Characteristics And Supplying Mechanism Of Soil Phosphorus In Different Aged Chinese Fir Plantations

Phosphorus is involved in plant growth and metabolism, and it is one of the essential nutrients for plant growth and development. Because of the low rate of utilization of phosphorus in soils of subtropical area, the amount of phosphorus has a direct impact on the productivity of forest ecosystem, phosphorus became the important elements of controlling forest ecological system of forest growth and maintaining the ecosystem balance and stability. In this paper,4 different ages (3,8, 18,26 years old) of Chinese Fir Plantation in Hunan province were selected as the research objects, and the physical and chemical properties of soil and the distribution characteristics of phosphorus in different seasons were studied. In order to provide a theoretical basis for sustainable development of Chinese fir forest, stepwise regression analysis and path analysis were used to study the effect of phosphorus availability on the system.The main research results showed as following:1. Soil total phosphorus:The order of soil TP content of annual mean in 0-60cm layer of soils:18 years old(375.55mg/kg)> 8 years old (370.54mg/kg)> 26 years old(351.38mg/kg)> 3 years old(191.54mg/kg). It showed that the content of TP in this study area was low.2. Soil Bray 1-P:The content of Bray 1-P in 4 stands was generally low.The order of soil Bray 1-P content of annual mean in 0-60cm layer of soils:18 years old> 8 years old>26 years old>3 years old. The seasonal variation of Bray 1-P content in four aged Chinese fir plantation forests was the highest in spring, decreased gradually in summer, and slightly picked up in autumn, and decreased gradually in winter.3. The availability of soil phosphorus:PAC in four aged Chinese fir plantation forests were all in the 0.10%-0.70%, which were far below 2%, and were all shown in October> July> April> January.4. Soil Bray 1-P:The content of MB-P decreased with the increase of soil depth, and showed a decreasing trend on the whole in four aged Chinese fir plantation forests. The annual average value of each stand was 8 years old> 3 years old> 26 years old> 18 years old.5. From spring to winter, Al-P and O-P gradually transformed to other forms of phosphorus or passive plant absorption, while Fe-P and Ca-P were transformed by other forms of phosphorus.6. Total inorganic phosphorus accounted for the proportion of TP in 60.79%-72.28% in four aged Chinese fir plantation forests, soil O-P content accounted for the highest proportion of total inorganic phosphorus, Fe-P and Ca-P times, Al-P accounted for the lowest proportion of total inorganic phosphorus.7. The content of LO-P in four aged Chinese fir plantation forests was April> July> October> January, and the seasonal variation of MLO-P was not the same. MRO-P content was highest in April and lowest in 10, while HRO-P content was lowest in April and highest in October.8. Soil MLO-P content accounted for the highest proportion of total organic phosphorus, MRO-P is slightly lower than that of MLO-P, HRO-P third, and the lowest proportion was LO-P.9. By stepwise regression and path analysis, in 3-year-old stand, soil TN maximum effect on Bray 1-P, followed by MB-P. The total effect of MB-P on 1-P Bray was the largest, and the indirect path coefficient of Bray 1-P through MB-P was also larger, so MB-P was an important contribution to soil Bray 1-P. In 8-year-old stand,soil TP had the greatest impact on Bray 1-P, and the direct contribution to Bray 1-P was also the largest. The correlation coefficients of TP and were 0.910**,and the total effect of Fe-P on 1-P Bray was second. Fe-P was an important contributor to the soil Bray 1-P, and the plant played a major role in the activation of phosphorus in 8-year-old stand. In 18-year-old stand, the direct effect of soil SOC on Bray 1-P was greatest, and the total effect on 1-P Bray was second. TN through SOC to Bray 1-P had a larger positive effect, so that the total effect of TN on Bray 1-P was the biggest.The important contribution of soil Bray 1-P came from the promoting effect of SOC and TN. In 26-year-old stand, soil TN and LO-P were the two factors that affected the total 1-P Bray, and TN was the most direct impact on 1-P Bray, and the total effect on Bray 1-P was also the highest, LO-P second. LO-P had a great positive effect on Bray 1-P mainly through direct effect, so the important contribution of soil Bray 1-P came from the promoting effect of TN and LO-P.