Lanthanides represent a category of rare earth elements that, in numerous nations, are integrated into fertilizers as micronutrients to enhance plant development. However, their absorption by plants and effects on photosynthesis remain largely unexplored, possibly leaving their advantages underutilized.
Researchers from MIT have now illuminated the pathways through which lanthanides traverse and function within plants. These revelations could assist farmers in fine-tuning their application to cultivate some of the globe’s most prevalent crops.
As detailed today in the Journal of the American Chemical Society, the research indicates that a singular nanoscale application of lanthanides on seeds can enhance resilience against UV stress in widely grown crops. The scientists also identified the chemical reactions through which lanthanides engage with chlorophyll pigments that facilitate photosynthesis, revealing that various lanthanide elements reinforce chlorophyll by substituting the magnesium located at its core.
“This marks an initial stride toward comprehending how these elements function in plants, and serves as an illustration of how they could be more effectively delivered to plants rather than being simply incorporated into the soil,” explains Associate Professor Benedetto Marelli, who conducted the study alongside postdoc Giorgio Rizzo. “This is the first comprehensive investigation demonstrating the impact of lanthanides on chlorophyll and their protective role against UV stress in plants.”
Inside plant connections
Certain lanthanides are utilized as contrast agents in MRI technologies and for uses such as light-emitting diodes, solar cells, and lasers. Over the past half-century, the application of lanthanides in agriculture to boost crop production has steadily increased, with China alone employing lanthanide-based fertilizers on nearly 4 million hectares annually.
“For a long time, lanthanides were regarded as biologically insignificant, but that perspective has shifted, particularly in the agricultural sector in China,” notes Rizzo, the lead author of the paper. “Yet, we still largely lack insights into how lanthanides preferentially benefit plants, as well as their uptake mechanisms from plant tissues.”
Recent investigations have indicated that minimal levels of lanthanides can encourage plant growth, root elongation, hormone production, and stress resilience, though excessive amounts can be detrimental. Achieving an optimal dosage has proven challenging due to our limited understanding of how lanthanides are assimilated by plants and their interactions with root soil.
In this research, the scientists utilized seed coating and treatment technologies they previously developed to examine how the plant pigment chlorophyll interacts with lanthanides, both externally and internally. Until now, uncertainty remained regarding whether chlorophyll had any interaction with lanthanide ions.
Chlorophyll facilitates photosynthesis, but the pigments lose their capacity to absorb light efficiently when the magnesium ion at their core is absent. The researchers found that lanthanides can fill this gap, aiding chlorophyll pigments in partially restoring their optical characteristics through a process referred to as re-greening.
“We discovered that lanthanides can enhance several aspects of plant health,” states Marelli. “They generally accumulate in the roots, yet a minor quantity also reaches the leaves, where some of the newly formed chlorophyll molecules contain lanthanides within their structure.”
This investigation also presents the first experimental proof that lanthanides can augment plant resilience to UV stress, which the researchers describe as completely unforeseen.
“Chlorophylls are quite sensitive pigments,” remarks Rizzo. “They can convert light into energy for plants, but when detached from the cellular structure, they rapidly hydrolyze and degrade. Nevertheless, when lanthanides occupy their core, they remain relatively stable, even after being extracted from plant cells.”
The research team, utilizing various spectroscopic techniques, found that the benefits extend across a range of staple crops, including chickpeas, barley, corn, and soybeans.
The results could be harnessed to enhance crop yields and bolster the resilience of some of the world’s most prevalent crops to extreme weather conditions.
“As we enter an era marked by persistent heat and extreme climatic events, particularly during extended periods of sunlight in agricultural fields, we aim to present new methods to safeguard our plants,” informs Marelli. “There are current agrochemicals available for application on leaves to shield plants from stressors like UV, though they may be toxic, contribute to microplastic pollution, and necessitate multiple applications. This could serve as a complementary approach to providing protection against UV stress.”
Identifying new applications
The researchers also determined that larger lanthanide elements, such as lanthanum, proved more effective in reinforcing chlorophyll pigments than their smaller counterparts. As a low-value byproduct of rare earths mining, lanthanum poses a challenge to the rare earth element (REE) supply chain because of the need to separate it from more sought-after rare earths. Heightened demand for lanthanum could diversify the economics surrounding REEs and enhance the stability of their supply chain, the scientists propose.
“This research illustrates the potential applications for these lower-value metals,” Marelli asserts. “We recognize lanthanides as incredibly valuable in electronics, magnets, and energy. In the U.S., there is a significant movement toward their recycling. Hence, for our plant studies, we concentrated on lanthanum as it is the most abundant and cost-effective lanthanide ion.”
Moving ahead, the team intends to investigate how lanthanides interact with other biological molecules, including proteins in the human body.
In the realm of agriculture, the group aspires to scale their research to encompass field and greenhouse experiments to further assess the effects of UV resilience across various crop types and in experimental farming contexts.
“Lanthanides are currently widely utilized in agricultural practices,” Rizzo notes. “We anticipate this study will offer evidence that encourages a more mindful application of these elements, as well as a novel method for their incorporation through seed treatments.”
The research received support from the MIT Climate Grand Challenge and the Office for Naval Research.