Needles Resistance in Pinus sylvestris L. var. mongolica Litv. Exposed to Elevated Air Temperature and Cadmium-Contaminated Soils for 3 Years

Abstract

The co-occurrence of increasing air temperature and heavy metal contamination of soils has important effects on plants. This study investigated needles resistance in Pinus sylvestris L. var. mongholica Litv. seedlings exposed to elevated air temperature and cadmium (Cd) for 3 years and assessed Cd accumulation. Elevated air temperature (1.96 °C) stimulated Cd accumulation in plants, and Cd uptake by roots was significantly (p < 0.05) greater than uptake by needles under elevated temperature. Elevated air temperature significantly (p < 0.05) decreased malondialdehyde content in needles exposed to Cd. Peroxidase and catalase activity in needles increased under elevated temperature + 1.0 mg Cd kg−1 dry weight soil and decreased under elevated temperature + 5.0 mg Cd kg−1 dry weight soil relative to Cd alone. Elevated temperature significantly (p < 0.05) increased chlorophyll, carotenoids, carbon, nitrogen, hydrogen, sulfur, proline, soluble sugars, flavonoids, saponins, and phenolic compounds in needles under Cd stress. Secondary metabolites, proline, soluble sugars, sulfur, glutathione, phytochelatins, and cysteine contents increased with increasing Cd levels irrespective of temperature. Overall, 3 years of exposure to elevated air temperature can enhance needles stress resistance in seedlings exposed to Cd pollution by stimulating antioxidant enzymes, osmotic adjustment, and production of secondary metabolites and thiol-containing chelators and Cd accumulation in seedlings.