A submerged clonal plant, Vallisneria spinulosa, was grown for three months in greenhouse under ambient CO2 (400±20) μmol·mol-1 and elevated CO2 (1000±50) μmol·mol-1 to test the dynamic change of its growth and nutrient accumulation during its life cycle. It is credible to estimate the biomass of the submerged macrophyte continuously by multiplex parameters of morphology without destroying the experimental material. The sprouting of turions had not been affected by elevated CO2. The growth rate of ortet above-ground responded positively to elevated CO2 during prophase and metaphase of life cycle, while the opposite result occurred during anaphase because much more photosynthetic substance transferred to blow-ground to reproduce turions under elevated CO2 condition. Both primary and secondary ramets had higher growth rate under elevated CO2 than under ambient CO2. There was no difference in C content of the same clonal modules under two experimental conditions. Elevated CO2 significantly stimulated P accumulation in all modules of V. spinulosa except turion compared with ambient CO2. However, due to bio-dilute resulted from quickly increasing biomass, a 12％ 14% of N content of leaf and turions reduced under elevated CO2, while no significant difference in root and rhizome under both CO2 concentrations was detected. Total C, N and P accumulated in submerged plant under elevated CO2 were much more than those under ambient CO2 because the growth rate of plant increased quickly under the former condition. It is concluded, therefore, from the present study that (i) elevated CO2 significantly stimulates V. spinulosa clonal growth which will be of great benefit to its competition with other species among the community; (ii) more carbon will sink in the water-ecosystem because aquatic plants biomass increases; (iii) the content of N、P will influence directly aquatic clonal plants’ growth in the global climate change.

Soil surface carbon dioxide flux, the sum of plant and microbial respiration, is an important component of the carbon cycle of terrestrial ecosystems. Temperature is a key factor that regulates many terrestrial biogeochemical processes, such as soil respiration. Numerous studies show that soil respiration increases with temperature, creating a positive feedback to global warming. Accurately quantifying the relationship between soil respiration and temperature is necessary, because it will help to develop mechanisms of the feedback, which will aid in predicting the tendency of global change. In order to determine the law of soil respiration dynamics driven by temperature, and to detect the sensitivity of soil respiration in response to temperature in different communities of temperate grassland, in summer and autumn, we measured soil respiration in eleven communities using the alkali absorption method. We examined seasonal patterns of soil respiration, average respiration rate and responses of soil respiration to temperature. All the communities were located in Xilin River Basin, which has a typical temperate and semi-arid climate.The seasonal variations of soil respiration were similar to those of temperature, but were not completely consistent with each other. The highest value of soil respiration was in summer (June to Aug.). Average soil respiration rates of all communities varied from 565.07 mg C·m-2·d-1 to 1 349.56 mg C·m-2·d-1, and the difference was significant (p<0.001). Respiration was greatest in wet mixed grasses community and least in Caragana stenophylla community. There was no notable relationship between average soil respiration and air temperature in all eleven communities, though relation of soil respiration and temperature could be described well by exponential functions for each community (R2 = 0.330 5 - 0.731 2, p<0.000 1-0.022 0). The modeling was better at lower temperature than at higher. Q10 values of all communities were between 1.47 and 1.84, which were similar to or a little higher than the value in global scale. The Q10 value of wheat community was higher than that of other communities, which implied that land use could affect the sensitivity of soil respiration to temperature, and cultivation of the soil in grassland might be a CO2 source for atmosphere along with global warming.

To determine how transpiration characteristics and water use efficiency of annual C4 plants respond to simulated photosynthetic radiation enhancement and CO2 enrichment, we used LI-6400 Portable Photosynthesis System to examine photosynthesis rate (Pn), transpiration rate (Tr), intercellular CO2 concentration (Ci), stomatal conductance (Gs) and vapor deficit at the leaf surface (Vpdl) of Setaria viridis under simulated photosynthetic radiation (SPR) intensities from 0 to 2400μmol·m-2·s-1 and CO2 concentration from 300 to 1000μmol·mol-1. Pn, Tr and Gs increased with enhanced SPR intensity. The increase in Pn, Tr and Gs with each unit SPR added was reduced as SPR intensity increased. At last, these physiological parameters tend to dynamic balance. Water use efficiency (WUE) increased with enhanced SPR, then plateaued as SPR intensity exceeded 1200μmol·m-2·s-1. For photosynthesis process demands CO2, so Ci intensity enhancement. Vpdl also decreased with SPR intensity increase, then reached dynamic balance as SPR intensity exceeded 600μmol·m-2·s-1. Pn increased with CO2 concentration between 300 and 600μmol·mol-1, and then decreased as CO2 concentration increased from 600 to 1000μmol·mol-1. Ci, Vpdl and WUE of Setaria viridis rose with the elevation of CO2 concentration. Both Gs and Tr dropped as the CO2 concentration was elevated. We conclude that Pn of annual C4 plants was not sensitive to CO2 concentration variation. The response of Tr and WUE to CO2 enrichment was most significant. It is obvious that the function of instantaneous simulated CO2 enrichment to increased photosynthesis rate was gradually diminished. However, it could enhance primary production by improving the use efficiency of existing water.

