Influence Of Plants-microbes On Phosphorus Forms In Tidal Wetland

Excess phosphorus input is one of the main factors for water eutrophication. Coastal watereutrophication and the resulting impact on the tidal flat ecological environment caused byphosphorus pollution has become a major global environmental issues today. The tidalwetlands can prevent coastal waters eutrophication by reducing the offshore pollution of riversinto the seam, especially phosphorus nutrition salt. The retention for phosphorus nutrition intidal wetland mainly through biological processes such as plants–microbial absorption andutilization and abiotic processes such as physical and chemical mechanisms. Compared withphysical and chemical mechanisms to the phosphorus retention, biological mechanismsincluding plant, microorganisms and enzymes is not clear currently. Therefore, this studyinvestigated in the temporal and spatial distribution of soil phosphorus forms, phosphorusbacteria and alkaline phosphatase activity from Hangzhou Bay tidal flat, together with soilcharacteristics, and evaluated the phosphorus purification ability of Phragmites australis （PA）by simulation wetland.The main conclusions are as follows:The numbers of three major groups （Bacteria, Fungi and Actinomycetes） in soils werecounted separately, the number of microorganisms changed distinctively in four months. In thesoil microorganism profile, bacteria was most abundant and determined the number of thewhole community in the four type of soils, which accounted more than98%in the fourmonths.Compared with the bare flat, soils from the vegetations had more microorganisms，aswell as the phosphorus bacteria. Biolog-Eco technique were utilized together for microbialcommunity analysis. The results showed that the vegetatation might facilated microbialcommunity. There some differences of microbial functional diversity were observed amongdifferent vegetation types. In0-5cm and10-20cm soil PA had the most largest K value, fromcurve fitting, bare flat（CK） came last, Scirpus mariqueter（SM） was in the middle level on thewhole. Microbial community of Bare Flat soil had higher richness indicated by McIntosh index. This suggested that microbial communities of Bare Flat soil may had more species than the soilwith vegetation preliminarily. Microbial community were no significant differences in theSimpson index. It seemed that because of a very short succession time of Hangzhou Baywetlands, vegetation deveolpment did not changed the microbial community speciescomposition remarkbley. Four kinds of soil microbial communities had similar dominantspecies.Soil inorganic and organic phosphorus were measured using continuous extractionmethods separately. Exchangeable phosphorus（Exch-P） content, iron/aluminum boundphosphorus（Fe/Al-P） content and calcium bound phosphorus （Ca-P） content were all highestin May and lowest in February, with significant differences between May and February（p<0.05）. For labile organic phosphorus （L-P） content, it was highest in July, followed by May,October and February; for moderately labile organic phosphorus （ML-P） content, it washighest in February, followed by May, October and July; while for nonlabile organicphosphorus （NL-P）, it was not significantly different among the four months. There weresignificant temporal and spatial variations of alkaline phosphatase activity in the intertidal soils.Alkaline phosphatase activity was the highest in July (104.74³8.59mg·kg^-1· h^-1)and thelowest in February (40.61⁸.21mg·kg^-1·h^-1). Significant differences of alkaline phosphataseacitivity were detected among four months （p<0.05）. The vegetation types aslo affectedalkaline phosphatase activity and significant differences were found between Bare flat（CK） andother types （p<0.05）. The soil lkaline phosphatase activities for the different vegetation typeswere as follows: CK(49.50⁸.21mg·kg^-1·h^-1), PA(104.63³9.72mg·kg^-1·h^-1), Spartinaabcerniflora（SA）(73.23³2.18mg·kg^-1·h^-1) and SM(83.48⁹.68mg·kg^-1·h^-1). The alkalinephosphatase activities were significantly correlated to the numbers of organic phosphatebacteria（r=0.58,p<0.01）. It suggested that number of organic phosphorus bacteria may controlalkaline phosphatase activities. Furthermore, soil alkaline phosphatase activities werepositively correlated with Fe/Al-P （r=0.39, p<0.05）, and L-P （r=0.37, p<0.05）, NL-P （r=0.31,p<0.05）. It suggested that NL-P may be a potential phosphorus source of in the tidal flatwetland. Different concentrations of phosphorus treatment, T1(0.6mg·L^-1), T2(1.6mg·L^-1), T3(2.0mg·L^-1), was used to study the PA wetland root box on the overlying water and soilpurification rate of phosphorus phosphorus transformation. The purification rate of overlyingwater phosphorus increased rapidly within0-4days, then fluctuated at a certain range.Compared with CK, rootbox with PA had significant differences at T1levels（p<0.05）.Therewas is no significant difference at T2and T3, but in the whole course of the experiment, thePA simulated wetland purification rate between4.05%¹2.16%and2.87%¹4.51%. Thegrowth of PA did not significantly affect the distribution of the total phosphorus（TP） in the soil,but effectively promote the accumulation of total organic phosphorus （TOP）, and the reductionof the total inorganic phosphorus（TIP）. Due to the absorption of the PA, Exch-P weredecreased an average of a38%reduction at T1,52.1%at T2and31.1%. T3, compared withCK. Al/Fe-P was significantly less than other（p<0.05） at S0of PA rhizobox. Meanwhile,Al/Fe-P was less than CK at S1, S2, S3, S4of three treatments. Microbial communitymetabolic activity performanced: S0was largest, then was S1, S2and T1. S3, S4was at thesame level with S2. It performanced from largest to smallest in S0to S4at T2and T3. Itsuggested that the growth of PA enhanced the absorptive ALP activity of the overlying water ofphosphorus and distribution of soil phosphorus forms by effectting on the surroundingenvironment and microbial activity indirectly.