Soil Organic Matter Dynamics Along a Vertical Vegetation Gradient in the Gongga Mountain on the Tibetan Plateau

Our knowledge about soil organic matter (SOM) dynamics is limited although this is an important issue in the study of responses of ecosystems to global climate changes. Twelve sampling plots were set up every 200 m from 1 700 to 3 900 m along the vertical vegetation gradient along the east slope of Gongga Mountain. Samples were taken from all 12 plots for SOM content measurement, although only 5 of the 12 plots were subjected to radiocarbon measurements. A radiocarbon isotope method and a time-dependent model were used to quantify the SOM dynamics and SOM turnover rates along the vertical vegetation gradient. The results showed that the SOM turnover rate decreased and turnover time increased with soil depth for all vegetation types. The litter layer turnover rates presented a clear trend along the gradient. The litter layer turnover rates decreased with an increase in elevation, except that the litter layer turnover rate of mixed forest was higher than that of evergreen forest. Climatic factors, such as temperature and precipitation, were the main factors influencing the surface soil carbon dynamics. The turnover rates of the subsoil (including the A, B, and C horizons in the soil profiles) along the vertical gradient had no clear trends. The SOM of subalpine shrub and meadow turned over more slowly than that of the forest types in almost all soil horizons. The characteristic of short roots distributing in the upper part of the soil profile leads to different SOM dynamics of shrub and meadow compared with the forest types. Coniferous and mixed forests were susceptible to carbon loss from the young carbon pool, but their long and big roots resulted in high △^14C values of the deep soil profiles and increased the input of young carbon to the deep soil. In evergreen forest, the carbon cumulative ability from the B horizon to the C horizon was weak. The different vegetation types, together with their different modes of nutrient and carbon intake, may be the mechanism conditioning the subsoil organic matter dynamics.     

Study on optimization of moisture retention for golf green rootzone soil mixtures

Most golf course green have been constructed with pure sand or sand-based rootzone mixes. As we know, high sand content provides rapid drainage despite sand’s inefficiency in retaining moisture. However, drainage capability and water retention are both essential elements to the golf course green, and the addition of peat could increase the soil moisture retention, therefore, the research on the drainage capability and water retention of the sandy golf green has become more and more important these years. In this study, extreme vertex design was applied which is one of the mixture experiment designs widely used in mixture experiments, the study investigated the effects of the thirteen different rootzone soil mixtures using middle-coarse, fine sand, very fine sand plus silt and clay as well as peat as the materials under three kinds of golf green profile (1-layer profile, 2-layer profile, 3-layer profile) conditions on the water retention of green rootzone. Through the qualitative, quantitative and optimization analysis of water retention capability of the sandy golf green, evidence a basis for choice of green profiles and rootzone matrix could be provided. And the significantly correlative regression model was established between the moisture retention and components of rootzone soil mixture. In addition, the order of factor contribution ratio, effect of single and double factor and optimization of the model were analyzed in detail. The results were as follows: both green profile and soil mixture, which had interaction of each other, had significant effects on soil moisture retention. Additional attributes include high porosity and greater water holding capacity than sand, and the higher content of peat, fine sand plus silt and clay, the better water retention. The mixtures had much higher water content in 1-layer profile than that in the other two profiles. There was significantly higher water content in 2-layer profile for pure sand mixtures (A–E) and low peat mixture (F) than that in 3-layer profile, while there was no higher water content for other 7 high peat mixtures (G–M) (>5%) in 2-layer than that in 3-layer profiles. The significance of key factors in rootzone soil mixture on moisture retention were: very fine sand plus silt and clay > peat > middle-coarse > fine sand. According to the moisture retention 15–25% specification of USGA (United States Golf Association), the optimal soil mixture in 1-layer profile was: middle-coarse 71.4–73.5%; fine sand 17.8–21.5%; very fine sand plus silt and clay 6.8–8.4%; peat 0–1%. The optimal soil mixture in 2-layer profile was: middle-coarse 65.0–73.4%; fine sand 17.8–20.5%; very fine sand plus silt and clay 7.5–8.9%; peat 0.2–6.3%. The optimal soil mixture in 3-layer profile was: middle-coarse 62.3– 73.9%; fine sand 17.7–21.4%; very fine sand plus silt and clay 7.3–10.7%; peat 0–6.3%. These optimal recipes took through the limitation of previous research, which were practically important to golf green soil selection and profile design. Thus, both proportion and interaction should be considered when we choose the soil mixture.     

