| Soil organic carbon pool in tropical rain forest is very sensitive to temperature change and atmospheric CO2 concentration change,and plays an important role in regulating global climate change.Under the background of global climate change,it is particularly important to study the characteristics and influencing factors of tropical rainforest carbon pool.Lowland rain forest is one of the important types of tropical rainforest,which is greatly affected by human activities.The natural regeneration and restoration of tropical lowland rain forest in Ganshiling of Hainan Island can be divided into three types:shrubs and low trees restored under larger cutting intensity（I）,secondary rainforest with higher stand density restored under medium cutting intensity（II）,and secondary rainforest with less cutting interference due to inconvenient traffic conditions（III）The vertical distribution of soil organic carbon,the distribution and stability of soil aggregates,the contents of total organic carbon and oxidizable organic carbon in soil aggregates,and the influencing factors of soil organic carbon were studied by combining field investigation with indoor analysis,in order to provide scientific basis for the research and evaluation of soil carbon fixation capacity of secondary rain forest in tropical lowland.The main results are as follows:1.The vertical distribution characteristics of soil organic carbon content,carbon density and carbon storage were clarified.The soil organic carbon content in 0-20 cm soil layer was the highest,which was 3.07-4.49 g·kg-1.The soil organic carbon density of the 0-100 cm soil layer was 4.14-6.42 kg·m-2,which was only 50.8%of the national average level.The soil carbon storage of the 0-100 cm averaged 53.96 t·hm-2,and the soil C Stock in the Ganshiling natural reserve region averaged 1.13×108 kg C that estimated using the longitudinal fitting method.2.The distribution and stability of soil aggregates were studied.Soil aggregates of the three rain forest types were mainly composed of<0.25 mm and 0.5-1 mm particle size,accounting for 32.52±5.11%and 31.74±4.04%.With the decrease of particle size,the proportion of each particle size increased first,then decreased,and then increased,with the increase of>0.25 mm particle size The stability of the three types of soil aggregates was ranked asⅡ>Ⅲ>Ⅰ.3.The content characteristics of total organic carbon and readily oxidizable organic carbon in soil aggregates with different particle sizes were revealed.The total organic carbon content of soil aggregates in three forest types were 4.21±0.21 g·kg-1,6.38±0.11 g·kg-1 and 8.68±0.14g·kg-1;the contribution rate of total organic carbon of soil aggregates first increased and then decreased with the decrease of particle size,and the contribution rate of 0.5-1 mm particle size was the largest,32.81%,followed by 0.25-0.5 mm The results showed that the contribution rate was 28.77%.The content of readily oxidizable organic carbon in soil aggregates was 2.06-3.76g·kg-1,and it decreased first,then increased,and then decreased with the decrease of particle size.The maximum content of soil readily oxidizable organic carbon in the three forest types came from>2 mm aggregates.The total organic carbon of soil aggregates is closely related to the content of readily oxidizable organic carbon（R=0.9397）,which can be used as a sensitive index to measure the soil organic carbon pool in the lowland rainforest of Ganshiling.4.The main influencing factors of soil organic carbon pool were analyzed.The soil physical and chemical properties of the three forest types were determined that soil moisture content was2.24%-24.96%,soil bulk density was 1.79-1.86 g·cm-3,p H value was 4.66-4.74,the contents of total nitrogen,total phosphorus and total potassium were 0.49-1.29 g·kg-1,0.13-0.15 g·kg-1and 10.64-25.87 g·kg-1,the contents of alkali hydrolyzable nitrogen,available phosphorus and available potassium were 64.28-114.25 mg·kg-1,0.11-0.98 mg·kg-1,87.59-127.43 mg·kg-1;the litter thickness of three forest types was 0.35-5.30 cm,and the number of tree layer species was 5-39,which increased gradually with the recovery of the forest;the content of soil organic carbon was significantly positively correlated with the content of soil total nitrogen,alkali hydrolyzable nitrogen and available phosphorus（P<0.01）,and significantly positively correlated with the litter thickness and the number of tree layer species（P<0.05）.Strengthening the protection and restoration of tropical lowland rainforest in Ganshiling,improving soil nutrient content,litter thickness and species richness,is conducive to the accumulation of soil organic carbon. |