The depletion of the stratospheric ozone layer has been well documented. So ultraviolet-B (UV-B) radiation (280-320 nm) reaching the earth surface has increased since the 1970s. Although extensive studies were conducted about negative biological and ecological effects of enhanced UV-B radiation, little was known about the inside mechanism and effects of increased UV-B irradiation and feasible protective measures of plants. In this paper, the effects of naphthyl acetic acid (α-NAA) (2 mg·L-1) and UV-B radiation (0.029 J·m-2·s-1) on the growth and transpiration rate in pots in greenhouse-grown Trichosanthes kirilowii seedlings were investigated. Four treatments were included in the experiment: no addition of α-NAA and UV-B radiation (T0), addition of α-NAA (T1), exposure to enhanced UV-B radiation (T2), addition of α-NAA and exposure to UV-B radiation (T3). The results showed that enhanced UV-B radiation reduced the height and leaf area of plants, and the weight of roots, stems and leaves. As a result, total biomass and accumulation of dry matter were decreased. Exposure to UV-B radiation significantly increased the stomatal diffuse resistance and decreased the transpiration rate; however it hardly affected the water content of seedlings. Compared to the controls (T0), addition of α-あ??脴?膟?膗

Previous studies on responses of plants to drought stress were mostly performed with young plant seedlings subjected to experimental stress. Experimental stresses are usually abruptly imposed on plants. However, in the drought field, plants are subjected to gradual stress because water availability in the soil does not change quickly. Therefore, responses of plants might be different under the two stress conditions. The plasma membrane is very sensitive to drought, which causes alteration of its structure and functions. To our knowledge, few studies concerning the effects of gradual field drought on properties of the plasma membrane in the course of whole developmental stages have been published. In the present work, we took two spring wheat (Triticum aestivum) as materials and investigated changes in plant growth, fatty acid composition of polar lipids and activities of key enzymes in the plasma membranes of leaves under gradual field drought. Drought stress decreased water content of wheat leaves and inhibited plant growth. At early developmental stages, drought stress decreased fatty acid unsaturation of polar lipids in the plasma membranes, membrane protein content and activities of H+-ATPase (EC 3.6.1.35), while it increased 5'-AMPase (EC 3.1.3.5) activity and O2 resumption by plasma membranes. At late developmental stages, with drought progressing, membrane protein content and H+-ATPase activities were increased by continuing drought, and fatty acid unsaturation of polar lipids in the plasma membranes was increased or not significantly changed, whereas 5'-AMPase activities and O2 resumption by plasma membranes were decreased. These results suggest that wheat plants are sensitive to drought at early developmental stages, and the fluidity of plasma membranes as well as energy reservoirs decrease. At late stages, adaptive phenomena of plants to drought were observed. Our results might be able to help elucidate plant drought resistance under natural drought conditions.

The low price of rice has placed farmers in a cost-price squeeze, and extravagant nitrogen application in rice agriculture has resulted in a decrease in nitrogen uptake and utilization efficiency and serious environmental pollution. This has caused scientists to pay more and more attention to rice nitrogen uptake and utilization efficiency. These field experiments were conducted using indica hybrid rice (Oryza sativa) to explore the genetic potentiality of increasing nitrogen uptake and utilization efficiency. Seven parameters of nitrogen uptake and utilization, TNA (Total nitrogen accumulation), NDMPE (Nitrogen dry matter production efficiency), NGPE (Nitrogen grain production efficiency), NTE (Nitrogen transportation efficiency), NHI (Nitrogen harvest index), NAE (Nitrogen agronomy efficiency) and NRE (Nitrogen recovery efficiency), were measured. Results showed that there were significant or highly significant differences in these seven parameters among genotypes, except for TNA and NDMPE at tillering of early season rice, TNA at heading of early season rice and NTE at late season rice. Long growth duration could increase TNA, NDMPE, NGPE, and NAE. NDMPE, NGPE, NAE, NRE and NHI for hybrid rice were higher than for inbred rice. The seven parameters of two-line hybrid rice and three-line hybrid rice were almost equal at early season, and NGPE, NHI, NAE, NRE and TNA of two-line hybrid rice were smaller than that of three-line hybrid rice at late season. This indicated that both nitrogen uptake and utilization efficiency of two-line rice were not increased.Ranking methods were employed in order to make an exact valuation for nitrogen uptake and utilization efficiency of genotypes. Ranking results indicated that there were great differences among different parameters and between early and late season rice in the same parameter. The genotypes were ranked according to the means of the seven parameters after standard transformation, which provided a way for comprehensive valuation of nitrogen uptake and utilization efficiency of the genotypes. Considering the difference in integration ranking of genotypes at early and late season, a coincidence index (square root of means of square of integration ranking difference of identical genotypes at early and late season) was employed to evaluate the coincidence degree of integration ranking of genotypes at early and late season. Results showed that, of 30 genotypes, integration rankings of `Zhongyou 253’,’Zaoxiang 1’,’`Guyou 11’ and ’65396’ at early and late season coincided well, and of the seven parameters, integration rankings of NDMPE at early and late season coincided well.

