Agronomy and photosynthesis physiology of hemp (Cannabis sativa L.)

Hemp (Cannabis sativa L.) is a sustainable high-yielding crop that delivers valuable fibres, seeds and psychoactive substances. However, there is a lack of field experimental data on the cultivation of hemp because its production was largely abandoned in the last century. Hemp is now considered as an ideal crop to produce innovative biomaterials, and in particular, the dual-purpose hemp production (fibre + seed) is now the norm in European countries, driven by the shift of a rapidly expanding market for hemp seeds coupled with lower quality fibre requirements for innovative biomaterials. This study brought new information on the agronomy and photosynthesis physiology for the resurging production of hemp, particularly for dual-purpose production in Europe. The effects of important agronomic factors, i.e. cultivar, planting density, and nitrogen fertilization, on the performance of the hemp crop were investigated under contrasting European environments. Based on the experimental data, for dual-purpose hemp production, a planting density of 90–150 plants m-2 is recommended for a monoecious cultivar that gives a long vegetative phase while leaving enough time for seed growth. A nitrogen fertilization rate of 60 kg N ha-1 was generally sufficient in the tested environments whereas further optimization of nitrogen fertilization requires accurate and precise assessment of plant nutritional status. To facilitate assessing plant nutritional status, a critical nitrogen dilution curve was determined for hemp. The responses of leaf photosynthesis to nitrogen content and temperature were quantified using a biochemical model of C3 leaf photosynthesis, based on a complete set of photosynthetic measurements for hemp leaves. Then, by combining measurements and modelling, an upscaling was made from the leaf to the canopy level to analyse hemp’s photosynthetic nitrogen-use efficiency (NUE) and water-use efficiency (WUE) in response to water and nitrogen supply. The effect of nitrogen supply level on hemp’s NUE and WUE was largely determined by its effect on canopy size or leaf area index (LAI). The effect of short-term water stress on WUE and NUE was reflected in the stomatal regulation, whereas long-term water stress enhanced leaf senescence, reduced LAI but retained total canopy nitrogen content, and thus resulted in a further increase in WUE. Findings in this thesis provided an improved understanding of the agronomy and photosynthesis physiology of hemp, particularly in relation to the dual-purpose production of hemp in Europe. Such understanding not only provides additional evidence that hemp can be grown as a sustainable crop over a wide range of climatic and agronomic conditions, but also provides essential information for parameterizing crop growth models. Prospects for further research were discussed in view of using the findings in this thesis in combination with a crop growth model to develop strategies for optimization of hemp cultivation and breeding.</p

Hemp (Cannabis sativa L.) leaf photosynthesis in relation to nitrogen content and temperature: implications for hemp as a bio-economically sustainable crop

Hemp (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\uc2&nbsp;\uc2\ub1\uc2&nbsp;1.9\uc2&nbsp;\uce\ubcmol m\ue2\u88\u922 s\ue2\u88\u921 at 25\uc2&nbsp;\uc2\ub0C. The Amax initially increased with an increase in leaf temperature (TL), levelled off at 25\ue2\u80\u9335\uc2&nbsp;\uc2\ub0C and decreased when TL became higher than 35\uc2&nbsp;\uc2\ub0C. Based on a C3 leaf photosynthesis model, we estimated mesophyll conductance (gm), efficiency of converting incident irradiance into linear electron transport under limiting light (\uce\uba2LL), 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 \uce\uba2LL, 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 &lt;2.0\uc2&nbsp;g N m\ue2\u88\u922. 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

Presentation_1_Water- and Nitrogen-Use Efficiencies of Hemp (Cannabis sativa L.) Based on Whole-Canopy Measurements and Modeling.PDF

<p>Interest in hemp (Cannabis sativa L.) as a crop for the biobased economy is growing worldwide because hemp produces a high and valuable biomass while requiring low inputs. To understand the physiological basis of hemp's resource-use efficiency, canopy gas exchange was assessed using a chamber technique on canopies exposed to a range of nitrogen (N) and water levels. Since canopy transpiration and carbon assimilation were very sensitive to variations in microclimate among canopy chambers, observations were adjusted for microclimatic differences using a physiological canopy model, with leaf-level parameters estimated for hemp from our previous study. Canopy photosynthetic water-use efficiency (PWUE_c), defined as the ratio of gross canopy photosynthesis to canopy transpiration, ranged from 4.0 mmol CO₂ (mol H₂O)⁻¹ to 7.5 mmol CO₂ (mol H₂O)⁻¹. Canopy photosynthetic nitrogen-use efficiency (PNUE_c), the ratio of the gross canopy photosynthesis to canopy leaf-N content, ranged from 0.3 mol CO₂ d⁻¹ (g N)⁻¹ to 0.7 mol CO₂ d⁻¹ (g N)⁻¹. The effect of N-input levels on PWUE_c and PNUE_c was largely determined by the N effect on canopy size or leaf area index (LAI), whereas the effect of water-input levels differed between short- and long-term stresses. The effect of short-term water stress was reflected by stomatal regulation. The long-term stress increased leaf senescence, decreased LAI but retained total canopy N content; however, the increased average leaf-N could not compensate for the lost LAI, leading to a decreased PNUE_c. Although hemp is known as a resource-use efficient crop, its final biomass yield and nitrogen use efficiency may be restricted by water limitation during growth. Our results also suggest that crop models should take stress-induced senescence into account in addition to stomatal effects if crops experience a prolonged water stress during growth.</p

