Strong plant roots can penetrate compact soil

Researchers conclude from this discovery that plants with stronger roots will be better able to deal with climate change

A newly discovered trait has shown that some cereal plants have roots tough enough to punch their way through hard, compact soil.

This suggests that crops with strong roots will be better at dealing with a changing climate and drier conditions in the future.

Researchers at Pennsylvania State University have found that roots with a certain genotype have a greater concentration of lignin, a complex organic polymer that is important in cell walls, especially wood and bark. Polymers are materials with long, repeating chains of molecules. Natural polymers include rubber and cellulose.

“I have been engaged in the search for ways we can generate more stress-tolerant crops for my entire career,” said Jonathan Lynch, professor in plant science. “This is definitely the result of a focused research effort by my entire team.”

The root trait is called multiseriate cortical sclerenchyma (MCS). It is characterized by small cells with thick walls just beneath the surface of the roots. More lignin gives the MCS roots greater tensile strength, and the root tips have more bending force compared to roots that do not have the MCS trait. This allows for the rigidity needed to help roots penetrate hard soil layers.

“Compacted soil layers constrain crop productivity by restricting root growth and exploration in deeper soil layers, which in turn limits access to nutrients and water,” said lead researcher Hannah Schneider, postdoctoral scholar in Lynch’s research group.

“Plants with roots that are able to penetrate hard soil and forage deeper have an advantage in capturing water and nutrients and ultimately performing better in drought or low soil fertility.”

The researchers studied plants in the field and in greenhouse settings to assess root penetration in hard soils. The test fields were driven over with heavy machinery typical of many agricultural fields.

One field experiment was conducted at the Apache Root Biology Center in Willcox, Arizona, and the other at Penn State’s agricultural research centre at Rock Springs.

Researchers grew six corn genotypes that contrasted in root lignin content and each experiment involved either compaction or noncompaction treatments.

When the corn flowered, the soils of randomly selected plants were cored to assess root growth. In addition, the roots of two plants from each research plot were dug up, evaluated, and shoot biomass was collected.

The news release stated that 12 wheat genotypes and six corn genotypes were also raised in a greenhouse setting on the Penn State campus. The large growth containers were essentially mesocosms, an experimental tool used as a model of a larger ecosystem that allows scientists to investigate the reaction of organisms to environmental conditions or changes. In this study, the test plants were set up with a compacted soil layer to determine which roots were able to penetrate the hard substrate. After a month’s growth, root segments from each crop species were collected, measured and tested for strength and root tip bending force.

The team also used laser ablation tomography (LAT) to visualize the anatomy of the roots. LAT can measure the light spectra given off by different cells cut by the laser to show differences between various tissues.

The results were striking and showed that corn genotypes with MCS had root systems with 22 percent greater depth and 39 percent greater shoot biomass in hard soils compared to lines without MCS.

The genotype is not seen in ancient plants and Lynch believes that it evolved, or could have been selected for, during the development of agriculture.

“This discovery bodes well for American and global agriculture because the trait helps corn, wheat and barley grow deeper roots, which is important for drought tolerance, nitrogen efficiency and carbon sequestration,” he said. “I believe that it is worthwhile for crop breeders to select for this trait. Not all plants have it. It affords multiple benefits with no apparent downsides. It does not seem to inherently alter root growth but does increase root growth in hard soil.”

He said that as drought severity and occurrence increases, crops with deeper roots will do better.

The researchers found genetic variation for MCS in each of the cereals they examined, and they concluded that heritability was relatively high, which further suggested that the trait can be selected in breeding programs.

“We also identified this trait in wheat. (However) I am not sure how wheat breeders would react. They may not have seen (the research) yet.”

Of the plant lines reviewed in this study, MCS existed in 30 percent to 50 percent of modern corn, wheat and barley cultivars.

The research was recently published in the Proceedings of the National Academy of Sciences.

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