Abstract
Lead (Pb) and cadmium (Cd) are highly toxic and are widespread in agricultural soils, representing risks to plant and human health. In this study, Davidia involucrata was cultivated in soil with different concentrations of Pb and Cd and sampled after 90 days. We used ANOVA to analyse the photosynthesis of D. involucrata and the ability of Pb and Cd to enrich and migrate in roots, stems and leaves. Various results are described here. 1) Under individual and combined Pb and Cd stress, the accumulation factors in the roots were greater than 1, which was significantly greater than those in the stems and leaves (P < 0.05), and the translocation factors both were less than 1. The Pb and Cd enrichment ability of D. involucrata roots was significantly higher than that of stems and leaves, and the migration ability of the two heavy metals in D. involucrata was weak. 2) The Mg-dechelatase activities of chlorophyll degradation products increased under stress due to high concentrations of Pb and Cd. However, chlorophyllase activity was higher at relatively low concentrations of the two heavy metals (P < 0.05). δ-Aminolevulinic acid and porphobilinogen of chlorophyll synthesis products are easily converted to uroporphyrinogen III under low concentrations of Cd, which promotes the synthesis of chlorophyll. 3) The effect of Cd stress alone on the chlorophyll concentration was not significant. Under combined stress, concentrations of Pb and Cd in the range of 400~800 mg·kg-1 and 5~20 mg·kg-1 significantly promoted an increase in photosynthetic pigments (P < 0.05). 4) Inhibition of the net photosynthetic rate increased with increasing Pb and Cd concentrations under both individual and combined stress. In addition, the root of D. involucrata had a strong absorption and fixation effect on heavy metals, thereby reducing metal toxicity and improving the tolerance of D. involucrata to heavy metals.
Highlights
In recent decades, anthropogenic activities have accelerated the release of pollutants, especially heavy metals, into the environment, which has created potential hazards to ecosystems and human health [1,2]
Chlorophyllase activity was higher at relatively low concentrations of the two heavy metals (P < 0.05). δ-Aminolevulinic acid and porphobilinogen of chlorophyll synthesis products are converted to uroporphyrinogen III under low concentrations of Cd, which promotes the synthesis of chlorophyll
The photosynthesis characteristics of D. involucrata in response to heavy metal stress and the Pb and Cd accumulation and translocation ability in different tissues were comprehensively reported for the first time
Summary
Anthropogenic activities have accelerated the release of pollutants, especially heavy metals, into the environment, which has created potential hazards to ecosystems and human health [1,2]. Lead (Pb) and cadmium (Cd) are nondegradable, long-lived and exhibit strong toxicity in the soil [3]. They are highly toxic and pose a threat to plants and animals (including humans) by affecting their normal growth and health [4,5]. Excessive Pb and Cd in the soil reduces the uptake of minerals and micronutrients by plants, interferes with plant water balance, inhibits stomatal opening, and decreases plant quality [12,13,14,15,16] These stresses inhibit gas exchange and photosynthetic pigment biosynthesis because of the destruction of the chloroplast ultrastructure and the disassembly of thylakoids [17,18]
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