土地利用方式下岩溶湿地土壤无机磷形态特征及分析方法适用性探讨

Occurrence forms of inorganic phosphorus in soils of karst wetland under different landuses and comparison of two analysis methods

本研究利用SMT法和七步连续提取法对桂林市会仙岩溶湿地中典型土地利用方式(水稻田、果园、荒地)的土壤以及河流底泥中磷的赋存形态进行研究。结果表明:岩溶土壤总磷含量大小为底泥>果园>水稻田>荒地;底泥中Ex-P和Fe-P所占比例较大;荒地土壤中Or-P和Res-P为主要磷形态;水稻田和果园土壤中Fe-P所占比例较高。人为干扰明显的果园表层土壤有较大的磷淋溶风险;荒地土壤中磷的生物可利用性低,体现了其缓冲固持湿地水体中磷的生态功能。大量可溶性磷经淋溶迁移富集于底泥中,是河流富营养化的风险源。七步法表现出在提取多种复杂结合态磷上的优势,对岩溶土壤中Ca-P的提取更充分有效,更适用于研究岩溶土壤不同形态的磷分布特征。

The content and speciation of phosphorus(P)determine soil fertility and the risk of P leaching from soils.This work uses standard,measurement and testing(SMT)and seven-step sequential extraction methods(“seven-step method”)to investigate the occurrence of inorganic P(In-P)in typical karst soils(paddy land,orchard,barren land)and river sediment in the Huixian karst wetland of Guilin,to analyze the effects of different land utilization on the dis⁃tribution of In-P in karst soils and compares the two methods on this issue.The results show that total P content in the karst wetland soils from high to low is river sediment,orchard,paddy land,and barren land.This value is the highest in the river sediment(416.97 mg∙kg-1),in which highly bioavailable exchangeable P(Ex-P)and iron P(Fe-P)are dominant.In the barren land soil,organic P(Or-P)and residual P(Res-P)are the major forms;while In-P content(64.45 and 47.56 mg∙kg-1 for 0-20 cm and 20-40 cm depth)is the lowest in all four soils.The autologous P(Au-P),which has low bioavailability,has the highest proportion in In-P of this soil compared to that in other soils.In compari⁃son,the surface soil of the paddy land and orchard has relatively high In-P content(276.04 and 418.19 mg∙kg-1,re⁃spectively)in which Fe-P is the dominant form.In this analysis,the seven-step method has advantages in the extrac⁃tion of P with complex binding states.Specifically for the karst soils,which are characterized by high Ca content and al⁃kalinity,the seven-step method is more effective in the extraction of Ca-P.The In-P constitutes a great share in the to⁃tal P in karst soils,therefore the P pool is more active.Human disturbance greatly increases the In-P content and its bioavailability.Especially,the surface orchard soil has a great potential risk of P leaching.The barren soil has low In-P content and bioavailability,indicating its high P buffering capacity.The enrichment of P in sediment via leaching suggests the sediment is a risk source for river eutrophication.In general,the seven-step method is a more suitable ap⁃proach for P speciation analysis in karst soils.