Density and Seasonal Dynamics of Bemisia tabaci(Gennadius) Mediterranean on Common Crops and Weeds Around Cotton Fields in Northern China

The density seasonal dynamics of Bemisia tabaci MED were evaluated over two years in a cotton-growing area in Langfang, Hebei Province, northern China on cotton （Gossypium hirsutum L.） and six other co-occurring common plants, common ragweed （Ambrosia artemisiifolia L.）, piemarker （Abutilon theophrasti Medicus）, sunflower （Helianthus annuus L.）, sweet potato （Ipomoea batatas L.）, soybean （Glycine max L.）, and maize （Zea mays L.）. The whitefly species identity was repeatedly tested and confirmed; seasonal dynamics on the various host plants were standardized by the quartile method. B. tabaci MED appeared on weeds （the common ragweed and piemarker） about 10 days earlier than on cotton, or the other cultivated plants. The peak population densities were observed over a span of 2 to 3 weeks on cotton, starting in early （2010） or mid-August （2011）. The common ragweed growing adjacent to cotton supported the highest B. tabaci densities （no. on 100 cm2 leaf surface）, 12-22 fold higher than on cotton itself. Sunflower supported more B. tabaci than the other plants, and about 1.5-2 fold higher than cotton did, Our results indicate that weeds （esp. the common ragweed） around cotton fields could increase the population density of B. tabaci MED on cotton, while sunflower could act as a trap crop for decreasing pest pressure on cotton.

Profile distribution and seasonal dynamics of water-extractable carbohydrate in soils under mixed broad-leaved Korean pine forest on Changbai Mountain

Carbohydrate represents an important part of the soil labile organic carbon pool. Water soluble carbohydrate drives the C cycle in forest soil by affecting microbial activity and hot water extractable car- bohydrate is thought related to soil carbon sequestration due to the asso- ciation with soil aggregation. In a temperate forest region of northeast China, Changbai Mountain, we investigated the abundance, spatial dis- tribution, and seasonal dynamics of cool and hot-water extractable car- bohydrate in soils under mixed broad-leaved Korean pine forest. The concentrations of cool-water extractable carbohydrate （CWECH） in three soil layers （0-5, 5-10, 10-20 cm） ranged from 4.1 to 193.3 g.kg-1 dry soil, decreasing rapidly with soil depth. On an annual average, the CWECH concentrations in soils at depths of 5-10 and 10-20 cm were 54.2% and 24.0%, respectively, of that in the 0-5 cm soil layer. CWECH showed distinct seasonal dynamics with the highest concentrations in early spring, lowest in summer, and increasing concentrations in autumn. Hot-water extractable carbohydrate （HWECH） concentrations in three soil layers ranged from 121.4 to 2026.2 g.kgq dry soil, which were about one order of magnitude higher than CWECH. The abundance of HWECH was even more profile-dependent than CWECH, and decreased more rapidly with soil depth. On an annual average, the HWECH concentration in soils 10-20 cm deep was about one order of magnitude lower than that in the top 0-5 cm soil. The seasonality of HWECH roughly tracked that of CWECH but with seasonal fluctuations of smaller amplitude. The car- bohydrate concentrations in cool/hot water extracts of soil were positively correlated with UV254 and UV2s0 of the same solution, which has implications for predicting the leaching loss of water soluble organic carbon.

Concentrations and seasonal dynamics of dissolved organic carbon in forest floors of two plantations （Castanopsis kawakamii and Cunninghamia lanceolata） in subtropical China

The concentrations and seasonal dynamics of DOC in forest floors of monoculture plantations of Castanopsis kawakamii and Chinese fir （Cunninghamia lanceolata） were assessed in Sanming, Fujian, China （26°11′30″N, 117°26′00″E）. Forest floor samples were taken in January, April, July and October in 2002 and divided into undecomposed material （horizon Oi）, partially decomposed organic material （horizon Oe）, and fully decomposed organic material （horizon Oa）. Upon collection. DOC concentrations of samples were analyzed by a High Temperature TOC. The results showed that the annual average DOC concentration of Chinese fir （1341.7 mg·kg^-1） in the forest floor was higher than that of Castanopsis kawakamii （ 1178.9 mg·kg^-1）. Difference in DOC concentrations was observed among three horizons of the forest floor. DOC concentration of forest floor in the two forests was the highest in horizon Oe. Seasonal trends of DOC concentrations in different horizons of forest floors were similar and the maximal value occurred in autumn （or winter）. The concentration and temporal change of DOC in studied forests were probably related to the variation in moisture, temperature, biological activity and quantity of organic matter in the forest floor.

