Relationship of aluminium and calcium to net CO2 exchange among diverse Scots pine provenances under pollution stress in Poland.

Light-saturated net photosynthesis (Asat), dark respiration (RD), and foliar nutrient content of eight European Scots pine (Pinus sylvestris L.) provenances were measured at experimental sites in western Poland. Two-year-old seedlings were planted in 1984 at two sites with similar soils in areas of contrasting air pollution. One site was near a point source of SO2 and other pollutants, and another 12 km to the southeast in an area free of acute air pollution was treated as a control. The eight provenances were from a large north-tosouth latitudinal range (60 to 43° N). At the heavily polluted site Scots pine trees exhibited lower growth rates and crown dieback and deformation. Soil pH, Ca and Mg were at least 10 times lower, and Al 10 times higher at the polluted than the control site. In 1991, concentrations of Al, P, Ca, S, Mn, Fe, and Zn in oneyear old Scots pine foliage were higher and Mg lower at the polluted than control site. At both sites foliar Mg levels were within the range considered deficient (≤0.6 mg g-1), and at the polluted site, Al concentrations were very high (670 to 880 μg g-1). In all provenances, RD of one-year-old needles was higher (by 22% on average) and Asat was lower (by 37% on average) at the polluted than the control site. The ratio of Asat: RD was half as great in all provenances at the polluted (4 to 6) than control site (8 to 11). Provenances of southern origin had greater increases in RD and water-use efficiency at the polluted site than other provenances. Within the polluted site alone, or across both sites, Asat in Scots pine was negatively correlated to the Al: Ca ratio (p<0.001, r=-0.93). Across sites RD increased with needle N and Al (multiple regression, p<0.001). The data suggest that at the polluted site there is excessive soil Al and deficient Mg availability, low needle Mg and high Al concentrations and high Al: Ca ratios, and that these have resulted in reduced photosynthetic capacity and increased respiration.