Distribution and interspecific correlation of root biomass density in an arid Elaeagnus angustifolia–Achnatherum splendens community

Main objective of this study was to determine the interspecific relationships between two dominant species in terms of root distribution in a typical arid tree-herbage (Elaeagnus angustifolia–Achnatherum splendens) community at Xidatan, Pingluo County, Ningxia Autonomous Region, Northwest China. Eight concentric zones (namely, Z1–Z8) were set from the bases of E. angustifolia individuals to the open lands and five soil profiles were excavated in each zone. Each soil profile was divided into five layers at the depths of 0–10 cm, 10–30 cm, 30–60 cm, 60–100 cm and 100–150 cm. Roots were collected for each species, and soil water content (SWC) and soil bulk density (SBD) were measured for each layer. We found noteworthy roots layer separation in the sub-canopy zones (Z1–Z4). The soil layers with highest fine root biomass density (FRBD) of A. splendens was primarily in the 0–10 cm, which were significantly shallower than those of E. angustifolia; whereas in the inter-canopy zones (Z5–Z8), inconsistent separation, or even overlapping of highest-FRBD-layers emerged between the two dominant species. Correlation analyses showed that negative correlations of FRBD between the two species mainly occurred in those soil layers with relatively higher FRBD and lower SWC. In contrast, positive correlations corresponded with relatively lower FRBD and higher SWC.     

Distribution and interspecific correlation of root biomass density in an arid Elaeagnus angustifolia–Achnatherum splendens community

Main objective of this study was to determine the interspecific relationships between two dominant species in terms of root distribution in a typical arid tree-herbage (Elaeagnus angustifolia–Achnatherum splendens) community at Xidatan, Pingluo County, Ningxia Autonomous Region, Northwest China. Eight concentric zones (namely, Z1–Z8) were set from the bases of E. angustifolia individuals to the open lands and five soil profiles were excavated in each zone. Each soil profile was divided into five layers at the depths of 0–10 cm, 10–30 cm, 30–60 cm, 60–100 cm and 100–150 cm. Roots were collected for each species, and soil water content (SWC) and soil bulk density (SBD) were measured for each layer. We found noteworthy roots layer separation in the sub-canopy zones (Z1–Z4). The soil layers with highest fine root biomass density (FRBD) of A. splendens was primarily in the 0–10 cm, which were significantly shallower than those of E. angustifolia; whereas in the inter-canopy zones (Z5–Z8), inconsistent separation, or even overlapping of highest-FRBD-layers emerged between the two dominant species. Correlation analyses showed that negative correlations of FRBD between the two species mainly occurred in those soil layers with relatively higher FRBD and lower SWC. In contrast, positive correlations corresponded with relatively lower FRBD and higher SWC.     

Plant community complexity in the arid valley of Minjiang River, southwestern China

Biocomplexity theory is becoming increasingly important in understanding natural vegetation dynamics and interrelation among all components of the ecosystem. In this study, based on the field investigation of plant species and environmental factors (altitude, microtopography, soil water content, and soil nutrients) in an arid valley of the upper reaches of Minjiang River, Sichuan Province, southwestern China, plant community complexity and its relationship with environmental factors, community diversity, species evenness and richness were studied. Both total and structural complexities of the communities showed a “high- low-high” tendency with the increase in altitude of the area, which meant that the complexity of communities was the highest at the sites of low and high altitude, whereas it was the lowest at the sites of intermediate altitude. It was found that the total community complexity had significant quadratic correlations with soil organic matter (SOM) content, total nitrogen (N), hydrolyzable N, soil water content, and available potassium (K), whereas it had no significant correlations with soil total K, total phosphorus (P), available P, and pH value. The total community complexity positively correlated with community diversity, species evenness and species richness, whereas the structural complexity negatively correlated with the community evenness. Of the two components of the total community complexity, namely, the structural complexity and the structural diversity, the structural complexity was more sensitive than the structural diversity to the changes of species in the community, which was not only related to the community evenness but also to the community richness. The relative contribution of both the structural complexity and the structural diversity to the total complexity would be different for different study areas or ecosystems.     

