Hot days are becoming hotter and more frequent, threatening wheat yields worldwide. Developing wheat varieties ready for future climates calls for improved understanding of how elevated CO₂ (eCO₂) and heat stress (HS) interactively impact wheat yields. We grew a modern, high-yielding wheat cultivar (Scout) at ambient CO₂ (aCO₂, 419 μl l ⁻¹) or eCO₂ (654 μl l⁻¹) in a glasshouse maintained at 22/15 °C (day/night). Half of the plants were exposed to HS (40/24 °C) for 5 d at anthesis. In non-HS plants, eCO₂ enhanced (+36%) CO₂ assimilation rates (A_sat) measured at growth CO₂ despite down-regulation of photosynthetic capacity. HS reduced A_sat (–42%) in aCO₂- but not in eCO₂-grown plants because eCO₂ protected photosynthesis by increasing ribulose bisphosphate regeneration capacity and reducing photochemical damage under HS. eCO₂ stimulated biomass (+35%) of all plants and grain yield (+30%) of non-HS plants only. Plant biomass initially decreased following HS but recovered at maturity due to late tillering. HS equally reduced grain yield (–40%) in aCO₂- and eCO₂-grown plants due to grain abortion and reduced grain filling. While eCO₂ mitigated the negative impacts of HS at anthesis on wheat photosynthesis and biomass, grain yield was reduced by HS in both CO₂ treatments.

Glasshouse films with adjustable light transmittance and energy‐efficient designs have the potential to reduce (up to 80%) the high energy cost for greenhouse horticulture operations. Whether these films compromise the quantity and quality of light transmission for photosynthesis and crop yield remains unclear. A “Smart Glass” film ULR‐80 (SG) was applied to a high‐tech greenhouse horticulture facility, and two experimental trials were conducted by growing eggplant (Solanum melongena) using commercial vertical cultivation and management practices. SG blocked 85% of ultraviolet (UV), 58% of far‐red, and 26% of red light, leading to an overall reduction of 19% in photosynthetically active radiation (PAR, 380–699 nm) and a 25% reduction in total season fruit yield. There was a 53% (season mean) reduction in net short‐wave radiation (radiometer range, 385–2,105 nm upward; 295–2,685 nm downward) that generated a net reduction of 8% in heat load and reduced water and nutrient consumption by 18%, leading to improved energy and resource use efficiency. Eggplant adjusted to the altered SG light environment via decreased maximum light‐saturated photosynthetic rates (A_max) and lower xanthophyll de‐epoxidation state. The shift in light characteristics under SG led to reduced photosynthesis, which may have reduced source (leaf) to sink (fruit) carbon distribution, increased fruit abortion and decreased fruit yield, but did not affect nutritional quality. We conclude that SG increases energy and resource use efficiency, without affecting fruit quality, but the reduction in photosynthesis and eggplant yield is high. The solution is to re‐engineer the SG to increase penetration of UV and PAR, while maintaining blockage of glasshouse heat gain.

Protected cropping offers a way to bolster food production in the face of climate change and deliver healthy food sustainably with fewer resources. However, to make this way of farming economically viable, we need to consider the status of protected cropping in the context of available technologies and corresponding target horticultural crops. This review outlines existing opportunities and challenges that must be addressed by ongoing research and innovation in this exciting but complex field in Australia. Indoor farm facilities are broadly categorised into the following three levels of technological advancement: low-, medium- and high-tech with corresponding challenges that require innovative solutions. Furthermore, limitations on indoor plant growth and protected cropping systems (e.g., high energy costs) have restricted the use of indoor agriculture to relatively few, high value crops. Hence, we need to develop new crop cultivars suitable for indoor agriculture that may differ from those required for open field production. In addition, protected cropping requires high start-up costs, expensive skilled labour, high energy consumption, and significant pest and disease management and quality control. Overall, protected cropping offers promising solutions for food security, while reducing the carbon footprint of food production. However, for indoor cropping production to have a substantial positive impact on global food security and nutritional security, the economical production of diverse crops will be essential.

Optical films that alter light transmittance may reduce energy consumption in high-tech greenhouses, but their impact on crop physiology remains unclear. We compared the stomatal responses of Capsicum plants grown hydroponically under control glass (70% diffuse light) or the smart glass (SG) film ULR-80, which blocked >50% of short-wave radiation and ~9% of photosynthetically active radiation (PAR). SG had no significant effects on steady-state (g_s) or maximal (g_max) stomatal conductance. In contrast, SG reduced stomatal pore size and sensitivity to exogenous abscisic acid (ABA), thereby increasing rates of leaf water loss, guard cell K⁺ and Cl^– efflux, and Ca²⁺ influx. SG induced faster stomatal closing and opening rates on transition between low (100 µmol m^–2 s^–1) and high PAR (1500 µmol m^–2 s^–1), which compromised water use efficiency relative to control plants. The fraction of blue light (0% or 10%) did not affect g_s in either treatment. Increased expression of stomatal closure and photoreceptor genes in epidermal peels of SG plants is consistent with fast stomatal responses to light changes. In conclusion, stomatal responses of Capsicum to SG were more affected by changes in light intensity than spectral quality, and re-engineering of the SG should maximize PAR transmission, and hence CO₂ assimilation.

Key message: Heat stress (HS) under well-watered conditions was not detrimental to leaf photosynthesis or yield but modified the elevated CO₂ response of photosynthesis and yield in two contrasting wheat cultivars. Climate change is increasing the frequency of extreme events such as heat waves, adversely affecting crop productivity. While positive impacts of elevated carbon dioxide (eCO₂) on crop productivity are evident, the interactive effects of eCO₂ and environmental stresses are still unclear. To investigate the interactive effects of elevated CO₂ and heat stress (HS), we grew two contrasting wheat cultivars, early-maturing Scout and high-tillering Yitpi, under non-limiting water and nutrients at ambient (aCO₂, 450 ppm) or elevated (eCO₂, 650 ppm) CO₂ and 22 °C in the glasshouse. Plants were exposed to two 3-day HS cycles at the vegetative (38.1 °C) and/or flowering (33.5 °C) stage. At aCO₂, both wheat cultivars showed similar responses of photosynthesis and mesophyll conductance to temperature and produced similar grain yield. Relative to aCO₂, eCO₂ enhanced photosynthesis rate and reduced stomatal conductance and maximal carboxylation rate (V_cmax). During HS, high temperature stimulated photosynthesis at eCO₂ in both cultivars, while eCO₂ stimulated photosynthesis in Scout. Electron transport rate (J_max) was unaffected by any treatment. eCO₂ equally enhanced biomass and grain yield of both cultivars in control, but not HS, plants. HS reduced biomass and yield of Scout at eCO₂. Yitpi, the cultivar with higher grain nitrogen, underwent a trade-off between grain yield and nitrogen. In conclusion, eCO₂ improved photosynthesis of control and HS wheat, and improved biomass and grain yield of control plants only. Under well-watered conditions, HS was not detrimental to photosynthesis or growth but precluded a yield response to eCO₂.