Research On The Resources And Ecological Effects Of Arbuscular Mycorrhizal Fungi In Saline-alkaline Grassland Of Songnen Plain

Vegetation restoration is one of the most common and effective ways to combat soil degradation and prevent adjacent areas from further encroachment in many of the degraded regions. However, the poor water availability and nutrient supply are stressful for seed germination and/or seedling establishment in severely damaged areas. Successful revegetation with AM fungi has been reported in many degraded regions. To assess the role of AM fungi in vegetation restoration on saline-alkaline grassland, and provide theoretical and technological surpports, we conducted several researches with Leymus chinensis （Trin.） Tzvel, which included the investigation on the AM fungi resources surrounding roots of L. chinensis in saline-alkaline grassland, the indoor and outdoor experiments on the influence of AM fungi on saline-alkaline resistance of L. chinensis. The main results showed as below:1. From the 45 samples of saline-alkaline agrassland in western Jilin Province, we collected and identified 11 AMF species belonging to 4 genera. There were 8 species of Glomus, 72.42% of all speices, 1 species of Acaulospora, 1 species of Paraglomus, and 1 speices of Scutellospora. The AM colonization rates were between 30-60%, infection intensities were between 4-36%, and the spore densities were in 6-280 spores per 20 g soil surrounding roots of L. chinensis. There were negative relationships between pH of soil and colonization rate, infection intensity or species aboundance.2. There were negative relationships between species diversities and colonization rate and infection intensity of AM fungi to L. chinensis roots, but no relationship to CR and II of AM fungi to roots of Puccinellia tenuiflora or Carex duriuscula. These results showed that the influence of AMF to community diversity might be intermediated by their effects on species with high competitive ability. The community biomass increased by the increasing of AMF coloniation to roots, which suggested that the AMF-plant symbiosis impoved the accumulation of dry matter, and plant growth. This improvement of biomass mainly performed by AMF- L. chinensis symbiosis. As the saline-alkaline condition became intensive, the AMF species richness decreased, which from 5 species in pure L. chinensis community to 2 （G. mosseae and G. geosporum） in seriously saline-alkaline communities. However, the G. mosseae was always the dominant species in all communities. The AM fungi species number and spore density significantly increased with the increasing of nutrient concentration and organic matter content of soil, but decreased with the increasing of pH and electric conductivity of soil. There were significantly seasonal changes of colonization ability of AM fungi, which might resulted by the climate or soil moisture.3. The mycorrhizal growth response （MGR） was high when plants of L. chinensis were under intensive salt stress. The salinity response （SR） was significantly dereased by AMF- L. chinensis symbiosis. Therefore, the AMF- L. chinensis symbiosis was important for plant survival under salt stress. The biomass allocated to aboveground and belowground was changed by AMF wherever under salt or non salt environments. Mycorrihal L. chinensis allocated more biomass to roots, which enhanced the ability of absorbing and transfering water and nutrients. After colonized by AMF, the L. chinensis maintained higher N and P concentration, however, this advantage decreased by the increasing salt stress. There were higher Ca²⁺ concentration under low salt stress, and higher K⁺ concentration under middle and high salt stress in mycorrihal L. chinensis. The concentrations of Na⁺å’ŒCl^- were both lower in mycorrihal L. chinensis. Under high salt condition, the K⁺/Na⁺ of mycorrihal plant was higher than that of non-mycorrihal plants, however, under lower and non salt conditions, it was P/Na⁺ of mycorrihal plant that higher than that of non-mycorrihal plants. The results indicated that the saline-resistant ability of mycorrihal plants was increased by mycorrhizal P response （MPR） under lower salt stress, but by mycorrhizal K response （MKR） under high salt stress.4. The effects of P, salt stress and AM inoculation on biomass and ion contents of L. chinensis were complicated, which also influence the transformation of mutualism and parasitism of AMF- L. chinensis symbiosis. With the increase of P, the Na⁺ content of non-mycorrihal plants significantly decreased, and P/Na increased. As a result, the salinity response （SR） dereased for the non-mycorrihal plants. Under the salt stress condition, the mycorrihal growth response increased with the increasing P concentration, but decreased with the increasing P concentration without salt stress. The relationship between AMF and L. chinensis changed from mutualism to parasitism when the P supply of soil increased.5. The G. mosseae and G. geosporum could inoculate the L. chinensis in bare saline-alkaline soil. The improvement of survival, growth and asexual reproduction of inoculated plants indicated that the plant-AM fungi mutualism could improve the reestablishment of vegetation in bare saline-alkaline soil, drive the vegetation restoration to a community dominated by original species. Association with AM fungi increased the absorption of N, P, K⁺, Ca²⁺, but decreased Na⁺ and Cl^- uptake under saline-alkaline stress. The AMF enhanced the ability of plant to absorb nutriets from soil, which helped reduce the negative effect of salt stress on plant growth. Plants inoculated with AM fungi accumulated significantly higher root/shoot ratio than non-inoculated plants, which suggested that the significant higher root/shoot ratios of inoculated plants growing in three years might be a more important contributor for the successful establishment of plants under severe salt stress. The successful colonization by AM fungi under same severe saline-alkaline soil in both pot and field experiments implicated that the low natural colonization of non-inoculated plants in bare saline-alkaline land was resulted from the absence of propagules of AM fungi.