In order to evaluate the growth, nodulation and N-fixation of Sesbania rostrata-Azorhizobium caulinodans symbiosis on different water and N fertilizer conditions, a greenhouse experiment in Guangzhou was conducted in summer. Pots were filled with 1 kg homogenized, dried loam red soil. NH4NO3 was applied to obtain concentrations of 10, 20, 40 mg N·kg-1 in the soil. According to water supply to the experimental soil, the pots were divided into three groups as below: W1－no waterlogging, W2－shallowly waterlogged (soil water in field capacity) and W3－flooded. The results showed that the growth and nodulation of the symbiosis were greatly influenced by water supply. Though flooding depressed root nodulation, it, however, stimulated stem nodulation and roots growth. S. rostrata grew and nodulated best, and got the maximum N accumulation under the condition of field water capacity. The effect of mineral N on the symbiosis was affected by water supply. In the range of the applied N concentrations in the experiment, both nodulation and N accumulation showed no negative reaction to mineral N, such a result implied that S. rostrata-A. caulinodans symbiosis was quite different to ordinary leguminous root nodule N-fixation symbiosis in the aspect of mineral N reaction.

Studies of simulated grazing of Elymus nutans, a common species in subalpine meadows in Gannan, were conducted to assess the effects of population density and fertilization on the plant compensatory responses to mowing. We subjected Elymus nutans to different types of mowing treatment, early or late (3 June or 28 July, 2001) and light or heavy mowing (4 cm or 2 cm from the ground), to different levels of soil fertility (unfertilized or fertilized), and to different levels of intraspecific competition (five designed sowing densities: 100, 400, 800, 1 600 and 3 200 seeds·m-2).Plant responses to these treatments were measured as changes in plant aboveground biomass and inflorescence dry weight, and the degrees of compensation were measured as changes in compensation indixes that related plant aboveground biomass or inflorescence dry weight of mowed to control plots. Our results showed that population density, soil fertility and mowing treatments significantly affected plant growth, and there were no interactions between two factors and among three factors (density × soil fertility × mowing).Mowed plants growing in early and light mowing treatment plots were more or less enhanced, and grew better than in other treatment plots. Further, early and light mowed plants in the low-density (100 seeds·m-2) and unfertilized plots showed enhanced growth (overcompensation), and the number of tillers and plant compensatory ability decreased with increasing density. These results indicated that plant compensation ability was directly related to the number of tillers. The compensation may be considered as an indirect consequence of growth of low tillers when apical dominance is removed.Mowed plants in fertilized plots showed enhanced growth irrespective of the population density. Our results support the view that rapid plant regrowth was more likely to occur under low-stress conditions. We also found that plant vegetative growing than reproductive growing was enhanced when the soil was fertilized. We suggest that overcompensation should not generally be considered as an adaptive response, but rather as a maximal end in the continuum of plant responses to herbivory.

Coarse woody debris (CWD) plays important roles in forest structure and biogeochemical element fluxes between different parts within forest ecosystem, and affects the abundance and distribution of many organisms. Compared with the similar studies in temperate and tropical rain forest, CWD storage, annual increment, its structure and ecological functions are poorly documented in monsoon evergreen broad-leaved forests (MEBF) near the treaved forencer. In this paper, the amount of storage, annual increment of CWD was quantified in an old-growth MEBF at the Dinghushan Nature Reserve, South China. Based on inventory of all trees in a 1-ha permanent plot carried out in 1992, 1994, and 1999, we calculated CWD storage of this community. For sound standing and fallen dead tree, their stocks were separately calculated for bole, branch, leaf, and root using respective regression equations. For stumps, the stocks were calculated based on their volume and average density. Annual increment of CWD for MBEF in the duration from 1992 to 1999 was approximately estimated by calculating the average value of CWD storage increment between two close inventories correspondingly. We also analyzed soil nutrient conditions in a gap to discuss CWD roles in the forest nutrient cycling. Soil samples were collected in 5 subplots (20 m×20 m for each) in the gap area, numbered as No.7, 11, 12, 13, and 17, respectively, analyzing soil organic matter, available N, P, K and total N. The results showed as follows: 1) standing CWD storage in MBEF amounted to 25.278 t·hm-2, of which standing dead boles (snags), fallen boles, large branches were 8.094 t·hm-2, 12.544 t·hm-2, and 4.64 t·hm-2, respectively; 2) Castanopsis chinensis was the main contributor to CWD pool, which accounted for 29.95% of the total CWD storage in MBEF, then followed by Cryptocarya concinna, Aporosa yunnanensis, and Acmena acucminatissma, with the percentage of 26.39%, 3.87%, and 2.80%, respectively; 3) the average annual mortality rate during 1994-1999 was 2.4%, and the average annual increment of CWD in MBEF was 4.128 t·hm-2, and 4) soil organic matter and available K in sub-plot 12 were the highest of all the 5 subplots, while the highest available N and P and total N occurred in sub-plot 11.

