Climate-resilient agroforestry: physiological responses to climate change and engineering of crassulacean acid metabolism (CAM) as a mitigation strategy

Global climate change threatens the sustainability of agriculture and agroforestry worldwide through increased heat, drought, surface evaporation and associated soil drying. Exposure of crops and forests to warmer and drier environments will increase leaf:air water vapour-pressure deficits (VPD), and will result in increased drought susceptibility and reduced productivity, not only in arid regions but also in tropical regions with seasonal dry periods. Fast-growing, short-rotation forestry (SRF) bioenergy crops such as poplar (Populus spp.) and willow (Salix spp.) are particularly susceptible to hydraulic failure following drought stress due to their isohydric nature and relatively high stomatal conductance. One approach to sustaining plant productivity is to improve water-use efficiency (WUE) by engineering crassulacean acid metabolism (CAM) into C-3 crops. CAM improves WUE by shifting stomatal opening and primary CO2 uptake and fixation to the night-time when leaf:air VPD is low. CAM members of the tree genus Clusia exemplify the compatibility of CAM performance within tree species and highlight CAM as a mechanism to conserve water and maintain carbon uptake during drought conditions. The introduction of bioengineered CAM into SRF bioenergy trees is a potentially viable path to sustaining agroforestry production systems in the face of a globally changing climate. Global climate change is predicted to result in warmer and drier environments that will increase leaf:air water vapor-pressure deficits (VPD), thereby increasing the drought susceptibility and reducing the productivity of forests. Fast-growing, short-rotation forestry (SRF) bioenergy crops, such as poplar (Populus spp.) and willow (Salix spp.) are particularly susceptible to drought conditions due to their isohydric nature and relatively high stomatal conductance, which can result in hydraulic failure due to cavitation and carbon starvation. Improving water-use efficiency (WUE) by engineering crassulacean acid metabolism (CAM) into C (3) SRF crops could help sustain agroforestry production systems by allowing trees to conserve water and maintain carbon uptake during drought conditions, as exemplified by CAM-performing members of the genus Clusia.