Mycorrhizal fungal colonization promotes apparent growth and physiology of Alhagi sparsifolia seedlings under salt or drought stress at vulnerable developmental stage

Alhagi sparsifolia is a dominant species in the lower Tarim River desert ecosystem and an important mycorrhizal symbiont. However, it is unclear how its seedlings cope with salt and drought stresses and develop effective survival strategies with the assistance of arbuscular mycorrhizal fungi (AMF) during their vulnerable growth stage. Therefore, in this study, we investigated the effects of salt or drought stress on the growth rate; nutrient uptake; photosynthesis; and the levels of antioxidant enzymes, osmoregulatory substances, and hormones in A. sparsifolia seedlings. We included following six groups: control/CK&Non-AMF (without salt or drought stress and no AMF inoculation), Drought&Non-AMF (drought stress and no AMF inoculation), Salt&Non-AMF (salt stress and no AMF inoculation), CK&AMF (no salt or drought stress and AMF inoculation), Drought&AMF (drought stress and AMF inoculation), and Salt&AMF (salt stress and AMF inoculation). The results revealed that AMF inoculation promoted seedling growth, particularly root growth and phosphorus nutrient uptake, in A. sparsifolia. Salt and drought stresses negatively affected the growth, photosynthetic capacity, and nutrient accumulation in the above- and belowground parts of the seedlings and stimulated the antioxidant defense system and accumulation of osmoregulatory substances in them. AMF inoculation under salt or drought stress could alleviate toxic symptoms in A. sparsifolia by promoting root growth, enhancing nutrient uptake, activating antioxidant enzyme activity, and regulating hormonal levels. These effects of AMF were mainly reflected in root growth under drought stress and in antioxidant enzyme activity under salt stress. The beneficial effect of AMF under salt stress was better than that under drought stress. This study demonstrated that AMF plays a significant role in assisting A. sparsifolia seedlings to quickly pass through the vulnerable growth stage under salt or drought stress. Therefore, A. sparsifolia seedlings with AMF have potential application in the restoration of desert ecosystems.