The effect of wetland carbon element change on the global climate change has been a focus in the world for a long time. Some works have been done in studying carbon cycles of marsh wetland at Sanjiang Plain in China, but little was reported on the same work in Ruoergai Plateau situated in north-east part of Qinghai-Tibetan Plateau, which is one of the most sensitive areas with respect to global climate change in the world. The cold climate and abundant water in this area, vast marsh area and rich reserves of the peat are all very specific in China and in the world. To evaluate the effect of wetland carbon cycles on global climate change, the author studied organic carbon distribution and flow from three kinds of plant (Carex muliensis, Carex meyeriana and Kobresia tibetica) communities to three kinds of soil (peat soil, peat bog soil and meadow bog soil) using a field decomposition approach. The purposes are as follows: 1) to investigate the amount and distribution of soil organic carbon and 2) to verify the amount of C lost and C retained in the wetlands in Ruoergai Plateau. The results showed that the content of soil organic carbon was high and decreased with the increase of the depth of the soil layer. The disappearing rate of the organic carbon was different in different chemical constituents at different stages of living plants, standing dead and litter. Among several chemical constituents, the disappearing rate of the easy-decomposing C was the highest and reached 61.37%, 69.59% and 66.34% respectively in the three marsh plant communities, while the disappearing rate of the lignin C (44.53%-52.98%) was slightly higher than that of the cellulose C (38.23%-43.86%). The total disappearing rates of the plant carbon were 53.8%, 60.03% and 55.18% respectively in the three communities. The amount of C retained in soil from litter after 1 and 2 years of decomposition was 30 g·m-2 and 25.5 g·m-2 respectively, while the amount retained in the residual roots was 179-223 g·m-2 and 161-208 g·m-2 respectively. These results indicated that residual plant roots was the main source of soil organic carbon and the amount of organic carbon flow was large because of the higher biomass in wetland ecosystem in Ruoergai Plateau.

Biodiversity pattern impacts on flow of landscapes on different scales, and contrarily landscape and soil characteristics influence plant community structure. Variation in soil resource levels is common and important to plants. At larger spatial scales, the resources available to plants change as the soil type changes, and this variation effects the distribution of plant species. At smaller spatial scales, soil resources continue to show considerable spatial heterogeneity. Small-scale heterogeneity has large impact on performance of individual plants, and hence, on the structure and dynamics of plant populations and communities. It is important to examine their close relationships to understand the process of ecosystems. Many recent studies mainly concentrate on factors influencing plant in grassland or shrub land.The Donglingshan Mountain is an extension of Xiaowutaishan Mountains and belongs to the broader Taihangshan Mountains. The zonal vegetation of this region is highly fragmented warm temperate-zone deciduous broad-leaved forest. Focused on the landscape heterogeneity of this area, we investigated 76 plots of 20 m×20 m on a small watershed scale and analyzed the detailed community structure, landform and soil features.Using multivariate statistical analysis techniques (Principle Component Analysis, Cluster Analysis, Discriminant Analysis and Canonical Correlation Analysis), we examined the complex relationships between the soil properties, plant biodiversity and landscape factors. Soil organic matter is a sensitive factor of soil fertility and the coverage and richness of plants have different features under different soil fertilities. Three community types were distinguished by the arbor species characteristics. Twenty species existed in all plots of type III, but type I and II included sixteen species. The dominant species of type I was maple which accounts for 19.7% of total species in terms of importance value. Second was Quercus liaotungensis (19.1%). Type II included Q. liaotungensis (34.8%) and Betula dahurica (17.5%). Type III was B. dahurica (30.8%) and maple (21.6%). The results also show that high fertility plots often exist on the north-facing and upper slopes. Canonical correlation analysis was used as large numbers of variables were involved in this study. The analysis elucidated the relationships of three different indices (i.e. topography, soil and plant). Slope positions were closely related with tree layer coverage, while elevation was positively correlated with total nitrogen. The richness of tree layer in biodiversity factors had the greatest influence on soil organic matter.

We analyze the distribution patterns of the populations and the dominants of Ordos grassland in its degradation, using Combined Count-distance Analysis Method. `Statistica’ was used to analyze soil elements (total organic carbon, total nitrogen and dissolve nitrogen) in root-sphere and bare openings to show the process of soil element redistribution with changes of plant life-forms. The Stipa bungeana community, S. bungeana + Artemisia ordosica community，community，A. ordosica + Cynanchum komarovii community and C. komarovii community that presented successionally degraded stages in desertification were chosen for the study. The results show that, during the degradation course of the grassland, most of the distribution patterns of populations are clump and random distribution at different scales, but multi-population distribution in the S. bungeana + A. ordosica community and in the A. ordosica + C. komarovii community was even with A. ordosica and C. komarovii as the dominant species. There was soil element heterogeneity at different degrees in single-dominant communities. The soil elements had the strongest heterogeneity in A. ordosica community. The heterogeneity in co-dominant communities was inferior to single-dominant communities. At the beginning of degradation, invasion of the S. bungeana grassland by the shrub A. ordosica does not lead to the immediate development of “islands of fertility". Competition for soil elements between S. bungeana and A. ordosica makes the S. bungeana + A. ordosica community temporarily homogeneous. Similarly, the soil elements have weaker heterogeneity in A. ordosica + C. komarovii community. The competition for soil water and soil resources leads to plant spatially homogeneous distributions and spatial homogeneity of soil elements in co-dominant communities. The heterogeneity process of the soil chemistry was characterized first by total organic carbon (TOC) heterogeneity and later by total nitrogen (TN) heterogeneity. Soil TOC is derived mainly from decomposed plant material; soil TN is provided by nitrogen-plant detritus, either plant-fixed or gas-fixed nitrogen. Thus, it is tentatively concluded from the results that the heterogeneity process is initially characterized by plant spatially heterogeneity; then the plant spatial heterogeneity leads to the spatial heterogeneity of soil elements.

