Effects of AMF on growth and chlorophyll fluorescence characteristics of the seedlings of two desert plant species under drought stress

The aim of this study was to investigate the effects of mycelial transmission distance of arbuscular mycorrhizal fungi (AMF) on growth and chlorophyll fluorescence characteristics of Alhagi sparsifolia and Tamarix ramosissima seedlings under drought stress, which is of great significance for maintaining the stability of ecosystem structure and function in desertified areas. In this experiment, Alhagi sparsifolia was used as the donor plant in a pot experiment, with Tamarix ramosissima as the receiver plant. The effects of short (15 cm, S) and long (30 cm, L) distance of mycelial transmission on AMF infestation rate, plant height, basal diameter, root morphology, and root structure as well as chlorophyll fluorescence parameters were investigated under different moisture conditions. The results showed that, under severe moisture conditions, the infection rate of Tamarix ramosissima significantly decreased in the L treatment (P < 0.05), with a reduction of 73.22% when compared with the infection rate under normal moisture conditions. Under D1 (soil relative moisture content, 40% ± 5%) moisture conditions, AMF significantly increased the plant height, stem diameter, biomass, specific root length, root average diameter, and root tip number of receiver plants in both S and L treatments. Under moderate moisture conditions, AMF reduced the damage caused by drought to the photosystem by increasing the F_m, F_v/F_o, F_v/F_m, and qP values of receiver plants in the S and L treatments and decreasing F_o and NPQ, thus improving the photosynthetic capacity. The differences in Tamarix ramosissima in the different hyphal transmission distance treatments were not significant. However, under severe moisture conditions, AMF only had a significant promoting effect on plants in the S treatment (P < 0.05) and no significant promoting effect on aboveground and belowground growth and chlorophyll fluorescence parameters of seedlings in the L treatment (P > 0.05). In conclusion, under moderate moisture conditions, AMF colonization can alleviate the damage caused by drought stress to the receiver plants by significantly improving their aboveground and belowground growth and photosynthesis, thereby enhancing their drought tolerance and growth. However, under severe conditions, L treatment was not conducive to mycorrhizal colonization and seedling growth and the promoting effect of AMF on the receiver plants was limited.