| Land use change has significant effects on the soil physical,chemical and biological properties.In recent years,the phenomenon of converting natural forests to plantations was very common.Moso bamboo（Phyllostachys edulis）forest has the wide distribution area and is one of the major economic trees in China.Due to humanistic management practices and litter types has changed,characteristics of soil nutrient and carbon（C）pools have been significantly influenced.In recent years,forest managers have converted parts of the natural evergreen broad-leaved forests（EBLF）into Moso bamboo forests（MBF）in the pursuit of high economic benefit,and taken a series of human intensive management measures,such as fertilization,removal of understory weeds,plowing and so on.The research of the effects of evergreen broad-leaved forests converted into Moso bamboo forests on soil nutrients and carbon pools will provide basic data for the study of the effects of natural forest on soil nutrient and carbon cycle in terrestrial ecosystem and provide scientific basis for evaluating scientific effects of typical land use change on soil carbon pool dynamics and carbon sequestration function in subtropical regions.Therefore,this study selected adjacent natural evergreen broad-leaved forests and bamboo plots(bamboo forests was converted from evergreen broad-leaved forests and collected and analyzed characters of soil nutrient pools,including different forms of nitrogen,phosphorus and potassium element,the activity of soil enzymatic,organic carbon storage and different forms of activated carbon pools.Soil organic carbon functional compositions were determined by the 13C-NMR（nuclear magnetic resonance）technique.Using indoor incubation experiment to analyze the influence on SOC by land use change to prove the effects of natural evergreen broad-leaved forests converted into Moso bamboo forests on soil nutrients and carbon pools systematically.The main results obtained are as follows,（1）Conversion of EBLF to MBF significantly increased the NH4+-N and NO3--N concentrations,but decreased the water soluble organic N（WSON）and microbial biomass N（MBN）concentrations in both soil surface（0-20 cm）and subsurface（20-40 cm）layers and significantly increased the total N concentration for the soil surface layer（P < 0.05）,but had no significant change for the soil subsurface layer.Resin-Pi,NaHCO3-Pi,HCl-Pi and Residual-P concentrations in the soil surface layer were increased significantly.Converting EBLF to MBF decreased the NaHCO3-Po concentration significantly in both soil surface and subsurface layers（P < 0.05）.but increased the NaOH-Pi concentration in the soil surface layer,but decreased the soil NaOH-Po concentration（P < 0.05）.Converting EBLF to MBF significantly increased the available K and slowly available K concentrations in both soil surface and subsurface layers and significantly increased the total K and mineral K concentrations in the soil surface layer（P < 0.05）,but has no significant effect on these two characters in the soil subsurface layer.In addition,the decreased degree of the activity of types of enzyme is different,the activity of invertase,urease,catalase and acid phosphatase decreased significantly in the surface soil（P < 0.05）.（2）Converting EBLF to MBF,the organic carbon storage of surface（0-20cm）and subsurface（20-40cm）soil decreased by 19.7% and 13.5%,respectively.The water-soluble organic carbon,water soluble organic carbon,microbial biomass carbon and readily oxidizable carbon content of bamboo surface soil were decreased by 34.4%,25.8% and 30.4% and 25.2% and the water soluble organic carbon,water soluble organic carbon,microbial biomass carbon,readily oxidation carbon content of subsurface soil were decreased by 38.4%,19.8%,34.1% and 22.2%（P < 0.05）.Solid state 13 C NMR spectroscopy of soil samples showed that the difference of the percentage composition of organic carbon in carbon forms was significant.The proportion of organic carbon in natural evergreen broad leaved forest and Moso bamboo forest soil surface and subsurface was highest,followed by alkyl carbon.After the transformation of the natural evergreen broad-leaved forest to Moso bamboo forest,the proportion of the organic carbon,the aromatic carbon and the aroma of the natural evergreen broad-leaved forest were significantly decreased,while the proportion of alkyl carbon and the value of A/O-A increased significantly（P < 0.05）.（3）The analytic results of the indoor incubation experiment on SOC mineralization showed that the SOC mineralization rate and cumulative mineralization rate were significantly decreased by the conversion of EBLF to MBF（P < 0.05）.At the 180 days of incubation at 25℃,the cumulative mineralized amount of soil organic C at the soil depths of 0-20 cm and 20-40 cm in EBLF was 1.24 and 1.16 times of that in MBF.And at 35℃,these indexes were 1.11 and 1.18 times,respectively.In addition,temperature has a significant influence on soil organic carbon mineralization,the higher the temperature the greater the amount of soil carbon mineralization.Soil organic carbon mineralization rate and cumulative mineralization on EBLF and MBF at 0-20 cm and 20-40 cm soil layers increased with the increase of temperature were significantly increased（P < 0.05）.There was no difference in the released CO2-C ratio to the SOC within the same soil layer between EBLF and MBF,regardless of the incubation temperature. |
