The Research Of Phosphorus Forms And The Phosphatase Activity In The Soil Of Water-Level-Fluctuating Zone In Pengxi River,Three Gorges Reservoir

After the impoundment of Three Gorges Reservoir,The Water-Level-Fluctuation Zone（WLFZ）was formed.Phosphorus is the limiting factor of water eutrophication,while soil phosphorus in the WLFZ is considered as the potential source of water phosphorus in the reservoir area.The soil in the WLFZ undergoes periodic flooding,and the soil environmental conditions change,which has an important impact on phosphorus transformation and cycle in the WLFZ.Organophosphorus is a high turnover form of phosphorus in the phosphorus pool of the WLFZ,and its mineralization process is catalyzed by phosphatase,but there is little research at present.Therefore,the study on the characteristics of phosphorus forms and phosphatase activities in the WLFZ soil and the relationship between them can provide a new way to understand the phosphorus cycle between the soil in WLFZ and the water body of the reservoir area.In this paper,the phosphorus forms and phosphatase activities of the soil in the WLFZ of Pengxi River in the Three Gorges Reservoir area were studied at different elevations,before and after flooding,and in the rhizosphere/nonrhizosphere ebb zone.The correlation between the phosphorus forms and phosphatase activities in the WLFZ was discussed.The community characteristics of alkaline phosphatase pho D gene of the bacteria in WLFZ were preliminarily explored.The phosphorus forms and phosphates of the soil in the flooded plant residues were studied The effect of acid enzyme activity.The main conclusions are as follows:The TP content in the WLFZ soil was 556.08±97.94mg/kg.The contents of TP,IP and OP increased with the increase of elevation,while the contents of H₂O-P_i,Na HCO₃-P_i and Na OH-P_i of active inorganic phosphorus were higher than those of shore soil.There was a significant positive correlation between HCl-P_i and Fe_ox,and between Na OH-P_o and P_mic and OM.Fe_ox and OM were the important factors affecting the spatial distribution of phosphorus in the soil.Compared with that before flooding,the OP content of the soil in the drainage zone after flooding decreased by 14.43%.The contents of H₂O-P_o and Na HCO₃-P_odecreased by 68.60%and 29.52%respectively,and the content of P_mic related to microbial biomass decreased by 6.58%.The content of inorganic phosphorus in H₂O-P_iand HCl-P_i decreased by 59.80%and 3.11%respectively,while that in Na HCO₃-P_iincreased by 11.75%.The Olsen-P content of the soil in the drainage zone after flooding was 3.67 times of that before flooding,which greatly improved the availability of soil phosphorus in the drainage zone.The concentration rate of TP in the rhizosphere was 42.37%.The enrichment rate of H₂O-P_o is 180.34%,and that of P_mic is 37.28%.The contents of IP,H₂O-P_i and HCl-P_i in the rhizosphere soil of WLFZ were significantly lower than those in the nonrhizosphere soil,and the uptake and utilization of inorganic phosphorus in the rhizosphere soil by plants was stronger than that in the rhizosphere.（2）The activities of acid phosphatase,alkaline phosphatase,phosphodiesterase and phytase were 1.40±1.07μmol PNP/（g·h）,2.60±1.62μmol p NP/（g·h）,0.44±0.25μmol p NP/（g·h）and 11.43±μmol P/（g·h）,respectively.Except for phytase,the sequence of soil phosphatase activity in the fallow zone was alkaline phosphatase>acid phosphatase>phosphatasediesterase.Except for phytase,the activity of phosphatase increased with elevation.Compared with that before flooding,the activities of acid phosphatase,alkaline phosphatase,phosphodiesterase and phytase decreased by 70.27%,66.47%,17.39%and 11.86%respectively.The activities of acid phosphatase,alkaline phosphatase,phosphodiesterase and phytase were enriched in the rhizosphere,the enrichment rates were 95.34%,76.07%,22.03%and 1.61%respectively.The phosphatase activity in the WLFZ soil is related to the plant and microbial biomass.The activities of acid phosphatase,alkaline phosphatase and phosphodiesterase were positively correlated with OM,Fe_ox,OM and Fe_ox are important factors affecting soil phosphatase in the ebb zone.TP and op were positively correlated with acid phosphatase,alkaline phosphatase and phosphodiesterase activities,H₂O-P_o and Na OH-P_o were positively correlated with acid phosphatase,alkaline phosphatase and phosphodiesterase activities,Olsen-P was positively correlated with phytase activities.The highest relative abundance of pho D gene community was proteus.The species richness of soil at 165m elevation in the WLFZ soil was higher than that at 145m elevation.（3）The pH value,DO concentration and ORP value of overlying water decreased sharply,TAPA activity increased,TP,TDP,SRP and DOP content increased after the plant residue flooded.The peak value of TP per unit cumulative release of plant+water group was 0.71 mg P/g plant,and the peak value of tapa activity per unit plant residue decomposition was 0.74μmol/（h·g plant）.There was a significant positive correlation between pH value of overlying water and SRP content in plant+water group,and a significant positive correlation between TAPA activity and TP,TDP,SRP content.PH value and TAPA activity are important factors in the process of phosphorus release from plant residues after flooding.After the plant remains flooded,the increase of H₂O-P_i,Na HCO₃-P_i and Na OH-P_i in the soil of the fallow zone accounted for 60.56%of the total increase of inorganic phosphorus.However,the content of H₂O-P_o in organic phosphorus had little change,and the content of Na HCO₃-P_o decreased by 8.06mg/kg,and the content of Na OH-P_o increased by 14.09mg/kg.The activities of acid phosphatase,alkaline phosphatase and phosphodiesterase in the soil decreased after flooding.There was a significant positive correlation between OM content and acid phosphatase activity and alkaline phosphatase activity after flooding,and the decrease of OM content was an important reason for the decrease of phosphatase activity.