New judgement on the source of soil water in extremely dry zone

There is always a relatively high moisture content in the shallow soil layer in Gobi area on the top of the Mogao Grottoes in the extremely dry zone. This paper gives out a new judgement on soil water source through field experiments using the isolated water method, simulated rainfall method and greenhouse method. Under the condition of typical hyper-arid climate far away from rainfall effect and after cutting off the connection of soil and groundwater the simulated rainfall experiment was conducted, through putting up a plastic greenhouse to obtain a relatively closed space and extracting the condensed water on the film surface, the soil water output from the greenhouse was monitored. The experimental results show that generally the rainfall can be completely evaporated in about 20 days under the isolated condition. In the relatively closed space sheltered by arched greenhouse in the Gobi area water can be continuously transferred outward from subsoil and condensed on the roof film, with a daily output quantity of 3–5 g/m²d. After prolonged output soil water content remains significantly higher than that of the control and before covering by arched shed. Comprehensively judging from this, groundwater is an important source of soil water in addition to precipitation. The new judgement has a very important practical significance to the water research of the groundwater–soil–plant-atmosphere circle (GSPAC) and the recovery of the desertified environment.     

New judgement on the source of soil water in extremely dry zone

There is always a relatively high moisture content in the shallow soil layer in Gobi area on the top of the Mogao Grottoes in the extremely dry zone. This paper gives out a new judgement on soil water source through field experiments using the isolated water method, simulated rainfall method and greenhouse method. Under the condition of typical hyper-arid climate far away from rainfall effect and after cutting off the connection of soil and groundwater the simulated rainfall experiment was conducted, through putting up a plastic greenhouse to obtain a relatively closed space and extracting the condensed water on the film surface, the soil water output from the greenhouse was monitored. The experimental results show that generally the rainfall can be completely evaporated in about 20 days under the isolated condition. In the relatively closed space sheltered by arched greenhouse in the Gobi area water can be continuously transferred outward from subsoil and condensed on the roof film, with a daily output quantity of 3–5 g/m²d. After prolonged output soil water content remains significantly higher than that of the control and before covering by arched shed. Comprehensively judging from this, groundwater is an important source of soil water in addition to precipitation. The new judgement has a very important practical significance to the water research of the groundwater–soil–plant-atmosphere circle (GSPAC) and the recovery of the desertified environment.     

Effects of drought stress on the osmotic adjustment and active oxygen metabolism of Phoebe zhennan seedlings and its alleviation by nitrogen application北大核心CSCD

