Volume 13, Number 39: 29 September 2010
In a paper recently published in the Annual Review of Plant Biology, three scientists associated with the Institute of Genomic Biology at the University of Illinois at Urbana-Champaign (USA) write that meeting the global increase in agricultural demand during this century "is predicted to require a doubling of global production," but that "the world has limited capacity to sustainably expand cropland," while reporting that this capacity is actually "shrinking in many developed countries."
In terms of confronting this daunting challenge, Zhu et al. say that "meeting future increases in demand will have to come from a near doubling of productivity on a land area basis," and they opine that "a large contribution will have to come from improved photosynthetic conversion efficiency," for which they estimate that "at least a 50% improvement will be required to double global production."
The researchers' reason for focusing on photosynthetic conversion efficiency derives from the experimentally-observed facts that (1) increases in the atmosphere's CO2 concentration increase the photosynthetic rates of nearly all plants, and that (2) those rate increases generally lead to equivalent -- or only slightly smaller -- increases in plant productivity on a land area basis, thereby providing a solid foundation for their enthusiasm in this regard. In their review of the matter, however, they examine the prospects for boosting photosynthetic conversion efficiency in an entirely different way: by doing it genetically and without increasing the air's CO2 content. So what is the likelihood that their goal can be reached via this approach?
"Improving photosynthetic conversion efficiency will require," as the three scientists describe it, "a full suite of tools including breeding, gene transfer, and synthetic biology in bringing about the designed alteration to photosynthesis." For some of these "near-term" endeavors, they indicate that "implementation is limited by technical issues that can be overcome by sufficient investment," meaning they can "be bought." But a number of "mid-term" goals could well take 20 years to achieve; and they say that "even when these improvements are achieved, it may take an additional 10-20 years to bring such innovations to farms in commercial cultivars at adequate scale." And if that is not bad enough, they say of still longer-term goals that "too little of the science has been undertaken to identify what needs to be altered to effect an increase in yield," while in some cases they acknowledge that what they envision may not even be possible, as in the case of developing a form of Rubisco that exhibits a significant decrease in oxygenation activity, or in the case of designing C3 crops to utilize the C4 form of photosynthetic metabolism.
Clearly, we do not have the time to almost blindly gamble on our ability to accomplish what needs to be done in order to forestall massive human starvation of global dimensions within the current century, which suggests to us that -- in addition to trying to accomplish what Zhu et al. suggest -- we must rely on the "tested and true," i.e., the CO2-induced stimulation of plant photosynthesis and crop yield production. And all we need to do to do so is to not interfere with the natural evolution of the industrial revolution, which is destined to be carried for some time yet on the backs of fossil-fuel-fueled enterprises that can provide the atmosphere with the extra carbon dioxide that will be needed to provide the extra increase in crop growth that may well mean the difference between global food sufficiency and human starvation on a massive scale a mere few decades from now.
Sherwood, Keith and Craig Idso
Reference
Zhu, X.-G., Long, S.P. and Ort, D.R. 2010. Improving photosynthetic efficiency for greater yield. Annual Review of Plant Biology 61: 235-261.