Habitat preference has played an important role in the evolution of the genus Isoetes. Aquatic Isoetes species are generally distributed in oligotrophic softwater. However, it is still uncertain if chemical properties of the water have an impact on the pattern of distribution of Isoetes species. Investigation of habitat preference with regard to water chemistry in natural habitats of species would contribute significance to our understanding of evolution in the genus. Four species of Isoetes are known to occur in China: Isoetes taiwanensis in Taiwan island and I. hypsophila, I. yunguiensis and I. sinensis in the mainland, and their distribution regions do not overlap. All four species are endangered aquatic plants throughout their distribution range in the country.In this paper, 20 parameters of water chemistry in the natural habitats of three species of Isoetes in mainland China were measured, using HANNA Pocket-sized pH Meter HI98107 (resolution = 0.1 pH, accuracy = ±0.1 pH), HANNA Conductivity Meter Dist4/HI983004 (resolution = 0.1 m S·cm-1, accuracy = ±0.1 m S·cm-1) and HANNA C200 Multiparameter Ion Specific Photometer (resolution of NO3-N, NO3-, P, Mn and Mo = 0.1 mg·L-1, accuracy = ±0.1 mg·L-1；resolution of other factors = 0.01 mg·L-1, accuracy = ±0.01 mg·L-1). The character and variation of the chemical properties of the water were analyzed using mean, coefficient variability and difference significance tests (ANOVA and Kruskal-Wallis). Results showed a common character in that there were bigger variations in average and coefficient variability of the 20 parameters. Average Ni was overwhelmingly greater than the other factors, and lower conductivity indicated there was litter pollution in the water. However, of the 20 factors assessed, except for pH (p<0.05), P (p<0.05), NO3-N (p<0.05), NO3- (p<0.05) and Al (p <0.01), the rest displayed no significant difference among habitats of the three species. This indicated that most of the factors (75%) were relatively stable. pH had an identically positive correlation with NO3-N and NO3- (p<0.05); on the contrary, P had an identically negative correlation with NO3-N and NO3- (p<0.05). pH and P were also negatively correlated (p<0.05). Only Al had a positive correlation with P (p<0.05). An analysis, according to data from other research and this study, suggested the significant difference of chemical nature of the water among the three Isoetes species could be due to differences in physiological characters among them, and has no impact on their distribution.

In the Taklamakan desert region, water is the most important limiting factor to influence plant growth and distribution. The study of water relations is necessary to provide an ecological basis for the sustainable management of the vegetation at the transition between oasis and sandy desert to protect oasis environments. At the same time, the study also provided theory about how to use the limited water resources to regenerate vegetation. In the southern fringe of the Taklamakan desert Calligonum caput-medusae Schrenk (Polygonaceae) is an introduced species which serves as important shelter vegetation against sand drift at the foreland of the oasis. We investigated: 1) the degree to which plants suffered water stress during flooding conditions in summer; 2) the adaptability of physiological characters in water relations to this extreme environment; 3) the effect of irrigation on water status of vegetation (utilizing summer flooding). From April to October in 1999, around the 20th of each month, the predawn water potential (Ψp; between 5∶00 and 6∶00) and the afternoon water potential (Ψ; between 13∶00 and 14∶00) were measured using pressure chambers on six plants with three measurements per plant. Following the measurements of water potential, the pressure and volume (PV) curves from three or four samples were established. The results showed C. caput-medusae kept positive turgor during the growing season. Development of water deficit was not severe and the water stress that plants suffered was still in the normal range. Thus, the water stress induced by drought is not severe enough to threaten the survival of the artificial vegetation. During the growing season, C. caput-medusae still maintained relatively high water potential and osmotic potential as the environmental stress increased. At the same time, no experimental evidence indicated that the accumulation of solute (NsDM) reached high levels either. Therefore, the physiological process of plants still worked in normal conditions. The relative water content (RWCp) always remained high during the growing season, which was helpful to plants to prevent excess water loss in drought environments. Maintaining high level RWCp would be the adaptability of the plant to the extreme environment of the Taklamakan desert. Those adaptabilities of physiological characters exhibited in C. caput-medusae indicated the type of the plant to adapt drought environmental stress is resistance. The drought-adapted physiology of C. caput-medusae at the leaf level was mainly shown in an increase in the proportion of apoplasm, bulk modulus of elasticity (εmax), long standing high relative water content (RWCp), and increased RWCp and WCsat after irrigation. Irrigation in summer by flooding is helpful to recover the water status of C. caput-medusae and is probably one of the important reasons that the vegetation avoids serious water stress.