Aims Two-year-old seedlings of Phoebe zhennan were used in this study to explore the responses of osmotic adjustment and active oxygen metabolism to drought stress and the mitigation effect of nitrogen application. Methods The soil water content was firstly adjusted to four treatment levels, i.e. 80% of field water holding capacity (80% FC), 50% FC, 30% FC and 15% FC, respectively. The physiological variables of plants were measured after one week, and then three nitrogen application rates, control (N0), medium nitrogen (MN) and high nitrogen (HN) were performed at an interval of 7 days for four times (7 d, 14 d, 21 d and 28 d, respectively). The same physiological variables were determined again one month after the accomplishment of nitrogen application. Important findings 1) The free proline (Pro) and soluble sugar (SS) contents in the leaves increased significantly with the aggravation of drought stress after 7 days of drought, but the content of soluble protein (SP) was firstly increased and then declined. The increase of Pro content was especially obvious under severe drought (15% FC). After nitrogen application, the content of Pro raise further, but the values varied in drought treatment. The SS contents under sufficient water supply (80% FC) and mild drought (50% FC) were decreased by MN, but it did not change significantly when supplied with HN despite the soil water content. After nitrogen application, the SP contents under 80% FC and 50% FC were lower than those of no exogenous N, while they were opposite response under 30% FC and 15% FC. 2) Before nitrogen application, with the aggravation of drought stress, the hydrogen peroxide (H2O2) content, superoxide dismutase (SOD) activity, catalase (CAT) activity increased significantly, and the peroxidase (POD) activity showed an up-down trend. After nitrogen application, the content of H2O2 was generally deceased at each water condition, with the maximum decrease at MN, while the HN treatment was not conducive to reduce the content of H2O2. The activities of three kinds of enzymes responded differently to the severity of drought and the level of nitrogen application. 3) Before nitrogen application, the content of malondial-dehyde (MDA) in leaves increased significantly when the soil water content declined to and below 50% FC. The relative electrical conductivity (REC) was decreased at first, and followed by significant increase. Except severe drought (15% FC) stress, the MDA content showed a decreasing trend at MN, but a rebound at HN. As regards severe drought stress, however, the content of MDA increased at both MN and HN, indicating that nitrogen application is not a good choice to alleviate the damage caused by severe drought stress. 4)Two-factor ANOVA revealed an obvious interaction between nitrogen application and drought stress. In conclusion, a proper amount of nitrogen (1.35 g·a–1 for each sapling) could somewhat alleviate drought stress no severer than 15% FC on seedlings of Phoebe zhennan, but excessive nitrogen at rate of or more than 2.70 g·a–1 per sapling is not recommended. © 2018 Editorial Office of Chinese Journal of Plant Ecology. All rights reserved.     

Plant community complexity in the arid valley of Minjiang River, southwestern China

Biocomplexity theory is becoming increasingly important in understanding natural vegetation dynamics and interrelation among all components of the ecosystem. In this study, based on the field investigation of plant species and environmental factors (altitude, microtopography, soil water content, and soil nutrients) in an arid valley of the upper reaches of Minjiang River, Sichuan Province, southwestern China, plant community complexity and its relationship with environmental factors, community diversity, species evenness and richness were studied. Both total and structural complexities of the communities showed a “high- low-high” tendency with the increase in altitude of the area, which meant that the complexity of communities was the highest at the sites of low and high altitude, whereas it was the lowest at the sites of intermediate altitude. It was found that the total community complexity had significant quadratic correlations with soil organic matter (SOM) content, total nitrogen (N), hydrolyzable N, soil water content, and available potassium (K), whereas it had no significant correlations with soil total K, total phosphorus (P), available P, and pH value. The total community complexity positively correlated with community diversity, species evenness and species richness, whereas the structural complexity negatively correlated with the community evenness. Of the two components of the total community complexity, namely, the structural complexity and the structural diversity, the structural complexity was more sensitive than the structural diversity to the changes of species in the community, which was not only related to the community evenness but also to the community richness. The relative contribution of both the structural complexity and the structural diversity to the total complexity would be different for different study areas or ecosystems.     

Soil moisture ecological environment of artificial vegetation on steep slope of loess region in North Shaanxi Province, China

