Plants growing in drylands do double duty for the planet. Dryland plants absorb carbon dioxide from the atmosphere in the same way as other vegetation, but they do so under extreme challenges that include high air temperatures, low soil moisture and intense evaporation, all of which suppress growth and limit carbon sequestration, as highlighted in a 2024 Nature Sustainability News & Views article on cooling crops with selective films. These limitations mean the landscape's overall contribution to carbon sequestration falls well short of its potential: the more heat- and drought-stressed a plant is, the less it grows, and the less it grows, the less carbon it can absorb. Shading seems like an obvious fix, but common shade cloths or plastic sheets also block the sunlight that crops need for photosynthesis.
A three-layer film splits light into what plants need and what they don't
One of the two films was produced by a team of researchers at Nanjing University and consists of three layers stacked together to function as one. At its core is a photonic crystal layer, which selectively transmits the wavelengths of sunlight required by plants to perform photosynthesis: 71% of light in the range of 0.4 to 0.5 micrometers and 77% in the range of 0.6 to 0.7 micrometers, both critical for the chlorophyll absorption process. On one side of this core layer sits a layer of polydimethylsiloxane, a silicone-based polymer with mid-infrared emissivity of about 92% in the 2.5 to 20 micrometer range, which lets the film shed heat into the atmosphere without absorbing it. On the other side is an anti-fogging layer of polyacrylamide hydrogel, which prevents the condensation and shading that have hindered other cooling films placed directly on crops.
Field tests cut air temperature and water loss while yields climbed
The research, A photosynthetically active radiative cooling film (Li et al.), was published in Nature Sustainability in 2024. Field experiments, conducted on model plants such as gardenia, comparing growth under the film against a PVC sheet, a UV-NIR filter, and uncovered controls, found the film reduced surrounding air temperature by 1.9°C to 4.6°C and cut water evaporation by 2.1% to 31.9% compared with unshaded plants in similar conditions. Together, those two effects increased biomass yield by 20% to 370% across the plant types tested. Plants grown under the PVC sheet and the UV-NIR filter, by contrast, appeared wilted due to higher temperatures and greater water loss.
A different team reached comparable numbers with a cheaper build
Other groups that are solving this challenge have achieved a similar outcome using a different structure for their films. In another study, A Low‑Cost and Large‑Scale Producible Polymer Multilayer Radiative Cooling Film for Reducing Plant Heat Stress, published in ACS Photonics in 2024, the authors designed a film based on two spectrally selective polymer multilayer stacks paired with a separate polymer emitter, rather than using a photonic crystal and hydrogel combination. This film design allowed for the transmission of photosynthetic light: 52% at 0.4 to 0.48 micrometers and 85% at 0.6 to 0.7 micrometers.
