How does a "membrane" promote sustainable afforestation?

Produced by: Science Popularization China

Author: Shi Chang (PhD in Physical Chemistry)

Producer: China Science Expo

Editor's note: In order to decode the latest mysteries of life science, the China Science Popularization Frontier Science Project has launched a series of articles called "New Knowledge of Life" to interpret life phenomena and reveal biological mysteries from a unique perspective. Let us delve into the world of life and explore infinite possibilities.

Photosynthesis is the process by which plants, algae and some special bacteria use the sun's energy to convert carbon dioxide and water into organic matter and release oxygen. This process not only provides nutrients for their own growth, but also can slow down the accumulation of greenhouse gases in the atmosphere to a certain extent, thus helping us fight global warming.

Drought environment has a great impact on plant growth , including root damage, obstructed photosynthesis, water imbalance and restricted growth, which will eventually lead to a decrease in plant yield and pose a threat to the stability of the ecosystem and biodiversity.

China has a desert area of ​​more than 600,000 square kilometers, making it one of the countries with the largest desert area in the world. Planting plants in the desert can not only fix sand and prevent wind, reduce soil erosion, but also consume greenhouse gases, making a huge contribution to combating global warming. So how can we plant plants in arid deserts?

Desert Plants

(Photo source: veer photo gallery)

What’s so magical about a membrane?

On May 21, 2024, Chinese scientists published an article in the journal Nature Sustainability on the radiation cooling film that promotes plant photosynthesis, which is expected to solve the "water-food-energy" relationship problem in climate change.

The research results were published in the journal Nature Sustainability

(Image source: Nature Sustainability magazine)

Through modeling, the authors determined that the input of net radiation energy has a great relationship with plant growth, and the input of net radiation energy is closely related to the rate of temperature change and the rate of water loss. Based on this, the authors prepared a photosynthetically active radiative cooling film (PRCF) with a sandwich structure.

PRCF consists of a polydimethylsiloxane (PDMS) radiation layer, an optimized photonic crystal layer and a polyacrylamide (PAM) hydrogel layer . The polydimethylsiloxane layer has a high mid-infrared emissivity and can achieve maximum radiative cooling; the photonic crystal layer can selectively transmit light suitable for photosynthesis to promote photosynthesis; the polyacrylamide layer can prevent fogging and avoid the shading effect of water vapor condensation.

Design and characterization of photosynthetically active radiative cooling membranes.

a. The challenges of growing plants in drylands; b. The relationship between the rate of temperature change and the rate of water loss and net radiation; c. The effect diagram of the use of PRCF; d. The relationship between sunlight transmittance and mid-infrared emissivity and wavelength; e, f. Introduction to PRCF; g, h, i, j. Characterization of PRCF)

(Image source: Reference 1)

To verify the cooling and water-saving effects of the photosynthetically active radiative cooling film, the authors conducted outdoor temperature control experiments with it and soil covered with polyvinyl chloride (PVC) film, ultraviolet-near infrared (UV-NIR) filters, and uncovered soil.

The experimental results showed that the level of sunlight transmitted by PRCF that is effective for plant photosynthesis is similar to that of two control groups: polyvinyl chloride (PVC) film and ultraviolet-near infrared (UV-NIR) filter, but it can greatly reduce the input of sunlight at other wavelengths.

In addition, PRCF has a higher radiant energy output in the mid-infrared wavelength, which helps to reduce the radiant heat load. The minimum temperature in the PRCF experimental group was 35.4°C, which was 2.4°C, 4.6°C, and 1.9°C lower than the UV-NIR filter, PVC film, and no cover scenarios, respectively. PRCF showed an excellent ability to reduce water evaporation compared with the ultraviolet-near infrared (UV-NIR) filter, polyvinyl chloride (PVC) film, and no cover control group.

PRCF has the ability to passively cool and reduce water evaporation, which helps improve the growth of plants in hot and arid environments. Researchers estimate that globally, the application of films on dryland plants can increase carbon sinks by about 40% compared to the case where no film is used, which has a positive effect on mitigating climate warming.

Cooling and water-saving performance of photosynthetically active radiative cooling films

Photo of equipment used to test PRCF performance; b. Spectral graphs of different covering materials; c. Transmission and absorption of sunlight by different covering films; d. Mid-infrared energy output of different covering materials at different temperatures; e. Energy flow power of different covering materials; f, g. Comparison of air temperature and soil temperature under different covering film conditions; h. Water loss rate under different covering film conditions)

(Image source: Reference 1)

What other ways are there to consume carbon dioxide?

Absorption by seawater : The ocean is an important carbon dioxide storage reservoir in nature. Seawater can consume carbon dioxide through dissolution and the metabolic process of marine organisms, and plays an important role in regulating the concentration of carbon dioxide in the atmosphere.

ocean

(Photo source: veer photo gallery)

Microbial metabolism : Bacteria and plankton use carbon dioxide as a carbon source, fix carbon by synthesizing organic matter, and reduce the concentration of carbon dioxide in the atmosphere. Microorganisms are widely present in soil, water and other environments, and have an important impact on the consumption of carbon dioxide.

Chemical conversion : Chemical methods, such as carbon capture and storage (CCS) technology, can separate carbon dioxide from industrial emission sources and store it underground or in other safe locations. This method can significantly reduce the concentration of carbon dioxide in the atmosphere, but it requires a lot of technology investment and policy support.

Planting plants reduces carbon dioxide

(Photo source: veer photo gallery)

Conclusion

Consuming carbon dioxide and reducing greenhouse gas emissions have become urgent tasks in the process of responding to global warming. From plant photosynthesis to ocean carbon sinks, to microbial metabolism and innovative applications of artificial technology, we have witnessed the unremitting efforts of nature and human wisdom in responding to the greenhouse effect.

However, we must realize that these efforts are far from enough. To truly achieve the goal of reducing greenhouse gas emissions, it requires the joint participation and continuous efforts of the whole society. Let us start with the small things around us, save energy, reduce emissions, promote renewable energy, advocate low-carbon life, and contribute to the protection of the earth's environment.

References:

1.Li, J., Jiang, Y., Liu, J. et al. A photosynthetically active radiative cooling film[J]. Nat Sustain, 2024.

2. Zhang Yuanhui, Wang Weiqiang, Chen Liqi. Research progress on ocean carbon dioxide[J]. Advances in Earth Science, 2000, 15(5).

3. Tao Yuxuan, Guo Liang, Gao Cong, et al. Research progress on metabolic engineering of microorganisms for carbon dioxide fixation[J]. Chemical Industry Progress, 2023, 42(1).

4.Mackay E. Modeling the injectivity, migration and trapping of CO2 in carbon capture and storage (CCS)[J]. 2013.