Purple Phototrophic Bacteria Under Rice-Wheat Double-Cropping
Feng, Y., Lin, X., Zhang, J., Mao, T. and Zhu, J. 2011. Soil purple phototrophic bacterial diversity under double cropping (rice-wheat) with free-air CO2 enrichment (FACE). European Journal of Soil Science 62: 533-540.
More specifically, Feng et al. (2011) conducted a free-air CO2-enrichment or FACE experiment with a rice-wheat rotation system at the Nianyu Experimental Station, Jiangsu Province, China, on a field typical of the majority of agricultural lands used for rice production in that country. It began in 2002 and continued for a full six years, over which period community structures and abundances of PPB were determined by denaturing gradient gel electrophoresis (DGGE) and real-time quantitative polymerase chain reaction (PCR), respectively, targeting the pufM gene, which encodes a protein in the light reaction centre of PPB.
The four researchers with the State Key Laboratory of Soil and Sustainable Agriculture of the Chinese Academy of Sciences discovered that the extra 200 ppm of CO2 they supplied to the rice and wheat crops increased the abundance and biodiversity of PPB in the soil in which the crops grew, although the soil PPB communities were more diverse and larger under rice than wheat, which they attributed to flooding during the time rice was grown. Nevertheless, there was also a phylogenetically diverse mixture and large abundance of PPB when wheat was grown, the two dominant species of which were related to Bradyrhizobium and Rhodopseudomonas palustris. And this finding was most important, for they say that "Bradyrhizobium and Rhodopseudomonas palustris have been reported to promote the growth of rice (Biswas et al., 2000; Harada et al., 2005)."
The Chinese scientists write that "the positive responses of the PPB community to elevated CO2 concentration suggest that the ecological role of PPB in a soil environment has been neglected in the past," while noting that PPB "may also play an important role in soils, as well as in seas and lakes." And they say that that role may be to "enhance the microbial food chain and promote the growth and yield of crops," which the results of the studies of Elbadry et al. (1999) and Harada et al. (2005) suggest that PPB do indeed do.
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