The competition relationships among perennial ryegrass (Lolium perenne) and six other species (Trifolium repens, Dactylis glomerata, Imperata cylindrical, Miscanthus sinensis, Spiraea japonica var. nepalensis, and Sanguisorba officinalis) were studied in different conditions of stress and disturbance. The aim was to examine the mechanism of regressive succession of ryegrass community, in order to supply a basis for efficient management of this pasture.Two stress factors (water condition and soil fertility) and two disturbance factors (cutting frequency and cutting intensity) were included in the experiment. The water condition treatment included two levels, which were natural precipitation (about 1 800 mm) and precipitation + watering (about 2 300 mm). The soil fertility treatment included three levels at which fertilizer was applied: 0 kg·hm-2·a-1, 75 kg·hm-2·a-1 and 150 kg·hm-2·a-1. The cutting frequency treatment included three levels at which plants were cut: 1, 3 and 6 times per year. The cutting intensity treatment included two levels of stubble height, 2 cm and 3 cm. The plants were planted with the same density in monoculture and in mixture with ryegrass in a fixed device. After yields of plants in different treatments were measured, the plant relative crowding coefficient (RCC), which was quantified by de Wit, was estimated. Finally the competition relationships among ryegrass and six other species under different stress and disturbance conditions were determined. The experimental results showed that the competitive abilities of ryegrass were ordinal superior to T. repens, D. glomerata, S. officinalis, I. cylindrical, M. sinensis and S. japonica var. nepalensis. Moreover, the competitive ability of ryegrass increased when cutting frequency, moisture and soil fertility increased. Cutting frequency was the most important factor to affect competitive ability of ryegrass among the 4 factors studied. On the other hand, the experiment indicated that the growth rate, competitive ability and cutting disturbance tolerance of cultivated herbage (ryegrass, T. repens and D．glomerata) were higher than that of wild species. However, the stress resistance of cultivated plants was lower than that of wild species. When environmental stress increased, cultivated plant’s competitive ability relative to wild species would weaken, and wild species would predominate in the pasture. Meanwhile, the experiment implied that for ryegrass, S. japonica var. nepalensis was a plant of stress tolerance (S) in 6 studied species, T．repens and D．glomerata belonged to plants of disturbance tolerance (D), and the other species were intermediate in stress and disturbance tolerance.

The species association of Castanopsis community in Jinggangshan Mountain Nature Reserve was analyzed in this paper. The experimental results may be useful for forest management, vegetation restoration, and biodiversity conservation in Jinggangshan Mountain Nature Reserve, and sustainable development of Jinggangshan tourist resources. In the experiment, according to the factor of altitude, 15 plots were established, each of them containing four quadrats of size 10 m×10 m. For every quadrat, one sub-quadrat of 5 m×5 m was set for shrubs and one sub-quadrat of 2 m×2 m was set for herbaceous plants. Within each quadrat, the girths, plant name, heights, and coverage of all plants (H＞5 m, DBH＞10 cm) in tree layer, and individual number, plant name, heights, and coverage of all plants of all shrub and herbaceous plants were recorded. At the same time, the environment factors—slope, altitude, thickness of soil and so on were also recorded. Based on the data from the 15 plots, the species association for 20 dominant species in Castanopsis community was analysed. The data for statistics include the species numbers of the quadrats, the quadrats numbers of species and the relations between species pairs. Regarding the index value of the measure of species association as half-matrix, according toχ2 value as constellation diagrams. Variance analysis, χ2 test, association coefficient (AC), Jaccard index and point correlation index were used to examine the species association between 20 dominant species in Castanopsis community.There were 214 species of vascular plants in the Castanopsis community in Jinggangshan Mountain (including varieties), belonging to 75 families and 132 genera, in which the pteridophyte accounted for 14 families 19 genera and 24 species, the gymnosperm 3 families, 4 genera and 4 species, and the angiosperm 58 families, 109 genera and 186 species. The community structure was complicated, which was composed of tree layer, shrub layer and herb layer. The tree layer is consisted of three sub-layers.It was found that the overall association between 20 dominant species was significantly positive. W test indicated that significantly positive correlation exists among the 20 dominant species, which suggests that the Castanopsis community is stable. Theχ2 test showed that among these 20 dominant species, 10 species pairs exhibited highly significant positive association, another 10 species pairs showed significant positive association, 4 species pairs exhibited highly significant negative association, and 8 species pairs exhibited significant negative association. Most of the total 190 species pairs did not show significant association, which may be related to the serial stage of the community and the ecological characteristics of investigated species. Based on the results, it might be inferred that the community was at a stable late successional stage.

