However, there is some evidence suggesting the nutrient deficiency may stimulate
the production of cannabinoids. Poor soil conditions have been linked to increased
cannabinoid content (Krejci 1970 ), but the specific nutrient status utilized in the
study was unclear. In wild populations of hemp, potassium deficiency was corre-
lated with increased THC content (Haney and Kutcheid 1973 ). However, the
complex interaction between the various nutrients combined with the nature of the
study, which was only a survey, make any clear conclusions difficult. Overall, more
research is needed to fully evaluate the potential role of nutrient deficiency in
cannabinoid biosynthesis.
21.4 Drought Stress
While drought stress is known to greatly reduce plant growth, it can also increase
secondary metabolite content (Gorelick and Bernstein 2014 ). Mild water stress
significantly increased the content of the anti-inflammatory saikosaponins in
Blupleurum chinense(Zhu et al. 2009 ). In Crataegus, exposure to water stress
increased the level of bioactive polyphenols, including catechin and epicatechin
(Kirakosyan et al. 2004 ) Moderate drought stress also increased the production of
rosmarinic, ursolic, and oleanolic acid inPrunella vulgaris(Chen et al. 2011 ), and
glycyrrhizic acid content in roots ofGlycyrrhiza uralensis(Li et al. 2011 ).
There is some evidence linking drought stress to cannabinoid production.
Ecological observations have reported that cannabis plants growing in drier regions
correlated with increased trichome density (Sharma 1975 ). Decreased humidity was
also linked with increased THC content (Paris et al. 1975 ). This phenomenon was
also reported in hemp plants naturally lacking THC, which produced significant
amounts when grown in drier climates (Murari et al. 1983 ; Hakim et al. 1986 ).
However, the evidence is inconclusive and more work is needed to better under-
stand the role of water stress in cannabinoid production.
21.5 Temperature
Although thermal stress can greatly reduce plant growth and induce senescence,
elevated temperatures (heat-stress) or low temperatures (cold-stress) have also been
shown to increase secondary metabolite production. A 5° increase in temperature
significantly increased ginsenoside content in roots of Panax quinquefolius
(Jochum et al. 2007 ). Fifteen days at 35 °C significantly increased hypericin and
hyperforin content in shoots ofHypericum perforatum(Zobayed et al. 2005 ). In
some plants lower temperatures where shown to elicit increased secondary
metabolite production. In asparagus, lower soil temperatures increased the content
of bioactive saponins (Schwarzbach et al. 2006 ).
21 Chemical and Physical Elicitation... 443