三峡库区消落带典型植物根际土壤磷形态特征

三峡库区消落带生态系统演变对水库安全具有重要影响,其中植物群落演变与土壤氮磷形态转化及释放等广受关注。然而,消落带植物根际效应与土壤磷形态关系及潜在影响并不清楚。选择三峡库区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的消落区采集典型草本植物(狗牙根、香附子、苍耳)和农作物(玉米)根际、非根际土壤,分析无机磷和有机磷的形态特征,探讨了消落带典型植物生长对土壤磷形态的根际效应及潜在影响。结果表明,土壤类型对土壤磷含量及磷赋存形态具有显著影响,紫色土磷含量最高,且活性磷含量低于冲积潮土和水稻土,表现出磷库稳定性较高;4种植物根际土壤全磷、有效磷及不同形态无机、有机磷(弱吸附态磷WA-P、潜在活性磷PA-P、铁铝结合态磷Fe/Al-P、钙结合态磷Ca-P、残渣态磷R-P)含量均高于非根际,表现出明显的根际富集效应;不同植物根际土壤全磷和有效磷表现为狗牙根苍耳香附子玉米,但磷形态在不同植物根际富集水平不同:活性较高的WA-P、PA-P含量在玉米和苍耳覆盖区均高于狗牙根和香附子,而较稳定Ca-P_i、R-P_i、Fe/Al-P_o、Ca-P_o含量在狗牙根和香附子覆盖区更高,表明玉米和苍耳生长有利于稳定性磷的活化,提高消落带土壤磷流失风险。不同植物根际对不同形态磷富集率差异明显,且玉米根际对活性磷形态的富集率最高,表明农业活动可能加速土壤稳定性磷的活化。pH、土壤有机质、土壤容重与无机磷的赋存形态关系密切,而有机磷赋存形态受pH影响显著,植物根际有机质积累和有机酸分泌等是影响土壤磷形态变化的主要因素。消落带植物群落演变及恢复对土壤磷形态转化具有重要影响。

Phosphorus forms in rhizosphere soils of four typical plants in the Littoral Zone of the Three Gorges Reservoir

Three gorges reservoir (TGR), the largest water conservancy project ever built in the world, with about 348.93 km² of littoral zone produced due to the water level control, attracted more and more attention for its fragile environment. The variation of plant community and nutrient-release of the soil in the littoral zone, which were caused by long-term winter flooding and summer drought, are of great concerns for the ecological security of the TGR. However, little is known about the relationship between plant community and the combined forms of the soil nutrients. In this study, Pengxi river, an typical tributary of the TGR, with the largest area for littoral zone, were selected to perform an investigation on the phosphorus forms of the rhizosphere and non-rhizosphere soils of four typical plants (contained Cynodon dactylon L., Cyperus rotundus L., Anthium sibiricum Patrin ex Widder, and Zea mays L.) from three transects with different soil types (Paddy soil, Purple soil, and Fluvo-aquic soils). The variables measured included total phosphorus (TP), available P (AP), inorganic phosphorus (IP), organic phosphorus (OP), and different forms of IP and OP (i.e weakly adsorbed phosphorus WA-P, potential active phosphorus PA-P, Fe/Al-bound phosphorus Fe/Al-P, Calcium bonded phosphorus Ca-P and Residue phosphorus Re-P). The results showed that soil type was a crucial factor of determining nutritional status and species of phosphorus, while vegetation cover was an additional factor. 1) Compared with all non-rhizosphere soil, concentrations of TP, AP, IP, OP, and different phosphorus forms were obviously enriched in rhizosphere soil of different plants in three soil types as the result of the root absorption and activation. The TP, AP, IP and OP concentrations showed C. dactylon > A. sibiricum > C. rotundus > Z. mays. Enrichment rate of the IP showed the highest in the rhizosphere of C. dactylon and the lowest in Z. mays. 2) WA-P_i, PA-P_i and Fe/Al-P_i (representing some labile phosphorus) in rhizosphere of A. sibiricum and Z. mays were higher than those in the rhizosphere of C.rotundus and C.dactylon. The Ca-P_i and R-P_i, which are mainly stabilized phosphorus, were much lower in rhizosphere of A. sibiricum and Z.mays than those in C.r otundus and C. dactylon. Those indicated that the rhizosphere effect of different plants on the IP cycle was significant differences. The activation of stabilized phosphorus for the rhizosphere effect of A.sibiricum and Z.mays were much more obvious than that of C.rotundus and C.dactylon. 3) WA-P_o, PA-P_o, Fe/Al-P_o, Ca-P_o, R-P_o (different OP forms) were also showed a similar law with IP forms. WA-P_o and PA-P_o in the rhizosphere of C. rotundus and C. dactylon were much lower than those in rhizosphere of A. sibiricum and Z. maysL, while Fe/Al-P_o were lower in rhizosphere of A. sibiricum and Z. mays. Higher enrichment effect of WA-P_o and PA-P_o under Z. mays zone showed the higher activation efficiency of phosphorus in rhizosphere of Z. mays. 4) pH, organic matter and volume-weight was significantly correlated with the IP forms, while only pH related with OP forms. Our research could provide some indirect evidences that C. rotundus and C. dactylon was better than A. sibiricum and Z. mays to improve soil P holding and fixation. The vegetation recovery in the drawdown zone should consider the rhizosphere effect of different plants on N cycle.