Light dependence of photosynthesis and water vapor exchange characteristics in different high Δ9-THC yielding varieties of Cannabis sativa L.

Abstract

The effect of different levels of photon flux densities (000, 400, 800, 1200, 1600 and 2000μmolm−2s−1) on gas and water vapor characteristics of four high Δ9-tetrahydrocannabinol (Δ9-THC) yielding drug type varieties (HPM, K2, MX and W1) of Cannabis sativa was studied. Plants of each variety were grown from seeds. On flowering, male plants were removed and vegetatively propagated clones of selected female plants were used for gas and water vapor studies at different photosynthetic photon flux densities (PPFDs). Our data show an increasing trend in photosynthesis (PN), transpiration (E) and stomatal conductance (gCO2) with increase in PPFD up to 2000μmolm−2s−1 in all varieties at optimum growth temperature (25±3°C). However, the magnitude of increase and maximum rate of PN (PN max) varied considerably with the varieties. Highest PN was observed in W1 followed by MX, K2 and HPM. Water use efficiency (WUE) in W1, MX and HPM increased with PPFDs up to the highest level tested, whereas, in K2 the highest WUE was observed at 1600μmolm−2s−1. Our results suggest that this species is able to use high level of PPFDs for its PN and therefore, may be cultivated in sun exposed areas in the field or under high PPFDs using indoor grow lights for the optimum growth. Strict control of other environmental factors, however, needs to be maintained while growing the plants indoor.