nfluence of exogenous melatonin and arbuscular mycorrhizal fungi on growth and physiological characteristics of Rosa chinensis seedling under salt stress

[ Objective ] Salt stress leads to poor growth and development and decreased ornamental quality of Chinese rose ( Rosa chinensis Jacq. ), and seriously affects their outdoor greening applications in high salt environments or coastal areas. This study explores the effects of exogenous melatonin ( MT ) and inoc- ulation with arbuscular mycorrhizal fungi ( AMF ) on seedling growth , chlorophyll fluorescence parame- ters , and cytokinin metabolism , and analyzes their physiological and the biochemical mechanisms that pro- mote rose to adapt to salt stress , in order to enhance salt resistance and expand the application of rose. [ Methods ] The seedling of Chinese rose variety ‘ Yueyue Hong ’ was used as experimental material to con- duct indoor potting experiments. In addition , control ( CK ), 100 mol / L NaCl stress , root administration of MT , and root inoculation of AMF larvae of the genus Claroideoglomus etatunicum and their combina- tion were set to investigate the effects of each treatment on the growth of rose seedlings , chlorophyll fluo- rescence parameters , hormone metabolism , and antioxidant system. [ Results ] ( 1 ) Application of MT pro- moted AMF infestation of the roots of rose seedlings and increased the infection rate , bush growth rate , number of vesicles , and invasion points. ( 2 ) Under salt stress , the growth of rose seedlings was inhibited , and plant height , stem thickness , and biomass were decreased significantly. MT and AMF treatments in- creased the height , stem thickness , and biomass of rose seedlings , whereas AMF+MT treatment had no significant difference in plant height and stem thickness , aboveground dry weight and underground dry weight were increased by 24.1% and 37.0%. ( 3 ) Under salt stress , the chlorophyll content of rose seed- lings was decreased significantly while chlorophyll fluorescence parameters were decreased , and MT and AMF treatments could improve the chlorophyll content and chlorophyll fluorescence parameters. Under AMF+MT treatment , the total amount of chlorophyll and chlorophyll a / b was increased by 46.2% and 67.2% , respectively. PSⅡ maximum photochemical efficiency ( F v / F m ), potential activity ( F v / F o ), ac- tual photochemical efficiency ( Φ PSⅡ ), effective photochemical quantum efficiency ( F v ' / F m ' ), and photo- chemical quenching coefficient ( q P ) were increased by 4.9% , 51.0% , 175.0% , 168.7% , and 92.5% , re- spectively , whereas NPQ was decreased by 42.7%. ( 4 ) Under salt stress , zeatin ( ZT ), gibberellin ( GA ), auxin ( IAA ) content in leaves were decreased , whereas the abscisic acid ( ABA ) content was in- creased. MT and AMF contributed to the increase in ZT , GA , and IAA content and the decrease in ABA content. Under AMF+MT treatment , ZT , GA , and IAA content were increased by 146.9% , 116.9% , 35.7% , respectively , while ABA was decreased by 21.1%. ( 5 ) Under salt stress , the activity of SOD and CAT were increased , and the rate of superoxide anions ( O - · 2 ) production and H 2 O 2 accumulation was in- creased. MT and AMF treatments decreased O - · 2 production rate and H 2 O 2 content , while AMF+MT treatment activated SOD and CAT activity , and reduced the rate of O - · 2 production and H 2 O 2 accumula- tion. [ Conclusion ] Inoculation with AMF , addition of MT , or AMF+MT treatment could increase the chlorophyll content of rose seedlings under salt stress , protect the chlorophyll fluorescence system , main- tain the balance of endogenous plant hormones , activate the activity of antioxidant enzymes such as SOD and CAT , and reduce lipid peroxidation and H 2 O 2 accumulation , thereby reduce the damage caused by salt stress to rose seedlings , promote rose growth , and enhance the salt resistance of rose seedlings better with AMF+MT treatment.