Plants release Oxygen. That is a necessary evil for our survival In a high-CO2 experiment, plants released roughly 10 percent less CO2. “It’s not miniscule. It’s measurable, and it’s significant,” Drake said. It’s significant enough to have a major impact on the wetlands’ carbon budget, and potentially the global carbon budget. It was also significant enough to provoke controversy when Drake and his colleagues reported it in 1992, partly because no one could explain how it was happening.
The 28-Year Experiment
Drake works on the Global Change Research Wetland, an experimental marsh at the Smithsonian Environmental Research Center in Maryland. He created the experiment in 1987 to uncover how plants would respond to rising CO2. He surrounded 30 plots with open-top chambers and pumped half of them with an extra 340 parts per million CO2—roughly double atmospheric levels in 1987. He left the others exposed to normal air.
Climate change proceeded in the three decades since. Marsh sea level rose 20 centimeters. The growing season lengthened more than a week, and atmospheric CO2 rose nearly 18 percent, passing 400 ppm globally in May 2013. Inside the chambers, plants under higher CO2 soaked up more, as expected. But they also emitted less.
Drake and his colleagues weren’t the first to discover this. (Scientists noticed plants respiring less under high CO2 in the early 20th century.) But they were among the first to pay serious attention and evaluate it in terms of carbon budgets.
“This is a really controversial idea,” Drake said. Many doubted or dismissed it outright. Part of the controversy stemmed from the nature of their experiments. Before Drake, few had looked at the actual gas exchange between plants and the atmosphere, because it is technically challenging. Most had examined only the results of high CO2 on plant growth.
“You wouldn’t see what the total budget is,” he said. “You’d see only a piece of it. It’d be like you had an accounting system that didn’t measure inputs and losses, just the turnover of cash.”
The process was also counter-intuitive. It made sense for plants to avail themselves of extra CO2 for photosynthesis. But what would keep them from releasing the excess afterward?