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Effects of Elevated CO2 on Rice Leaves
Reference
Li, J.-Y., Liu, X.-H., Cai, Q.-S., Gu, H., Zhang, S.-S., Wu, Y.-Y. and Wang, C.-J. 2008. Effects of elevated CO2 on growth, carbon assimilation, photosynthate accumulation and related enzymes in rice leaves during sink-source transition. Journal of Integrative Plant Biology 50: 723-732.

What was done
The authors measured several physiological processes -- including dynamic changes in photosynthesis and photosynthate accumulation, as well as enzyme activities such as sucrose phosphate synthesis (SPS) and sucrose synthase (SS) and their specific gene (SPS1 and RSus1) expressions -- in both mature (leaf 6) and developing (leaf 7) foliage of plants growing hydroponically in nutrient solutions within controlled-environment chambers maintained at atmospheric CO2 concentrations of 350 or 700 ppm throughout the entire week of leaf 6 development and expansion.

What was learned
Li et al. determined that "elevated CO2 significantly increased the rate of leaf elongation and biomass accumulation of leaf 7 during the treatment without affecting the growth of leaf 6." Over days 4-7, for example, the net photosynthetic rates of the mature leaves were increased by an average of 15% by the CO2 enrichment provided them, while the mean dry weight of the developing leaves in the CO2-enriched air was 100% greater than it was in the developing leaves in ambient air on day 2, dropping to 50% greater on day 3, and leveling out at 15% greater on days 5-7, equivalent to the same stimulation provided concurrently to the process of photosynthesis in the mature leaves. In addition, they say that in both developing and mature leaves, the net photosynthetic assimilation rate, all kinds of photosynthate contents (such as starch, sucrose and hexose), activities of SPS and SS, plus transcript levels of sps1 and RSus1, "were significantly increased under elevated CO2."

What it means
The seven researchers concluded that the "elevated CO2 had facilitated photosynthate assimilation, and increased photosynthate supplies from the source leaf [six] to the sink leaf [seven], which accelerated the growth and sink-source transition in new developing sink leaves." Put another way, mature rice leaves provide all sorts of CO2-enhanced help to developing leaves as the growth process proceeds; and they should continue to do so in an ever-increasing fashion as the air's CO2 content continues to rise, which is good news for rice ... and even better news for humanity.

Reviewed 17 June 2009