Research On Improvement Effects On Degraded Saline-Alkali Grassland By Bioremediation Measures In Songnen Plains

Songnen grassland is a Green ecological belt in the west of our northeast region, having higheconomic value and important ecological significance. However, Songnen grassland is sufferingfrom soil degradation, alkalization and salinization resulting from natural factor and long termunreasonable utilization.70%of Songnen grassland is suffering from alkalization and salinizationwith different degree, and this trend is increasing with1.5-2%. About20-30%of the grassland hasbecome saline spot, which is useless completely. Decreasing of Grassland area, degradation andmore animals made the grassland alkalization and salinization worse and constrain the developmentof animal husbandry. Treatment and recovery of grassland have become the major task in currentgrassland research filed.The research located in the west of Songnen plain, ligong village Saline wasteland of Haerbincity, Heilongjiang province, and randomized block design was used. The research planted annual{Echinochloa crusgalli Beauv.cv.dongsi No.1and Chloris virgata Swartz}, perennial {Puccinelliatenuiflora （Turcz.） Scribn. and Hordeum brevisublatum （Trin.） Link} plants with no planting grassfor control, also coupled with4(2kg m^-2,1.5kg m^-2,1kg m^-2and0kg m^-2,respectively)kinds ofmaize straw mulC.20treatments were designed in sum. We investigated the experimental site from2010to2012, and following factors were test: grass development pattern under planting and mulch,soil nutrient of saline wasteland from0-10cm and10-20cm level, pH value, the amount of cationexchange, exchangeable sodium, electrical conductivity and salt content. The activity of soilenzyme includes urease, invertase, alkaline phosphatase, cellulose, polyphenol and catalase. Theamount of microbial include bacteria, fungi and actinomycetes. We also used Real-time PCR andPCR-DGGE to determine the response of rhizosphere soil-microbial community and structurediversity of salt-resisting herbage to four kinds of mulch, to evaluate the recover effect of differentstraw mulch amount, to select optimal herbage and straw mulch amount used to Saline wastelandtreatment and verified, and to develop a perfect model use to local soil verified. The main researchconclusions are as follows:（1） The effects of bioremediation on vegetation recoverOverseeding mulched with straw can effectively maintain soil moisture and fixed seed, andseedling emergence, seedling and growth are improved obviously. Compared with0M, the height and biomass of P. tenuiflora and H. Brevisublatum with1.5M treatment in2012are increased by15.75and14.06%,15.99and13.08%, respectively; the height and biomass of E. crusgalli and C.virgata with2M treatment in2012are increased by6.59and27.9%,9.25and10.88%, respectively.（2）The effects of bioremediation comprehensive measures on soil nutrientBioremediation comprehensive measures can significantly improve the contents of soil organicmatter（SOM）, total nitrogen（TN）, total potassium（TK）, available nitrogen, available potassium in0-10and10-20cm depth, and the contents were positively correlated with salt tolerant forage grassplanting years. We found that the combination of P. tenuiflora or H. brevisublatum with1.5Mtreatment were most helpful for soil nutrient. The amount of soil TP was increased slightly afterplanting salt-resisting herbage3years.（3） The effects of bioremediation comprehensive measures on soil chemical propertiesBioremediation comprehensive measures can significantly decreased pH value, electricalconductivity, and exchangeable sodium content in0-10and10-20cm depth, and the contentsnegatively correlated with salt tolerant forage grass planting years. With the increase of plantingyears, Soil dissolved Cl^-，Ca²⁺amounts were increased, but SO2-4、HCO-3、K⁺、Na⁺、Mg²⁺decreasedthan before, soil chemical properties are improved after planting and mulch to some extent. Thecombination of H. brevisublatum with1.5M treatment showed best effects in all treatmentscomparison to test of three years.（4） The effects of bioremediation comprehensive measures on soil enzyme activitiesBioremediation comprehensive measures can significantly improve urease, invertase, alkalinephosphatase, cellulase, polyphenol oxidase and catalase activity in0-10and10-20cm depth, andthe enzyme activity positively correlated with salt tolerant forage grass planting years. Further more,the activities of urease, alkaline phosphatase, cellulose and catalase were significantly higher whenplanting P. tenuiflora or H. brevisublatum than annual and CK. The activities of sucrase,polyphenol were remarkable increased when planting C. virgata. In sum, the activities of sucrase,alkaline phosphatase I were largest increased under2M treatments when planting C.virgata,whereas urease, sucrase, alkaline phosphatase and catalase were largest increased under1.5Mtreatments.（5） The effects of bioremediation comprehensive measures on soil microbial amountsBioremediation comprehensive measures can significantly improve the amount of bacteria, fungiand actinomyces in0-10and10-20cm depth, and the amount were positively correlated with salttolerant forage grass planting years. In0-10cm depth, amounts of bacteria, fungi andactinomycetes with overseeding H. brevisublatum increased by39.49%,44.39%and48.40%,respectively. However, in10-20cm depth, amounts of bacteria, fungi and actinomycetes withoverseeding P. tenuiflora increased by27.78%,44%and49.98%, respectively. After three years ofcontrasting, planting P. tenuiflora or H. Brevisublatum with2M significantly increased the amountsof soil microbial in degradation alkaline grassland.（6） The effects of bioremediation comprehensive measures on rhizosphere soil microbial community sizeThe result of Real-time PCR in2012showed that the copy number of rhizosphere soilbactetium16S rDNA and fungi18S rDNA when overseeding H. Brevisublatum and P. Tenuiflorawere significantly higher than E. Crusgalli, C. Virgata and CK（P <0.05）, and1.5M is the highestcopy number of bacterial16S rDNA and fungi18S rDNA.（7） The effects of bioremediation comprehensive measures on rhizosphere soil microbialstructure diversityPCR-DGGE results showed that soil bacterium and fungi community structure were changedafter bioremediation comprehensive measures. Plant rhizosphere soil bacteria, fungi,Shannon-Weaver index, Simpson index and evenness index increased with straw. The structure ofrhizosphere soil bacterial and fungal community of different species mainly displayed in thebrightness of the DGGE bands, migration, lack of specific bands.In conclusion, bioremediation strategies（straw mulch and planting herbage） have enhanced soilnutrient amount in saline and alkaline grassland of Songnen plains, and decreased soil pH value aswell as improved soil chemical prosperities and amount of salt cations. Soil microbial and enzymeactivities have also been enhanced by these strategies. The result of PCR-DGGE showed that soilbacterium and fungi community structure were changed after planting and straw mulC.Rhizosphere soil microbial community size have also been impacted using planting and strawmulch remediation in the Real-time PCR view. The most important finding is that the combinationof1.5kg m^-2and planting perennial obtained the best remediation effect and should be popularized.