Background Drought stress affects the biomass accumulation and distribution between the aboveground and roots, results in excessive accumulation of active oxygen and lipid peroxidation, while plants evolve antioxidant enzyme system. Gymnocarpos przewalskii originates from Tethys, is the rare relic species of the Tertiary period in the desert area of central Asia and plays an important role in keeping stable of desert ecosystem. The research is to analyze the biomass accumulation and distribution pattern of the seedlings, the antioxidant characteristics of the leaves and roots under drought stress for revealing the drought resistance mechanism and to provide some theoretical basis for rare species conservation and vegetation restoration in desert area.

Methods Taking one-year-old seedlings of Gymnocarpos przewalskii as the experiment material and using pot experiment, four water gradients were set, including the control, light water stress, moderate water stress and severe water stress, the soil water content was kept at 45%-50%, 30%-35%, 15%-20% and 5%-10% of the field capacity respectively by weighing method, with 10 repetitions per pot experiment, leaves and roots were collected after being treated 90 d and the biomass and physiological indexes were measured. The difference in biomass, root-shoot ratio, malondialdehyde (MDA) content and antioxidant enzyme activities in leaves and roots was analyzed.

Results Under drought stress, biomass of the whole plant and the aboveground significantly reduced, the underground biomass decreased remarkably under the moderate and severe stress, and the aboveground biomass decreased more, thus the root-shoot ratio increased and was significantly higher under the severe stress compared to the control. MDA content in roots and leaves increased remarkably under drought stress compared with the control, the higher the drought stress degree was, the more serious the peroxidation damage was, and the increase amplitude of MDA content in roots was higher than that in leaves under the same treatment. With the increase of the drought stress, superoxide dismutase (SOD) activity in leaves and roots first significantly increased then decreased, it was obviously higher than the control in roots but significantly lower in leaves under severe stress, which indicated that the scavenging effect of SOD to reactive oxygen was limited especially in leaves. Peroxidase (POD) activity markedly decreased in roots but significantly increased in leaves under stress treatments compared to the control, showing that POD played obvious antioxidation in leaves, and POD was not the key enzyme scavenging H₂O₂ in the roots under drought stress. Catalase (CAT) activity increased significantly in leaves and roots under drought stress. Ascorbate peroxidase (APX) activity showed increasing trend under stress treatment, the difference was significant among the treatments in roots, and it changed markedly under moderate and severe stress in leaves.

Conculsions Drought stress clearly affected the growth of Gymnocarpos przewalskii seedlings, but it could increase biomass distribution to roots to adapt the drought. Drought stress caused obvious peroxidation damage to the leaf and root membrane system, and the damage was more serious in roots. The leaves protected the membrane system by synergistic action of SOD, CAT, POD and APX enzymes, and the roots mainly reduced damage of reactive oxygen by SOD, CAT and APX.