Water-and nitrogen-use efficiencies of hemp (Cannabis sativa L.) based on whole-canopy measurements and modeling

Interest in hemp (Cannabis sativa L.) as a crop for the biobased economy is growing worldwide because hemp produces a high and valuable biomass while requiring low inputs. To understand the physiological basis of hemp\u2019s resource-use efficiency, canopy gas exchange was assessed using a chamber technique on canopies exposed to a range of nitrogen (N) and water levels. Since canopy transpiration and carbon assimilation were very sensitive to variations in microclimate among canopy chambers, observations were adjusted for microclimatic differences using a physiological canopy model, with leaf-level parameters estimated for hemp from our previous study. Canopy photosynthetic water-use efficiency (PWUEc), defined as the ratio of gross canopy photosynthesis to canopy transpiration, ranged from 4.0 mmol CO2(mol H2O) 121to 7.5 mmol CO2(mol H2O) 121. Canopy photosynthetic nitrogen-use efficiency (PNUEc), the ratio of the gross canopy photosynthesis to canopy leaf-N content, ranged from 0.3mol CO2d 121(g N) 121to 0.7mol CO2d 121(g N) 121. The effect of N-input levels on PWUEcand PNUEcwas largely determined by the N effect on canopy size or leaf area index (LAI), whereas the effect of water-input levels differed between short-and long-term stresses. The effect of short-term water stress was reflected by stomatal regulation. The long-term stress increased leaf senescence, decreased LAI but retained total canopy N content; however, the increased average leaf-N could not compensate for the lost LAI, leading to a decreased PNUEc. Although hemp is known as a resource-use efficient crop, its final biomass yield and nitrogen use efficiency may be restricted by water limitation during growth. Our results also suggest that crop models should take stress-induced senescence into account in addition to stomatal effects if crops experience a prolonged water stress during growth

Effects of Gibberellin Pre-Treatment on Seed Germination and Seedling Physiology Characteristics in Industrial Hemp under Drought Stress Condition

The present study aimed to explore the effects of exogenous gibberellins (GAs) on seed germination and subsequent seedling growth of hemp (Cannabis sativa L.) under drought stress. Seeds of two industrial hemp cultivars i.e., ‘Yunma 1’, (YM) and ‘Bamahuoma’, (BM) were treated with different concentrations of GA3 solution (0, 200, 400, 600, 800 mg/L) at 20 °C for 8 h. The effect of pre-treatment was assessed on germination characteristics and physiological indexes on subsequent exposure to drought stress using 20% (m/v) polyethylene glycol (PEG) for 7 days. The results revealed that seed germination in hemp was sensitive to drought stress, as the germination indexes (germination rate and germination potential) decreased significantly, and seedling growth (hypocotyl length and radicle length) was impeded under 20% PEG-6000 condition. GA3 pre-treatment affected germination rate, germination potential, hypocotyl length and radicle length. With increasing GA3 concentration, these indexes first increased and then decreased. For seedling physiology characteristics in hemp, GA3-pretreatment remarkedly increased the osmotic regulating substances (soluble sugar and soluble protein contents) and the activities of antioxidant enzymes (SOD, superoxide dismutase and POD, peroxidase), while sharply decreased the lipid peroxidation (malondialdehyde, MDA) in seedlings grown under PEG-6000 induced drought stress. These results suggested that seeds pre-treated with GA3 could enhance the drought tolerance of hempseeds, and the optimal effect of GA3 for seed pre-treatment of YM and BM could be obtained when the concentration of GA3 solution reached 400 mg/L and 600 mg/L, respectively

Hemp (<i>Cannabis sativa</i> L.) Tolerates Chelator Stress Showing Varietal Differences and Concentration Dependence

