Soil Organic Carbon Characteristics Of Torreya Grandis Cv. Merrillii In Kuaiji Mountain

In recent years,the phenomenon of natural secondary forest to plantations and long-term intensive management was very common.The changes in land use patterns and the differences in management measures have a significant impact on soil organic carbon pools.Torreya grandis cv.Merrillii is a unique tree species in China,and it is a multifunctional precious species with high economic value,which integrates edible,oil,medicinal and ornamental value.In this study,T.grandis cv.Merrillii forest land in Zhuji National Forest Park of Zhejiang Province was taken as the research object.Soil samples were collected in the secondary forests,T.grandis cv.Merrillii plantation of different fertilization measures and different ages to analyze the total soil organic carbon(TOC),readily oxidizable carbon(ROC),light fraction organic matter(LFOM),and soil nutrient contents in 0-20,20-40,and 40-60 cm soil layers,which provided theoretical basis for the soil quality evaluation and sustainable use of the T.grandis cv.Merrillii and the conservation of the old T.grandis cv.Merrillii.The main results were as follows:1.Effects of conversion of natural secondary forest into T.grandis cv.Merrillii plantation on soil active organic carbon.(1)The TOC of each layer significantly decreased by 27.2%-50.5%.The ROC increased in 0-20 cm soil layer.The LFOM of 20-40 cm and 40-60 cm increased significantly by 155.5% and 184.8%,respectively.(2)In the soil profile structure,TOC and ROC of T.grandis cv.Merrillii plantation in 0?20 cm decreased more than natural secondary forest,while LFOM decreased less than natural secondary forest.The ratio of ROC to TOC and activity of carbon pool in 0?20 cm markedly increased by 123.2% and 169.2%,respectively.(3)The correlation among TOC,ROC and LFOM were significant or extremely significant,and they have the highest correlation with total nitrogen and hydrolytic nitrogen.The ROC and LFOM were significantly/extremely correlated with(except for the correlation between ROC and available potassium).2.Effects of fertilization measures on soil labile organic carbon and nutrients under T.grandis cv.Merrillii plantation.(1)Compared with control,the organic-inorganic fertilizer used by farmers can significantly increase the TOC,ROC,LFOM,total nitrogen,hydrolytic nitrogen and available phosphorus in each soil layer;chemical fertilizer can significantly increase the ROC,hydrolytic nitrogen in 0-20 cm soil layer and available potassium and available phosphorus in each soil layer.(2)The ratios of ROC to TOC in each soil layer showed that organic-inorganic fertilizer > chemical fertilizer > control.(3)Organic-inorganic fertilizer increased soil p H in all layers,and chemical fertilizer significantly reduced soil p H in 20-40 cm and 40-60 cm.(4)The correlation among TOC,ROC and LFOM were extremely significant.The TOC,ROC and LFOM were significantly/extremely correlated with total nitrogen,hydrolytic nitrogen,available potassium and available phosphorus.3.Relationships between soil organic carbon characteristics and soil nutrients for different aged T.grandis cv.Merrillii.(1)The TOC,ROC and LFOM increased first and then decreased with the increase of the tree age,among which the content was the highest in the 300-500 years.The change of TOC was the most obvious.(2)The ratio of ROC to TOC for different aged T.grandis cv.Merrillii.showed that 50-100>0-50>100-300>300-500>over 500 years(except for 0-20 cm).(3)The correlations among ROC,LFOM,and TOC in all age groups are extremely significant.The correlations between TOC,ROC,LFOM,total nitrogen,available nitrogen and available phosphorus were relatively strong at different ages(except for 0-50 years).The correlation between TOC,ROC,LFOM,available potassium,exchangeable calcium and exchangeable magnesium were relatively weak(except for over 500 years).The correlations among TOC,ROC,LFOM and soil nutrients over 500 years were extremely significant.