By means of fixed-point monitoring and comparative analysis, soil water deficient situation, soil moisture dynamic variation laws, soil aridization and soil water compensation features under condition of different artificial vegetations were studied on 35–45° steep slope of loess region in North Shaanxi Province, China. The results showed that soil water was extremely deficient under condition of perennial artificial vegetation on steep slope, soil water storage (0–10 m) was only equal to 26.2%–42.0% of the field capacity in dry years, and in rainy years it was also only equal to 27.0%–43.3% of the field capacity. The order of soil water deficit was Caragana microphylla > locust > alfalfa > Chinese arborvitae > poplar > Chinese pine > wild land > apricot > Chinese date > farm land. Annual variations of soil moisture with the same vegetation were weakened with soil depth increasing, and occurred mainly in 0–200 cm soil layers. In the same growth season, all CVs (coefficients of variation) of soil moisture under condition of different vegetations were bigger and concentrated comparatively in 0–120 cm soil layers, but difference of CVs in different vegetations was small. Below 120 cm soil layers, CVs were smaller, but difference of CVs in different vegetations was bigger. Permanent dry soil layers always occurred under condition of perennial vegetation on steep slope, but the difference of soil aridization intensity was obvious among different vegetations and growth years. Soil water compensation and recovery depths in rainy seasons were 1.0–1.4 m, but the soil water storage increment and compensation degree in different vegetations were dramatically different. Soil water compensation depth in the same vegetation in rainy years was over 60 cm more than that in dry years, while the soil water storage increment in 5 m soil layers increased over 3 times. Under natural precipitation, the soil water deficit in artificial vegetation on steep slope cannot be ameliorated, and the soil aridization also can't be relieved.     

The effects of stubble retention and tillage practices on surface soil structure and hydraulic conductivity of a loess soil

The current cropping system of excessive tillage and stubble removal in the northwestern Loess Plateau of China is clearly unsustainable. A better understanding of tillage and stubble management on surface soil structure is vital for the development of effective soil conservation practices in the long term. Changes in surface soil structure and hydraulic properties were measured after 4 years of stubble management (stubble retained vs. stubble removed) under contrasting tillage practices (no-tillage vs. conventional tillage) in a silt loam soil (Los Orthic Entisol) in Dingxi, Gansu, the northwestern Loess Plateau, China. Our results indicated that after 4 years small but significant changes in soil properties were observed amongst the different tillage and stubble treatments. Surface soil (0–5 cm) under no-tillage with stubble retention had the highest water stability of macroaggregates (>250 μm), soil organic carbon (SOC) and saturated hydraulic conductivity. Significant correlation was found between water stable macro-aggregates and soil organic carbon content, indicating the importance of the latter on soil structural stability. The improvement in soil structure and stability was confirmed by higher soil hydraulic conductivity measurements. Consistently higher K_sat was detected in the no tillage with stubble retained soil compared to other treatments. Therefore, no-tillage with stubble retention practice is an effective management technique for improving physical quality of this fragile soil in the long term.     

The effects of stubble retention and tillage practices on surface soil structure and hydraulic conductivity of a loess soil

The current cropping system of excessive tillage and stubble removal in the northwestern Loess Plateau of China is clearly unsustainable. A better understanding of tillage and stubble management on surface soil structure is vital for the development of effective soil conservation practices in the long term. Changes in surface soil structure and hydraulic properties were measured after 4 years of stubble management (stubble retained vs. stubble removed) under contrasting tillage practices (no-tillage vs. conventional tillage) in a silt loam soil (Los Orthic Entisol) in Dingxi, Gansu, the northwestern Loess Plateau, China. Our results indicated that after 4 years small but significant changes in soil properties were observed amongst the different tillage and stubble treatments. Surface soil (0–5 cm) under no-tillage with stubble retention had the highest water stability of macroaggregates (>250 μm), soil organic carbon (SOC) and saturated hydraulic conductivity. Significant correlation was found between water stable macro-aggregates and soil organic carbon content, indicating the importance of the latter on soil structural stability. The improvement in soil structure and stability was confirmed by higher soil hydraulic conductivity measurements. Consistently higher K_sat was detected in the no tillage with stubble retained soil compared to other treatments. Therefore, no-tillage with stubble retention practice is an effective management technique for improving physical quality of this fragile soil in the long term.     

