FACTORS AFFECTING PLANT SENSTIVITY TO AIR POLLUTANTS

Pollutant	Factor	Sensitivity	Comment
C2H4 pollution	Tissue age	Epinasty in immature leaves. Other symptoms on oldest leaves first.	Tissues with high natural C2H4 are more sensitive.
C2H4 pollution	High temperature	Sensitivity increased
C2H4 pollution	Other pollutants	Effects inhibited by high levels of SO2 or CO2
Cl2 pollution	Bright sunshine	Sensitivity increased
Cl2 pollution	Tissue age	Little effect; in conifers, current year’s needles most sensitive	Immature leaves tolerant in some species.
Cl2 pollution	Wet leaves	No effect
Cl2 pollution	Drought	Sensitivity decreased
Cl2 pollution	Low temperature	Sensitivity decreased in pines	Symptoms take longer to develop.
Cl2 pollution	Plat age	Seedling less sensitive than oleder plants
HCl pollution	Tissue age	Young, fully expanded leaves most sensitive	Immature leaves tolerant.
HCl pollution	Plant age	Seedlings less sensitive than mature plants	Older plants become more tolerant.
HCl pollution	High relat. Humidity	Sensitivity increased
HCl pollution	Ca-deficit	Sensitivity decreased	Effect shown for Nasturtium. May be different for other species.
HCl pollution	Ca-excess	Sensitivity increased	Effect shown for Nasturtium. May be different for other species.
HCl pollution	Cl-deficit	Sensitivity increased	Effect shown for Nasturtium. May be different for other species.
HCl pollution	Cl-excess	Sensitivity increased	Effect shown for Nasturtium. May be different for other species.
HCl pollution	Mg-deficit	Sensitivity increased
NH3 pollution	Concentration	Variable	Some conifers sensitive at moderate but tolerant at high levels.
NH3 pollution	Tissue age	Little effect
NH3 pollution	Darkness	Variable
NH3 pollution	Drought	Sensitivity decreased
NH3 pollution	Wet leaves	Sensitivity increased	Symptoms develop faster.
NOx pollution	Ca-excess	Sensitivity decreased	Opposite effect in some species.
NOx pollution	Tissue age	Immature leaves/needles most sensitive
NOx pollution	Cultivar	Highly variable; especially in gladiolus & tomato	In gladiolus, sensitivity related to flower colour
NOx pollution	High relat. humidity	Sensitivity increased
NOx pollution	Low temperature	Sensitivity decreased; symptom expression delayed
NOx pollution	Drought	Sensitivity decreased; symptoms induced in conifers needles previously exposed.	Sensitivity increased in some fruit trees.
NOx pollution	N-deficit	Sensitivity decreased	Opposite effect in some species.
NOx pollution	Ca-deficit	Sensitivity decreased	Opposite effect in some species.
NOx pollution	N-excess	Sensitivity decreased	Opposite effect in some species.
NOx pollution	P-excess	Sensitivity increased	Opposite effect in some species.
NOx pollution	Other pollutants	Interaction with SO2, NO2, O2 & hydrocarbons	Response varies with concentrations and relative proportions.
NOx pollution	K-deficit	Sensitivity increased	Opposite effect in some species.
O3 pollution	K-excess	Variable sensitivity
O3 pollution	N-excess	Variable sensitivity
O3 pollution	Plant age	Young plants most sensitive
O3 pollution	Tissue age	Intermediate leaves usually most sensitive
O3 pollution	Darkness	Sensitivity decreased	Plants grown in low light are more sensitive. High light during exposure increases injury.
O3 pollution	Wet leaves	Variable sensitivity
O3 pollution	Drought	Sensitivity decreased
O3 pollution	Other pollutants	Interactions with SO2, NO2, PAN & heavy metals	Response varies with species, concentration & relative proportions
O3 pollution	High soil salinity	Sensitivity decreased
O3 pollution	High relat. Humidity	Sensitivity increased
O3 pollution	S-excess	Sensitivity decreased
O3 pollution	N-deficit	Variable sensitivity
O3 pollution	P-deficit	Sensitivity decreased
O3 pollution	Low temperature	Sensitivity decreased	Sensitivity decreases again above 30 degree C. Response varies according to dose.
O3 pollution	K-deficit	Variable sensitivity
PAN pollution	High relat. Humidity	No effect
PAN pollution	Tissue age	Young, rapidly expanding leaves most sensitive	Sensitivity strongly affected by physiological age, results in bands of damage.
PAN pollution	Other pollutants	Interactions with O3 & SO2	Response varies with concentrations & pollutant.
PAN pollution	Drought	Sensitivity decreased
PAN pollution	Time of day	Sensitivity more in morning than after noon
PAN pollution	Darkness	Injury eliminated. Sensitivity increases with increased light intensity	Presence of light before, during and after exposure must for injury to occur.
PAN pollution	Low temperature	Injury decreased
PAN pollution	Plant age	Young plants more sensitive
SO2 pollution	Other pollutant	Interaction with O3, NO2, HF	Response varies with concentrations and relative proportions.
SO2 pollution	Time of day	More sensitivity when sugar content low	In many plants in the morning.
SO2 pollution	High relat. Humidity	Sensitivity increased
SO2 pollution	Drought	Sensitivity decreased
SO2 pollution	High wind	Sensitivity increased
SO2 pollution	Wet leaves	Variable; may increase
SO2 pollution	Darkness	Sensitivity decreased	Some plants e.g. Potato not closing stomata at night may be unaffected.
SO2 pollution	Low temperature	Sensitivity decreased	Susceptibility to frost injury increased by SO2 exposure
SO2 pollution	Plant age	Seedlings more sensitive than older plants
SO2 pollution	Season	Grasses more sensitive in winter; conifers more in April/May than in July/August	Not vry important for very short exposures.
SO2 pollution	N-deficit	Sensitivity decreased
SO2 pollution	S-deficit	Sensitivity decreased
SO2 pollution	P-deficit	Sensitivity decreased
SO2 pollution	N-excess	Sensitivity decreased
SO2 pollution	K-deficit	Sensitivity increased
SO2 pollution	S-excess	Sensitivity increased
SO2 pollution	Tissue age	Most in young, fully expanded leaves
SO2 pollution	Ca-deficit	Sensitivity increased