Effects of arbuscular mycorrhizal fungi on photosynthesis, ion balance of tomato plants under saline-alkali soil condition

Arbuscular mycorrhizal fungi (AMF) affect plant metabolism in different ways and help plants resist stress. In this study, AMF were added into substrate to cultivate mycorrhizal seedlings of processing tomato (Lycopersicon esculentum Mill.). These mycorrhizal seedlings were then transplanted into moderate saline-alkali soil and the physiological aspects of AMF in reducing the harm from saline-alkali soil were studied. The results show that saline-alkali soil inhibited plant growth. With the addition of AMF to the substrate, the tomato plants and AMF formed a symbiotic relationship that significantly improved the growth of plants and increased the concentration of soluble solids, vitamin C (VC), soluble sugar and lycopene in the fruit. AMF promoted tomato plants absorption of nitrogen (N) and reduced the absorption of Na+. AMF restricted the transport of Na+ from roots to shoots in plants, which increased K+/Na+, Ca2+/Na+, and Mg2+/Na+ in leaves and stems, in addition to protecting the photosynthetic organs from damage. AMF also increased the chlorophyll concentration, net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (Tr) of plants. The addition of AMF also optimized the microbial community structure in the plant rhizosphere by increasing the density of bacteria and actinomycetes and reducing the density of fungi. On the other hand, AMF also enabled the tomato plants to accumulate more soluble sugars and proline and alleviated oxidative damage to plant leaves under saline-alkali stress. AMF promoted plant growth and reduced the harm to plants from saline-alkali soil by optimizing the physiological processes of tomato plants under saline-alkali stress.