三峡库区消落带4种典型植物根际土壤养分与氮素赋存形态

Nutrient Characteristics and Nitrogen Forms of Rhizosphere Soils Under Four Typical Plants in the Littoral Zone of TGR

三峡水库消落带土壤N循环受到植被覆盖和季节性淹水的影响,对三峡水库水质具有潜在的不利影响,进行消落带植被恢复和提高土壤N保持能力成为保护库区水环境的重要措施.选择三峡库区一级支流澎溪河消落带为研究对象,分别在冲积潮土、紫色土和水稻土分布区采集狗牙根、香附子、苍耳以及玉米这4种典型植物根际、非根际土壤,分析了根际与非根际土壤理化性质与N赋存形态特征,并比较了不同植物类型根际富集效果,初步探究不同植物根际效应对消落带土壤N循环的影响.结果表明,所有植物根际土壤p H均低于非根际,有机质、全氮、全磷、速效氮均高于非根际,且根际富集率表现为香附子>狗牙根>玉米>苍耳;不同植物根际对土壤全钾、有效磷、速效钾影响作用不一致;植物根际土壤中可转化态氮TF-N及其不同赋存形态离子交换态氮(IEF-N)、碳酸盐结合态氮(CF-N)、铁锰氧化态氮(IMOF-N)和有机态和硫化物结合态氮(OSF-N)均高于非根际土壤,植物根际效应能够改变土壤N赋存形态及其对N循环的贡献率,但狗牙根和香附子根际土壤中TF-N占TN的比率低于非根际,而玉米和苍耳相反,表明消落带玉米和苍耳覆盖加快了N素向TF-N转化,不利于土壤N素保持;消落带土壤有机质、总磷和有效磷含量与可转化态N形态显著相关,是土壤N形态转化的主要因素.研究表明,消落带狗牙根和香附子覆盖对土壤N素的保持优于玉米和苍耳,植物根际效应对消落带土壤N循环的影响为消落带植被恢复中植物选择提供了参考.

The Three Gorges Reservoir( TGR),which is the largest water conservancy project ever built in the world,produced a drawdown area of about 348. 93 km2 because of water level control. The biological geochemical cycle of the soil in the drawdown zone has been changed as the result of long-term winter flooding and summer drought and vegetation covering. The loss of soil nitrogen in the drawdown zone poses a threat to the water environmental in TGR. Pengxi river,is an important anabranch,which has the largest drawdown area has been selected in the present study. The four typical vegetation,contained Cynodon dactylon,Cyperus rotundus,Anthium sibiricum and Zea mays L. as the control,were studied to measure nutrient characteristics and nitrogen forms of rhizosphere and non-rhizosphere soils in three distribution areas with different soil types( paddy soil,purple soil and fluvo-aquic soils). The variables measured included organic matter( OM),total nitrogen( TN),total phosphorus( TP),total potassium( TK),hydrolysis N,available P and available K,p H,ion-exchangeable N( IEE-N),weak acid extractable N( CF-N),iron-manganese oxides N( IMOFN),organic matter sulfide N( OSF-N),added up four N forms for total transferable N( TF-N) and TN minus TF-N for nontransferable N( NTF-N). The results showed: 1 p H of rhizosphere soil was generally lower than that of non-rhizosphere soil under different vegetation in different type soils because the possible organic acid and H+released form plant roots and cation absorption differences,and the OM,TP,TN and hydrolysis N of rhizosphere soil were generally higher than those of non-rhizosphere soil,and that the enrichment ratio( ER) of all the four nutrient indicators showed Cyperus rotundus > Cynodon dactylon > Zea mays L. > Anthium sibiricum. Available P showed enrichment in the rhizosphere of three natural vegetations but lose under corn,and available K,TKshowed different ER in different conditions. 2 IEF-N CF-N,IMOF-N,OSF-N and TF-N of rhizosphere soil were generally higher than those of non-rhizosphere soil,but the TF-N to TN ratio in rhizosphere of Cyperus rotundus and Cynodon dactylon were lower than those of non-rhizosphere soil,and in rhizosphere of Anthium sibiricum and Zea mays L. were higher,the rhizosphere effect of different vegetations on the N cycle was significant difference. 3 the correlation between nutrient characteristics and nitrogen forms was evaluated to explore the influence factor for the N forms changing. There was a significant correlation between soil OM and four N forms,TP was significantly correlated with CF-N,OSF-N,TF-N,and soil available P content was significantly negatively correlated with IMOF-N,OSF-N,TF-N and TN. Our research could provide that the drawdown zone covered with Cyperus rotundus and Cynodon dactylon was better than Anthium sibiricum and Zea mays L. to improve soil N holding and fixation. The vegetation recovery in the drawdown zone should consider the rhizosphere effect of different vegetations on N cycle.