Elevated CO2 Affects the Soil Organic Carbon Fractions and Their Relation to Soil Microbial Properties in the Rhizosphere of Robinia pseudoacacia L. Seedlings in Cd-Contaminated Soils

摘要

As the global climates change, elevated CO 2 and soil contamination by heavy metal co-occur in natural ecosystems, which are anticipated to affect soil organic carbon fractions (SOC) and their relation to soil microbial activities, but this issue has not been extensively examined. We investigated the response of SOC and their relation with soil microorganisms and enzyme activities in rhizosphere soils of Robinia pseudoacacia L. seedlings to elevated CO 2 plus cadmium (Cd) contamination. We found that elevated CO 2 significantly ( p ?0.05) stimulated total organic carbon (TOC) (8.6%), dissolved organic carbon (DOC) (32.6%), microbial biomass carbon (MBC) (13.5%), bacteria (11.6%), fungi (20.9%), actinomycetes (15.3%), urease (20.1%), dehydrogenase (15.8%), invertase (11.1%), and β-glucosidase (11.9%), and DOC, MBC, bacteria, actinomycetes, urease, and invertase presented smaller growth trend in the range of 500–700?μmol?mol ?1 CO 2 than in the range of 385–500?μmol?mol ?1 CO 2 . Cd decreased DOC (30.1%), MBC (24.9%), bacteria (21.5%), actinomycetes (15.9%), and enzyme activities. Elevated CO 2 offsets the negative effect of Cd on SOC and microbial activities (except for TOC and L-asparaginase). Procrustes rotation test was used to determine the drivers (elevated CO 2 , Cd, and CO 2 ? ?Cd) of the relation between SOC and microbial activities, revealing the correlations between SOC, soil microorganisms, and enzyme activities were higher under elevated CO 2 than under elevated CO 2 ? ?Cd. Our results suggest elevated CO 2 could stimulate soil fertility and microecological cycle in the rhizosphere microenvironment exposed to heavy metal by affecting the relationship between SOC and soil microbial properties.