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Responses of microbial activity and diversity to cadmium in the rhizosphere of winter wheat seedlings

Yonghua Zhao, Xia Jia

Pot experiments were conducted to investigate the effect of cadmium on the rhizospheremicrobial community and activity ofwinterwheat seedlings. The addition ofCd resulted in increases of the SMBC(soilmicrobial biomass carbon), SBR (soilmicrobial respiration), andMQ(microbial quotient) by 6.31 - 48.60%, 9.35 - 113.67%, and 8.29 - 76.24%, respectively, at the third week. However, the SMBC decreased at the seventh and twelfth weeks by 0.48-36.91% and 0.46-18.89%, respectively. The TOC (soil total organic carbon) decreased significantly (p<0.01) at the third and seventh weeks, except for the 5 and 10mg/kgCd treatments. TheMMQ(metabolic quotient) increased at the third and seventh weeks by 8.490-44.739% and 2.79 - 46.48%, respectively, but significantly decreased by 1.72 -26.52% at the twelfth week. Furthermore, the microbial functional diversity decreased, and the ability of the rhizosphere microbes to utilize carbon resources was noticeably affected byCd pollution. Cd resulted in the increase of phenolic acid utilization and the decrease of carbohydrate, carboxylic acid, and amino acid utilization.Moreover, theMQ was also found to be a sensitive ecophysiological parameter, indicating an environmental pressure. The responses to Cd of all of the microbial parameters determined did not display obvious time and dose dependences. The SMBC, MMQ, and MQ would be sensitive and precise indicators of the rhizosphere soil health under the stress of Cd.