Background
The authors write that rice fields "represent the most important agricultural ecosystems in Asia since rice and wheat are the main source for food supply, and more than 90% of rice fields around the world are located in Asia," and they indicate that "purple phototrophic bacteria (PPB) are thought to be crucial in the nutrient cycling of rice fields." Indeed, the Chinese researchers say that PPB "thrive in the anaerobic portions of all kinds of aquatic environments, and have long been recognized as one of the key players in global carbon and nitrogen cycles."

What was done
In a free-air CO2 enrichment or FACE study conducted within a rice/wheat rotation system at the Nianyu Experimental Station in Jiangsu Province, China, Feng et al. grew rice (Oryza sativa L.) plants under standard paddy culture at two levels of soil nitrogen (N) fertility -- low (150 kg N/hectare) and high (250 kg N/hectare) -- at ambient and ambient plus 200 ppm CO2 concentrations, throughout which period they measured a number of characteristics of PPB within the rhizosphere and bulk soils of the two CO2 treatments.

What was learned
The seven scientists report that (1) "based on denaturant gradient gel electrophoresis (DGGE) analysis of pufM gene encoding the M subunit of anoxygenic PPB light reaction center, elevated CO2 appeared to enhance the biodiversity of PPB in flooded paddy soils," that (2) "this was further supported by canonical correspondence analysis (CCA) of DGGE fingerprinting pattern of pufM genes in paddy soils as well as Shannon diversity indices," that (3) "real-time quantitative PCR analysis of pufM gene further indicated that PPB abundance was stimulated by elevated CO2 in bulk soil," and that (4) "N fertilization enhanced the biodiversity of PPB under elevated atmospheric CO2."

What it means
The significance of Feng et al.'s findings is brought into perspective by their noting that it has been found that "PPB inoculation into the flood water [in rice paddy culture] could lead to grain yield increase by 29% (Elbadry et al., 1999; Harada et al., 2005)," as well as the fact that "PPB are thought to be capable of fixing nitrogen." As a result, these two phenomena -- enhanced by the ongoing rise in the air's CO2 content -- can help provide the boost in food production that will be needed to feed the planet's still-growing human population in the years and decades ahead. For more insight into the need for this help, see our Editorial The Future of Life on Earth: What to Do about CO2.

References
Elbadry, M., Gamal-Eldin, H. and Elbanna, K. 1999. Effects of Rhodobacter capsulatus inoculation in combination with graded levels of nitrogen fertilizer on growth and yield of rice in pots and lysimeter experiments. World Journal of Microbiology and Biotechnology 15: 393-395.

Harada, N., Nishiyama, M., Otsuka, S. and Matsumoto, S. 2005. Effects of inoculation of phototrophic bacteria on grain yield of rice and nitrogenase activity of paddy soil in a pot experiment. Soil Science and Plant Nutrition 51: 361-367.