Researchers discover that plants exposed to higher carbon dioxide levels in the atmosphere take up less phosphorus
Researchers have discovered that when plants are exposed to increasing levels of carbon dioxide in the atmosphere, the phosphorus levels in their shoots and leaves decrease. Phosphorus is essential for growth but researchers at Michigan State University have discovered that the phosphorus reduction is an adaptive response of plants to increasing carbon dioxide levels worldwide.
Phosphorus is vital to plant growth and is found in every living plant cell. It is involved with key plant functions such as energy transfer, photosynthesis, transformation of sugars and starches, formation of seeds and flowers, root health, nutrient movement, and overall plant health and genetics.
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The mineral is a finite resource yet, while widespread in the Earth’s crust, it is relatively scarce in concentrated forms. The top five countries with significant reserves include Morocco, Egypt, Algeria, Syria and China. Phosphorus production in concentrated forms is largely for agricultural fertilizers.
“In my research I focused on phosphorus because it is an essential nutrient for all organisms,” said Hatem Rouached, professor with the Plant Resilience Institute in the Department of Plant, Soil and Microbial Sciences at MSU. “In plants, phosphorus deficiency causes a severe reduction of growth and yield. Current crop production strategies rely heavily on phosphorus fertilization. However, this practice is not sustainable due to the expected exhaustion of phosphorus resources and harmful environmental impacts. Therefore, plant varieties with improved phosphorus use efficiency are becoming a prerequisite to improve yields and reduce environmental consequences. To this end, it is essential to understand how plants regulate phosphorus homeostasis and adjust growth to phosphorus availability.”
Given the importance of phosphorus as a component of crop fertilizers, the limited worldwide reserve of the chemical element is concerning. Reserves are being depleted at an alarming rate with estimates that those reserves could run out in less than 100 years.
“We can’t synthesize phosphorus like we can nitrogen,” said Rouached. “We need to develop a better understanding of how plants regulate phosphorus to survive.”
Working with Arabidopsis thaliana, a common laboratory plant, the researchers focused on why plants were not taking up more phosphorus in step with rising carbon dioxide. They looked at the sub-cellular level and found that plants were avoiding overloading their chloroplasts with phosphorus in response to increasing carbon dioxide. Chloroplasts are responsible for carrying out photosynthesis in the process of converting sunlight energy into sugar.
“What was really important in our discovery was that when we tried to force the plant to put a lot of phosphorus in the chloroplast, the plant failed to grow,” he said. “We discovered that the increase in phytic acid levels needs to be tightly controlled in plants to allow the plants to grow under elevated carbon dioxide.”
Rouached said that phytic acid is an antinutrient because it blocks mineral absorption. It contains six phosphates that are negatively charged and makes these essential metals less available for proper cell functioning.
“Phytic acid also plays a role in plant development by acting as a signal or activating signaling pathways. Perturbation of the signaling may cause an alteration in plant growth and development.”
The phosphorus reduction as a result of increased carbon dioxide is seen primarily as an evolutionary development. He said that is the reason that they used the natural population of plants to discover the genetic factors controlling phosphorus concentrations in chloroplasts under high carbon dioxide.
“We used genome-wide (211 genotypes) arabidopsis (dicots) and (validated the discovery) in rice (monocots). I am confident that our discovery would apply to all plants.”
The adaptive response of phosphorus to increasing carbon dioxide in the face of climate change is problematic in that crops could be less nutritious in the future.
“This will aggravate hunger and possibly cause a malnutrition worldwide health problem if we do not understand and address the issue,” he said. “Currently there are 7.7 billion people populating Earth and that number is expected to reach more than nine billion by 2050. The current carbon dioxide emission level is 414 parts per million and rapidly rising, possibly reaching nearly 700 parts per million by 2050 (at current levels). If we produce more food, it is bound to be less nutritious. This is attributed to our recent research showing a decrease of all nutrients, except carbon, in plants grown under elevated carbon dioxide conditions.”
Since publication of its report, the research team has received feedback from farmers and agricultural companies interested in learning more about the discovery and seeking practical solutions for the future.
“In the article, we showed that the decrease in phosphorus levels in the chloroplast is an adaptive response to increasing carbon dioxide,” he said. “This indicates that the increase of carbon dioxide imposes changes in the intracellular (between cell organelles) nutrient content.”
He said that the future research projects are to gain a better understanding of the mechanism used by plants to regulate nutrient uptake and accumulation under high carbon dioxide. Attention will be on the underground processes including nutrient uptake by roots and interactions with the microbiome. They will also look at other organelles (possibly mitochondria) to see if they are similarly affected by high carbon dioxide. The research will focus on how farmers can produce bigger plants and nutritious food under high carbon dioxide conditions without compromising the final yield or, ideally, increasing it.
“This paper is the first to show that there is an urgent need for discussion on how we can protect plant malnutrition against the increase of carbon dioxide worldwide,” said Rouached.
