Barley, field beans, potatoes, cabbage and even sun-hungry maize adjust their photosynthesis to the shading created by agrivoltaic installations, according to a study by researchers from the Plant Ecology Department at the University of Hohenheim. Working with Forschungszentrum Jülich, the team conducted a field study showing that typical sun-loving crops are more adaptable than was previously assumed. Under partial shading, the plants' light requirements fall significantly, allowing them to use CO₂ more efficiently for photosynthesis when less light is available.
What this means for crop selection
For the researchers, this adaptive capacity, already present in conventional varieties, is a promising starting point for the targeted selection and breeding of crops suited to agrivoltaic and agroforestry systems. Both approaches are considered promising strategies for making agriculture more climate-resilient and for using land more efficiently, differing mainly in what casts the shade: trees in agroforestry, solar modules in agrivoltaics.
To determine how field crops adjust to altered light conditions, the research team examined the photosynthetic performance of five widely grown varieties at five sites across Germany in 2023 and 2024: barley (Hordeum vulgare), maize (Zea mays), cabbage (Brassica oleracea), potatoes (Solanum tuberosum) and field beans (Vicia faba). Performance was compared with identical plantings on fully sunlit reference plots at the same location. Using a mobile photosynthesis measurement system, the researchers recorded key physiological parameters directly at the leaves under real field conditions.
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Less light, less CO2 lost
The results showed that under shaded conditions, both dark respiration and the light compensation point fell across all the crops studied. "Put simply, this means that the plants lost less CO₂ through respiration and, at the same time, needed less light to fix the carbon they require to grow and produce fruit," explains study leader Jennifer Moore. "That points to a clear physiological adaptation to partial shading."
This was true even for maize. For Andreas Schweiger, professor at the University of Hohenheim and head of its Plant Ecology Department, it is particularly striking that the effect appeared in all the crops examined, even though they do not typically grow under shaded conditions. "They therefore have a considerably greater capacity to adapt than we had previously assumed," he says. These adaptations occurred regardless of location, soil, cultivation method or shading pattern. "Field crops do not necessarily reach their limits under moderate shading, but can adjust their metabolic activity," summarises Moore.
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Maize proved more sensitive
The plants did, however, respond differently. Most C3 crops coped well with partial shading. Maize, as a C4 plant, proved, not unexpectedly, somewhat more sensitive to reduced light availability. "The C4 metabolism is an adaptation to hot and dry conditions. In weaker light, C4 plants cannot make full use of their photosynthetic capacity," explains Moore.
These findings are particularly relevant because the shading conditions studied were not artificially generated. The plants grew under real agroforestry and agrivoltaic systems. Even so, differences emerged between the two setups. Photosynthetic performance generally remained comparatively stable beneath PV modules, whereas values fluctuated more strongly when plants grew in the shade of trees. Moore suspects this is because tree canopies create a more irregular pattern of shade. "Our results show that shade is not simply shade," she says. "Crops can adapt well to moderate partial shading. However, areas with permanently heavy shading should be avoided wherever possible," she advises.
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Finding the right crops
Such studies are important, because physiological parameters such as dark respiration and the light compensation point could in future be used to identify more shade-tolerant varieties and select them for cultivation systems involving partial shading. “Our results will help to plan agroforestry and agrivoltaic systems more precisely,” Schweiger emphasises. “Anyone who knows which crops can maintain their productivity under which light conditions can match varieties and land more effectively.” The researchers also see new perspectives opening up for plant breeding. (su)
