Effects Of Arbuscular Mycorrhizal Fungi On Resistance Of Greening Plants To Snow Melting Agent Stress

Snow melting agent(SMA)is the indispensable substance in winter in northern China.SMA based on chloride salt(CS-SMA)is used more and more.However,CS-SMA causes serious environmental problems during its utilization,such as soil salinization,groundwater pollution,green plants death,road corrosion,etc.Although environmental-friendly SMA(EF-SMA)is recommend more and more in recent years,its utilization is limited due to its expensive price.Under the fact that CS-SMA has to be consumed,one of the most available measures is to increase greenery plant tolerance to SMA.Arbuscular mycorrhiza(AM)fungi is one of the most widely distributed soil fungi in the environment,which could improve plant tolerance to saline-alkali stress and increase plant growth under stress conditions.However,it is little known how AM fungi affect greenery plants tolerance to SMA.In this study,we discussed the different effects of CS-SMA and EF-SMA on soil biological properties through soil-SMA cultivation experiment,studied the effects of AM inoculation on greenery plant tolerance to CS-SMA and the related mechanism through pot experiments,and clarify the possibility to increase plant tolerance to CS-SMA through combined effects of AM and polyaspartic acid(PASP).This study will provide reference for reducing the negative effects of CS-SMA on greenery plants and reducing urban greening maintenance costs.The main results are as follows:(1)Soil-SMA culture experiment showed that soil urease activity was stimulated by CS-SMA 150g/m2 but was inhibited by EF-SMA 150g/m’.Soil urease activity was slightly affected by EF-SMA 150g/m2 but was stimulated by EF-SMA 300g/m2.Soil microbial community was slightly affected by EF-SMA 150g/m’,while was significantly affected by CS-SMA 150g/m2,CS-SMA 300g/m2 and EF-SMA 300g/m2.In addition,biomasses of soil G+ and G-bacteria as well as fungi were significantly affected,but actinomycete biomass was slightly affected.(2)The pot experiment of urban greenery plants showed that the mycorrhizal inocolization rates in roots of sabina(Sabina vulgaris),manglietia(Iris ensata)and holly(Gaultheria fragrantissima)decreased with increasing CS-SMA concentrations(0,150 and 300g/m2).AM fungi enhanced the ability of greenery plants tolerance to CS-SMA stress.Sabina biomass reached a maximum increase of 69.35%relative non-mycorrhizal treatment at CS-SMA 400g/m2.In sabina and manglietia plants,CS-SMA stress caused higher SOD enzyme activity,higher MDA content,and lower chlorophyll content,while AM fungi inoculation reduced the degree of increase or decline of above indices.This indicates that AM fungi alleviated CS-SMA stress on two plants.In addition,AM fungi also alleviated the stress effects of CS-SMA on the physiological metabolism of holly relative to non-mycorrhizal plant,such as higher photosynthetic rate,transpiration rate and stomatal conductance,and lower intercellular CO2.AM fungi significantly increased the levels of K+,Ca2+,and Mg2+ in the aboveground and underground part of plant,but decreased Na+content.This may be one of the ways in which AM improves the plant tolerance to CS-SMA stress.(3)Determination on soil microbial biodiversity in rhizosphere of holly showed that the number of OTUs,Chaol index,ACE index and Shannon index decreased with increasing CS-SMA concentration,indicating CS-SMA could decrease microbial biodiversity in rhizosphere.After AM fungi inoculation,the degree of increase or decline of above indices reduced,indicating that AM fungi alleviated stress of CS-SMA on microbies in rhizosphere.Urease acivity in rhizosphere showed an increase at CS-SMA 150g/m2 and a decrease at CS-SMA 300g/m2,indicating that urese activity could be stimulated by certain CS-SMA while was inhibited by high CS-SMA.AM fungi inoculation reduced the inhibitive effect of CS-SMA on urease activity,indicating that AM fungi could reduce inhibitive effect of CS-SMA on plant growth.(4)The pot experiment on combined of AM and polyaspertate(PASP)showed that AM formation was inhibited by CS-SAM 300g/m2,while PASP could increase AM formation in sunflower.PASP alone or with AM fungi together could enhance plant tolerance to CS-SMA stress,and the positive effect increased with increasing PASP concentrations.Sunflower height and biomass were the highest at PASP 20g/kg.Under CS-SMA 200g/m2,AM and PASP alone could increase nitrogen content in sunflower,while the presence of PASP could increase AM function in nitrogen uptake.It was needed to point out that synergistic effect of PASP at 20g/kg was lower than that at PASP 10g/kg.The contents of K+,Ca2+,and Mg2+in aboveground and underground of sunflower showed similar trends as nitrogen concent.Under CS-SMA 200g/m2,AM and PASP alone could decrease Na+content in sunflower,while the coexisted presence of PASP and AM could cause lower Na+content.The synergistic effect of PASP at 20g/kg was lower than that at PASP 10g/kg.This experiment indicated that it is possible to largely reduce CS-SMA stress on plant by combined of AM fungi and PASP.