leaves absorb water directly (fog, rain)

Fog 3

• Reduces water stress

• Provides direct water (foliar uptake)

• Lowers transpiration demand