Arbuscular mycorrhizal fungi (AMF) form mutualistic symbiotic associations with the roots of approximately 80% of terrestrial plant species. AMF are an important component of ecosystems, and the diversity of the AMF could largely influence plant biodiversity, ecosystem variability and productivity. Dujiangyan, located in the upper reaches of the Yangtze River in subtropical region of Sichuan province in southwest China with a complex geographic environment, is rich in biodiversity. To investigate the effect of environmental factors, particularly altitude-related factors and disturbance, on AMF diversity, a survey of the diversity and ecology of AMF was carried out in Dujiangyan in August 2001.Three sampling sites were selected in the present study, which represented different habitats: Banruosi, the natural evergreen broadleaved forest; Longchi, the natural subalpine forest; and Mantoushan, a seriously disturbed site, in which all woody plants were cut about 20 years ago and annuals were dominant. A total of 85 common plant species were chosen, of which 51 plant species were sampled from Banruosi, 19 from Mantoushan, and 19 from Longchi (some species were simultaneously collected from the different sites). Of the 85 plants, 51 species belong to the angiosperms, 31 belong to the pteridophytes, and 3 belong to the Gymnosperms. Roots collected from each plant were cleaned and preserved in 50% ethanol. The percentage of root length colonized by AMF was quantified according to the magnified line-intersect method. Concurrently with root sample collection, a total of 58 rhizosphere soil samples were collected, of which 30, 16, and 12 were sampled from Banruosi, Longchi and Mantoushan, respectively. The soil samples were placed in sterilized cotton-cloth bags, labeled, and air-dried in shade for one week. The soils were cleaned, ground, sieved with a 2 mm sieve, stored at 4 ℃, and processed within three months. AMF spores were isolated from 100 g air-dried soil from each sample using the wet-sieving and decanting method.Seventy-eight (91.8%) out of 85 plant species examined were colonized by AMF; this group included 49 (96.1%) out of 51 angiosperms, 26 (83.9%) out of 31 pteridophytes, and 3 (100%) out of 3 gymnosperms. In total, 47 taxa of AMF belonging to 5 genera were isolated from the 58 soil samples, of which 35, 31, and 9 taxa were found in Banruosi, Mantoushan and Longchi, respectively. Thirty-two (68%) taxa were identified at species level, and the other 15 (32%) taxa were identified at genus level. In the 47 taxa, 35 belonged to the genus Glomus, 7 to Acaulospora, 1 to Archaeospora, 2 to Entrophospora, and 2 to Gigaspora. Acaulospora and Glomus both were the dominant genera in the three sites. Acaulospora laevis was the dominant species in Longchi, and Glomus versiforme was the dominant species in Banruosi and Mantoushan. There were no significant differences in spore density or species richness between Banruosi and Mantoushan, while they were significantly higher in Banruosi and Mantoushan than in Longchi. The highest AMF diversity index occurred in Banruosi (2.66), followed by Mantoushan (1.96) and Longchi (1.71). There was no significant correlation between the spore density and the percentage of root length colonized by AMF based on the analysis of linear regression (R2=0.024 8). It could be concluded that the species composition of AMF was greatly influenced by altitude-related factors, but lightly influenced by deforestation.

The study area, Shapotou district (37°27′N, 104°57′E) of Ningxia Hui Autonomous Region is situated in the southeastern fringe of the Tengger Desert of China. A study of species identification, coverage and biomass in the soil microbiotic crusts of fixed sand dunes was conducted in Shapotou district, from which we found two families, seven genera and sixteen species of mosses. Didymodon constrictus (Mitt.) Saito and D. tectorum (C. Muell.) Saito were reduced to synonymy of D. vinealis (Brid.) Zand. by Zander and Redfearn. Crossidium chloronotos (Brid.) Limpr., Crossidium aberrans Holz. & Bartr. Aloina obliquifolia (C. Muell.) Broth. and Tortula atrovirens (Sm.) lindb. are new to Shapotou district. Bryum argenteum is an eurytopic species that survives on all kinds of habitat, and is the dominant component that forms moss synusia. The community of Didymodon vinealis, D. rigidulus Hedw. var. ditrichoides and Syntrichia bidentata are found on hillocks and are randomly distributed in crusts. Diversity of species is the highest in this area in the natural fixed dunes, with sixteen species, followed by five species of mosses (31.3%) in the fixed dunes of 1956, four species of mosses (25.0%) in the fixed dunes of 1964, and only two species of mosses (12.5%) in the fixed dunes of 1981. The total coverage of mosses and algae increased with the fixed-sand time. In different ages, the coverage of mosses and algae exist in an equal distance gradient, while in the fixed dunes they exist along the slope with the coverage of mosses decreasing as that of algae increased. A determination of biomass and binding-sand quantity of the dominant species—Bryum argenteum showed that its biomass (944.03 kg·hm-2) and binding-sand (3.925×104 kg·hm-2) quantity increased when the fixed sand time prolonged in moss crusts of the fixed dunes of 1950s. While the rate of binding-sand of Bryum argenteum decreased, its saturated water absorption had a positive correlation with biomass of 7.06×103 kg·hm-2. Therefore the results indicate that the moss crusts had a strong ability to absorb and reserve water, which is of ecological significance in arid desert region.

All viable seeds present on or in the soil or associated litter constitute the soil seed bank. Seed bank input is determined by the seed rain. Seed rain comes from seed dispersion from mother plants and also from secondary dispersion. Seed losses result from germination, animal predation, deep burial, redispersal, natural senescence and death caused by pathogens and some animals. Seeds in the soil display horizontal and vertical dispersion, reflecting initial dispersal onto the soil and subsequent movement. Investigation of the seed and spore bank has become a recognized and indispensable part of plant ecology now and has been an active research area. The soil seed bank is one of the life history stages of plant populations, which is called subpopulation stage. Some soil seed bank classification methods had been provided by scientists, but simply the soil seed bank can be classified into the transient soil seed bank, with seeds that germinate within a year of initial dispersal, and the permanent soil seed bank, with seeds that remain in the soil more than one year. Even given ideal germination conditions such as season, temperature and moisture, some seeds in the soil still remain dormant; these comprise the persistent soil seed bank. Temporal and spatial heterogeneity is the basic characteristic of the soil seed bank. Not only are the floristic composition, size and diversity of the soil seed bank different in different plant communities, but microsites or microhabitats greatly affect the distribution patterns of the soil seed bank. The number of reproductive individuals existing in a dormant state is significantly greater than that of aboveground individuals in most habitats dominated by higher plants. Because of reasons such as germination, predation and decay, soil seed banks have seasonal dynamics. The soil seed bank, seedling bank and adult vegetation can interconnect and interact with each other. The relationship between soil seed banks and their aboveground vegetation is similar or dissimilar because of different plant community types, different succession stages and different sampling time. Germination in the greenhouse and physical separation methods were used to research the soil seed bank. The soil seed bank can partly reflect the history of communities, and plays an important role in the restoration of degraded ecosystems.The main hot topics about soil seed bank research are summed up as following: 1) the research methods about soil seed banks; 2) the classification of soil seed banks; 3) the temporal and spatial distribution patterns of soil seed banks; 4) the relationships between aboveground vegetation and soil seed bank; 5) the dynamics of soil seed banks.