The world’s arable land has been contaminated by heavy metals to a large extent, which has led to the decreasing availability of farmland. Thus, the remediation of heavy metal pollution deserves due attention, and phytoremediation is preferred. Hemp has been proposed as an ideal alternative crop for remediating heavy-metal-contaminated soil, owing to its well-developed roots, large biomass, and tolerance to heavy metals. Chelators can activate heavy metals to enhance plant absorption, but they may cause stress to plant growth. Therefore, it is very important to optimize the combination of chelator and plant (cultivar) for efficacious phytoremediation. The effects of different concentrations (2, 5, 10, 15, and 25 mmol·L−1) of the chelators disodium ethylene diamine tetra-acetate (EDTA) and citric acid (CA) on the seed germination and plant growth of hemp cultivars were investigated. Triple application of increasing concentrations of EDTA or CA two days apart gradually reduced the germination potential, germination rate, radicle length, and embryonic shoot length of hemp seed, although 2 mmol·L−1 of CA could even promote seed germination. Distinct varietal differences were found in the response of hemp to chelator stress. Under the scheme of four-time uses one week apart, both chelators caused a concentration-dependent linear decrease in the plant height, stem diameter, and biomass of hemp plants, but the growth inhibition due to CA was relatively milder. This could be partially explained by the change in tested physiological indices in hemp leaf. In conclusion, 2 mmol·L−1 of CA helped with seed germination and was almost nontoxic to plant growth; cultivar BM was more tolerant to the chelators than cultivar Y1

The effect of agronomic management of hemp (Cannabis sativa L.) on stem processing and fibre quality

Hemp (Cannabis sativa L.) is a multi-purpose crop that finds applications in technical textile, paper, food, cosmetic and automotive industries. Due to the increasing demand for sustainable fibres, the hemp fibre sector is expected to grow in the future. However, overall information on the effect of agronomic practices on decortication efficiency and hemp fibre quality traits is very limited. This study aims to evaluate the relationship between agro-technique, decortication process, and energy consumption properties. In this paper, four planting densities, four levels of nitrogen fertilisation and two harvesting times were compared in different environments to evaluate the effect of agronomy on stem and fibre processing properties, including energy requirements, using a lab-scaled hemp stem decorticator. The present work highlights that the optimal plant density and nitrogen fertilisation levels to reach high decortication efficiency are 120 plants m−2 and from 0 to 100 Kg N ha−1, respectively. The effect of nitrogen and density on the considered properties is mediated by their influence on stem diameter. The highest decortication efficiency and the highest efficiency in energy use were observed at full flowering. On the contrary the fineness of the fibre, which was only evaluated in one environment, was highest in stems harvested at seed maturity, in particular when plant densities above 120 plants m−2 and when 60–100 Kg N ha−1 were applied. The methodology used in this work effectively evaluates the impact of agro-technique on the efficiency and energy requirements of hemp decortication.11552018

Comparing hemp (Cannabis sativa L.) cultivars for dual-purpose production under contrasting environments

tInterest in hemp as a multi-purpose crop is growing worldwide and for the first time in 2015 it wascultivated in Europe on more than 20.000 ha as a dual-purpose crop, for the seeds and for the fibre. Inthe present study, fibre and seed productivity of 14 commercial cultivars were tested in four contrastingEuropean environments (Latvia, the Czech Republic, France, Italy). At full flowering, the stem yield rangedfrom 3.7 Mg ha−1to 22.7 Mg ha−1, the bast fibre content ranged from 21% to 43%, and the bast fibre yieldranged from 1.3 Mg ha−1to 7.4 Mg ha−1. When harvesting was postponed from full flowering until seedmaturity, the stem yield of monoecious cultivars significantly increased but in dioecious cultivars itdecreased at all tested sites, except for Italy. Only the early cultivars Fedora 17 and Markant producedseed in the most northern location Latvia. The seed yield ranged from 0.3 Mg ha−1to 2.4 Mg ha−1in Italy,France and the Czech Republic. The cultivar effect on stem and seed yield was mainly determined by thegenetic variation in time of flowering. Stem yield at full flowering was strictly related to the durationof the vegetative phase while seed yield was lowest in the late flowering cultivar. The late cultivar CS issuitable for stem and fibre production as it had the highest stem yield at full flowering in all locations.Both Fedora 17 and Futura 75 are candidate cultivars for dual-purpose production in Italy, France andthe Czech Republic, with Fedora 17 being more suitable for seed production and Futura 75 for fibreproduction.The application of modelling to design production strategies for dual-purpose hemp is promising.However, accurate parameterisation is needed based on large data sets and diverse genetic backgroun