Heavy concentrations of bicarbonates present throughout karst ecosystems necessitate identification of the role of HCO3- in plant growth, especially when under drought stress. We aim to elucidate effect of different concentrations of HCO3- on paper mulberry (Broussonetia papyrifera L.) seedlings growth under drought stress. Effects of four bicarbonate concentrations (0, 3, 6, and 9 mM) with simulated mild drought stress on growth, glucose metabolism, photosynthetic traits, self-protective abilities and extent of cell damage were examined. Compared with other treatments, plants under 3 mM bicarbonate with simulated mild drought stress showed the best osmotic adjustment and reactive oxygen species scavenging ability, the highest total activity of glucose catabolism enzymes and glucose-6-phosphate dehydrogenate activity, and the highest growth rate. Specific concentration of HCO3- reduce negative influence in Broussonetia papyrifera L. under drought stress. Due to both producing more metabolic substrate and activating pentose phosphate pathway, those plants showed stronger resistance, therefore might suffer less harm and retain a better growth status under mild drought stress. This suggests that when specific plants in a karst environment are suffering drought stress, specific concentration of HCO3- benefit to their growth.

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