| The paper gains the bankroll of special research of forestry public welfare industry (item 201304317) and innovation program for graduates of Central South University of Forestry and Technology (item CX2014B29).Phosphorus (P) is one of the essential nutrients for plant growth, an important part of soil fertility, and also the most crucial limiting nutreint factor for ecosystem. While more than 95% of total phosphorus (TP) in soil exsist as slow acting forms, little portion of TP can be absorbed by plant. Therefore, P-deficiency has become a primary problem of subtropical ecological restoration and land resources management. Different land use patterns can alter soil properties and soil environmental conditions. Irrational land use patterns lead to the degradation of soil quality, and accelerate soil erosion. Rational land use patterns can improve soil structure, increase soil resistance. With the development of mountains, ecosystem structure, funcation and landscape pattern have been radically changed. Evolution of soil environment has been significantly affected.In order to reveal the impact mechanism of human activities on soil P availability, find effective ways of improving P utilization rate, and provide the systemic reference for solving the problems of the fixation of P, we selected C. lanceolata plantation forest, natural secondary forest (P. massoniana+ L. glaber mixed forest, C. axillaries deciduous broad leaved forest, L. glaber+ C. glauca evergreen broad-leaved forest), P. edulis plantation, wasteland in mid-subtropical region, and used the improved Hedley method to study the P element grading, P component proportions and status, and the relationships between P components and soil nutrients, litter, fine root biomass. The main results are:(1) The soil in mid-subtropical was acidic. And soil acidity declined with soil depth. There had significant difference of soil pH among different land use types. Soil pH was ranked in the order wasteland> P. edulis plantation> natural secondary forests> C. lanceolata plantation forest. It showed that soil pH was obviously affected by fertilize and tillage.(2) Contents of total organic carbon (TOC), total nitrogen (TN), TP, available P (AP) and P components in different land use types declined with soil depth. There had significant differences of TOC, TN, TP, and AP among different land use types. In P. edulis plantation and wasteland, contents of soil TN, TP, AP were higher than the contents in natural secondary forest and C. lanceolata plantation forest, while TOC content was lower than that in natural secondary forest. It indicated that land use patterns had a significant impact on soil nutrients.(3) Contents of soil inorganic P components had significant differences among different land use types. And contents of inorganic P components were highest in wasteland (except that Resin Pi content was highest in P. edulis plantation). The proportion of NaOH Pi to inorganic P was the highest. NaOH Pi was the main forms of inorganic P. And the proportions were higher in C. axillaries deciduous broad leaved forest, L. glaber+C. glauca evergreen broad-leaved forest and P. edulis plantation. Proportion of Sonicate Pj (23.14%) was lower than that of NaOH Pi, and higher in C. lanceolata plantation forest. The ratios of Resin Pi, NaHCO3 P; to inorganic P were lower. The ratio of Resin Pi in wasteland and C. lanceolata plantation forest was lower than that in natural secondary forest and P. edulis plantation. The ratio of NaHC03 Pi was on the contrary. The proportion of HCl Pi was the lowest (2.59%) in inorganic P components, while was highest in wasteland.(4) There had significant differences of NaOH Po, Sonicate Po among different land use types, and had no difference of NaHC03 Po. NaoH Po was the main forms of organic P, and the content was highest in wasteland, next in P. edulis plantation and natural secondary forest, and lowest in C. lanceolata plantation. Content of Sonicate Po was highest in P. massoniana+L. glaber mixed forest, lowest in L. glaber+C. glauca evergreen broad-leaved forest. The ratio of Sonicate Po to organic P was similar to the ratio of NaHCO3 Po. And the ratio was highest in P. massoniana+L. glaber mixed forest, followed in C. lanceolata plantation, lowest in C. axillaries deciduous broad leaved forest, L. glaber+C. glauca evergreen broad-leaved forest, P. edulis plantation and wasteland. The ratio of NaHCO3 Po was highest in C. lanceolata plantation, lowest in wasteland.(5) The differences of soil residual P and microbial biomass P (MBP) among different land use types were significant. The average content of residual P varied at a range of 121.36-640.28 mg/kg, and was highest in wasteland, followed in P. edulis plantation, lowest in natural secondary forest and C. lanceolata plantation. Content of MBP varied at a range of 2.34～49.24mg/kg, and was highest in P, edulis plantation, lowest in C. lanceolata plantation.(6) The percentages of 7 kinds of P fractions graded by Hedley method showed the tendency of Residual P (62.89%)>NaOH P (19.45%)>Sonicate P (6.84%)>NaHCO3 P (5.91%)>MBP (4.11%)>HCl P (0.44%)>Resin P (0.36%). In the research region, the percentage of soil available P fractions was lower. And the percentage of Resin P and NaHCO3 P was highest in C. lanceolata plantation, followed in natural secondary forest, lowest in P. edulis plantation and wasteland. While the percentage of slow acting forms of P fractions (NaOH P, Sonicate P) was highest in wasteland, next in P. edulis plantation and C. lanceolata plantation, lowest in natural secondary forest. It indicated that soil P availability was lower in this region. And the transformation of soil P fractions was significantly affected by human activities.(7) Content of residual P was the highest, followed by the contents of organic P and inorganic P. Content of MBP was the lowest. And organic P content was higher than inorganic P. The percentages of organic P and inorganic P to TP were 20.60% and 11.20%. The contents of organic and inorganic P had similar variation tendencies with residual P content, which were ranked in the order wasteland> P. edulis plantation> natural secondary forest, C. lanceolata plantation.(8) In the whole research area, there had very significant positive correlations between soil inorganic P, organic P, residual P, MBP and soil pH, TN, TP, AP. Soil MBP had a siginificant correlation with TOC. In the forest region, soil inorganic P was significantly positively correlated with soil pH and TN, and negatively correlated with litter and fine root biomass. Soil organic P and MBP was significantly positively correlated with soil pH, TOC and TP. Residual P had positive correlations with soil pH and TP. It showed that the differences of soil pH and contents of TP, TOC, TN among different land use types were the main factors which led to the differnces of P fractions contents. Litter and fine root biomass were also the factors. |
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