Leaf defense system of Robinia pseudoacacia L. seedlings exposed to 3years of elevated atmospheric CO(2) and Cd-contaminated soils.

Short-term exposure to elevated CO2 increases cadmium (Cd) uptake in some plant species (wheat, poplars, and willows), which triggers an increase in antioxidative system activity to deal with additional reactive oxygen species that are generated. Here, we examined leaf defenses in Robinia pseudoacacia L. seedlings exposed to elevated CO2+Cd for 3years. Three years of elevated CO2 decreased Cd uptake into leaves and the Cd content in soils and increased the pH of rhizosphere soil relative to ambient CO2. In plants exposed to Cd stress, leaf chlorophyll content was greater under elevated CO2 than under ambient CO2. Superoxide dismutase, peroxidase, and catalase activity increased, glutathione content increased, and malondialdehyde and phytochelatins contents decreased under elevated CO2+Cd relative to Cd alone. Proline, soluble sugars, flavonoids, saponins, and phenolic acids contents were greater under elevated CO2+Cd than under Cd alone, and condensed tannin content was lower. Overall, long-term elevation of CO2 enhanced the leaf defense system of R. pseudoacacia exposed to Cd by stimulating antioxidant enzyme activity, osmotic adjustment, and the production of glutathione, flavonoids and phenolic acids. Future research should focus on understanding the mechanisms involved in the decrease in Cd uptake into leaves and Cd content in soils and the increase in rhizosphere soil pH under long-term exposure to elevated CO2.

Jia X ，Zhao YH ，Liu T ，He YH ... -  《-》

Three years of exposure to lead and elevated CO(2) affects lead accumulation and leaf defenses in Robinia pseudoacacia L. seedlings.

Few studies have explored the long-term effects of elevated atmospheric CO2 combined with lead (Pb) contamination on plants. The objective of this study was to examine the effects of 3 years of elevated CO2 (700 ± 23 μmol mol-1) on Pb accumulation and plant defenses in leaves of Robinia pseudoacacia L. seedlings in exposed to Pb (500 mg kg-1 soil). Elevated CO2 increased Pb accumulation in leaves and Pb removal rate in soils. In plants exposed to Pb stress, total chlorophyll and carotenoid contents in leaves were lower under elevated CO2 than under ambient CO2, but seedling height and width increased under elevated CO2 relative to ambient CO2. Elevated CO2 significantly (p < .01) stimulated malondialdehyde content in leaves under Pb exposure. Superoxide dismutase and catalase activity increased significantly (p < .01), peroxidase activity decreased significantly (p < .01), and glutathione, cystine, and phytochelatin contents increased under elevated CO2 + Pb relative to Pb alone. Elevated CO2 stimulated the production of soluble sugars, proline, flavonoids, saponins, and phenolics in plants exposed to Pb stress. Ove rall, long-term elevation of CO2 increased Pb-induced oxidative damage in seedlings, but enhanced the phytoextraction of Pb from contaminated soils.

Jia X ，Zhang C ，Zhao Y ，Liu T ，He Y ... -  《-》

Elevated CO2 affects secondary metabolites in Robinia pseudoacacia L. seedlings in Cd- and Pb-contaminated soils.

Secondary metabolites play important roles in plant interactions with the environment. The co-occurrence of heavy metal contamination of soils and rising atmospheric CO2 has important effects on plant. It is important to explore the ways in which production of plant secondary metabolites is affected by heavy metals under elevated atmospheric CO2. We examined the effects of elevated CO2 on secondary metabolite contents in Robinia pseudoacacia seedlings grown in Cd- and lead (Pb)-contaminated soils. The increase in secondary metabolites was greater under Cd + Pb exposure than under exposure to individual metals regardless of elevated CO2 with the exception of condensed tannins in leaves and total alkaloids in stems. Except for phenolic compounds and condensed tannins, elevated CO2 was associated with increased secondary metabolite contents in leaves and stems of plants exposed to Cd, Pb, and Cd + Pb compared to plants exposed to ambient CO2 + metals. Changes in saponins in leaves and alkaloids in stems were greater than changes in the other secondary metabolites. Significant interactive effects of CO2, Cd, and Pb on secondary metabolites were observed. Saponins in leaves and alkaloids in stems were more sensitive than other secondary metabolites to elevated CO2 + Cd + Pb. Elevated CO2 could modulate plant protection and defense mechanisms in R. pseudoacacia seedlings exposed to heavy metals by altering the production of secondary metabolites. The increased Cd and Pb uptake under elevated CO2 suggested that R. pseudoacacia may be used in the phytoremediation of heavy metal-contaminated soils under global environmental scenarios.