Effects of conservation tillage on soil organic matter in paddy rice cultivation

In this study, the effect of conservation tillage on soil organic matter (SOM) in paddy rice cultivation after 10 yr was investigated. Four treatments, disk till-fallow (DTF), disk till-wheat (DTW), conservation till-fallow (CTF) and conservation till-wheat (CTW) were used. The results indicated that the combinative application of no-tillage, ridge culture and wheat cultivation was a sound conservation practice in paddy rice cultivation. It not only significantly increased the concentration of SOM in the topsoil, but also affected optical and pyrolysis characteristics of humic acids (HA) through changing the composition and structure of SOM. At 0–10 cm, the greatest SOM content was in CTW, but declined sharply with depth, while in DTF, DTW and CTF the SOM content was not as high at the surface as in CTW, but did not decline as fast as in CTW. The oxidation stabilization of SOM was generally greater in no-tillage and ridge culture than that in disk till. The HA optical density in CTW at wavelength 665 nm and 465 nm was 0.122 and 0.705, while in DTF was 0.062 and 0.321, respectively. E₄/E₆ ratio in CTW was higher than that in the other treatments. The enthalpy capacity of the exothermal peak (360–365°C) for the HA DTA curve in no-tillage and ridge culture was lower than that in disk till, while the HA absorption peaks in 1000–1050 cm^?1 presented the reverse trend. The oxidation stabilization coefficient of HA in no-tillage and ridge culture was higher than that in disk till, indicating that the polycondensation degree and aromatization of HA were stronger. These findings suggest that it may be possible to manipulate paddy soil through conservational tillage and crop practices, and thereby maintain adequate SOM concentrations, and mitigate soil organic carbon loss from soil to atmosphere.     

Effects of fire disturbance on the soil physical and chemical properties and vegetation of Pinus massoniana forest in south subtropical area

A variety of studies on the impact of fire disturbance on ecosystems has shown that the physical and chemical properties of soil after fire disturbance change notably. Meanwhile, little is known about the effects of different fire intensities on the soil properties and vegetation after fire disturbance, especially in the south subtropical area. In this paper, we analyzed the soil physical and chemical properties, vegetation species and species diversity of fire center, fire edge (which was burned a year ago) and non-burned Pinus massoniana plantation in Gaoyao, Guangdong province, China. The results showed that the soil conductivity, water content, total nitrogen, total potassium, and available potassium content of fire center were significantly higher than those of the non-burned land, and pH was higher than that of fire edge, whereas the available nitrogen, total phosphorus and organic matter content were much lower, which were generally existed in 0–10 cm soil layer and 10–30 cm soil layer. Changes of the soil properties of fire edge were similar with those of fire center, but less significant, and seemed to be more complex. Effects of burning on the vegetation of fire disturbance plots were found to be notable, species number and average height of plants of fire disturbance plots were lower than those of the non-burned plots, a difference of species diversity and uniformity were also shown, and finally, the composition of plant community also changed, e.g., pioneer species such as D. dichotoma, etc., dominated, and drought-resistant plants, heat-resistant plants and positive plants increased after burning.     

Effect of rock fragments on the percolation and evaporation of forest soil in Liupan Mountains, China

The water-retaining capacity, percolation and evaporation of stony soil in Liupan Mountains, China, were measured in order to understand the effect of rock fragments on soil hydrological processes. The results indicated that the effective water-retaining capacity of soil is positively related with the volumetric content of rock fragments, but there is no relation between saturated water-retaining capacity and rock fragment content. For the soil layers within 0–40 cm, the steady infiltration rate increases with increasing volumetric content of rock fragments until it reaches the range of 15%–20%, and then it decreases when the rock fragment content further increases. For the soil layers below 40 cm, the steady infiltration rate always increases with increasing rock fragment content. The soil evaporation rate decreases with increasing volumetric content of rock fragments when it varies in the range of 0–20%, while the soil evaporation rate keeps basically stable when the rock fragment content is higher than 20%. The soil evaporation rate shows a rising tendency with increasing size of rock fragments.     

