Effects Of Arbuscular Mycorrhizal Fungi On Growth And Photosynthesis In Melon Seedlings Under Weak Light With Salt Stress

Arbuscular mycorrhizal fungi (AMF) form a mutualistic symbionts with plant roots, many researches showed that AMF can help to improve plant stress resistance. Study including AMF on various measures and methods of improving the efficiency of cultivation facilities, have a broad application value and realistic meaning. Cucumis melon, as one of the important horticultural crops, in the cultivation of the sunlight greenhouse, especially in the southwest of China, is often faced with the problem of insufficient light and salt accumulation. In this study, a systematic study was conducted on the physiological and photosynthetic mechanisms of'zhongmi NO.3' inoculated with AMF in the low light and salt tolerances, the main results were as follows:(1) Salt stress will hinder the formation and development of arbuscular mycorrhizal, but the single weak light factor had no significant effect on the infection rate of mycorrhizal fungi. Weak light and low concentration of salt composite treatments will promote plant aboveground spindling, while high concentration of salt stress inhibited the growth of the underground, but AMF can effectively inhibit the above two kinds of adverse effects. At the same time, plants inoculated with AMF can effectively inhibit the above two kinds of adverse effects. In addition, plant inoculated with AMF can increase material accumulation under weak light; and salt stress can transiently increase the starch content of plant leaves, and AMF can promote and prolong the effect.(2) Plants began to appear symptoms of salt injury When the rhizosphere EC value reached 3.0 ms·cm-1, performance for yellow leaf edge, the plants withered and even death after continue to irrigate, but AMF could protect the root system by increasing the salt absorption of the plant rhizosphere and reducing the salt concentration. Within a certain degree of stress and time, AMF can resist and alleviate salt stress by reducing MDA content in plants. A single factor of weak light can also cause membrane lipid peroxidation to some degree of damage, but AMF can reduce the damage in a certain extent. and AMF can to some extent reduce membrane lipid over oxidation of plant damage; AMF inoculated plants increased the proline content decreased root Pro content to strengthen plant osmotic adjustment ability. Melon inoculated with AMF can increase the free proline content in leaves but decrease the content in roots to enhance the osmotic adjustment ability.(3) The changes of superoxide dismutase (SOD), peroxidase activity (POD) and catalase activity (CAT) were the same as the synergistic action under weak light and salt stress, and AMF can increase the activity of antioxidant enzymes to enhance the ability of scavenging free radicals in plants. Low concentration salt stress can accelerate the adaptation of plant antioxidant system to weak light. AMF can accelerate the activity of catalase (CAT) and shorten the time of plant adaptation to stress.(4) Transient low concentration salt treatment can promote the formation of photosynthetic pigments in the leaves of plants under weak light, thus improving the ability of plants to enhance the weak light tolerance and promote the growth of plants under weak light, While the high concentration of salt resulted in the decomposition of photosynthetic pigments in the early stage of stress. AMF has the function of maintaining the stability of plant cells, enhancing and maintaining the double tolerance of plants under weak light and salt stress.(5) Under the effect of the salt and weak light stress, the light absorption of plants could be promoted in a short time, which was consistent with the changes of the photosynthetic pigment, and AMF could make the effect more obvious. Salt stress will damage the PS ? reaction center and with the increasing of salt concentration and stress time increased, the AMF effect will also disappeared. Excitation energy divergence of PS ? in leaves of Melon under weak light will change. Through non photochemical quenching, the leaves can improve the heat dissipation and consume the excess excitation energy in order to adapt to the weak light environment, and AMF and salt stress showed a negative synergistic effect.(6) Adversity effect on plant location and function time are both different, and a short time of low concentration salt treatment would promote the light absorption and the primary light energy conversion efficiency (Fv/Fm) of the PS ? to a certain extent in the plant leaves. In the photosynthetic electron transport rate (ETR) and net photosynthetic rate (Pn) change trend is inconsistent, which led to a completely inconsistent change in the photosynthetic electron transport rate (ETR) and the net photosynthetic rate (Pn). The weak light and salt stress had a synergistic effect on reducing plant net photosynthesis, and AMF promoted the net photosynthetic rate (Pn) of leaves. AMF can increase the light saturation point (LSP) of the blade under stress under the weak light and salt stress and the mximum net photosynthetic rate (Amax) under high salt concentration stress, but it also improves the optical compensation point (LCP) in the lower light radiation. Low salt treatment and inoculation of AMF have a synergistic effect on improving the dark respiration rate (RD) in the leaves of melon seedlings.(7) Stomatal conductance (Gs) and transpiration rate (Tr) in the same trend, but there was no significant correlation with net photosynthetic rate (Pn). The main factor of the decline of photosynthetic rate in leaves was non stomatal limitation under the single factor of weak light, while plants under the common stress was affected by stomatal limitation and non-stomatal limitation, in the same time, plants inoculated with AMF can significantly reduce the stomatal limitation factor (Is) and promote the plant to adapt to the stress environment more quickly under salt stress.