Jia X ，Zhao Y ，Liu T ，Huang S ... -  《-》

The combined effects of elevated atmospheric CO(2) and cadmium exposure on flavonoids in the leaves of Robinia pseudoacacia L. seedlings.

Flavonoids participate in several plant processes such as growth and physiological protection in adverse environments. In this study, we investigated the combined effects of eCO2 and cadmium (Cd)-contaminated soils on the total flavonoid and monomer contents in the leaves of Robinia pseudoacacia L. seedlings. Elevated CO2, Cd, and eCO2+ Cd increased the total flavonoids in the leaves relative to the control, and eCO2 mostly increased (p < 0.05) the total flavonoid content under Cd exposure. Elevated CO2 increased (p < 0.05) robinin, rutin, and acacetin contents in the leaves of 45-day seedlings and decreased (p < 0.05) the content of robinin and acacetin at 90 and 135 d under Cd exposure except for robinin at day 45 under Cd1 and acacetin on day 135 under Cd1. Quercetin content decreased (p < 0.05) under the combined conditions relative to Cd alone. Kaempferol in the leaves was only detected under eCO2 on day 135. The responses of total chlorophyll, total soluble sugars, starch, C, N, S, and the C/N ratio in the leaves to eCO2 significantly affected the synthesis of total flavonoids and monomers under Cd exposure. Overall, rutin was more sensitive to eCO2+ Cd than the other flavonoids. Cadmium, CO2, and time had significant interactive effects on the synthesis of flavonoids in the leaves of R. pseudoacacia L. seedlings. Elevated CO2 may improve the protection and defense system of seedlings grown in Cd-contaminated soils by promoting the synthesis of total flavonoids, although robinin, rutin, quercetin, and acacetin yields may reduce with time. Additionally, increased Cd in the leaves suggested that eCO2 could improve the phytoremediation of Cd-contaminated soils.

Zhang C ，Jia X ，Zhao Y ，Wang L ，Cao K ，Zhang N ，Gao Y ，Wang Z ... -  《-》

Elevated CO(2) benefits the soil microenvironment in the rhizosphere of Robinia pseudoacacia L. seedlings in Cd- and Pb-contaminated soils.

Soil contamination by heavy metals in combination with elevated atmospheric CO2 has important effects on the rhizosphere microenvironment by influencing plant growth. Here, we investigated the response of the R. pseudoacacia rhizosphere microenvironment to elevated CO2 in combination with cadmium (Cd)- and lead (Pb)-contamination. Organic compounds (total soluble sugars, soluble phenolic acids, free amino acids, and organic acids), microbial abundance and activity, and enzyme activity (urease, dehydrogenase, invertase, and β-glucosidase) in rhizosphere soils increased significantly (p < 0.05) under elevated CO2 relative to ambient CO2; however, l-asparaginase activity decreased. Addionally, elevated CO2 alone affected soil microbial community in the rhizosphere. Heavy metals alone resulted in an increase in total soluble sugars, free amino acids, and organic acids, a decrease in phenolic acids, microbial populations and biomass, and enzyme activity, and a change in microbial community in rhizosphere soils. Elevated CO2 led to an increase in organic compounds, microbial populations, biomass, and activity, and enzyme activity (except for l-asparaginase), and changes in microbial community under Cd, Pb, or Cd + Pb treatments relative to ambient CO2. In addition, elevated CO2 significantly (p < 0.05) enhanced the removal ratio of Cd and Pb in rhizosphere soils. Overall, elevated CO2 benefited the rhizosphere microenvironment of R. pseudoacacia seedlings under heavy metal stress, which suggests that increased atmospheric CO2 concentrations could have positive effects on soil fertility and rhizosphere microenvironment under heavy metals.

Huang S ，Jia X ，Zhao Y ，Bai B ，Chang Y ... -  《-》