Hydrological Status of the spawning ground of Acipenser sinensis underneath the Gezhouba Dam and its relationship with the spawning runs

The spawning runs of Chinese Sturgeon (CS; Acipenser sinensis) were observed 37 times below Gezhouba Dam of Yangtze River between 1983 and 2004. Five hydrological factors (water temperature, water level, flow discharge, silt content and current velocity) were monitored on a daily basis at the spawning ground between October and November for 22 consecutive years (1983–2004). The effect of current velocity on the spawning ground at the bottom layer of the river, where CS was spawning for four years, was measured (1996–1999). The authors of this study analyzed the relationship between the five hydrological factors and the respective spawning runs. Twenty-two years of continuous observations indicated that the daily mean values of all the five hydrological factors fluctuated within a certain range when CS was spawning. It was concluded that the optimal values for the hydrological factors during the spawning runs are 18.0–20.0°C for temperature, 14100 m³/s for discharge volume, 42.0–45.0 m for water level above the sea level, and 0.2–0.3 kg/m³ for silt content in the water, wherein the current velocity above the bottom layer to stimulate the fish to spawn should be between 1.0–1.7 m/s. The optimal water temperature might provide an essential precondition for other factors to trigger spawning. As water temperature reaches the optimal values and most of the other parameters are at the brink of deviation from their optimal range of values (water level, current velocity and silt content in the water), CS would begin to spawn. By 2009, when the Yangtze Three Gorges Project, which is located 45 km upstream of the Gezhouba Dam, is completed and begins to operate normally, changes in the downstream water temperature are expected to occur, which may have a negative effect on the development of gonad and the stimulation of spawning of CS; however, the anticipated decrease of the silt content in the water may be considered favorable for the performance of the spawning site.     

Hydrological Status of the spawning ground of Acipenser sinensis underneath the Gezhouba Dam and its relationship with the spawning runs

The spawning runs of Chinese Sturgeon (CS; Acipenser sinensis) were observed 37 times below Gezhouba Dam of Yangtze River between 1983 and 2004. Five hydrological factors (water temperature, water level, flow discharge, silt content and current velocity) were monitored on a daily basis at the spawning ground between October and November for 22 consecutive years (1983–2004). The effect of current velocity on the spawning ground at the bottom layer of the river, where CS was spawning for four years, was measured (1996–1999). The authors of this study analyzed the relationship between the five hydrological factors and the respective spawning runs. Twenty-two years of continuous observations indicated that the daily mean values of all the five hydrological factors fluctuated within a certain range when CS was spawning. It was concluded that the optimal values for the hydrological factors during the spawning runs are 18.0–20.0°C for temperature, 14100 m³/s for discharge volume, 42.0–45.0 m for water level above the sea level, and 0.2–0.3 kg/m³ for silt content in the water, wherein the current velocity above the bottom layer to stimulate the fish to spawn should be between 1.0–1.7 m/s. The optimal water temperature might provide an essential precondition for other factors to trigger spawning. As water temperature reaches the optimal values and most of the other parameters are at the brink of deviation from their optimal range of values (water level, current velocity and silt content in the water), CS would begin to spawn. By 2009, when the Yangtze Three Gorges Project, which is located 45 km upstream of the Gezhouba Dam, is completed and begins to operate normally, changes in the downstream water temperature are expected to occur, which may have a negative effect on the development of gonad and the stimulation of spawning of CS; however, the anticipated decrease of the silt content in the water may be considered favorable for the performance of the spawning site.     

Effects of fire disturbance on the soil physical and chemical properties and vegetation of Pinus massoniana forest in south subtropical area

A variety of studies on the impact of fire disturbance on ecosystems has shown that the physical and chemical properties of soil after fire disturbance change notably. Meanwhile, little is known about the effects of different fire intensities on the soil properties and vegetation after fire disturbance, especially in the south subtropical area. In this paper, we analyzed the soil physical and chemical properties, vegetation species and species diversity of fire center, fire edge (which was burned a year ago) and non-burned Pinus massoniana plantation in Gaoyao, Guangdong province, China. The results showed that the soil conductivity, water content, total nitrogen, total potassium, and available potassium content of fire center were significantly higher than those of the non-burned land, and pH was higher than that of fire edge, whereas the available nitrogen, total phosphorus and organic matter content were much lower, which were generally existed in 0–10 cm soil layer and 10–30 cm soil layer. Changes of the soil properties of fire edge were similar with those of fire center, but less significant, and seemed to be more complex. Effects of burning on the vegetation of fire disturbance plots were found to be notable, species number and average height of plants of fire disturbance plots were lower than those of the non-burned plots, a difference of species diversity and uniformity were also shown, and finally, the composition of plant community also changed, e.g., pioneer species such as D. dichotoma, etc., dominated, and drought-resistant plants, heat-resistant plants and positive plants increased after burning.     

