| Puccinellia tenuiflora is a plant belonging to the genus Puccinellia,which is widely distributed in the Songnen saline-alkaline grasslands in the northeast.The characteristic of salt and alkali tolerance makes it a pioneer plant in this region.It is also a kind of herbage with high quality and has good effects on soil improvement,so P.tenuiflora was also cultivated in large areas for application in animal husbandry and soil improvement.AMF is a kind of beneficial fungi in soil,who can increase the plant's tolerance to stress and improve soil physical and chemical properties.These functions are benefited from the mycorrhizal structure.AM fungi can establish a symbiotic relationship with 80%of the plants on the land and form a mycorrhizal structure.The large mycelium network underground promotes the connection of plant roots,soil and microorganisms.AM fungi invade the plant roots and form arbuscular structures to exchange nutrients with the plants to meet their own growth needs and provide them with a steady stream of nitrogen sources byactivating the organic substances.For their own reproduction,they secrete large amounts of vesicles.In this study,the plant materials needed for the experiment were P.tenuiflora.The dom:inant arbuscular mycorrhizal fungi,Funeliformis mosseae and Rhizophagus intraradices,which were identified in the previous study,are the inoculants.All above are used to explore the effect of AMF on the physiological characteristic of P.tenuifolia under NaCl and NaHCO3.At the time of sowing,arbuscular mycorrhizal fungi are also colonized in soil.Salts(NaCl)and alkali(NaHCO3)are individually stressed after 80 days of sowing.The concentration range of stress is 0 to 400 mM,and the stress gradient is 100 mM.After stress treatment for 10 days,growth and physiological indexes are measured.The experimental results are briefly summarized as follows:1.After 80 days of sowing,the arbuscular mycorrhizal fungi formed a symbiotic relationship with P.tenuiflora.However,arbuscular abundance,colonization rate,vesicles abundance,and the colonization density have a certain degree of reduce because of high saline-alkaline stress concentration.The colonization indexes reach the lowest value when the stress concentration is 400 mM.At this time,the infestation density of P.tenuiflora after inoculation with F.mosseae on NaHC03 stress is reduced to 0.9%,and the vesicle abundance is 0.07%,and the arbuscular abundance is only 0.06%.While the colozization density of P.tenuiflora roots inoculated with R.intraradices was reduced to 1.3%,and the abundance of vesicles is only 0.12%.In general,the colonization indexes of P.tenuifolia roots after inoculation with R.intraradices are lower than that of F.mosseae.2.The above results indicate that F.mosseae and R.intraradices have formed a symbiotic system with P.tenuiflora respectively.Based on this,this study investigates the growth index changes of P.tenuiflora under salt and alkali stress,including dry weight,fresh weight,root length,leaf length,tissue water content,and water saturation deficit.The results show that both inoculations with two kinds of arbuscular mycorrhizal fungi could increase the growth of P.tenuiflora.In general,the inoculation of R.intraradices have a significant effect on the growth of P.tenuiflora.However,only at certain specific stress concentrations,the promotion effect of inoculation with F.mosseae is greater than that of inoculated with R.intraradices.For example,the dry weight of P.tenuiflora colonized with F.mosseae was higher than that of colonization with R intraradice under 400 mM NaCl stress.3.In addition to growth indicators,this study investigates the effects of two arbuscular mycorrhizal fungi,F.mosseae and R.intraradices,on physiological indexes of P.tenuiflora leaves under NaCl and NaHCO3 stress,which includes soluble sugar,chlorophyll,tannin,phenolic acid and flavonoid content,also SOD,POD,CAT,PPO and PAL activity.The results show that the content and activity of the above physiological indicators almost reach a peak at a concentration of 200 mM.In this study,this two kinds of AM fungi can increase the chlorophyll content,thus improving the photosynthesis of P.tenuiflora;increasing the soluble sugar content to maintain the structure and osmotic balance of P.tenuiflora cells;AM fungi also increase the antioxidant enzyme activities of P.tenuiflora and the metabolism of enzymatic reactions accordingly.Substances of tannins,phenolic acids and flavonoids are also accumulated to deal with the damage caused by saline-alkali stress.From the physiological point of view,NaHCO3 stress has a great influence on the physiological indicators of P.tenuiflora.At the same time,P.tenuiflora is found to inhibit growth when NaCl and NaHCO3 concentrations were greater than 200 mM,indicating that 200 mM is the critical concentration for growth of P.tenuiflora under these two stresses.4.The improvement effects of F.mosseae and R.intraradices on increasing the tolerance of P.tenuiflora to salt and alkali also appears in selective absorption of metal ions.In this study,the contents of metal ions K,Ca,and Na in the upground and underground parts of P.tenuiflora under stress conditions are determined.The results show that AM fungi can promote the accumulation of K+ and Ca2+ and reduce the accumulation of Na+.However,Na+ content in P.tenuiflora also tends to increase gradually with the increase of the stress concentration.AM fungi have the most significant effect on reducing Na+ content in the unground part of P.tenuiflora under NaHC03 stress.In addition to 100 mM,inoculation of any arbuscular mycorrhizal fungi could effectively reduce the accumulation of Na+ in the unground part of P.tenuiflora and reached a significant level(P<0.05). |
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