The melon millennium
Melons offer something for everyone. Fragrant yet humble muskmelon is the highlight of an elegant breakfast; red, juicy watermelon the family picnic favorite; and pale green honeydew a salad bar staple. Even the more exotic casaba and galia melons grace produce departments everywhere. Rich in vitamin C, potassium, calcium, and phosphorous, melons are available essentially year-round, and are easy to incorporate into breakfast, lunch, or dinner.
Cultivated melons have thrived for centuries. But will they disappear as the biosphere changes?
In the twentieth century, carbon dioxide levels rose from about 300 parts per million (ppm) to 370 ppm. Scientists have wondered how melons respond to this increase. And what happens when melon plants encounter stressors such as increased saline (salt) content in their water source?
G.N. Mavrogianopoulos and colleagues recently grew a type of honeydew melon (Parnon melons) in separate greenhouses with atmospheric CO2 levels set for five hours each day at 400 ppm, 800 ppm, and 1,200 ppm; the plants were well irrigated throughout the experiment, using water of varying levels of salinity.
Compared with measurements of plants exposed daily to 400 ppm CO2, those at 800-ppm exposure showed a 75 percent increase in net photosynthesis rate; those exposed to 1,200 ppm CO2 showed an even greater increase in net photosynthesis, of 120 percent.
At all levels of CO2 enhancement, the response was basically the same. The higher level of CO2 decreased the negative effects of higher salinity on shoot growth, leaf growth, and leaf chlorophyll content.
The big question? Will there be more melons to go around? Maybe so. Melon yield increased significantly at all water salinity levels—and the effect was particularly pronounced at the lower saline levels.
So, at least one variety of melon will be enhanced by the future elevations of CO2, and as Mavrogianopoulos’s results reveal, that enhancement doesn’t taper off as the level reaches 1,000 ppm and above. Melon lovers worldwide should rejoice at the prospect of higher levels of CO2—we seem to be entering the melon millennium.
One peculiarity of vines (including melons) is that they respond even more favorably than other plants to elevated CO2, as countless carbon dioxide–plant experiments have shown. So what’s good for melons is likely to be good for cucumbers, squash, pumpkins, and gourds.
Robert C. Balling Jr., Ph.D. is director of the Laboratory of Climatology at Arizona State University and coauthor of The Satanic Gases.
Mavrogianopoulos, G.N., et al., 1999. Effect of carbon dioxide enrichment and salinity on photosynthesis and yield in melon. Scientia Horticulturae, 79, 51–63.