The Phosphate Occurrence Form And Environmental Significance Of Mountain Soil At Different Attitude

Phosphorus is an essential elements of plants, the biological availability of phosphorus in the ecological system depends on the content and form. Due to the inorganic phosphorus can be directly used by plants and microorganism, previous studies have focused on inorganic phosphorus, and the study of organic phosphorus receive relatively little attention. The organic phosphorus is important to phosphorus pool, the contribution of organic phosphorus to plant nutrition is still not enough to be understood. Influences of artificial disturbance on the moutain soil are relatively small, hydrothermal condition change on the moutain soil regularly, which provide advantages to study the transformation and speciation characteristics of phosphorus in the natural environment. The objectives of the present study were to study the distribution of inorganic phosphorus and organic phosphorus in the soil,form and its evolution process under the action of various factors such as different altitudes of mountain soils with different soil types, different parent material and vegetation. The main results are shown as follows:(1)The soil samples are collected from different altitudes(560m, 834 m, 1200 m,1552m, 1750 m, 2115 m, 2425 m, 2687 m and 3093m) in Shennongjia forest region,Hubei province on different layers at 0-10 cm 、 10-20 cm, which the soil types are yellow brown soil, mountain yellow brown soil, mountain brown soil, dark-brown soil,mountain brown coniferous forest soil. The main soil parent materials are shale and shale pottery, in high altitude area there can be mainly diabase. The main vegetation are broad-leaved forest, deciduous broad-leaved forest, mixed needle leaf and so on.The soil moisture increases of altitude first, then gradually decreases; The temperature decreases with the increasing of altitude; The clay minerals of the soils are mainly 2:1typed minerals(the content of 1.4 nm mineral and hydromica is more than 85%), the1:1 type minerals kaolinite are relatively rare, it means that the soil weathering process of Shennongjia is weak. With the increasing of the elevation, 1.4 nm mineral contents decrease in the first stage, and then rise. The hydromica contents show the opposite trend. These results suggest that the potassium dissolving and interlayer hydroxyl aluminized effect of the 2:1 type mineral weakened after the first increase accordingly.The difference of layer A and layer B is not significant, the soil p H decreasein the first stage, and then rise; the soil organic matter content of layer A is significantly higher than B. The difference of the iron and aluminum oxides in different altitude of soils are significant, and with the increasing of altitude, the contents of the amorphous iron oxides and the activation degree increase sharply, we can get that with the increasing of altitude, soil oxides are mainly in amorphous form.(2)Soil total phosphorus contents increase along with the altitude increasing,which means that with the increasing of altitude, soil phosphorus turnover slowly,leach little. The contents of layer A soil total phosphorus was higher than B, with the redistribution and leaching of soil phosphorus, and total phosphorus contents in soil decrease with soil depth gradually reducing, shows that the ability of phosphorus enrichment in surface soil affected by vegetation is strong. Various fractions of phosphorus are generally low in yellow-brown soil at 834 m, which may be that the fixation phosphorus ability affected by terrain of vegetation decrease. soil total phosphorus content is consistent with the change of organic matter, except mountain-brown coniferous forest soil at an altitude of 3093 m, it suggests that P is closely related to the organic matter in soil.(3)By using the sequential extraction method we divide the soil phosphorus into resin P, organic phosphorus and inorganic phosphorus extracted by 0.5M(p H8.5)Na HCO3 solution, organic phosphorus and inorganic phosphorus extracted by 0.1M Na OH solution, inorganic phosphorus extracted by 1M HCl, concentrated hydrochloric acid P(organic phosphorus and inorganic phosphorus) and residue phosphorus, the content of different phosphorus fractions change by the different altitude is significant.Labile phosphorus(resin-P and Na HCO3-P) changing from 6% to 26% of sum of soil total P, this content is relatively less, the change is not ob viously and a weekly decrease trend, it shows that between the long time of soil formation the supplementary material release of phosphorus; Na OH-P is also the main existence form of soil phosphorus, accounted for 24% of the total phosphorus content to-57%. With the increasing of altitude, Na OH-P content present a rising tendency.Phosphorus extracted by concentrated hydrochloric acid(Conc. P is closed state of phosphorus storage) accounted from 10.8% to 39.5% of sum of soil total P, the large content of Conc.- P in the soil is thought to be related to the soil weathering, the soil development. Residue phosphorus(resual-P) content change is not significant,accounting for total phosphorus range from 8.5% to 22%.Organic P accounted from 44.8% to 70% of sum of soil total P by the increasing of attitude, it shows that organic P is the mainly form of soil P pool, and the change not significant. Percentage of Na HCO3-Po for the organic P increase by the enhanced weathing process. So we can get that high temperature and rainy, dry wet seasonal obvious, strong weathering leaching effect in the low altitudes, the laible organic P and Na HCO3-Po are relative high. Na OH-Po(moderate stable P) is the dominant organic P, changing from 40.4% to 77.4% of sum of soil total organic P, far greater than the content of inorganic phosphorus, which is thought that the large amount of P mineralized by the iron-aluminum oxides. The form of the moderate stable P by using X-ray diffraction, we can know that there are trace amounts of goethite.(4)The organic P fractions have different changing trend by the influences of soil parent material, climate, vegetation, temperature and p H. The laible P(resin-P+Na HCO3-Pi) in relation to the attitude, it’s highly related to the soil organic matter, increasing by the attitude increasing. Na HCO3-Po 、 Na OH-Po are highly positive correlated with soil organic matter, Fed and Ald, indicating that iron and aluminum oxides play an important role in the stability of soil organic phosphorus pool.The results above provide scientific basisfor research of organic forms, evolution and other geochemical cycling processes.