Withering Crops

Air Date: 02/11/2011
Source:
NBC Learn
Creator:
Anne Thompson
Air/Publish Date:
02/11/2011
Event Date:
02/11/2011
Resource Type:
Science Explainer
Copyright:
NBCUniversal Media, LLC.
Copyright Date:
2011
Clip Length:
00:05:50

As the global population continues to increase, scientists and farmers are concerned about the impacts that climate change could have on the world's crops. To better understand the process of photosynthesis and how plants use water and carbon dioxide to thrive, scientists are studying the stress limits of plants. "Changing Planet" is produced in partnership with the National Science Foundation.

Withering Crops

ANNE THOMPSON, reporting:

Earth is a place of tremendous bounty. From the Corn Belt of North America, the wheat fields of Africa, the rice paddies of Asia, come the crops that feed billions of people every day.

Today 6.8 billion people live on this planet. By 2050, Earth's population could top 9 billion. Those fields will need to feed more people. But global temperatures are rising, and farmers and scientists alike worry about the impact of climate change on the world's bread baskets.

Dr. BILL EASTERLING (Penn State University): All crops at some level are sensitive or vulnerable to climate change. But the ones that we worry about the most are the grain crops, mainly because those are the crops that provide so much of our global food supply.

THOMPSON: A report issued in October of 2010 by the National Center for Atmospheric Research shows how warmer temperatures associated with climate change could bring drier conditions across much of the globe over the next three decades. Severe drought means less food, and that could threaten many of the world's most densely populated regions later in the century.

EASTERLING: If climate change begins to dictate a much smaller grain supply globally, we're going to have some very serious social choices to make in our diets.

THOMPSON: Dr. Bill Easterling at Penn State has spent years looking at how the increased levels of carbon dioxide in the atmosphere are affecting crops in different countries.

When we talk about climate change, we think about okay there is carb-- more carbon dioxide in the air, more greenhouse gases. But how is that impacting crops?

EASTERLING: There are positive sides and there are negative sides to this global climate change. Carbon dioxide in the atmosphere is a necessary ingredient for photosynthesis, so all crops have to have carbon dioxide. and if you increase the amount of carbon dioxide for certain crops, it acts as almost as a fertilizer.

THOMPSON: Photosynthesis is a chemical process whereby plants convert carbon dioxide and water into energy. Water from the soil is taken into the plant through its roots, while carbon dioxide is absorbed from the air through tiny openings in the leaves, called stomata. While the rising amount of carbon dioxide in the atmosphere can boost this energy, the rising global temperatures may also become a recipe for disaster.

EASTERLING: The increase in temperature begins to become a problem for the crops and what happens in very simple terms is that photosynthesis, as temperatures rise, begins to be diminished.

THOMPSON: So how much variation in climate can plants withstand? Dr. Kelly Caylor at Princeton University is testing the limits of plants worldwide.

Dr. KELLY CAYLOR (Princeton University): The relationship between plants and-- and-- in terms of the water they use and the water that's in the soil, is very important, because one of the things that's always happening with-- with crops or any vegetation is that they're-- they're transpiring. They're losing water through their leaves.

THOMPSON: After a plant absorbs water from the soil, the moisture is carried through every part of the plant until it exits through the stomata, the same portals through which CO2 enters. As it leaves through the stomata, the water evaporates and cools the plant.

CAYLOR: It's almost like the way we sweat. The-- the plant is using that water as a means of-- of preventing overheating. And so when the soil water starts to be depleted, so when there's less water in the soil for plants to use, they can become stressed.

THOMPSON: When less water is available, the plant begins to close its stomata to regulate water flow. With the stomata closed, not only less water can escape, but also less CO2 can get in.

CAYLOR: And when they do that, they're-- they're really going to first limit their growth, but also they'll start to heat up. And that-- that heating up is-- can be really catastrophic for crops.

THOMPSON: In his laboratory, Caylor is able to predict the stress limits of certain plants by measuring how much water they give off under specific climate conditions.

CAYLOR: At some point the water that's in the soil is really insufficient to allow the plant to continue to grow. And the plant starts to lose its own water. It starts to dehydrate. And that's usually what we're talking about when we talk about crop withering.

THOMPSON: If the plants are stressed too much, they begin to whither, and are no longer able to be productive.

CAYLOR: Once that wilting happens, you're really moving into in an area where the plant is no longer growing productively, but really just trying to survive.

THOMPSON: And if crops in an entire country cease producing, social problems can erupt, such as food shortages experienced in Ethiopia in 2000, and Somalia and Haiti in 2008.

THOMPSON: Can we manage this problem?

EASTERLING: We're really doing a lot of work not just here Penn State, but in agricultural research universities worldwide trying to understand how we can increase the yields of the critical food plants that we grow, and do it in a way in which it doesn't necessarily consume more resources, more fertilizer, more water.

THOMPSON: And it's the work of scientists like Easterling and Caylor that could mean the difference between a continued feast in important agricultural regions, or potential famine for entire countries.

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