| Phosphorus(P)is an essential nutrient for plant growth and development.Plants mainly absorb phosphorus from the soil,but 95%-99%of the phosphorus in the soil exists in the form of polymer which is difficult for plants to absorb,and plants are often in the state of phosphorus deficiency stress.In subtropical acid red soil hilly region,the content of total phosphorus(TP)is low,only 200-300 mg/kg.In addition,the soil pH is less than 6,rich in iron and aluminum oxides,strong adsorption and fixation of phosphorus,and extremely low content of available phosphorus,which has more obvious restrictions on forest ecosystem productivity and important ecological processes,and has become the primary problem of forest restoration and management in this region.Soil phosphatase activity can reflect the level of soil phosphorus supply and is an important component of soil phosphorus cycle;The composition of soil phosphorus components determines the extent to which it can be directly absorbed and utilized by plants.There is a large area of evergreen broad-leaved forest in subtropical China,which is also an important timber production base and forest soil resource in China.However,due to the dense population and the sharp contradiction between people and land in this area,the evergreen broad-leaved forest has been seriously disturbed by human beings for a long time,and a variety of forest types including plantation and secondary forest have emerged.However,up to now,there are few reports on soil phosphatase activity and phosphorus fractionation composition of different forest types in subtropical areas.Therefore,five typical forest types in the hilly area of central Hunan Province,namely,Chinese Fir Plantation(CFP),Pinus massoniana Plantation(PMP),Pinus massoniana coniferous and broad-leaved mixed forest(PLF),jujube deciduous broad-leaved forest(CAF)and Cyclobalanopsis glauca evergreen broad-leaved forest(LGF),were selected as the research objects,In order to provide scientific basis for sustainable management and management of subtropical forest ecosystem,the effects of forest types on soil phosphorus availability transformation were studied by studying soil phosphatase activity,composition of soil phosphorus fractions and its influencing factors.The main results are as follows:(1)CAF and LGF were better than PLF and CFP in soil physical properties and nutrient content,while PMP was the worst.The pH values of the five forests ranged from 3.51 to 4.27,showing typical acid red soils.According to the nutrient standard of the second national soil survey,the contents of TP,total potassium(TK),available phosphorus(AP)and available potassium(AK)were low or very low.There were significant differences in soil bulk density,mechanical composition,pH,soil organic carbon(SOC),TN,TP,TK and AK among different forest types(P<0.05).Soil physical properties(except bulk density),nutrient content and the content of phosphorus fractions decreased with the deepening of soil depth.(2)Different forest types had significant effects on soil microbial biomass,fine root biomass,litter standing crop and TP content.Microbial biomass carbon(MBC),microbial biomass nitrogen(MBN)and microbial biomass phosphorus(MBP)of five forest soils ranged from 367.70 to 1176.70,58.66 to 170.03 and 2.45 to 21.12 mg/kg,respectively.MBC,MBN and MBP of different forest types were significantly different(P<0.05),and MBC,MBN and MBP of PMP soil were the lowest.The fine root biomass was 1097.07-2759.90 kg/ha,and there was significant difference among different forest types(P<0.05).The fine root biomass of LGF in 15-30 cm soil layer was significantly higher than that of the other four forests(P<0.05).The total stock of litter layer and TP content of litter layer ranged from 1136.76 g/m2 to 1823.64 g/m2 and 0.18 g/kg to 0.42 g/kg,respectively.The standing crop and TP content in litter layer of different forest types were significantly different(P<0.05).The standing crop and percentage content of standing crop in decomposed layer of PMP and PLF were higher than those of CFP and caf,and similar to LGF,the TP content in decomposed layer of CFP was significantly lower than that of the other four forests(P<0.05).(3)Soil phosphatase activity is significantly affected by forest types and is regulated by many factors.The activity of soil acid phosphatase(SACP)was significantly higher than that of soil alkaline phosphatase(Saip)(P<0.05).The activity ranges of SACP and Saip were 1.32-4.54 and 0.26-0.38 mg/g for 12 h,respectively.There were significant differences in SACP activity among different forest types(P<0.05),and the activities of SACP and Saip of CFP were the lowest.The main factors affecting SACP activity were soil silt content,fine root biomass and TP content in litter layer;TP content in litter layer is the main regulator of Saip activity.(4)The P activity of CAF and LGF was higher than that of PMP,while that of CFP was secondary and medium.The contents of Resin-Pi,NaHCO3-Pi,NaOH-Pi and HCl-Pi in five forest soils were 3.10-8.56,5.17-11.88,14.79-23.73 and 0.60-3.29 mg/kg,respectively,accounting for 8.73%-19.21%,18.80%-27.20%,49.42%-65.34%and 1.78%-9.44%of Pi content,respectively.The contents of NaHCO3-Po and NaOH-Po in five forest soils were 1.74-14.68 and 20.13-47.47 mg/kg,respectively,accounting for 13.21%-25.49%and 74.51%-86.79%of Po content,respectively.There were significant differences in the content of components in the same classification among different forest types(P<0.05).(5)The contents of soil phosphorus fractions were mainly affected by soil microorganism,plant root biomass and soil TN and TP contents.The main influencing factors of resin PI were MBP and silt content.The increase of MBP and the decrease of silt content were beneficial to the improvement of SACP activity,and promoted the transformation of moderately active phosphorus and residual phosphorus to resin Pi,the main influencing factors of NaHCO3-Pi were MBP and MBC,the main influencing factors of NaHCO3-PO were soil TP content,MBP and fine root biomass,the main influencing factors of NaOH-Pi were soil TN and TP content,and the main influencing factors of NaOH-Pi were soil TN,TP content and MBN,HCl-Pi and MBN The main influencing factors of Residual-P were fine root biomass and soil TP content.The results showed that CFP was better than PMP in soil remediation,and PMP had low demand for soil conditions,which was suitable for vegetation restoration of poor soil.CAF and LGF had excellent soil nutrients,soil phosphatase activity and soil phosphorus availability,which was a better choice for vegetation restoration in this area. |
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