In today’s Academic Minute, Dr. Katie Field of the University of Sheffield explains how the earliest plants survived on an Earth that didn’t yet have soil.
Katie Field is a postdoctoral research associate in the Department of Plant and Animal Sciences at the University of Sheffield. Her current research project is focused on the functional and evolutionary significance of symbiotic fungal associations in early land plants. She holds a Ph. D. from the University of Sheffield.
Dr. Katie Field – Survival Strategy of Early Plants
Many obstacles faced the first plants that moved from an aquatic to terrestrial existence more than 450 million years ago. One of the most significant challenges was the land itself onto which they were emerging. Earth’s land masses were little more than bare rock, with many growth-essential nutrients locked away within minerals. The first plants didn’t have roots - so how did these land colonisers get at the nutrients and become the super-successful and diverse Kingdom we are familiar with today? Our research sheds new light on the importance of the role of fungi during the “greening of the Earth”.
The ancient fungi we study are excellent extractors of nutrients from rocks. By partnering up with mineral-mobilising fungi, the earliest plants stood a much better chance at succeeding at life on land. However, it wasn’t a simple giveaway on the part of the fungus - how to gain enough carbon to satisfy its appetite? The answer lay in plants’ ability to turn atmospheric carbon dioxide (CO2), which was over three times the concentration of today, into sugar through photosynthesis. By exchanging sugar for nutrients, a mutually beneficial relationship – or symbiosis – was formed. We wanted to know how plant-fungal symbiosis has functioned over evolutionary time, alongside the fall in atmospheric CO2 concentration.
Our study used representative species of the most primitive plants through to modern day garden weeds and measured the efficiency of the carbon-for-nutrient exchange. We showed that under the high, prehistoric CO2 atmosphere, symbiosis was most efficient in the primitive plants, while under a modern day CO2 atmosphere the modern weeds fared better. These findings suggest that as CO2 fell, plants evolved roots and leaves which powered a more efficient exchange of carbon-for-nutrients with their fungal partners. This put them at an evolutionary advantage leading to their further diversification into the wonderfully varied ecosystems we are familiar with today.