岩溶石漠化区不同植被恢复模式土壤无机磷形态特征及影响因素

为分析岩溶石漠化区不同植被恢复模式土壤无机磷的形态特征,评价植被恢复的土壤供磷潜力,阐明有机碳及钙素在无机磷形态转化中的作用,选取研究区内8种有代表性的样地,采用蒋柏藩无机磷分级方法对土壤无机磷形态特征及影响因素进行研究。结果表明:研究区土壤全磷与速效磷含量分别在0.25—1.35 g/kg、1.05—53.01 mg/kg范围,无机磷总量在123.94—934.61 mg/kg,耕地与退耕地以及各退耕地之间全磷、速效磷、各形态无机磷含量水平差异明显,各退耕地磷素含量水平介于耕地与次生马尾松林地之间,退耕地中桃林地、花椒林地磷素含量水平较高、樟树林地、柳杉林地、撂荒草地次之、撂荒灌丛地较低。各样地土壤无机磷占全磷比例在51.2%—72.4%,不同形态的无机磷含量表现为O-PFe-PCa-PAl-P,其中Ca2-P、Al-P对速效磷的贡献率大,Fe-P、Ca8-P贡献较小,O-P、Ca10-P献率最小。不同活性土壤有机碳与不同形态钙素对各形态无机磷在总无机磷中比例的影响较大,p H、容重、粘粒含量、含水量等其它理化性质影响较小。

Factors influencing the distribution of inorganic phosphorus fractions in different vegetation restoration areas in karst rocky desertification areas

Phosphorus is an essential element for plant growth. It is taken up from the soil where it is found in two main forms, organic phosphorus and inorganic phosphorus. In cultivated soils, inorganic phosphorus is the main form found. Phosphorus is very active chemically in soils. Mineral phosphorus added to cultivated soils in fertilizer is readily fixed, which results in low availability of phosphate. Furthermore, the availability of inorganic phosphorus is different in different inorganic phosphorus fractions. The fractionation of inorganic phosphorus allows us to understand the geochemical behavior of inorganic phosphorus and measure the potential availability of the soil phosphorus pool. Limestone soils are typical azonal soils, which are formed from a parent material of carbonate rock and are typically characterized by high concentrations of calcium. This property strongly influences the geochemical behavior of inorganic phosphorus.To analyze the characteristics of soil inorganic phosphorus in areas with different patterns of vegetation recovery in karst rocky areas, and evaluate the potential capacity of different fractions to provide phosphorus and the roles of organic carbon and calcium in the process of inorganic phosphorus transformation in karst areas, we studied the characteristics of inorganic phosphorus in these areas by applying the Jiangbofan method for fractionating inorganic phosphorus. This allowed an investigation of the factors influencing the transformation of inorganic phosphorus in eight representative types of land. Concentrations of total and available phosphorus in the soils ranged from 0.25-1.35 g/kg and 1.05-53.01 mg/kg, respectively. Total inorganic phosphorus contents ranged from 123.94-934.61mg/kg and it was the main form in the study area. The concentrations of total phosphorus, available phosphorus and inorganic phosphorus fractions showed significant differences between cultivated land and abandoned land, and also among the abandoned lands. By comparison with secondary Masson pine woodland, phosphorus concentrations in cultivated lands showed an accumulation process, whereas abandoned lands showed a consumption process. Phosphorus concentrations in abandoned lands were higher than in secondary Masson pine woodland and lower than in cultivated land. In abandoned lands, the Peach land and Pepper land had the highest phosphorus concentrations, followed by Camphor tree land, Cryptomeria land, ruderal land, and scrubland which had the lowest concentrations of phosphorus. The proportion of inorganic phosphorus to total phosphorus ranged from 51.2%-72.4% in different soil profiles. Concentrations of inorganic phosphorus fractions followed the order: O-P > Fe-P > Ca-P > Al-P, with Ca₂-P and Al-P providing the highest contribution to available phosphorus, Fe-P providing a lower contribution, and the contributions of Ca₈-P, O-P and Ca₁₀-P being the lowest. Soil organic carbon of different active levels and different calcium fractions play important roles in the transformation of inorganic phosphorus, whereas pH, bulk density, clay content, water content, and other soil physical and chemical properties have a lesser impact. TOC, LOC, and DOC were significantly or very significantly positively correlated with Ca₂-P, Al-P, Fe-P, and Ca₈-P, significantly negatively correlated with O-P, and showed no significant correlation with Ca₁₀-P. Soil total calcium, exchangeable calcium were significantly or very significantly negatively correlated with Ca₂-P, Al-P, Fe-P, and positively correlated with Ca₁₀-P. Soil pH, bulk density, clay content, water content showed no significant correlation with fractions of inorganic phosphorus.