Studies On Influence Of The Rhizosphere Micro Ecology System Of Wheat Seedlings Treated With Cd And Cd-Pb

In a pot experiment, Influence of different concentrations of Pb and Cd on the Soilphysico-chemical indices in winter wheat of Xiaoyan22were investigated in order toelucidate the toxicity of Pb and Cd to the rhizosphere Micro Ecology system of wheatseedlings. we studied the influence by measuring different parameters,such as the soilenzyme activities、the soil microorganism quantity、the microbial community functionaldiversity and the root exudates. The main conclusions of investigation as follows:1、The results showed that the activities of soil catalase and polyphenol oxidase wereobviously increased by Cd on21-day-old wheat seedlings, but the activations by Cd-Pbcompound pollution were weaker on99-day-old wheat seedlings. Cd could inhabited thedehydrogenase activity in21days, and the influence on dehydrogenase activity wasinhabition-activation with the rising of Cd concentration in66days, but the influence byCd-Pb compound pollution was opposite to sole Cd pollution. The activities of urease andalkaline phosphatase were inhabited by Cd, but less influence on invertase. The commoneffects of Pb、Cd on the rhizosphere dehydrogenase and catalase activities were cooperation,but on the soil polyphenol oxidase、urease、alkaline phosphatase and invertase activities wereantagonism.2、Heavy metal pollution could destroy the microbial community structure in rhizospheresoil, reduced the bioactivity and decreased the microbial community diversity indices. Cdcould inhibit soil microbes multiplying on21-day-old wheat seedlings, the microbial countdropped, the proportion of bacteria to microbial count declined, the ratio of fungi to bacteriaincreased; With the winter wheat growthing, the bacteria quantity increased shapely, but thequantities of actinomycetes and fungus decreased, the microbial count increased, and the ratioof fungi to bacteria decreased. The common effects of Pb、Cd on bacteria and fungi werecooperation, and on synergistic were antagonism. The sensitivity of soil microbes to heavymetal was as follows: actinomycetes> bacteria> fungi.3、The toxicity on nitrogen-fixing bacteria and nitrosobacteria by Cd was inhibition–activation-inhibition while the wheat growth period prolonged, but the Cd-Pb compoundpollution could inhibit the nitrosobacteria multiplying on21-day-old and66-day-old wheat seedlings, and the common effects of Pb、Cd on nitrogen-fixing bacteria and nitrosobacteriawere cooperation.4、Cd could enhance the soil respiration. when in21days, the soil microbial biomass C、soil microbial quotient(Cmic/Corg) and soil respiration quotient increased, the soil microbialbiomass C and microbial quotient reduced as the age of wheat seedling increased, but the soilrespiration quotient increased; when in99days, Cd-Pb compound pollution inhibitedmicrobial biomass C and microbial quotient, but promoted the soil respiration quotient. Thecommon effects of Pb、Cd on soil microbial biomass C were cooperation, and on the soilrespiration were antagonism.5、To some extent, the secretion amount of phenolic acid and simple sugar secretingfrom wheat seedling root increased by Cd, but Cd-Pb compound pollution inhibited thesecretion of simple sugar.