Life Sciences Icon Life Sciences

Biology Helps Us Understand the Blessing of Grasses

David Coppedge
Photo credit: Ochir-Erdene Oyunmedeg via Unsplash.

The journal Science offers a special section devoted to grasses. Bianca Lopez, Pamela J. Hines, and Caroline Ash introduce the cover story with some startling facts about these “often undervalued” plants. In “The unrecognized value of grass,” they say,

Grasses are highly diverse, yet only six or seven grass species provide most of the calories that humans consume. … In addition to cultivated fields and pastures, grassy ecosystems (both Poaceae and Alismatales) cover large swaths of the planet, forming terrestrial grasslands and submarine meadows. Grasslands create and stabilize fertile soil; store carbon; generate oxygen; and provide animal habitat, building materials, and food. Even so, these species and systems are often undervalued. Land-use conversion and climate change pose threats, as do climate change mitigation efforts that prioritize carbon stored in trees over that stored in grasslands. Nevertheless, grasses could offer solutions to many of our societal challenges, if only we would fully recognize their diversity and value. [Emphasis added.]

Appreciating Grasslands

Here are a few points to increase our appreciation for the 12,000 known species of grasses.

  • Grasslands store about a third of the world’s terrestrial carbon stocks.1
  • Most of us will have either eaten, stepped on, or burned a grass within the past 24 hours.2
  • 50 percent of the calories consumed by humans come from three species of grass: wheat, rice, and maize.2
  • Meat, eggs, and dairy products come from animals that eat grasses.2
  • Grasses are the predominant plants on all the continents except for Antarctica.2

Not all grasses live on land. About 72 species in 4 families are “seagrasses” that live in water.3

  • Seagrasses have adapted to live underwater, where light is limited, where salt and nutrients can be problematic, and where soils can become highly toxic.3
  • Seagrass is the world’s only underwater flowering plant.4
  • Seagrass “meadows” are important carbon dioxide sinks that can provide significant carbon sequestration yet are on the decline due to human activity. Conservationists are considering ways to help them recover.3
  • Seagrass meadows promote biodiversity for fish, reptiles, crustaceans, echinoderms and other marine organisms like sea cucumbers, clams, manatees, sea turtles, and crocodiles who use them for food or shelter.3, 4
  • Along with mangroves and coral reefs, seagrass meadows help stabilize coastlines. They also reduce water acidity and purify water from viruses, bacteria, and heavy metals, helping coral reefs to flourish.3,4
  • Seagrass can be used as construction material, fertilizer, and habitat for seafood farming. When cotton is scarce, it can be used as an alternative fiber for clothing.4

The Smithsonian Ocean site adds additional praise for seagrasses:

Seagrasses can form dense underwater meadows, some of which are large enough to be seen from space. Although they often receive little attention, they are one of the most productive ecosystems in the world.Seagrasses provide shelter and food to an incredibly diverse community of animals, from tiny invertebrates to large fish, crabs, turtles, marine mammals and birds.

Grass Classification

Since grasslands comprise nearly 40 percent of Earth’s terrestrial biosphere,5 it’s worth getting to know these amazing and diverse plants that do so much for us. 

All grasses are angiosperms (flowering plants) in the monocot clade, meaning their leaves display parallel venation and spring from a single seed leaf (cotyledon). They comprise about 20 percent of 60,000 known species of monocots, so while all grasses are monocots, the majority of monocots are not grasses, but other beautiful and useful plants like orchids, lilies, asparagus, and pineapples. The roots of grasses are fibrous, making them good for binding soil and preventing wind erosion while providing habitat for earthworms, moles, and gophers. We’re all familiar with the term “grass roots” as a metaphor for bottom-up popular movements. 

Grasses have long been staples for balanced nutrition. The endosperms of grass seeds (whole grains) are rich in proteins, carbohydrates, fats, vitamins, and fiber. They also are good sources of the metalloenzymes Michael Denton discusses that are essential for life: iron, copper, zinc, and magnesium.

Though all grass genomes are collinear (i.e., genes in the same order), the details are surprisingly diverse. McSteen and Kellogg note,2

Beneath this broadly conserved genome architecture lurks extensive diversity, including variation in nucleotides (single-nucleotide polymorphisms), gene structure, and even the presence or absence of genes. The nucleotide differences between two lines of Zea mays (maize) are greater than those between humans and chimpanzees. Genes central for plant structure in maize are missing in wheat and rice, and vice versa. In other words, not all grasses have the same complement of genes, and their morphology is altered accordingly.

Putting Grasses to Good Use

Artificial selection — a form of intelligent design — has enriched our lives with big ears of corn derived from meager teosinte, whole wheat bread, nutritious rice in Chinese and Mexican foods, and long rows of boxed cereals in grocery stores, to say nothing of sugar to sweeten our tea and coffee. Even some beverages derive from grasses, like beer from barley and rum from sugarcane. Corn waste lately has augmented our transportation fuel with ethanol. 

Only a few grasses have been domesticated for food. There could be much more nutrition in “orphan crops” that have not yet been tapped. But none of the benefits we enjoy could have been magnified by breeders unless the information for the ingredients were first encoded in the genomes of crop grasses. Artificial selection is only possible because of originally designed information in the plants and animals we favor.

Grass lawns beautify our yards, and decorative species like pampas and Mexican feather enhance our gardens. Grassy fields provide venues for sports like golf, soccer, and baseball. With their pleasing green shades that titillate the cones of our eyes at the center of human color sensitivity, grasses enhance our life in many, many ways.

Many refer cheerfully to “God’s green earth” when thinking of natural beauty, and grasses are a big part of that glorious world picture. Why should our planet be so blessed with these marvelous plants that do so much for the biosphere? Grasses are prime examples of the prior fitness of the universe for complex life that Michael Denton has elucidated with such clarity and passion in his Privileged Species series. It is likely that humans and other complex animals could not exist but for these abundant and nutritious little plants that help bind the biosphere together. Let us stand in awe at the grass beneath our feet.

References

  1. Bai and Contrufo, “Grassland soil carbon sequestration: Current understanding, challenges, and solutions.” Science 4 Aug 2022: 377:6066, pp 603-608.
  2. McSteen and Kellogg, “Molecular, cellular, and developmental foundations of grass diversity.” Science 4 Aug 2022: 377:6066, pp 599-602.
  3. Unsworth et al., “The planetary role of seagrass conservation.” Science 4 Aug 2022: 377:6066, pp 609-612.
  4. Swansea University press release, “The value of seagrass to the planet’s future is far greater than appreciated.” Aug 5, 2022.
  5. Buisson et al., “Ancient grasslands guide ambitious goals in grassland restoration.” Science 4 Aug 2022: 377:6066, pp 594-598.
  6. Harvard Nutrition Source, “Whole Grains.”