Effects Of Cd Contamination On Soil Microbial Community And Physiological-biochemical Indexes Of Glycine Max

This research studied systematically the relationships between soil Cd pollution levels and biological indexes related to the environmental quality in the soils through laboratory incubation and pot experiments and by taking yellow-red soil and Glycine max as experimental materials. The fields of this research involved the relationships between soil Cd pollution levels and microbial biomass, enzymes, metabolic entropies, microbial entropies in the Cd pollution soils, the effects of Cd pollution in soil on the physiological-biochemical indexes in Glycine max leaves, and the interactions among soil Cd pollution levels, soil microbial community, and physiological-biochemical indexes in Glycine max. The purposes of this research were to offer helpful data for soil remedy of heavy metal pollution, for evaluation of soil environmental quality, and for establishment of forecast systems of heavy metal pollution in soils. The main results from this research are given as follows.1. The laboratory incubation experiment of microbes in Cd-polluted soils showed that no obvious changes were observed for soil base respiration when Cd concentrations were relatively low for the soil treatment, but soil base respiration increased gradually with prolonging in incubation time and with increasing in Cd concentrations. Microbial biomass carbon and nitrogen and microbial entropy in the Cd-polluted soils increased with the treatments of lower Cd concentrations and seriously decreased with the treatments of higher Cd concentrations. Metabolic entropy and the ratios of biomass carbon to nitrogen increased generally with increasing in Cd concentrations. The results also indicated that activities of acid phosphatase and urease in soils decreased with increasing in Cd concentrations treated with a same incubation time. However, with increasing in incubation time, activities of these two soil enzymes increased when Cd concentrations were in a range of 0-2 mg/kg, and decreased when Cd concentrations were in a range of 2-20 mg/kg.2. The pot experiment of Glycine max planting in Cd-polluted soils showed that contents of abscisic acid (ABA) in Glycine max leaves increased with increasing in Cd concentrations. Contents of gibbrellins (GA3), activities of peroxidase (POD) and proline (MDA), however, increased when the soils were treated with lower Cd concentrations and decreased when the soils treated with higher Cd concentrations. Contents of chlorophyll a or b in Glycine max leaves reduced with increasing Cd concentrations, and a extremely negative linear relation was observed for contents of chlorophyll a or b in Glycine max leaves and Cd concentrations in soils (r=-0.998**, or r =-0.996**). From the experiment, effects of Cd pollution on microbial indexes in soils depended on the patterns of soil management. For example, the change scopes of amounts of bacteria, epiphytes, and actinomycetes were lower in the Glycine max planted soils than those in the unplanted soils. In the range of Cd concentration from 0 up to 20 mg/kg, microbial biomass carbon decreased from 352 to 333 mg/kg in the planted soils (a decrease of 5.40%) and from 320 to 284 mg/kg in the unplanted soils (a decrease of 11.25%); meanwhile, microbial biomass nitrogen decreased from 69 to 63 mg/kg in the planted soils (a decrease of 8.70%) and from 62 to 40 mg/kg in the unplanted soils (a decrease of 35.48%). When Cd concentration higher than 5 mg/kg, soil base respiration and metabolic entropy enhanced suddenly in the unplanted soils, and those two indexes were much higher than those in the planted soils.3. A comparison of physiological-biochemical indexes in Glycine max leaves and soil microbial indexes indicated that contents of chlorophyll, MDA, and GA3 in Glycine max leaves were negatively related to soil base respiration, and activities of POD and ABA positively related to soil base respiration. Microbial biomass nitrogen was extremely negatively related to ABA content, but positively related to GA3 in Glycine max leaves. The correlation coefficient of POD activities in Glycine max leaves and biomass nitrogen in soils was -0.816, and that of MDA in Glycine max leaves and biomass carbon in soils was 0.746. The positive relations were also observed between activities of acid phosphatase or urease in soils and contents of chlorophyll, MDA, or GA3 in Glycine max leaves; while the negative relations were observed between activities of acid phosphatase or urease in soils and activities of POD or ABA in Glycine max leaves. Generally, the relativities of chlorophyll contents and soil microbial indexes were the most remarkable among all of these relations.The subject comes from State Natural Sciences Foundation (20677080)...