| Jinyunshan national forest park is located in north suburb of Chongqing, 32.5 km away from the city center, at 106°20'east longitude and 29°49'north latitude, beside Jialing River which is upstream of Three Gorge reservoir. It covers 7600.0 hm2, with the peak altitude of 952.2 m. Annual average temperature of it is 13.6℃, mean annual relative humidity is 87%, and average annual precipitation amount is 1611.8mm. Soils in it can be classified as acidic zheltozem that developed from quartzose sandstone in the Triassic Xujiahe Formation (T3Xi).Mt. Jinyun is abundant in plants and there are diversiform vegetation types that belong to north semitropical evergreen broad-leaved forests. The semitropical evergreen broad-leaved forests in our nation are the largest in the world, which can be regarded as representative of such forests. And north semitropical evergreen broad-leaved forest is one of the most typical vegetation types in the semitropical area of China. Because of locating in suburb of large city, the ecosystem was interfered severely. The disturbances acted on the ecosystem in history including tourism, trampling, lopping, cultivation, fire, etc. Vegetation types of Mt. Jinyun in exist formed under the influence of long-term disturbance by human beings and diversity of microenvironments in a climatic zone. Nowadays, the disturbing factors mainly include tourism, trampling and forestation. There are 6 vegetation types in the forest park at present, which can be divided into 32 series, 54 clumps, including Evergreen broad-leaved forest, Coniferous forest, Bamboo forest, Evergreen broad-leaved shrub, Shrub-grassland and aquicolous vegetation. The succession of vegetation is in accordance with Shrub-grassland →Coniferous forest → Coniferous-Broad leaved mixed forest → Evergreen broad-leaved forest. Meanwhile there are some non-linear successive processes, such as Shrub-grassland → Fir-broad-leaved mixed forest, or Shrub-grassland → Coniferous-broad leaved mixed forest. In addition, the bamboo forest cultivating by people forms large polyclimax. These comparatively integrated secondary succession communities in the forest park are good examples for studying secondary succession of semitropical forest communities interfering by the activities of human beings.With sparse vegetation, soil erosion was serious in Yangtze River Three Gorges area, so that vegetation restoration and regeneration had to be operated to conserve soil and water. Vegetation restoration and regeneration was essentially a progress of forest progressive Succession. So plant secondary succession in Mt.Jinyun could be recognized as the epitome of the engineering of vegetation restoration and regeneration in Three Gorges area.In any forest, plant and soil always change together during vegetation succession. So the relationship between plant and soil changes was one of the most important content of ecological research. We studied all of the following factors that impacted on forest soil and plant development, such as changes of Communities structure, variation of forest floor, chemical characteristics of runoff water and anthropocentric disturbance. The aim of this study was to investigate the relationship between plant succession and soil properties. We also studied hydrological cycle in thesystem, which aimed to realize forest's capacity of holding soil and water, and to recognize nutrient cycling of the ecosystem.These studies are important on evaluating state of natural vegetation in north semitropical areas under influence of human beings, protecting natural vegetation and supplying information on reforestation of this area.We selected some typical plant communities to represent different successive stages. Existing Disturbances in forest were classified to 5 degree. Selected communities included Shrub-grassland, Coniferous forest, Coniferous broad-leaved mixed forest, Evergreen broad-leaved forest, Phyllostachys pubescens forest, Fir broad-leaved mixed forest and bare soil, 7 treatments, and each of them were replicated four times.The mainly investigated contents were as follows: (1)Species diversity analysis: Species richness, Brillouin index of species diversity and even degree. (2)Forest floor analysis: Litters amounts, nutrient content, decomposing content and water holding capacity, etc. (3) Soil physical properties analysis: Mechanical compositions, bulk density, porosity and water holding capacity, etc. (4)Soil chemical analysis: Organic matter, total and available nutrients (nitrogen, phosphorous and potassium), pH, cation exchange capacity and base saturation, etc. (5)Chemical characteristics of runoff under different vegetation types: COD, BOD, DO, pH, Total N, Total P, cation (Ca2+, Mg2+, K+, Na+, NH4+) and anion (SO42\ NO3', NO2\ Cl"), electric conductance, etc.Specie diversity indices and canopy density were investigated in many standard squares. Soil samples were collected from many spots which the number was calculated with statistics theory. Soils, litters and runoff water contents were analyzed with national standard methods. Data processing and statistics was counted by DPS system. The results as follows:1. MtJinyun existed typical and rich breed genotypes. Vegetations structure, density and function were different in successive communities. Species diversity indexes of herbaceous layers and shrub layers in successive communities changed in accordance with plant successive discipline. Species diversity increased in primary successive stages, reduced in high stages. The most diversified stage was not the climax type, but the two mixed forest, and the lowest was the shrub grass-land. Different from those two layers, Species diversity of tree layers increased along with the process of succession, Reaching the highest in Evergreen broad-leaved forest, the S, H, J was 12.8, 2.790 and 0.906 respectively, and the lowest was in Phyllostachys pubescens forest as 5.5, 0.350 and 0.167, showed the order as X4>X6>X3>X2>X5.The climax X4 was the most stable states. Different from other successive communities, every species diversity indexes of Phyllostachys pubescens forest was always low. In a word, we can conclude that plant secondary succession in this ecosystem was complex and orderly.2. According to the capacity of storing and supplying nutrients, forest floor was very important in forest ecosystem. It could be recognized as nutrient source as well as nutrient sink in the same time.This