Decreasing, not increasing, leaf area will raise crop yields under global atmospheric change. Srinivasan V, Kumar P & Long SP (2017) Global Change Biology. 23:1626-1635.
The world’s population continues to grow. As it grows so does our dependence on food and crop production. By 2030 the world’s demand for staple food crops is projected to increase by 50% of what it is today and then nearly doubles by 2050. So how do we feed all these people? The simple answer is to grow more crops!
Unfortunately, it’s not that simple: there is a tradeoff between much of the remaining land we would hope to expand for our agricultural needs and its use for conservation (Check out this Envirobites article). In some cases, that land is also not suitable for agriculture. In order to solve our growing food problem, we have to think outside the box. Venkatraman Srinivasan and his colleagues have a suggestion; let’s cut leaves off our soybeans.
Soybeans are the world’s fourth largest food crop in terms of seed production and are a rich source of protein. The Midwestern United States is the largest single producer of soybeans, producing about 25% of world’s soybeans. While we sure produce a lot of them, the need for more soybeans, and other crops, increases by the year.
Healthy soybeans have a high density of leaves, to the point where leaves on the bottom of the plant are shaded out by leaves above. This can be quite costly in terms of energy the plants expend. In addition to our growing food problem, carbon dioxide levels are expected to increase in the future. Previous studies suggest as CO2 levels rise, plants like the soybean, will innately produce more leaves (Check out this Envirobites article). But what if we stop growing leaves and grow more soybeans?
The researchers of this study believe the amount of leaves the plant produces is excessive for growth of seeds. The energy exploited for these extra leaves could be more effectively used for bean production.
To test their idea, researchers at the University of Illinois at Urbana Champaign, used a computer simulator to model their experiment. By inputting a multitude of factors such as previous weather patterns, tilling the soil, and physical and biological properties the researchers were able to predict how fewer leaves (a lowered leaf area index; LAI) would affect the growth and reproduction of the soybeans.
They also conducted an experiment. Over half an acre at the University was planted with soybeans. Portions of the population were subjected to higher CO2 concentrations, other portions had seven leaves clipped off the plant and another portion was subjected to both higher CO2 and had leaves removed.
What They Found
The control (normal CO2 levels and untrimmed leaves), had the lowest yield of soybeans. Even at higher CO2 levels with untrimmed leaves, the soybean yield wasn’t the largest; soybeans with trimmed leaves produced the greatest yield.
But why? If you recall learning about photosynthesis back in school you will remember that plants need sunlight, water and CO2 to grow. Plants absorb CO2 through their leaves. With higher concentrations of CO2 we might expect more growth, right? But leaves come at a cost. During the day, plants with the most leaves are able to conduct photosynthesis more efficiently and are more willing to grow, but as soon as they stop for the day when the sun goes down, all these leaves act like holes in a water barrel, releasing a lot of energy through respiration. This experiment simply comes down to budgeting energy: what goes in must go out. Fully-leaved soybean plants may take in energy but they also release a significant portion back out into the atmosphere, while soybean plants with fewer leaves are more efficient.
What About the Leaf-cut?
By simply cutting seven of the growing leaves during the growing season, these soybean plants expended less energy than their fellow fully-leaved counterparts. Through their model and experiment they found that this led to an 8% and 10% increase in yield for normal and future CO2 levels. If this strategy was expanded to all the soybean farms in the US an estimated 6.5 metric tons of soybeans would be produced annually.
What It All Means
We know we need to produce more food to ensure a sustainable future. We know we are very limited on expanding our current agriculture regime. Findings by Srinivasan and colleagues give us a potential solution. By altering the physical makeup of plants, not just the soybean, we may be able to increase the annual yields of staple food crops. This could positively impact both national and international food and water supply as we traverse into the daunting future.