Phosphorus fertilisation differentially influences growth, morpho-physiological adaptations and nutrient uptake of industrial hemp (Cannabis sativa L.)

Abstract
Background and Aims Phosphorus (P) is a restricting nutrient for crop productivity worldwide. P deficiency can lead to stunted growth and development, eventually affecting crop yield. Butless is documented about the impact of P fertility on industrial hemp (Cannabis sativa L.) production in the low-P soils of southwestern Australia. We aimed to investigate the effect of P rates on growth, physiology, rhizosphere carboxylate exudation, nutrient uptake, and P-use efficiency in hemp. Methods The study was conducted in a randomized complete block design with four P rates (0, 40, 80and 120 mg P kg–1 dry soil) and three hemp varieties (Morpeth, Han FNQ, and Fedora 17). Plants were grown and raised in a controlled-environment phytotron until harvested 35 days after sowing at the vegetative growth stage (3rd to nth leaf pair). Results Our results revealed a strong influence of treatment (P rate) on hemp growth, physiology, biomass, nutrient uptake, and P-use efficiency compared to variety and the variety × treatment interaction. Hemp roots predominantly released citrate in P-deficient conditions and gradually shifted to malate exudation with increasing P supply. TheN:P ratio, leaf chlorophyll, and gas exchange data coupled with shoot and root length data suggest that Morpeth and Fedora 17 differ in morpho-physiological adaptations for optimum photosynthesis and growth, with high leaf chlorophyll and coarse root length achieved by Morpeth and high intercellular CO2 concentration and shoot length by Fedora17. Conclusions Morpeth and Fedora 17 had high shoot biomass, root length, root surface area, and agronomic P-use and P-utilisation efficiencies in response to increasing soil P, while Han FNQ had moderate shoot yield, root growth, high citrate exudation, tissue P concentration, and P-uptake efficiency.