Background
The nutrition and strength-building properties of spinach were long promoted to the American public by the comic-cartoon character of "Popeye the Sailor Man," whose theme song was indelibly imprinted upon the memories of untold millions of people throughout the 20th century:

And so we dedicate this review to him, assuming he would have reveled in what it reveals.

What was done
The authors grew well-watered and fertilized spinach (Spinacia oleracea cv. Huangjia) plants from seed (five to each 3.5-liter pot filled with a loam soil) for approximately three weeks in controlled-environment chambers containing ambient air of 350 ppm CO2 or enriched air of 800 ppm CO2, after which they harvested the plants, weighed them, and measured the concentrations of several of the nutritive or health-promoting substances contained in their leaves.

What was learned
As best we can determine from Jin et al.'s graphs of their results, the extra 450 ppm of CO2 increased the fresh weight of the spinach shoots by about 67% and their dry weight by approximately 57%. In addition, it boosted the soluble sugar concentrations of their leaves by approximately 29% and their soluble protein concentrations by about 52%. As an added bonus, the extra CO2 also increased spinach leaf concentrations of ascorbate, glutathione and total flavonoids by 21%, 16% and 3%, respectively.

What it means
As time progresses, and as the air's CO2 content continues its upward climb, spinach grown everywhere on earth should become more nutritious. And more of it should be produced on every square meter of every hectare of land on which it is grown. We suspect, therefore, that Popeye -- if he were here -- would be overjoyed that everyone everywhere should be able to acquire ever more of his ever-more-nutritious and beloved spinach as the atmosphere's CO2 concentration continues to rise.