Seedling physiological characteristics of Viola phillipina under salt and drought stress

To investigate the effects of different levels of salt, drought and cross-stress on the physiological and biochemical characteristics of Viola phillipina seedlings, 16 treatments of single salt stress (NaCl concentration: 0, 0.2, 0.4, and 0.6%), single drought stress (soil field water-holding capacity: 80, 65, 50, and 35%) and salt and drought cross-stress were established, and 0 NaCl concentration and 80% field water-holding capacity treatments were used as the control, to determine the malondialdehyde (MDA) content in the leaves of the plants under the treatments, and the activity of antioxidant enzymes, osmotic adjustment substances and chlorophyll content. The results showed that MDA, soluble protein (SP), soluble sugar (SS) and proline (Pro) contents increased with an increase in salinity and drought stress; peroxidase (POD), catalase (CAT) and superoxide dismutase (SOD) activity first increased and then decreased, however, POD activity remained higher than that of the control at 0.6% NaCl and 35% of field water-holding capacity under severe salt–drought stress; the chlorophyll content increased and then decreased. POD activity remained higher than that of the control at 0.6% NaCl and 35% of field water-holding capacity, and chlorophyll content increased and then decreased. POD is an antioxidant enzyme that plays a major role in Viola phillipina seedlings when facing high salt and severe drought stress. Affiliation function analysis showed that Viola phillipina seedlings exhibited strong salt and drought tolerance under the cross-treatment of 0.6% NaCl and 65% field water-holding capacity during mild droughts.