Accumulation Of Carbon, Nitrogen, Phosphorus, And Fractionation Of Soil Phosphorus In The Subtropical Human-assisted Natural Regeneration Secondary Castanopsis Carlesii Forests

A massive afforestation campaigns were launched in subtropical China in the last few decades. It resulted in the homogeneity and conifer problem that caused a series of problems, such as reduction of biodiversity, plant diseases by insects and pests invasion and soil erosion, which enormously hazarded regional ecological security and weakened the response ability to climate change of forest. Considering the existing problems of forest managements, as well as the increased global climate changing, reasonable forest management practices in the 21st century have been attracted a worldwide interest. Nowadays large quantities of investigations have been devoted into multi-function forest managements in many regions of China Human-assisted natural regeneration of evergreen broad-leave forest is an important practice and is widely used in forest afforestation recovery in Fuji an Province. However, the before studies focused more on the forest timber yield and soil fertility The researches of assessments of ecosystem carbon (C) accumulation, nitrogen (N) and phosphorus(P) dynamics were lacking. Soil P availability may be a key factor that impedes the understanding of forest production and carbon accumulation in red soil region of subtropical China This study was carried in Castanopsis fissa nature reserve and human-assisted natural regeneration secondary Castanopsis carlesii forests (HC) of Sanming, Fuji an. Therefore, The purpose of research were to:(1) compare the impact of different types of forest regeneration on biomass, the characteristics of C, N and P accumulation and soil P fractions among human-assisted natural regeneration secondary Castanopsis carlesii forests, the plantation of Cunninghamia lanceolata (CF) and Pinus massoniana (PM), and natural primary forest (NF). It illuminated the long effects of forest regeneration on the characteristics of C, N and P accumulation and soil phosphors fractions; (2) evaluate the characteristics of C, N and P accumulation and the variations of phosphorus availability in an age sequence of HC (21,31,49 years-old stand) in Shun-Chang County, Fujian province The main resul ts were as follows:(1)The total ecosystem C storage of NF, HC, CF and PM were 331.57 t hm-2,291.87 t hm-2,218.79 t hm-2 and 213.91 t hm-2, respectively. The plant C pools occupied by an average of 56.5%,48.9%,42.1% and 39.7% of the total C storage, followed by soil C pools (42.3%,50.0%,56.6% and 59.4%); The plant and soil C pools in HC were higher than those in CF and PM. It caused by the differences of species, stand structure and regeneration types. The fast C pools (leaf and fine root) and slow C pools (branch, stem and coarse root) of HC were higher than those of CF and PM. The subsurface soil C pool (20-100 cm) of HC was higher than that of CF and PM. And the proportion of subsurface soil C pool in HC was higher than that of CF and PM.The N pools of NF, HC, CF and PM were 9.93 t hm-2,8.40 t hm-2,6.08 t hm-2 and 6.05 t hm-2, respectively. The plant N pools occupied by an average of 12.7%,13.3%, 5.5% and 5.4% of the total N pool, followed by soil N pools (86.5%,86.0%,94.1% and 94.4%).The P pools were 3.95 t hm-2,3.70 t hm-2,3.74 t hm-2 and 3.73 t hm-2, respectively. The plant P pools occupied by an average of 2.2%,1.6%,0.8% and 0.6% of the total P pool, followed by soil P pools (97.9%,98.3%,99.2% and 99.4%). The fast cycling nutrition pools (leaf and fine root) and the slow cycling nutrition pools of HC were higher than those of CF and PM. The soil N pool in HC was higher than that in CF and PM, but there were no significantly differences of the soil P pool among the three forests. Above research results indicated that the poolsof C, N and P were higher in HC.(2) The total ecosystem C pools in 21,31 and 49 years-old of HC were 223.6 t hm-2 239.4 t hm-2 and 320.5 t hm-2, respectively. The plant C pools occupied by an average of 44.9%,52.8% and 61.2% of the total C pools, followed by soil C pools (54.0%,46.2% and 38.0%, respectively). The accumulated rates of C of HC were various in different stand ages. The stems rapidly accumulated C in young stage. In mature stagethe rate of C sequestration declined, but the leaves, branchs and roots still kept higher accumulation rate of C. The results showed a higher level of C sequestration of HC. However, the soil C pool s were not increase si gnificantly i n ages of HC.The N pools in 21,31 and 49 years-old of HC were 9.16 t hm-2、9.30 t hm-2 and 11.46 t hm-2, respectively. The plant N poolsoccupied by an average of 7.7%,12.5% and 20.8% of the total N pools, followed by soil N pools (91.5%,86.7% and 78.6%, respectively); The P pools were 3.13 t hm-2,3.12 t hm-2 and 3.58 t hm-2. The plant P pools occupied by an average of 1.5%,1.7% and 3.5% of the total P pools, followed by soil P pools (98.4%,98.1% and 96.4%, respectively). The N and P pools were increased in ages of HC. And the soil N and P pools showed a trend of increasing with stand ages.(3)Compared to temperate and tropical forests, soil total P(231-312mg kg-1), Labile P (5.04-18.74 mg kg-1) and Bray-I P (0.63-3.87 mg kg-1) of four types of forests (NF, HC、CF and PM) were lower. The deficiency of total P and avai lable P of soil may be the important reason of limitation of forest productivity. Organic P and availability P in surface soils were significantly affected different regeneration forest types. Total organic P of HC was significantly lower than that of CF and PM, but labile organic P was significantly higher than that of them. The Labile P of HC was the highest but the slowly cycling P was the lowest in three types of forests. The significantly highest amounts of occluded P were found in PM. The differences of forest regeneration and vegetation types might be the key factors that affected ecosystem plant-avai lability P stock.(4)The total organic P of soil increased significantly in ages of HC. In different organic P forms, NaCHO3-Po and NaOH-Po increased significantly but the c.HCI-Po was no significant increase in ages of HC. The total inorganic P of soil was not significantly increased in ages of HC. The labile P and slowly cycling P of soil were significantly increased in ages of HC but occluded P was no significantly difference(5)The N, P contents had significant differences between species and components in HC. The N, P contents of leafs and fine roots were higher than those of branches, stems and coarse roots. The effects of DBH on N and P contents in each component of C.carlesii and C.fissa and Schima superba were various The leaf contents of N, P and species were limited by P according the ratios of N/P and the contents of P.In all, comparing to CF and PM, there were higher biomass, C, N and P accumulation in HC, and the types of human-assisted natural regeneration in HC also improved the soil organic P and labile P of different types of forest.