Screening And Application Of Salt-tolerant Phosphorusdissolving Fungi In Coastal Saline Soils Of The Yellow River Delta

The saline soil of Yellow River Delta is a typical coastal saline soil in China,which is the fastest self-renewing land resource in China’s land area and in the world,and it is an important back-up land resource with great potential for agricultural development.However,its water-salt movement continues to occur,leading to soil salinization,mainly in the form of poor soil structure,easy slabbing,and deviations in land quality.Studies have shown that phosphorus in saline soils is often immobilized by calcium,resulting in low biochemical effectiveness and difficulty in its improvement.The current phosphorus-dissolving microbial amendment of saline soils is a combination of economic and ecological benefits.Studies have shown that phosphorusdissolving microorganisms can increase the supply of active phosphorus in the soil,improve the inter-root microbial environment of plants,and regulate the secretion of plant growth hormones,etc.Most of the current studies on phosphate solubilizing microorganisms have focused on bacteria,and studies on phosphate solubilizing fungi are unclear and the number of phosphate solubilizing fungi adapted to saline soils is low.Therefore,there is a need to develop more fungi with salt-tolerant phosphorus solubilizing properties to meet the needs of agricultural development.At present,the association between soil available phosphorus and soil salinity in coastal saline soils of the Yellow River Delta is unclear,information on salt-tolerant phosphorus-dissolving fungi is insufficient,and the mechanism of salt tolerance promotion is unclear.Therefore,this article relies on the Shandong Base Experiment Station of the Institute of Geography of the Chinese Academy of Sciences in the Yellow River Delta,based on ITS gene sequencing technology,dilution plate screening bacteria and pot experiments.The following research components were carried out:(1)Analysis of changes in soil nutrients,wheat growth and microbial communities under different salt concentration environments;(2)To find the association of plant biomass with changes in soil nutrients and microbial communities at different salt concentrations;(3)Screening and identification of key salt-tolerant phosphorus-dissolving fungi;(4)To verify the effects of salt-tolerant phosphorus-dissolving fungi on the growth,soil nutrients and inter-root microbial communities of wheat in saline soils.The main findings were as follows:(1)The crop biomass,soil biochemical properties and microbial communities under three treatments of low salt stress(LS),medium salt stress(MS)and high salt stress(HS)at the Shandong Base Experimental Station of the Institute of Geography,Chinese Academy of Sciences in the Yellow River Delta were analyzed to clarify the effects of different salt stresses on crop growth,soil biochemical properties and microbial community structure.The biomass of wheat plants under low salt stress was2.64 times higher than that under high salt stress,the ratio of Na~+/K~+ in leaves was 1/4of that under high salt stress,the soil available phosphorus content was 2.20 times higher than that under high salt stress,and the changes in soil available phosphorus nutrients were significantly negatively correlated with changes in soil salinity(P < 0.01).The alkaline phosphatase activity in high salt stress decreased by 15.84%,and C:P and N:P increased by 13.34% and 17.32% compared to low salt stress.Secondly,the structure of soil inter-rhizosphere fungal communities differed significantly under different salt stresses,and at the genus level,the highest relative abundance in medium and high salt stress was in the genus Blumeria,and the highest relative abundance in low salt stress was in the genus Mortierella.The highest relative abundance in low salt stress was in the genus Mortierella.(2)Correlations between fungal communities and soil physicochemical indicators were analyzed by CCA and Mantel,and it was found that changes in fungal communities were mainly correlated with AP and TP at significant levels(P < 0.01);secondly,by constructing structural equation models,it was found that changes in soil TS led to negative changes in AP,which further positively influenced changes in soil fungal community composition and Mortierella,and subsequently produced positive effect on plant biomass(P < 0.05).(3)The fungal strains were isolated from saline soils by the plate dilution method,and a total of 8 strains of culturable salt-tolerant fungi were isolated,subsequent screening of phosphorus solubilizing fungi by NBRIP,and finally 4 target strains were screened,and the isolated strains were sequenced and compared with the sequences in the gene bank(Gen Bank).Strain S9 was identified as Mortierella alpina,P8 as Trichoderma harzianum,155 as Talaromyces flavus,and S5 as Penicillium oxalicum.(4)Five treatments were set up by pot experiments: no treatment control(CK),inoculation with Mortierella alpina(S9),Trichoderma harzianum(P8),Talaromyces flavus(155)and Penicillium oxalicum(S5).The test soil was saline farmland soil.The results showed that inoculation of S9,S5,155 and P8 reduced soil salinity by 11.56%,30.17%,40.06% and 17.76% compared with CK,and increased soil available phosphorus content by 12.11%,8.97%,12.68% and 10.85%,respectively;soil Nacetyl-β-glucosaminidase activity increased by 72.06%,86.77%,72.53% and 94.59%,respectively;soil alkaline phosphatase activity increased by 58.04%,72.92%,30.66%and 36.84%,respectively.Inoculation of S9,S5,155 and P8 increased the biomass dry weight of wheat plants by 57.28%,70.74%,12.21% and 11.74%,respectively,compared to CK;the abscisic acid content increased by 24.75%,21.95%,5.30% and24.59%,respectively;inoculation of S9,S5,155 and P8 significantly changed the fungal community structure.Among the OTUs in which enrichment occurred in abundance Chrysosporium and Preussia could promote plant growth hormone production playing a significant role in promoting plant growth,and the fungi whose abundance decreased were mainly Blumeria.The application of phosphorus-relieving fungi not only reduces soil salinity,activates soil nutrients and improves plant resistance,but also reduces the occurrence of plant diseases to a certain extent.In summary,this study concluded from field investigation experiments that the activation of phosphorus utilization in saline soils of the Yellow River Delta coast was gradually limited with increasing salt concentration.When the salt concentration decreases,the fungal species with certain phosphorus solubilizing properties gradually become the dominant species.Subsequently,the screening and potting experiments of phosphorus solubilizing fungi were conducted to explore the improvement mechanism of phosphorus solubilizing fungi on saline soils,and the microbial fungicides were successfully prepared to effectively promote plant growth and soil nutrient activation,which provided some theoretical support for the microbial improvement of coastal saline soils.