Effects Of 3 Years Of Elevated Temperature On Leaf Resistance In Pinus Sylvestris L. Var. Mongolica Litv. In Cd-and Pb-contaminated Soils

Global warming is increasingly recognized as one of the most important environmental problems.In addition,soil contamination by heavy metals including lead?Pb?and cadmium?Cd?is another severe global problem.The co-occurrence of increasing air temperature and heavy metal contamination of soils has important effects on plant growth and physiology.There has been a great deal of reports on the effects of temperature rise and soil heavy metal pollution on plants.While many studies have reported the separate effects of elevated temperature or heavy metal contamination on plant stress resistance,the response of plants to Cd-and Pb-contaminated soils has not been studied in our knowledge.Here,we explored the response of needles resistance of Pinus sylvestris var.mongolica Litv.seedlings to the combined effects.The resuts are as follows:?1?Elevated temperature alone significantly stimulated the contents of chlorophyll a,b,total chlorophyll,carotenes,carbon?C?,and sulfur?S?and the ratios of chlorophyll a/b,C/N,and C/H in the needles of Pinus sylvestris var.mongolica Litv.seedlings,while decreased the contents of nitrogen?N?and hydrogen?H?in the needles.Under Cd pollution alone,the contents of chlorophyll a,b,total chlorophyll,carotene,C and the ratios of C/N and C/H decreased,however,the chlorophyll a/b ratio and N content increased.Chlorophyll a,b,total chlorophyll,carotene,C,and H content decreased,however,N content,the ratios of chlorophyll a/b,C/N,and C/H increased under Pb treatment alone related to the control.Compared to Cd treatments,the contents of chlorophyll a,b,total chlorophyll,carotene,C,H,N,and S decreased under Cd+Pb treatment.Elevated temperature increased chlorophyll a,b,total chlorophyll,carotene,C,N,and S contents and the ratios of C/N and C/H under Cd+Pb treatments.?2?Elevated temperature significantly resulted in increased Cd and Pb uptake by the roots and needles of seedlings.Under Cd pollution alone,the content of Cd increased.Under the Cd+Pb treatment relative to Cd treatment,the content of Cd increased in roots and needles of seedlings.Under elevated temperature+1.0 mg Cd kg^-1 dry soil weight treatment,the content of Cd in needles was increased compared with 1.0 mg Cd kg^-1 dry soil weight.Under elevated temperature+5.0 mg Cd kg^-1 dry soil weight treatment,the content of Cd in needles was decreased compared with 5.0 mg Cd kg^-1 dry soil weight.Under elevated temperature+Cd treatment,the content of Cd in root was increased compared with Cd treatment.Under elevated temperature+Pb+1.0 mg Cd kg^-1 dry soil weight treatment,the content of Cd in root was increased relative to Pb+1.0 mg Cd kg^-1 dry soil weight treatment treatment.Under elevated temperature+Pb+5.0 mg Cd kg^-1 dry soil weight treatment,the Cd content in the root decreased relative to Pb+5.0 mg Cd kg^-1 dry soil weight treatment.?3?Elevated temperature alone increased the contents of flavonoids,phenolic acids,saponins,osmotic substances,and plant chelates and antioxidant enzyme activity and decreased the contents of tannin and malondialdehyde?MDA?.Under Cd stress alone,the contents of secondary metabolites,osmotic regulators,plant chelating peptide?PCs?,and MDA increased,however,the activity of superoxide dismutase?SOD?and catalase?CAT?increased with increasing Cd level,however,peroxidase?POD?activity increased under the low Cd concentration and decreased under high Cd concentration.Under the Cd+Pb treatment relative to Cd treatment,the contents of flavonoids,phenolic acids,tannins,osmotic substances,PCs,and MDA and the activity of SOD and CAT increased,however,POD activity decreased.Elevated temperature increased the contents of tannin,phenolic acids,flavonoids,osmotic adjustment substances,and glutathione?GSH?and CAT activity under Cd treatments.The activity of SOD and POD increased at 1.0 mg Cd kg^-1 dry soil weight while decreased at 5.0 mg Cd kg^-1 dry soil weight,however,MDA content decreased under 1.0 mg Cd kg^-1 dry soil weight.Under the combined treatments of elevated temperature,Cd,and Pb relative to Cd+Pb treatments,the contents of flavonoids,phenolic acids,osmotic adjustment substances,cysteine?Cys?,and PCs and the activity of POD and CAT increased,while MDA content decreased.?4?In conclusion,elevated air temperature?+1.95??could stimulate the resistance of Pinus sylvestris var.mongolica Litv.seedlings to Cd-and Pb-contaminated soils by regulating the secondary metabolites,osmotic substances,plant chelates contents and antioxidant enzyme activities,thus reduce the toxicity of heavy metals to plants.