| At present,soil heavy metal pollution is becoming more and more serious.Using 6-month-old seedlings of Melaleuca alternifolia(Pinenol-4)as the test material,the concentration gradient of soil Cd in pots was determined by designing a pretest and observing the pretest results in the order of 0 mg/kg(CK),100 mg/kg(T1),200 mg/kg(T2),400 mg/kg(T3),and 600 mg/kg(T4).The effects of soil Cd contamination on the growth characteristics,physiological and biochemical characteristics and the ability to absorb Cd enrichment of Melaleuca alternifolia seedlings at different soil Cd concentrations and different test durations were investigated to provide a theoretical basis for the treatment of soil Cd contamination in Melaleuca alternifolia.The study showed that(1)Soil cadmium stress has a significant impact on the growth factors of Melaleuca alternifolia.Under cadmium stress,the morphological characteristics of Melaleuca alternifolia changed,showing the phenomena of yellow wilting,emaciation,reduced germination and death.At the same test time,with the increase of Cd content in soil,the height,ground diameter and biomass of Melaleuca alternifolia showed a decreasing trend,and the difference gradually increased with the increase of test time.In March,June and September,2021,compared with the control group,the tree height of the four experimental groups decreased by 2.5%～12.9%,15.9%～36.3%and 3.07%～31.03%,and the ground diameter decreased by 14.1%-22.0%and 5.6%～25.3%.(2)Soil cadmium stress has significant effects on all indexes of chlorophyll content in Melaleuca alternifolia leaves.Under cadmium stress,chlorophyll a,chlorophyll b and total chlorophyll of Melaleuca alternifolia seedlings decreased gradually with the increase of culture time,and were significantly lower than those of the control group at the same period In March,June and September of 2021,compared with the control group,the contents of chlorophyll a in four experimental groups decreased by 8.9%～26.8%,19.3%～53.5%and 6.5%～35.3%,and the contents of chlorophyll b decreased by 17.5%～39.8%and 29.1%～56.0%.(3)Soil cadmium stress has significant effects on physiological and biochemical indexes of Melaleuca alternifolia leaves.With the increase of test time,MDA content increased first and then decreased,SOD activity,SP content and SS content increased gradually,and POD activity and CAT activity decreased first and then increased.In March,June and September of 2021,compared with the control group,the MDA content of the four experimental groups increased by 33.1%379.8%,45.80%～872.4%and 32.5%～52.7%.SOD activity increased by-2.4%～22.4%,12.1%～121.5%;POD activity decreased by 15.9%～41.1%,-8.0%～13.2%and 1.0%～40.8%;CAT activity increased by-17.1%～30.6%,7.6%～181.8%,-13.2%～41.35%;SP content increased by 0.9%～36.2%,22.2%～66.7%,2.6%～31.9%;SS content increased by-16.5%～52.8%,4.3%～39.2%and 13.9%～20.4%.(4)There are significant differences in cadmium content of Melaleuca alternifolia seedlings at different time nodes,different soil Cd concentrations or different plant organs.With the increase of test time or soil Cd concentration,the Cd content in various organs of Melaleuca alternifolia gradually increased.In March,June and September of 2021,the Cd contents of roots,stems and lateral branches of Melaleuca alternifolia were 3.63～835.14 mg/kg,3.31～207.68 mg/kg and 2.56～85.64 mg/kg,respectively.4.13～1723.25 mg/kg、3.65～819.17 mg/kg、2.75～157.88 mg/kg,8.16～2519.5 mg/kg、6.56～956.14 mg/kg、6.19～549.88 mg/kg.In addition,the Cd content in different organs is as follows:root>stem>lateral branch.(5)In different time nodes,different soil Cd concentrations or different plant organs,there are some differences in cadmium enrichment coefficient or transfer coefficient of Melaleuca alternifolia seedlings.With the increase of test time,the accumulation ability of cadmium in roots,stems and lateral branches of Melaleuca alternifolia gradually increased.In March,June and September of 2021,the Cd enrichment coefficients of roots,stems and lateral branches of Melaleuca alternifolia were 1.391～2.384,0.346～2.179,0.143～1.684,2.717～5.349,1.365～2.388 and 0 respectively.In addition,the Cd enrichment ability of different organs is as follows:root>stem>lateral branch.The study showed that Melaleuca alternifolia seedlings had a good growth state when the soil Cd concentration was 100 mg/kg.With the increase of Cd concentration,Melaleuca alternifolia seedlings began to suffer from growth restriction,seedling withering and even death,accompanied by physiological and biochemical characteristics such as the decrease of chlorophyll content,the increase of MDA content,and the first increase and then decrease of protective enzyme system activity.Generally speaking,Melaleuca alternifolia has a certain enrichment and transfer capacity for Cd in soil,and its roots have a strong enrichment capacity,so it can be used as an alternative plant to control Cd pollution in soil. |
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