A Greenhouse Pickle

By Robert C. Balling Jr., Ph.D.
Arizona State University

Each crisp, savory pickle at your summertime picnic began its life as a mere cucumber, drawing nourishment from the carbon dioxide that is its lifeblood. How will the cucumber fare as CO₂ and temperatures rise? Because the day-to-night temperature ratio is decreasing at most reporting stations worldwide, scientists are researching this combined effect on plants.

Several Canadian scientists grew two varieties of cucumbers in controlled environments in which they altered the day and night temperatures. Papadopoulos and Hao maintained day temperatures at 18°C, 21°C, or 24°C; night temperatures were held at 16°C, 18°C, and 20°C. All nine possible combinations were tested, including the rather unrealistic chamber with 18°C day and 20°C night temperatures.

They found that "Plant development rates (leaf and flower number) were linearly increased with increasing average air temperature" and were largely unaffected by variations in the day–night temperature difference. The plant development rate increased with increasing air temperature regardless of whether that increase comes at night, in the day, or both.

As for fruit mass—the actual size of what will one day become a pickle, at the highest mean temperatures and lowest diurnal temperature ranges (a possible glimpse into the future?), the overall fruit production decreased slightly despite the increased plant development rates.

That sounds like some rare bad news for Greening Up enthusiasts. Will future cucumber lovers find themselves in a pickle? No, indeed. The authors write:  "Increasing air temperature increases fruit growth rates and thus the growth period is reduced."

They go on to note "the strong increase in growth rate with increasing temperature more than compensates for the reduction of fruit growth period, resulting in an increase in marketable fruit size."

Furthermore, "Because of the positive relationship between fruit size and preferred fruit grades, raising air temperature should improve fruit quality." That increase in fruit size "might turn out to be a positive effect on cucumber flavour because fast-growing cucumber (shorter growing period to harvest) usually has better flavour."

So even when elevated atmospheric CO₂ fails to cause the expected boost, it appears that a warmer world would produce larger more delicious cucumbers than ever!

As for the "burpless" factor, results were inconclusive.

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