Abstract
AbstractHemp (Cannabis sativa L.) may be a suitable crop for the bio‐economy as it requires low inputs while producing a high and valuable biomass yield. With the aim of understanding the physiological basis of hemp's high resource‐use efficiency and yield potential, photosynthesis was analysed on leaves exposed to a range of nitrogen and temperature levels. Light‐saturated net photosynthesis rate (Amax) increased with an increase in leaf nitrogen up to 31.2 ± 1.9 μmol m−2 s−1 at 25 °C. The Amax initially increased with an increase in leaf temperature (TL), levelled off at 25–35 °C and decreased when TL became higher than 35 °C. Based on a C3 leaf photosynthesis model, we estimated mesophyll conductance (gm), efficiency of converting incident irradiance into linear electron transport under limiting light (κ2LL), linear electron transport capacity (Jmax), Rubisco carboxylation capacity (Vcmax), triose phosphate utilization capacity (Tp) and day respiration (Rd), using data obtained from gas exchange and chlorophyll fluorescence measurements at different leaf positions and various levels of incident irradiance, CO2 and O2. The effects of leaf nitrogen and temperature on photosynthesis parameters were consistent at different leaf positions and among different growth environments except for κ2LL, which was higher for plants grown in the glasshouse than for those grown outdoors. Model analysis showed that compared with cotton and kenaf, hemp has higher photosynthetic capacity when leaf nitrogen is <2.0 g N m−2. The high photosynthetic capacity measured in this study, especially at low nitrogen level, provides additional evidence that hemp can be grown as a sustainable bioenergy crop over a wide range of climatic and agronomic conditions.
Highlights
The multiple societal challenges such as climate change, natural resource scarcity and environmental pollution have fuelled interest in bio-economy (Jordan et al, 2007)
With the aim of understanding the physiological basis of hemp’s high resource-use efficiency and yield potential using a modelling approach, this study focuses on analysing leaf photosynthesis of hemp as a primary source of biomass production
Measurements to assess the effect of leaf nitrogen on leaf photosynthetic capacity of hemp (N-trial) were conducted on leaves having an average Specific leaf nitrogen (SLN) of 0.87 g N mÀ2, 1.25 g N mÀ2 and 1.75 g N mÀ2 at the top of the canopy, or 0.65 g N mÀ2, 0.78 g N mÀ2 and 1.22 g N mÀ2 at the middle of the canopy, for the three N treatments, respectively
Summary
The multiple societal challenges such as climate change, natural resource scarcity and environmental pollution have fuelled interest in bio-economy (Jordan et al, 2007). Previous comprehensive research programmes indicated that hemp (Cannabis sativa L.) fits well in the concept of bio-economy (Mccormick & Kautto, 2013; Amaducci et al, 2015). Hemp has the potential to produce up to 27 Mg haÀ1 biomass yield (Tang et al, 2016) at relatively low inputs (Struik et al, 2000; Amaducci et al, 2002) and has a positive impact on the environment (Bouloc & Van der Werf, 2013; Barth & Carus, 2015). & Van der Werf, 1994), the seeds contain high-quality oil (Oomah et al, 2002), and the inflorescence contains valuable resins (Bertoli et al, 2010). From speciality pulp and paper to nutritional food, medicine and cosmetics, there are as many as 50 000 uses claimed for hemp products derived from its stem, seed and inflorescence (Carus et al, 2013; Carus & Sarmento, 2016). Recent research demonstrated that hemp is a suitable feedstock for bioenergy production (Rice, 2008; Kreuger et al, 2011; Prade et al, 2011)
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