| Saline soils occupy 7%of the earth’s land surface and increased salinization of arable land will result into 50%land loss by the middle of the 21st century.In China,there are about 0.1 billion hm2 saline soil,0.02 billion hm2 coastal saline land.Soil salinity significantly reduces absorption of mineral nutrients,especially P because phosphate ions precipitate with Ca2+ ions in salt-stressed soil and become unavailable to plants.Nevertheless,the repeated and not proper applications of chemical P fertilizers can later lead to P pollution,and can lead to the loss of soil fertility by disturbing microbial diversity and reducing crops yield.Consequently,use of microbial inoculants(biofertilizers)including phosphate solubilizing microorganisms(PSM)and arbuscular mycorrhizal fungi(AMF)in remediation of coastal saline soil represents an environment friendly alternative to further applications of bio-fertilizers.The objective of this dissertation was to study the variation of soil enzymes activities,soil physical and chemical indicators when saline soil inoculated with PSF and AMF,and identification of the mechanism of two type’s soil microbes improving plant growth under salt stress.We organized a synthesis paper that first to select the best combination of fungi which stimulating plant growth.Then distinguish the optimal proportion of PSF and AMF which have positive effects on saline soil and stimulating plant growth.Based on this,the most effective quantity of the mix-inoculums of PSF and AMF to improve soil fertility was selected.Finally,establish the model of AMF,PSM and chemical fertilizer applicated in coastal saline soil.The main research contents and results as follows:(1)Two AMF(Glomus mosseae and Glomus aggregatum)and one PSF(Mortierella sp.)were inoculated in soil-sand culture,watered with four levels of salinity,to verify hypotheses that(a)inoculation of AMF and PSF can promote growth of the typical halophyte species(e.g.,Kosteletzkya virginica)under salt stress;and(b)inoculated microorganisms can synergistically influence enzyme activities(i.e.,invertase,catalase,urease,neutral phosphatase,and alkaline phosphatase)and available P concentrations of rhizosphere saline soil.The results indicated that the dual inoculation of AMF and Mortierella sp.significantly affected plant growth,but the triple inoculation was less effective.The increased enzyme activities and available P of soil after inoculation with AMF and Mortierella sp.may alleviate the negative effects of increasing salinity on plant growth.To obtain the maximum benefit for plant growth,it is needed to select the right combination of AMF and PSF,to be inoculated in saline soils.However,further research is needed to understand the underlying mechanisms.(2)Make use of the saline soil,which collected form seashore of Jiangsu province,we compared the effects of different proportioning of PSF(Mortierella sp.)and AMF on Castor bean growth and soil quality by evaluating plants biomass,soil enzyme activities,available P concentrations of saline soil in one pot experiment.The results showed combined inoculation of AMF and Mortierella sp.significantly stimulated soil enzymes activities(i.e.,urease,invertase,neutral phosphatase,alkaline phosphatase activity),improved the content of available P of saline soil,enhanced the ability of P-uptake of roots,and had positive effects on plant growth.The optimal proportion is 28.56:11.5×105 CFU(number of AMF spores:Ms colony)which have positive effects on saline soil and stimulate plant growth.(3)Under field conditions,one experiment was carried to evaluate the effect of different quantity of AMF and PSF on Castor bean plant growth,yield,and soil character(chemical,biological,and biochemical)in the rhizosphere soil.This study revealed that the mixed inoculation of PSF and AMF improved plant vitality and caused a dramatic increase in yield of dry matter and seeds in saline soil under field conditions.The mixed inoculums have a positive influence on saline soil fertility by stimutating soil enzymes activity,reducing EC,and increasing the available P and N contents of soil.The most effective co-inoculation to improve soil fertility was 20g/plant of AMF and Mortierella sp.(number of AMF spores was 78,Ms colony were 2.4×106 CFU).Therefore,it is possible that AMF and PSF in unsterilized soil could be managed in order to reduce external inputs.(4)One field experiment was devised to determine the effects of different levels of P or N fertilizers on mycorrhiza and PSM development,interaction between two factors and their effects on plant and saline soil quality response to salt stress.From the point of view improvement of plant growth,the results revealed that when soil inoculated with microbial inoculums,plant dry matter increasing with increasing P or N fertilizer level under field conditions.From the point of view saline soil quality,40g/plant of the mixture inoculums of AMF and Mortierella sp.(number of AMF spores was 185,Ms colony were 3.7×106 CFU)were applied with Superphosphate(30%P)120 kg/ha or Urea(46%N)240kg/ha per annum had the better effects on some indictors of soil quality.Fertilizer and bio-fertilizer had different effects on these indictors of soil quality(e.g.,Soil microbial community and soil enzyme activity)in different growth period.Because many soil enzymes are immediately responsive to soil disturbance or restoration,they can be used as indices of environmental stability and soil quality for sustainable management.Therefore,temporal changes in enzyme activities should be accounted for when evaluating the sustainability of land management practices. |
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