AUTHOR=Wu Xiaohong , Ge Tida , Wang Wei , Yuan Hongzhao , Wegner Carl-Eric , Zhu Zhenke , Whiteley Andrew S. , Wu Jinshui 

TITLE=Cropping systems modulate the rate and magnitude of soil microbial autotrophic CO2 fixation in soil

JOURNAL=Frontiers in Microbiology

VOLUME=6

YEAR=2015

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2015.00379

DOI=10.3389/fmicb.2015.00379

ISSN=1664-302X

ABSTRACT=<p>The effect of different cropping systems on CO<sub>2</sub> fixation by soil microorganisms was studied by comparing soils from three exemplary cropping systems after 10 years of agricultural practice. Studied cropping systems included: continuous cropping of paddy rice (rice-rice), rotation of paddy rice and rapeseed (rice-rapeseed), and rotated cropping of rapeseed and corn (rapeseed-corn). Soils from different cropping systems were incubated with continuous <sup>14</sup>C-CO<sub>2</sub> labeling for 110 days. The CO<sub>2</sub>-fixing bacterial communities were investigated by analyzing the <italic>cbbL</italic> gene encoding ribulose-1,5-bisphosphate carboxylase oxygenase (RubisCO). Abundance, diversity and activity of <italic>cbbL</italic>-carrying bacteria were analyzed by quantitative PCR, <italic>cbbL</italic> clone libraries and enzyme assays. After 110 days incubation, substantial amounts of <sup>14</sup>C-CO<sub>2</sub> were incorporated into soil organic carbon (<sup>14</sup>C-SOC) and microbial biomass carbon (<sup>14</sup>C-MBC). Rice-rice rotated soil showed stronger incorporation rates when looking at <sup>14</sup>C-SOC and <sup>14</sup>C-MBC contents. These differences in incorporation rates were also reflected by determined RubisCO activities. <sup>14</sup>C-MBC, <italic>cbbL</italic> gene abundances and RubisCO activity were found to correlate significantly with <sup>14</sup>C-SOC, indicating <italic>cbbL-carrying</italic> bacteria to be key players for CO<sub>2</sub> fixation in these soils. The analysis of clone libraries revealed distinct <italic>cbbL</italic>-carrying bacterial communities for the individual soils analyzed. Most of the identified operational taxonomic units (OTU) were related to <italic>Nitrobacter hamburgensis, Methylibium petroleiphilum, Rhodoblastus acidophilus, Bradyrhizobium, Cupriavidus metallidurans, Rubrivivax, Burkholderia, Stappia, and Thiobacillus thiophilus</italic>. OTUs related to <italic>Rubrivivax gelatinosus</italic> were specific for rice-rice soil. OTUs linked to <italic>Methylibium petroleiphilum</italic> were exclusively found in rice-rapeseed soil. Observed differences could be linked to differences in soil parameters such as SOC. We conclude that the long-term application of cropping systems alters underlying soil parameters, which in turn selects for distinct autotrophic communities.</p>