Can grapevine physiology inform best management practices for new techniques in agrivoltaics and agroforestry? A commentary on ‘Source–sink manipulations through shading, crop load and water deficit affect plant morphogenesis and carbon sink priorities leading to contrasted plant carbon status in grapevine’

Gazing out onto manicured vineyard trellises, one could reflect that grapevine domestication has been more about canopy management than genetic selection. Cultivated Vitis vinifera L. is a tendrilled liana with the potential to produce prolific vegetative growth, requiring extensive pruning to produce a more compact and balanced architecture conducive to berry production and mechanical spraying and harvesting (Smart et al., 1990). Building on efforts to use physiological knowledge to improve vineyard management practices further, Poupard et al. (2025), in this issue of Annals of Botany, investigate responses of potted vines to shade, water stress and pruning. Intriguingly, the authors highlight that such research could also inform the alternative ‘sustainable’ production systems of agroforestry and agrivoltaics (Fig. 1). In agrivoltaics, partial coverage of crops with arrays of photovoltaic solar panels provides both renewable power and shade protection (Chopdar et al., 2024), whereas in the alley cropping version of agroforestry, tree rows interspersed among crop rows offer benefits of wind protection, shade, soil health and pest insect control (Favor et al., 2024). The atypical shade and soil moisture conditions encountered in these systems necessitate a new level of understanding of vine physiology to identify optimal configurations of vines, trees and panels.

Fig. 1.

Alternative grapevine production systems. (A) Experimental agrivoltaics array on grapevine cv. Merlot vines, University of Adelaide, Australia. (B) Alley cropped agroforestry with grapes at the Restinclières research farm in southern France. Image courtesy of Erik Hoffner/Mongabay.

As demonstrated by Poupard et al. (2025) and others, grapevine can adapt to some level of shade, drought and changes in source-to-sink ratio, which seems to bode well for its use in alternative production systems. To alter the source-to-sink ratio, Poupard et al. (2025) applied bunch removal with or without partial defoliation. Fruit load reduced leaf expansion rates and final total leaf area, suggesting that leaf growth was constrained by diversion of photosynthate to the fruit. In the first experiment, there was essentially no effect of removing bunches on photosynthetic capacity (A_sat), whereas in the second experiment, bunch removal combined with partial defoliation increased A_sat by 45 % and stomatal conductance to water vapour (g_SWmax) by 118 % relative to plants subjected to removal of fruit but not leaves. It was not possible to apportion this effect to either defoliation or fruit load because the treatments were not applied singly in this experiment; however, a main effect of defoliation rather than fruit load seems likely based on the work of Martínez-Lüscher and Kurtural (2021). This suggests that grapevine can compensate somewhat for foliage loss by upregulating assimilation to maintain photosynthate supply to developing bunches, but the process might be largely insensitive to fruit load. Nonetheless, a critically low source-to-sink (leaf-to-fruit) ratio attributable to canopy mismanagement (‘overcropping’) has consequences such as reduced berry size, berry abortion, reduced berry soluble solids and delayed berry development; effects that can carry over or accumulate across seasons owing to depleted reserves of non-structural carbohydrates in the roots (Martínez-Lüscher and Kurtural, 2021).

Poupard et al. (2025) examined leaves that had expanded prior to application of the 80 % shade treatment (H1) or during shade (H2). Shade increased specific leaf area (area per gram dry mass), mostly in H2 leaves but not H1 leaves, indicating that leaves while expanding had the ability to become thinner in shade, although the final total plant leaf area was essentially unaffected, reflecting a known shade adaptation strategy to limit leaf construction costs while retaining area for light capture. Shade decreased water lost per unit leaf area (measured as g_SWmax) only in H2 leaves, perhaps owing to a sparser stomatal distribution in these more expanded leaves. This meant that shade reduced photosynthesis more in H2 leaves than in H1 leaves (by 50 vs. 20 %).

Under the ‘mild’ drought treatment, g_SWmax (reflecting stomatal aperture) was reduced to conserve water, which lowered both photosynthetic capacity and leaf starch accumulation. In plants with or without fruit, leaves under drought expanded more slowly, and final total leaf area was reduced by >50 %, although the leaves reached a specific leaf area that was similar to the well-watered controls. Therefore, as for shade, drought had major effects on leaf form and function, although the nature of the effects was fundamentally different depending on the stress type, notwithstanding the common consequence of reducing photosynthesis. The authors suggested that these contrasting responses might be attributable to different signalling hormones involved: abscisic acid for drought versus auxin and gibberellin for shade.

Although the drought and shade responses reported by Poupard et al. (2025) were perhaps not unexpected, their work brings value by including the two stresses in a single study and finding that there were no significant interactions in the responses to the two stresses. As they suggested, this independence could be helpful for informing modelling approaches for carbon assimilation and resource allocation. For leaf growth rate and final leaf area, which responded to fruit load, drought and shade, there were also no interactions involving fruit load. Regarding combined stresses in alternative production systems, agrivoltaics reduces water stress in the presence of shade (Chopdar et al., 2024), whereas agroforestry could potentially create some level of drought stress if trees are placed too close to the vines.

Clearly, grapevine has shade adaptive mechanisms, but would shade reduce berry yield? Not necessarily! For grapevines growing in Adelaide, Australia, Caravia et al. (2016) reported that photosynthetic capacity saturated at photon flux densities between 500 and 900 µmol m⁻² s⁻¹, and photon flux density in the open was routinely measured at 1500 µmol m⁻² s⁻¹ during veraison to harvest, indicating there were photons to spare. At temperatures of >40 °C, assimilation was higher in leaves under 62 % shade than in control leaves, perhaps owing to a known reduction in photosynthesis beyond an optimum of ~35 °C. In a 2-year trial at Wagga Wagga, Australia, Abeysinghe et al. (2016) found that 50 % shade reduced berry yield but 30 % shade did not.

In a warming climate, extreme heat events are an increasing concern by causing sunburn browning and necrosis of berries (Gambetta et al., 2021), undesirably high levels of berry sugar and pH, and loss of flavour characteristics, whereas increased average temperatures pose logistical challenges by narrowing the window of harvest times; however, some direct light to bunches and a level of water stress can also be beneficial for winemaking quality (Gutiérrez-Gamboa et al., 2021). Shading from solar panels or trees could be beneficial in mitigating these undesirable effects of high temperatures, and renewable power from solar panels would help to reduce greenhouse emissions that are the root cause of global warming. Agrivoltaics and agroforestry also deliver the potential sustainability benefit of improving land-use efficiency, i.e. total production of electricity plus grapes, or grapes plus timber/nuts, per unit of land area.

There are a multitude of possible agrivoltaics configurations, involving inter-row bifacial vertical photovoltaic panels or overhead panels with variations in tilt, orientation and spacing, and use of semi-transparent or wavelength-selective panels (Chopdar et al., 2024). Furthermore, dynamic orientation of photovoltaic panels could be used to alter the extent and timing of vine shading, e.g. to minimize vine shading at times of peak sink demand. In finding the optimal balance between vine shading versus power generation, vine responses clearly present the trickier side of the equation to understand. Agroforestry poses the additional complication of growing two plant types together. These complex systems could herald a new era in physiology research and vine management practices.