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Effect of Elevated CO2 on Lodging in Rice
Reference
Shimono, H., Okada, M., Yamakawa, Y., Nakamura, H., Kobayashi, K. and Hasegawa, T. 2007. Lodging in rice can be alleviated by atmospheric CO2 enrichment. Agriculture, Ecosystems and Environment 118: 223-230.

Background
The authors note that lodging - the beating down of a crop - "can occur under heavy rains and strong winds," and that this phenomenon "decreases canopy photosynthesis due to self-shading (Setter et al., 1997) and disturbs the translocation of carbon and nutrients to the rice grains (Hitaka and Kobayashi, 1961), resulting in lower yield and poor grain quality." In fact, they report that Setter et al. (1997) showed that a moderate degree of lodging, which reduced canopy height by 35%, decreased yield by about 20%, and that severe lodging, which reduced canopy height by 75%, decreased yield by up to 50%."

What was done
In a Free-Air CO2-Enrichment (FACE) study designed to discover the effect of atmospheric CO2 enrichment on lodging in rice (Oryza sativa L.) plants, Shimono et al. grew the cultivar Akitakomachi in paddy fields at Shizukuishi, Iwate, Japan, under three nitrogen (N) fertilization regimes - low N (6 g N m-2), medium N (9 g N m-2) and high N (15 g N m-2) - at two different season-long 24-hour mean CO2 concentrations - 375 ppm (ambient) and 562 ppm (enriched) - while the degree of naturally-occurring lodging was measured at the time of grain maturity on a scale of 0-5 based on the bending angles of the stems at 18 intervals, where 0 = 0 from the vertical, 1 = 1-18, 2 = 19-36, 3 = 37-54, 4 = 55-72 and 5 = 73-90.

What was learned
As expected, and as often has been observed before, the six scientists found that lodging was significantly higher under high N than under medium and low N. However, they found that the lodging experienced in the high N treatment "was alleviated by elevated CO2," because the lowest internodes of the rice stems "became significantly shorter and thicker under elevated CO2," which presumably "strengthened the rice culms against the increased lodging that occurred under high N." In addition, they found that the reduced lodging experienced under elevated CO2 in the high N treatment increased the grain ripening percentage of the rice by 4.5% per one-unit decrease in lodging score.

What it means
Some people have worried, in the words of Shimono et al., that "to increase rice yield under projected future CO2 levels, N fertilization must be increased to meet increased plant demand for this nutrient as a result of increased growth rates," but that greater N fertilization might enhance lodging, thereby defeating the purpose of the fertilization. However, they learned from their study that "elevated CO2 could significantly decrease lodging under high N fertilization, thereby increasing the ripening percentage and grain yield," in what amounts to another CO2-induced success story for what the researchers call "the most important crop for feeding the world's population."

References
Hitaka, H. and Kobayashi, H. 1961. Studies on the lodging of rice plants. (II) Source of decreasing yield due to lodging. Japanese Journal of Crop Science 32: 270-276.

Setter, T.L., Laureles, E.V. and Mazaredo, A.M. 1997. Lodging reduces yield of rice by self-shading and reductions in canopy photosynthesis. Field Crops Research 49: 95-106.

Reviewed 14 February 2007