lecture 16 : Factors affecting primary productivity

Long term vs short term direct controls

Long = broad scale

• climate and parent material

short= basic resouces for photosynthesis

• light

• temp

• co2

• water and nutreints

state factors of GPP and what type of control is it

Long term

• Biota ( whats growing there)

• time ( since last disturbance)

• parent material

• climate/enviorment

interactive controls that affect GPP

• plant functional type

• soil resources

direct(short-term) controls that affect GPP

• leaf area

• nitrogen

• season length

• temperature

• light

• co2

PAR

portion of sunlight spectrum that drives photosyntehsis

leaf area

total surface area of leaves

• relates to capacity of a canopy to absorb light

photosynthetic effiencey

efficiency by which leaves convert PAR to biomass

• measured as proproton of ligt energy converted to chemical energy

direct factors affecting photosyntethic rate at site level and genetic level

site - affecting leaf area

• light (par)

• water

• nutrient

• temperature

• CO2

Genetic- affecting phtosyntehic efficney

• physiological constraints ( c4or c3? what the plant does)

define leaf area index and the differnces in broadleaf vs conifers

leaf area per area of ground units

• broadleaf - just top leaf surface

• conifers- total needle area

structural differnces of leaves at the top of crowns

optimized for high light levles

• more vertical

• thicker ( lower SLA)

• higher respiration

• higher light saturation levels

structural differnces of leaves at the bottom of crowns

optimized for low-light levels

• more horizontal

• thinner ( higher SLA)

• lower respiration ( less light)

• lower llight saturation level

• lowere light compensation point

photosynthesis vs leaf

canopy structure can increase phtosyntehiss past light sat. point of individual leaves through

• leaf arrangement

• leaf movement

• photo-oxidation

chlorophyll is damaged by too much light

• light saturation:

level where more light doesn’t contribute to more photo

• light limitation

levels where photosynthesis is limited by light

• light comp point

• gross Photosynth = respiration

  • minimum amount of light where plant is breaking even with photosyntehisis and respiration

    • lower in shade-tolerant species

light that passes through canopy….

their intensity decreases exponetnially as it gets further down the canoopy

photosynesis vs TEMP

• low

  • P limited directly by T

• High

  • declines due to photorespiration ( Rplant)

• extreme conditions

  • enzyme inactiveation and chlorophyll damaged

  • while Respiration continues

how do plants respond to water limitation in terms of phtotsynthesis

short term

• reduce stomatal conductance

long terrm

• reduce leaf area

photosynt vs Foliar N

often limting

• productvity tightly linked to nutrient cycling

how is leaf longevity related to phtosyn efficency

trade off beetween photosynthesis and leaf longevity

• longer longevity= lower net photosynthesis

• more investment, containing non-photosynthetic compounds for:

  • herbivore protection (poisonous layer)

  • desiccation resistance (waxy cuticle, multiple layers)

why is productivity often limted by multiple resources

to prevent overwhelming limitation by one resource

• evniroment changes seasonally and anually

how do plants make adjustments to incrase supply of limting resources

• root developments = water

• change distro and structure of leaves = max sunlight and min water loss

long term / large scale adjustmances to balance soil resource availabiity

• photosyntehtic capacity

• stomatal conductance

• leaf area

• change in speceis composition

specific leaf area

leaf area ( m²) / weight (g) ]

how can plants allocate C when other factors become lmiting

• increase allocation to roots to compensate for nutrient limits

• open and close stomata to increase water use effiecny
  

net photosynthesis

gross photosyntehtisis - respiration