Bio-signalling transduction is one of the exciting fields in life sciences. There are variously physical and/or chemical modes for communication among organisms and their cells and organs. Actually, the environment is replete with chemicals, many of which have become part of a system of chemical communication. Chemical signals may operate on any of five levels of increasing complexity that correspond to cells, organs, organisms, groups and communities. It is unclear whether there is physically intraspecific or interspecific signals between plants. However, it was confirmed that plant can interpret and respond to secondary metabolites released by neighboring plants. Interplant chemical communication can occur among one species and another species of plant through air or soil media. Plant might warn each other about an imminent attack. The chemical recognition might occur between host and parasitic or associated plants. Methyl jasmonate(MJ) is a volatile chemical messenger that diffuses through the air from wounded plants, is potent in very small quantities, and starts a general signal cascade for increased production of defense chemicals in a wide range of plant families. Precursor of MJ is jamonic acid (JA), which occur in plant tissue and is also intercellular signal molecule in the systemic resistance of plants against herbivory. When interplant communication occurred through airborne signal, JA was converted to MJ, which is more volatile at room temperature, potentially allowing it to affect both remote parts of the releaser plant as well as nearly plants. More recently, other volatile chemicals implicated in plant to plant information transfer also were revealed. Methyl salicylate, ethylene and some α,β-unsaturated carbonyls have been reported for airborne plant to plant signals. Interplant chemical signals can also mediate through soil. The root-soil interface is a site where many interactions occur between plants and their environment. Some plants exuded chemical messengers by root tissue. A few chemicals from root exudates of host plant are germination stimulants and may be recognized by associated and parasitic plant. The seed of parasitic witchweed may be rapidly germinated by hydroquinone and sesquiterpene that respectively released from gramineous crops and cotton root tissues. Apigenin and cyclic xanthmine from legume root exudates were possible chemical messages through the root-soil interface. Nevertheless, it was difficult to capture and identify active chemicals from root tissues. As a result, interpretation of chemical signal on the root-soil interface has few progresses. In a word, the chemical messenger plays an important role in plant communication. Interpretation of the chemical signals among plants will be important scientific significance.

A reciprocal transplant-replant experiment was carried out to investigate clonal plasticity and local specialization of forest gap population and forest undergrowth population of a stoloniferous herb Potentilla reptans var. sericophylla in the Pinus tabulaeformis forest at Dongling Mountain, Beijing. The experiment was conducted from 19 May to 23 August 1996 in Dongling Mountain (115°26′-115°30′E，40°00′-40°02′N), 114 km southwest of Beijing. At the beginning of the experiment, one forest gap population and one forest undergrowth population of Potentilla reptans var. sericophylla in the Pinus tabulaeformis forest was selected. In each population, 120 ramets of Potentilla reptans var. sericophylla were selected at random as target plants. Target plants experienced one of four treatments during the experiment. 1) Half of the target ramets in the forest gap population were transplanted to the forest understorey. 2) The other half in the forest gap was replanted in their native site. 3) Similarly, half of the target ramets in the forest undergrowth were transplanted to the forest gap. 4) The other half in the forest understorey was replanted in their native site. The distance between the two field experiment sites was about 100 m. The gap was about 15 years old. During the experiments, the experimental plants all grew naturally. There were three times of harvesting on 23 June, 23 July and 23 August, 1996. In each of the harvests, 20 target ramets were chosen randomly and harvested for each of the treatments. The genet biomass, ramet number, blade length, blade width, petiole length, stolon internode length and total stolon length were measured after each harvest to investigate clonal plasticity and local specialization. A One-way and a Two-way ANOVA, with the native habitat and the growing habitat of the experiment plants as the main effects (GLM procedure, SAS), were applied for analyzing responses in all measured characters. The results show that the biomass, number of ramets and total stolon length of the experimental plants under the forest undergrowth was smaller than those under the forest gap. Petiole length, leaf blade width, leaf blade length and internode length did not differ between the different growing habitats. The plants from the forest gap grew better than those from the forest undergrowth. These results indicate that there was no local specialization in the plasticity of characters related to clonal growth and clonal morphology in forest gap and forest undergrowth. Clonal plasticity rather than local specialization is the main strategy of Potentilla reptans var. sericophylla in heterogeneous habitats.