Selenium in lemon balm plants: Productivity, phytotoxicity and drought alleviation

Since studies on the effects of selenium (Se) supplementation in water-stressed plants have mainly focused on cereal crops, the specific reports regarding Se-mediated adaptation to drought stress in medicinal vegetables are scant. Thus, we investigated the responses of Melissa officinalis to Se supplementation. Selenium contents were increased in leaves and grains by supplemental Se. Selenium foliar application at 1mg l(-1) could be useful to increase the vegetative and reproductive growth of Se-enriched plants under well-watered conditions but at 20mg l(-1) led to toxicity and caused damage to shoots. Drought stress significantly inhibited plant growth by chlorophyll degradation and reduced net carbon dioxide (CO2) assimilation rate. Although Se at 1mg l(-1) could increase biomass production under well-watered conditions in addition to the stimulation of antioxidant system under water stress, it could not ameliorate the negative effect of drought on productivity.