| Soil is the largest carbon pool of terrestrial ecosystem carbon cycle,which plays an important role in the global carbon cycle,and its storage and release process has an important impact on global climate change.The accumulation and dynamic changes of forest soil organic carbon have a profound impact on soil carbon pool storage.In this study,planted forests and natural forests of tropical mountain rainforests in Wuzhi Mountain,Qixian Ridge and Diaoluo Mountain in eastern Hainan Province were selected.Through field investigation and sampling,indoor determination of physical and chemical properties and data statistical analysis,The differences of soil organic carbon content(TOC),soil labile organic carbon content(LOC),soil active organic carbon distribution ratio,soil p H value and particle composition were compared and analyzed under different origins of different stands at different points.The correlation between soil topography(elevation and slope)and soil physical and chemical properties with soil organic carbon and active organic carbon was revealed.The main factors affecting soil organic carbon and reactive organic carbon in tropical rain forest were discussed.The main research results were as follows:(1)The average TOC in the 0-50 cm soil depth of the tropical rain forest in the eastern part of Hainan Island is 77.54g/kg.TOC of plantation forest was higher than that of natural forest,but the difference was not significant.TOC of planted forest in Wuzhi Mountain was significantly higher than that in Qixian Ridge and Diaoluo Mountain,and the TOC of natural forest in Wuzhi Mountain and Qixian Ridge was significantly higher than that in Diaoluo Mountain.TOC in the surface layer(0-10cm)was significantly higher than that in the middle layer(10-30cm)and the bottom layer(30-50cm),showing obvious surface aggregation effect of organic carbon.(2)The average LOC at 0-50 cm depth in the study area was 4.65mg/g.The content of LOC in natural forest was significantly higher than that in planted forest.The LOC in planted forest and natural forest in Wuzhi Mountain was significantly higher than that in Qixian Ridge and Diaoluo Mountain.In 0-50 cm soil depth,LOC increased with the increase of soil depth,which in the surface layer of natural forest was significantly higher than that in the middle and bottom layers.(3)The proportion of LOC in TOC was 4.24-20.54%.The proportion of LOC in natural forest was higher than that in plantation forest.The TOC and LOC of the planted forest and the natural forest in the three sample sites were highly significant or significant positive correlation.(4)The TOC and LOC in each soil layer of the planted forest and natural forest at the three sample sites increased with the increase of altitude,and the TOC of the surface,middle and bottom layer of the planted forest and the LOC of the middle layer increased significantly.The TOC and LOC in the surface layer of natural forest were most significantly affected by altitude.However,there was no significant difference in TOC and LOC between plantations and natural forests at different points with the change of slope.(5)The soil p H at 0-50 cm depth in the study area ranged from 3.75 to 6.86.In general,soil p H value and TOC and LOC are significantly negative relationship,which the soil p H value of Wuzhi Mountain natural forest and the correlation coefficient of TOC and LOC reached extremely significant level,and soil p H and the correlation of TOC and LOC is not significant.Soil particles in the study area were mainly composed of sand and silt.TOC was negatively correlated with soil silt and sand,and positively correlated with soil clay.LOC was positively correlated with soil clay and silt,but negatively correlated with sand.The correlation between soil particle composition and TOC and LOC was different under different stand origins.(6)Principal component analysis showed that altitude and soil p H were the main controlling factors of TOC and LOC.In conclusion,in the vertical direction,TOC and LOC decreased with the increase of soil depth in the eastern tropical rain forest of Hainan Island.In the horizontal direction,there were significant differences in TOC at different points,and there were significant differences in LOC under different stand origins.Elevation,slope,soil p H and soil particle composition were correlated with TOC and LOC,and elevation and soil p H were the main controlling factors.Therefore,we should pay attention to slope surface water and heat conditions of tropical rain forest mountain and soil acid and alkaline regulation. |
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