Water-holding capacity of ground covers and soils in alpine and sub-alpine shrubs in western Sichuan, China

The water-holding functions of soils and ground covers in terms of moss and litters in the three major shrubs at different altitude gradients were studied using field investigation. The water-holding functions were measured and expressed with Biomass (t/hm²) of moss and litters, along with their maximal water holding capacity (MWHC, t/hm²) and maximal water holding rate (MWHR, %). The physical characteristics of the soils included bulk density, MWHC, capillary water holding capacity (CWHC), and least water holding capacity (LWHC). The result showed that Rhododendron przewalskii shrub exhibited the highest water-holding capacity among the three types. The average MWHC of the moss, litters, and at a depth of 0–40cm in R. przewalskii at different elevation gradients was 46.73,139.98 t/hm², and 2216.92 t/hm², respectively, whereas the average MWHC of the moss, litters, and soils in Quercus aquifolioides was 1.64, 72.08 t/hm² and 2114.88 t/hm², respectively. There was no moss in Quercus cocciferoides, and the average MWHC of litters and soils at a depth of 0–40 cm at different elevation gradients was 84.55 t/hm² and 2062.83 t/hm², respectively. The biomass and MWHC of the moss layer in R. przewalskii shrub significantly decreased with increasing elevation, whereas the reverse occurred in Q. aquifolioides before the maximum was reached at 3400 m, and then the SCM and MWHC decreased. MWHR of the moss layer in R. przewalskii was higher than that in Q. aquifolioides. The biomass and MWHC of the litters in R. przewalskii and Q. aquifolioides decreased with increasing elevation, whereas the reverse occurred in Q. cocciferoide. Regardless of shrub types, soil bulk density increased significantly with increasing soil depth, whereas MWHC decreased significantly with increasing soil depth. Significant decrease in CWHC and LWHC were found only in certain shrub communities. The MWHC with respect to the 0–40cm soil depth significantly decreased with increasing elevation only in R. przewalskii shrub, whereas there was no significant difference in MWHCs among the different elevation gradients for the other two types.     

Effects of water gradients on soil enzyme activity and active organic carbon composition under Carex lasiocarpa marsh

The responses of soil enzyme activity of freshwater marsh, microbial biomass carbon (MBC), dissolved organic carbon (DOC) and aboveground biomass to water gradients were studied with Carex lasiocarpa pot culture experiment. The relationships between soil enzyme activity and MBC, DOC and aboveground biomass were discussed. The water gradients were W1, 15 cm; W2, ?5 cm; W3, ?5–5 cm; W4, submerged. The results indicated that acid phosphatase, invertase and urease activities were decreased with the increase of water level, while catalase activity was increased with moisture content increasing. Drying-wetting alternation (W3) increased soil enzyme activities if compared with W1. MBC content followed the order of W3 > W1 > W2 > W4, and the activities of invertase, urease and catalase were significantly positively correlated with MBC (p < 0.05). DOC content presented the order of W4 > W1 > W3 > W2, and the activities of urease and acid phosphatase were most significantly negatively correlated with DOC (p < 0.01). In addition, drying-wetting alternation promoted the growth of Carex lasiocarpa. When water submerged plants, the growth of Carex lasiocarpa was significantly inhibited. The aboveground biomass was positively related to soil enzyme activities. There were close relationships between the activities of invertase, urease and catalase and the growth situation of Carex lasiocarpa.