Physiological Responses Of Leymus Chinensis- Arbuscular Mycorrhizal Symbiont To The Interaction Of Nitrogen Deposition And Salt-alkali Stress

Nitrogen deposition is an important environmental factor affecting terrestrial ecosystems. Arbuscular mycorrhizal fungi (AMF), as a kind of widespread soil microbes, which symbiosis with most terrestrial plants, and significantly affected plant growth, nutrient uptake and resistance to stress conditions. Based on the problem of soil salinization increased salinity songnen plain soil and the current status of atmospheric nitrogen deposition, this research used Leymus chinensis and Glomus mosseae as the experimental material, simulated salt and alkali stress (NaCl:100 mM,200mM NaHCO3:100 mM,200mM) and simulated atmospheric nitrogen deposition (NaCl:100 mM,200 mM NaHCO3:100 mM,200 mM) in order to reveal an important role in the regulation of arbuscular mycorrhizal fungi on Leymus chinensis adapt to salt and alkali stress and physiological responses of symbiotic to nitrogen deposition. The main results of this study were summarized as follows:(1) Salinity stress significantly reduced the colonization rate and colonization intensity of AM, and the inhibitory effect of alkaline stress was much stronger. Under the different stress treatments, different forms of nitrogen deposition also inhibited the AM colonization effect, the inhibition was more obvious under NH4+-N.(2) Inoculation Glomus mosseae enhanced the biomass, photosynthetic parameters (Pn, Gs and Ci), and photosynthetic pigment content (chlorophyll a, b and Car) of Leymus chinensis seedlings under stresses, and the inhibitory effect of alkali stress was stronger. In addition, due to the different forms of nitrogen, the colonization effect of mycorrhizal fungi was decreased.(3) With the improvement of salt-alkali stresses, the seedlings of Leymus chinensis accumulated a lot of Na+, Ca2+, and Mg2+, and also inhibited the absorption of K+. Meanwhile, it has accumulated a large amount of Cl- to maintain the osmotic and ionic balance. Inoculation with AM fungi reduced the accumulation of Na+, and the decreases of K+ content was relieved under stresses, improving the content of NO3- to improve the ion balance of Leymus chinensis. Na+ content have increased under nitrogen deposition, and resulted in the Leymus chinensis-arbuscular mycorrhizal symbiosis decreased resistance to salt stress.(4) Salt stress has little effect on organic acid content of Leymus chinensis seedling. Under alkaline stress, the content of organic acid was increased. Inoculation of AM fungi decreased the content of organic acid. In addition, when the ammonium nitrogen was dominant (NH4Cl: NH4NO3=3:1), the organic acid content increased more significantly. There was no significant difference in organic acid content compared with -AM. Moreover, there was no significant accumulation of proline and soluble sugar in the symbionts under the salt-alkali stress after inoculation with AM fungi. Under ammonium nitrogen, the accumulation of the proline and soluble sugar was significantly higher than the nitrate nitrogen treatment.(5) Under salt-alkali stress, the activity of SOD, POD, CAT and APX were significantly increased by inoculation with AM, and enhanced the scavenging ability of oxygen free radicals in the host plant. In nitrogen deposition, especially under the NH4+-N, the antioxidant enzyme activity decreased significantly, which reduces the ability of active oxygen scavenging system, and influenced of AM fungi on Leymus chinensis saline resistance increase effect, and influenced the resistance effect of AM fungi on Leymus chinensis.