| Under the background of global warming, research on carbon (C) and nitrogen (N) cycling of forest ecosystem becomes one of scientific focus. As "an important ecological barrier of the Yangtze river basin", the Rainy Area of West China was one of the ideal place for study on the function and benefit of different kinds of vegetation restoration ecosystem. To estimate the C and N storage of vegetation restoration ecosystems and several kinds of vegetation restoration has been studied in central area of the Rainy Area of West China. Methods of typical plots and standard tree field investigation combined with laboratory analysis was closed to calculate the organs biomass, compare the allocation pattern of C and N in the tree shrub herbs of ecosystems, analysis soil physical chemical properties and soil organic carbon (SOC) components. The C sink function of different types of vegetation restoration ecosystem was discussed in the Rainy Area of West China. Major conclusions were as follows:(1) When vegetation restoration, the impact of site preparation was strong, effective soil depth of all forest land was below to 50cm, soil horizon differentiation was not obvious, the feature of lithogenic soil was apparent. Forest vegetation restoration has improved slightly the 0-20cm surface soil physical properties (soil density, water content, porosity, etc.). Compared to subsoil of two coniferous forest soils, topsoil pH decreased about 0.8-1.0 units. Concentration of soil organic matter, available N, phosphorus (P) and potassium (K) in forest surface soil were mostly higher than that of in wasteland soil and gradually decreased with depth.30 years of vegetation recovery, the impact on forest soil properties mostly exist in 0-20 cm top soil layer.(2) Stand density was about 1200 to 1600 tree/hm2. The density of afflnis was 500 clump/hm2. The average tree height (21.3 m), diameter at breast height (18.3 cm) and volume (422.9 m3/hm2) of Metasequoia were higher than other forest stand. Based on the biomass, five forest vegetations were divided into two levels, secondary forest, affinis, Metasequoia (170.240 t/hm2～193.743 t/hm2) was first layer, Alder and Cryptomeria (85.234 t/hm2～94.149 t/hm2)was second layer. The stand organs biomass was roughly as follows:trunk> roots> branches> leaves, concentrations of C, N, P, and K in these forest stand were 479.54 g/kg、4.00 g/kg、0.58 g/kg and 3.41 g/kg, respectively. Carbon storage and biomass showed a consistent stratification, but C storage between two layers was approximately doubled. The average concentrations of organs was trunk> branches> roots> leaves, about 57.6%-57.6% of total C was stored in the trunk. The average concentrations of N> P and K in organs were trunk> branches> roots> leaves, stand N> P and K storage were all below to 1 t/hm2.(3) Shrub biomass of alder forest (2.353 t/hm2) was significantly higher than secondary forest (0.276 t/hm2). Shrubs average C concentration was 448.96 g/kg. The C storage was alder forest> secondary forest. In herb layer, biomass in wasteland was the largest, followed by secondary forest. There was no understory plants growth within affinis. In herb layer, the average C concentration was 407.08 g/kg. C storage was 0.543 t/hm2～3.195 t/hm2. The highest of wasteland was 5.9 times higher than the lowest of sequoia groves. The average concentrations of N P K in different plant layer were as follows:herb> shrub> tree; sum of the storage of N P K (N+P+K) of shrub layer in alder was higher than that of in secondary forest, it also shown an order in Herb layer of wasteland> secondary forest> Metasequoia> alder>Cryptomeria. Vine biomass was 0.545 t/hm2 and 0.299 t/hm2 of the alder and secondary forest, respectively.(4) Forest litter was mostly composed by Branches and leaves. The existing average amount was 5.416 t/hm2 (change in 1.826 t/hm2 to 9.565 t/hm2). The average C concentration was 452.33 t/hm. The average C storage was 2.475 t/hm. Existing amount, C concentration and C storage were highest in Cryptomeria forest, the lowest was in Metasequoia forest. There was no litter accumulated in wasteland. The average N P K concentration of litter was 5.38 g/kg,0.55 g/kg and 2.92 g/kg, respectively. The average N, P, K storage was 0.0305 t/hm2,0.0030 t/hm2 and 0.0126 t/hm2 respectively. The highest of concentration and storage of N and P were in affinis litter, the lowest was in Metasequoia litter. K concentration and storage in Metasequoia litter were the highest still, but the lowest was in Cryptomeria litter. As the existing amount increased litter C repository rose.