capacity could enhance with community succession. Primary successive stage as shrub grass-land which plant biomass production and Utters amount (703 kg/hm2) was low, caused to low storing nutrient capacity, low decomposing amount, and low species diversity. Storage amount of climax was the largest in successive communities, up to 1.13x104 kg/hm2, with the highest nutrient contents and the highest decomposing amount that could supply a large number of nutrients for plant producing, and led to the highest species diversity and biomass production.On the other hand, forest floor significantly affected ecosystem hydrological cycling, because litters covered on forest soil could prevent soil eroding. But litters could prevent soil water complement from precipitation because of its water holding capacity and water vaporizing.3. Along with plant successive processing, soil clay content increased, which indicated the good condition of soil development, and soil depth became thicker, structure improved, bulk density diminished and porosity augmented at the same time. All of the study data testified that soil structure of evergreen forest was the best one and the shrub grass-land was the worst one. Soil physical properties strongly impacted on soil condition of water, fertility, air, temperature etc.Forest ecosystem hydrological cycle was influenced by changes of soil physical properties. The study proved that water holding capacity was greater in high successive series than that in primary ones. Meanwhile, hydrological cycle in woodland was essentially different from bare land. Because of the powerful water holding capacity of plant canopy and litters, the whole evapo-transpiration rates was greater in woodland, thus soil water content in woodland were less than bare land, and the runoff rates were also less than it.4. As the plant community developed from primary stage to climax, concentrations of organic matter was 19.46 g/kg (XI), 36.96 g/kg(X2) , 50.13 g/kg (X3) . 71.58 g/kg (X4) > 31.64 g/kg (X5) . 59.02 g/kg (X6) and 49.95 g/kg (X7) respectively. Total N and available N, K also increased at the same time. These changes related to litters accumulating and decomposing. Correlation analysis results indicated that total nutrition and available nutrition in soil had positive linear regression to litters nutrient content and decomposing amount. Contrasted to Climax soil, soil properties in other successive communities showed the order: X6>X7>X3>X5>X2>X1, thrown out that soil fertility improved in company with community succession. So soil properties always changed along with forest ecosystem community succession. These changes occurred together, mutually affecting one another, with hardly any simple cause-and-effect relationships becoming evident. When edaphic conditions adapted to the next generation, vegetation replace occurred. This was the self-fertility function of ecosystem, and was one of the driving functions of community succession.At the same time, soil pH decreased significantly in successive communities. The mean pH was 5.23 (XIX 4.65 (X2X 4.09 (X3X 4.07 (X4X 4.84 (X5X 4.40 (X6) and 4.08 (X7) .Soils in the forest almost can be classified as severe acidic sandy loam. According to soil acidification process, the mainly cause of soil acidification was acid sediment, acid leaching, plant nutritionalcharacteristics and litters decomposing. The study was conducted plant, soil, hydrological and geological cycle to find out soil acidification mechanism. Results showed that there was a long-term of stable flat and a limit range existing in pH of forest soil. Soils could not be continuously undergoing acid. The Evergreen broad-leaved forest in the experimental stands showed no severe damage or nutrient deficiencies despite the relatively low pH (4.07). It is feasible to afforest in this area.The concentrations of soil organic matter , total N and available nutrition in soil layers showed A>B>C. For example, total nitrogen in Evergreen broad-leaved forest was 2.31g/kg (A), 0.66g/kg (B), 0.12g/kg (C). This reflected significant differences of soil properties in soil profiles which affected by the litters, the root growth, the edaphon and the fauna, etc.The relationship of soil properties between the climax and other succession communities in different season was studied. The relational order was the same as X6>X7 or X3 >X5>X2>X1.5. The results of runoff water chemical composition in different vegetation types showed that, among the 17 water quality parameters in runoff water, difference of Ca2+ concentration was the greatest, and Ca2+ difference could make for differences of electric conductance and hardness. According to correlation analysis, the significant changes in Ca2+ were associated with the exchangeable Ca2+ and pH in soils in a sense. On the other hand, research on the process of hydrodynamics could conclude that slope, soil infiltration practices and plant greatly impacted on Ca2+concentration. Water quality parameters such as COD, BOD, DO, Total N, Total P, pH, Mg2+, K\ Na\ NH4+, SO42', NO3", Cl* had not showed statistical significantly difference.All of the results suggested that chemical composition of runoff water mainly controlled by climate, parent material and air quality, and different plant-soil system influenced little to it under the same conditions.In this ecosystem, most of nutrients accumulated as it imported with precipitation more than that outpoured with runoff. These nutrients included total N, total P, Mg2+ NH4+, NO3", NO2", Cl" and SO42' etc. Otherwise, Ca2+, K+ and Na+ had severely outpoured from forest, showed negative accumulation in some communities.As nutrients concentrations were not high in runoff water, nutrients didn't outpour greatly either in bare land. Soil quality declined in sparse vegetation land didn't cause by nutrients outpoured with runoff. Without vegetation pose a significant risk to the soil, causing clay and sandy erosion and depletion of nutrients in severe cases.6. We could conclude that secondary succession of vegetation always occurred under anthropocentric disturbance on MtJinyun. Although anthropocentric disturbance intensively affected plant-soil system in shrub grass-land, the shrub grass-land area was not large enough to cause damage on whole forest structure and function; neither did disturbances transform progressive succession to retrogressive succession.
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