Title: A lignin-derived material improves plant nutrient bioavailability and growth through its metal chelating capacity

Authors: Qiang Liu, Tsubasa Kawai, Yoshiaki Inukai, Dan Aoki, Zhihang Feng, Yihui Xiao, Kazuhiko Fukushima, Xianyong Lin, Weiming Shi, Wolfgang Busch, Yasuyuki Matsushita & Baohai Li    

Journal: Nature Communications

Year: 2023

DOI: https://www.nature.com/articles/s41467-023-40497-2

Featured image by Tomasz Filipek  

World hunger and food shortage are global issues that affect millions of people, especially in developing countries. According to the World Food Programme, the scale of current global hunger and malnutrition is massive where more than 333 million people are facing food insecurity in 2023. Unfortunately, the trend is a rise of approximately 200 million people compared to pre-COVID-19 pandemic levels.

The factors that contribute to food insecurity are complex, but one of the factors is related to environmental issues. Climate change and global warming are impacting several areas including the production and distribution of crops, livestock, fisheries, and forestry, by altering the suitability of land, water, and biodiversity for agriculture, and by increasing the risks of pests, diseases, and natural disasters. The combination of these factors significantly affects millions of individuals placing those, especially from developing countries at higher risk. As a result, one major challenge is hidden hunger. Hidden hunger typically is a result of nutrient-poor diets where individuals will experience multiple micronutrient deficiencies such as iron and zinc.

Iron deficiency is one significant contributor to hidden hunger, which can be attributed to its low bioavailability in alkaline soils. Low iron content in soils is known to reduce crop yield and potential accumulation in food. As such, improving iron bioavailability in crops provides a healthy and sustainable method to combat hidden hunger. One method to accomplish this includes fertilizing with water-soluble iron chelates. A common example is ethylenediaminetetraacetic acid (EDTA) which is used as a fertilizer additive to improve metal ion bioavailability and update in food crops. However, these additives are costly and are harmful to the environment through its non-biodegradable properties and contribution to heavy metal pollution. Therefore, the development of alternative environmentally friendly iron chelates is critical. One potential solution stems from lignin-derived materials where its chemical properties such as active function groups (i.e. aliphatic hydroxyl, phenolic hydroxyl) and unshared electron pair on an oxygen atom have the potential to be used as metal chelators to improve nutrient bioavailability.

A study by Qiang Liu and colleagues (2023), demonstrates the development and use of a water-soluble lignin-derived material, hydrothermal sulfuric acid lignin (HSAL) to improve plant nutrient bioavailability and growth through its metal chelation capacity. Figure 1 demonstrates that HSAL can promote growth in multiple plant species, where it was experimented with roots from rice (Oryza sativa L. ssp. japonica cv. Nipponbare) and corn (Zea mays L.) seedlings. The rice root seedlings were tested with various concentrations of HSAL in water without additional nutrients. Of the tested parameters, the most pronounced growth is observed with 0.05% HSAL with greater root length, root biomass, shoot length and shoot biomass (Figure 1a-e). The authors also note that similar results were observed in other rice species suggesting that HSAL has similar effects in common rice crops. Given this information, the root length and shoot length of the rice seedlings were further tested in 0.05% HSAL (exposed) and no HSAL (control) for 12 days (Figure 1f-g). The results show that differences can be seen about 3 days after germination, where roots kept growing past 7 days with HSAL despite stopping in control.     

In addition to rice seedlings, the study (Figure 1h-l) also evaluated other species such as corn seedlings. The experiments were conducted in soil instead of water like the rice, comparing common fertilizer and HSAL treatments. It was observed that plant growth, including root length, root biomass, shoot length, and shoot biomass was considerably greater in HSAL versus fertilizer and control, but HSAL and fertilizer treatments showed the greatest impact.  

Overall, the study demonstrates several key points including the development of a hydrothermal sulfuric acid lignin (HSAL) and its impact on improving plant nutrient bioavailability and growth. The readers are encouraged to read the original paper to further understand the production of HSAL, its chemical properties and how it impacts metal (e.g. iron) bioavailability in plants compared to well-known metal chelators such as EDTA. The study highlights the importance of developments towards an environmentally friendly metal chelator and its significance in plant growth, nutrient bioavailability and potential applications towards mitigating hidden hunger and global world food issues.