(5) A slight vertical changes had down through the soil profiles, main change appeared in 0-20 cm topsoii. The concentrations of SOC, TN, TP in topsoii of alder higher than other topsoii, followed by affinis, similar levels appeared in secondary forest, Metasequoia and wasteland.1 m deep soil varied in soil C repository from 56.737 t/hm2 to 104.821 t/hm2, the highest of alder was 1.9 times storage of secondary forest. Topsoii C repository of different vegetations occupied total C storage with 39%-56%. The surface aggregation of SOC was obviously, especially forest soil. Except secondary forest, both forest topsoil and the whole soil profile had higher storage of TN and TP than wasteland soil, especially alder forest and affinis forest.(6) Differences in SOC and N fractions displayed in topsoil mainly. The concentration varied with the vegetation types, also had closely relationship with SOC and TN, respectively. Concentrations of SOC and TN fractions all showed a slightly downward trend in soil profiles. Surface soil humic acid (HA) was lower than the fulvic acid (FA), soil humic acids (HA+FA) concentration was as follows:broad-leaved forest and affinis forest> wasteland> coniferous forest. After the forest vegetations restoration, concentration of topsoil easily oxidized carbon (EOC), particulate organic carbon (POC), water dissolved organic carbon (WDOC) and salt dissolved organic carbon (SDOC) was increased. Surface soil water dissolved nitrogen (WDN), salt dissolved nitrogen (SDN), hydrolyze nitrogen (HN) also increased to a certain extent. SOC and N components of alder forest topsoil increased more conspicuous. Except alder forest, concentrations of soil forest topsoil microbial biomass carbon (MBC), microbial biomass nitrogen (MBN) were lower than that of wasteland. SDOC leaching was obvious. There were good linear relationship between HA, FA, EOC, POC and SOC, and between WDN, SDN, MBN, HN and TN too. There were significant (a< 0.05) correlation between SOC and N, P, K, while soil density and SOC was significant (a< 0.05) negative correlation (r=-0.300). The negative correlation were between pH, sand silt clay contents and SOC but no significant (a> 0.05). The purple soil had similar machinery composition and heavy-texture, the relationship between SOC decomposition and accumulation and soil texture was smaller.(7) the average C storage in the forest ecosystem was 154.03 It/hm2 (136.306 t/hm2-180.235 t/hm), was about 2.5 times of the wasteland ecosystem, Affinis, Metasequoia and Alder forest has a great advantage. Storage of vegetation, litter and soil of forest ecosystem occupied total storage of SOC with 29.69%-59.99%,0.55%-3.71%,3.71%-68.83%, respectively. The proportion of soil C pool was less than the proportion of the soil layer C pool in National and Sichuan forest ecosystems (74.0%,83.2%). in wasteland, about 95% of total SOC was in soil C pool, the system anti-interference ability of C pools was very weak. With the increase in biomass of trees, vegetation C repository increased and soil C storage was reduced, the soil C repository of alder deciduous tree was the largest. The vegetation C repository of forest vegetation types was bigger, the average ratio of soil C repository to vegetation C repository was 1.3 (0.7-2.3:1), well below 18.4 of wasteland. The forest ecosystem C storage was higher 2.20～2.90 times than the wasteland ecosystem, its C sink function was obviously. Nitrogen storage of several types of vegetation ecosystem was about 7.435 t/hm2～14.694 t/hm2, alder forests was the largest, wasteland was minimum, the allocation of N pools in vegetation ecosystems was soil N pool> litter N pool> vegetation N pool; The alder forest soil N pool was the highest and 1.6 times higher than the wasteland,2.0 times higher than the secondary forest, its N storage function was better than the others. About (63.3%-89.7%) of total N storage was stocked in soil pool of forest ecosystems, in wasteland, soil N pool had 99.3% of the total N storage. Nitrogen storage was more concentrated than C sinks, and more fragile. In summary, the forest vegetation restoration of ecosystems C and N sink function were better than mat of wasteland. The C sink capacity of different forest stands were different, vegetation was the main repository, soil C and N repository had large potential. |
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