Effect Of Heavy Metals Stress On Three Woody Plants

The different gradient concentrations of Cu²⁺, Zn²⁺, Pb²⁺and Cd²⁺ to pollute three woodplants in the paper. The toxic effects of these heavy metals on Cinnamomum camphora,Syzygium hancei (Hce.) and Gordonia axillaris were analyzed by means of some index, suchas: growth, physiological and biochemical characteristics, absorption and enrichment alongwith distribution ratio aspect. The major results were summarized as follows:1. Four heavy metals inhibited three woody plant growth obviously, and this got moreserious with concentration of heavy metals increasing. Since different plants have differentbiological and ecological characteristics, their growth was inhibited by heavy metals was alsodifferent to extent. The order was: Gordonia axillaris＞Syzygium hancei(Hce.)＞Cinnamomumcamphora. Among four heavy metals, the inhibition of Cd was the largest. When itsconcentration was 20mg/L, the biomass of Gordonia axillaris fell short of 20% comparing tocomparison.2. Heavy metals effect evidently on the membrane leakage and SOD activity of plants.With the increasing of treatment concentration, the membrane leakage also increased.Theinfluence of Cu and Zn on membrane leakage of Cinnamomum camphora was the largest,however, the Gordonia axillaris was effectde mostly by Pb and Cd.Under the different heavy metal stress, SOD activity in different plant leaves existeddifference. When Cinnamomum camphora was treated with low concentration of Cu²⁺and Cd²⁺,the activity of SOD in leaf increased. However, when the concentration of Cu²⁺exceeded150mg/L, the Cd²⁺ exceeded 20mg/L, its leaf SOD activity decreased. Under the stress of Pb²⁺,with the increasing of heavy metal concentration, the activity of SOD decreased all the times;In contrast with Cu²⁺ and Cd²⁺, SOD activity in leaf under the pollution of Zn²⁺decreasedfirstly and increased when concentration exceeded150mg/L. With the increasing of heavymetals concentration of Cu²⁺ and Cd²⁺, the leaf SOD activity of Gordonia axillaries wasuplifted and descendent under the stress of Zn²⁺ and Pb²⁺. With the increasing of heavy metalsconcentration of Zn²⁺and Pb²⁺, the Syzygium hancei(Hce.)'s leaf SOD activity was decreased;however, the leaf SOD activity was increased with the increasing of heavy metal concentrationof Cd²⁺; When Syzygium hancei(Hce.) was polluted by low concentration of Cu²⁺, its leaf SODactivity was increased and decreased when the concentration of Cu²⁺exceeded 150mg/L.3. The most important component for heavy metals of three wood plants was root, the second was stem, the leaf was last. The accumulation to four heavy metals in plant rootsincreased with the increasing of concentration, stems and leaves reflected the similar laws. Theallocation ratio of different heavy metals in three wood plants was discriminative. Most of Cu²⁺was accumulated in roots, the allocation ratio was from 77.77% to 99.54%, the allocation ratioin stem was 0.08～21.94% and the allocation ratio in leaf was the least. The allocation ratio ofZn2+ in stems of Syzygium hancei(Hce.) was 34.14%, whereas the ratio was very low inCinnamomum camphora(its allocation ratio was 6.68%) and Gordonia axillaries(its allocationratio was 0.34%) stems; The allocation ratio of Pb²⁺ in Cinnamomum camphora stems was40.25～81.12%,in Syzygium hancei(Hce.) stems the maximal ratio reach to 55.08%, inGordonia axillaries was 11.10%, The figure showed that: pb²⁺migrated easily from roots tostems and leaves. The allocation ratio of Cd²⁺ in Cinnamomum camphora stems was 17.03～45.48%, the maximal radio in Syzygium hancei(Hce.) stems was 30.21%, but the allocationratio was very low in Gordonia axillaries.4. With the increasing of treatment concentration, the accumulation ratio became smaller.Different plants had different accumulation ration. Among three woody plants, theaccumulation ratios of Gordonia axillaris to Zn. Pb and Cd were the largest, however, theaccumulation of Syzygium hancei(Hce.) to Cu was the largest. The accumulation ratios ofCinnamomum camphora to four heavy metals were all the least.