Water conservation and assimilation is driven by stomatal behaviour in industrial hemp (Cannabis sativa L.)

As rainfall becomes increasingly erratic due to climate change, reliable water availability for crops will decrease, leading to reductions in crop productivity. Crops that can moderate water loss during periods of water deficit but rapidly upregulate physiological and photosynthetic processes when water is available will be valuable. In a controlled environment study, we used gas exchange and chlorophyll fluorescence methods to investigate how industrial hemp (Cannabis sativa L.) responds to differing watering frequencies (well-watered every two, four, or six days). Here, we report that hemp has a strong conserved relationship between stomatal conductance (g_s) and assimilation (A_n), limiting water loss at the expense of biomass production. Generally, hemp exhibits low g_s relative to high A_n, meaning that while a decrease in g_s limits A_n, it shows favourable high intrinsic water use efficiency (W_i). Hemp stomata respond quickly to water re-supply, recovering rapidly from periods of water deficit via stomatal behavioural mechanisms and rapidly upregulating A_n. These stomatal behaviour traits mean hemp may be a suitable choice for water-efficient cropping in climates with sporadic water availability. Rapid stomatal responses in hemp could also be used to understand the interactions between A_n and W_i, and to help meet plant productivity targets without significant water losses.