不同退耕年限下菜子湖湿地土壤磷素组分特征变化

选取菜子湖区不同退耕年限(2、5、8、10a和20a)湿地为研究对象,以仍耕作油菜地和原始湿地为参照,分析了土壤全磷(TP)、有效磷(AP)、有机磷(OP)和无机磷(IP)各形态含量,探讨退耕还湖后湿地土壤磷素组分特征变化规律。结果表明:研究区土壤无机磷各形态含量大小顺序为:铁磷(Fe-P:73.55—391.76 mg/kg)钙磷(Ca-P:21.64—108.04 mg/kg)闭蓄态磷(O-P:17.15—29.57 mg/kg)铝磷(Al-P:5.84—25.97 mg/kg),其中Fe-P占了土壤无机磷总量的54.20%—74.13%;退耕还湖2—8a期间,湿地土壤Al-P、Fe-P和O-P含量有逐渐降低趋势,而退耕8—20a后逐渐上升,以Fe-P为主的这3形态磷左右着退耕后土壤无机磷的变化;Ca-P随退耕年限增加整体呈上升趋势,对土壤无机磷的贡献逐渐增加;无机磷占土壤全磷的比例为35.90%—67.27%,主导着退耕后湿地土壤全磷变化;有机磷占土壤全磷的17.82%—50.51%,在退耕2a后下降,随后开始逐渐上升,对退耕后湿地土壤磷库恢复的贡献逐渐增加;其中Fe-P、O-P和Al-P控制着退耕后土壤磷素有效性变化。退耕后水文条件、植被生长和土壤黏粒含量变化不仅影响退耕后湿地土壤磷素组分特征,也影响着退耕后湿地土壤磷素有效性。

Characteristics of soil phosphorus fractions in wetlands with various restoration age in caizi lake, Anhui Province

Phosphorus (P) is often the critical limiting nutrient controlling the productivity of wetlands. However, water eutrophication caused by P over enrichment impairs water quality and destroys wetland ecosystem. Very limited information is available on the characteristics change of P pool in wetland soils after returning farmland to lake (RFL). We used P fractionation techniques to investigate P distribution in soils, sampled from wetlands with various age (2, 5, 8, 10 and 20a) of RFL, rape field, and native wetlands in the Caizi lake, Anhui province. The results showed that the contents of inorganic P (IP) were in the order: Fe-P (73.55-391.76 mg/kg) > Ca-P (21.64-108.04 mg/kg) > O-P (17.15-29.57 mg/kg) > Al-P (5.84-25.97 mg/kg), moreover Fe-P, as a main component, accounted for 54.20%-74.13% of IP in studied field. All of Al-P, Fe-P and O-P declined within the restoration period of 2-8a, and began to increase gradually after 8a of RFL. The contents of Ca-P increased progressively with the age of RFL, and showed more and more contribution to IP. Soil inorganic P accounted for 35.90%-67.27% of soil total P, owning the same change tendency as Fe-P with various age of RFL, and dominated the change tendency of TP after RFL. Soil organic P accounted for 17.82%-50.51% of total P and increased gradually with the RFL age. With restoration age, the contribution of Ca-P to inorganic P pool and organic P to total P pool increased. The results also indicated Al-P, Fe-P and O-P controlled P availability in wetlands with RFL age. The changes of soil P contents, composition, and availability were attributed to soil clay content, and shift of hydrological condition and recovery status of vegetation after RFL.