Vertical Distribution and Seasonal Dynamics of Fine Root Parameters for Apple Trees of Different Ages on the Loess Plateau of China

The vertical distribution pattern and seasonal dynamics of fine root parameters for the apple trees of different ages （3, 10, 15, and 20 years old） on the Loess Plateau of China were studied. Soil coring method was used to determine the vertical distribution and seasonal dynamics of fine roots at different root radial distances （1.0, 1.5, and 2.0 m from the main tree trunk）. The fine root biomass density （FRD）, fine root length density （RLD）, and specific root length （SRL）, as well as soil water content and soil temperature were also measured. The FRD and RLD for the 10, 15, and 20 years old trees reached peak values in the 20-30 cm soil layer. For the 3 years old tree, the highest FRD and RLD were observed in the 10-20 cm soil layer. The FRD and RLD decreased with increased soil depth from the 10-20 or 20-30 cm soil layer for all age apple trees. The SRL declined with the increase of tree age. The FRD at the 1.0 m radial distance from the main tree trunk was higher than that at other radial distances in the 3 and 10 years old orchard. However, in the 15 and 20 years old orchards, especially the 20 years old orchard, the FRD at the 2.0 m radial distance was nearly equal to or higher than that at the 1.0 and 1.5 m radial distances. For all the root radiuses or the tree ages, the FRD, RLD, and SRL were the highest in spring and the lowest in autumn. The age of an apple tree does not affect the vertical distribution pattern but the biomass of fine roots and the SRL. Radial distance affects the root horizontal distribution of 3 and 10 years old trees but the 15 and 20 years old trees. Additionally, effects of soil temperature and soil moisture on fine root distribution or seasonal dynamics are not significant.

Protist Interactions and Seasonal Dynamics in the Coast of Yantai, Northern Yellow Sea of China as Revealed by Metabarcoding

Facilitated by the high-throughput sequencing(HTS)technique,the importance of protists to aquatic systems has been widely acknowledged in the last decade.However,information of protistan biotic interactions and seasonal dynamics is much less known in the coast ecosystem with intensive anthropic disturbance.In this study,year-round changes of protist community composition and diversity in the coastal water of Yantai,a city along the northern Yellow Sea in China,were investigated using HTS for the V4 region of 18S rDNA.The interactions among protist groups were also analyzed using the co-occurrence network.Data analyses showed that Alveolata,Chlorophyta,and Stramenopiles are the most dominant phytoplanktonic protists in the investigated coastal area.The community composition displayed strong seasonal variation.The abundant families Dino-Group-I-Clade-1 and Ulotrichales_X had higher proportions in spring and summer,while Bathycoccaceae exhibited higher ratios in autumn and winter.Alpha diversities(Shannon and Simpson)were the highest in autumn and the lowest in spring(ANOVA test,P<0.05).Nutrients(SiO42−,PO43−),total organic carbon(TOC),and pH seemed to drive the variation of alpha diversity,while temperature,PO43−and TON were the most significant factors influencing the whole protist community.Co-variance network analyses reveal frequent co-occurrence events among ciliates,chlorophytes and dinoflagellate,suggesting biotic interactions have been induced by predation,parasitism and mixotrophy.

Seasonal dynamics of meiofaunal distribution in the Dagu River Estuary, Jiaozhou Bay, China

Sediment samples were collected in the intertidal zone of the Dagu River Estuary, Jiaozhou Bay, China in April,July and October 2010 and February 2011 for examining seasonal dynamics of meiofaunal distribution and their relationship with environmental variables. A total of ten meiofaunal taxa were identified, including free-living marine nematodes, benthic copepods, polychaetes, oligochaetes, bivalves, ostracods, cnidarians, turbellarians,tardigrades and other animals. Free-living marine nematodes were the most dominant group in both abundance and biomass. The abundances of marine nematodes were higher in winter and spring than those in summer and autumn. Most of the meiofauna distributed in the 0–2 cm sediment layer. The abundance of meiofauna in hightidal zone was lower than those in low-tidal and mid-tidal zones. Results of correlation analysis showed that Chlorophyll a was the most important factor to influence the seasonal dynamics of the abundance, biomass of meiofauna and abundances of nematodes and copepods. CLUSTER analysis divided the meiofaunal assemblages into three groups and BIOENV results indicated that salinity, concentration of organic matter, sediment sorting coefficient and sediment median diameter were the main environmental factors influencing the meiofaunal assemblages.

Seasonal Dynamics of the Soil Moisture in Yuanmou Dry-Hot Valley of Yunnan

[ Objective] The research aimed to study seasonal dynamics of the soil moisture in Yuanmou Dry-Hot Valley of Yunnan. [ Method] We investigated soil moisture in rainy season in Yuanmou Dry-Hot Valley. By combining completed research about soil moisture in dry season, data in rainy and dry seasons were contrasted to study seasonal dynamics of the soil moisture in the zone. [ Resultl Soil moisture in rainy season increased with the depth of soil, but would decrease within 1.0 m below the root layer. The soil moisture of grassland was higher than that of the woodland, while soil moisture of the savanna was higher than that of the woodland but lower than that of the grassland. In addition, compared with soil mois- ture in dry season, it is clear that to avoid forming permanent soil desiccation, based on soil and hydrology conditions in Yuanmou, it is better to plant grass not tree in Yuanmou when we do something about ecological restoration. [ Condusion] The research had certain guidance significance for planting agricultural and economic crops and carrying out ecological restoration in Yuanmou Dry-Hot Valley.

Satellite Images Applied to Assess the Influence of Amazon River Seasonal Dynamic on the Floodplain Lake Morphology

The objective of this study is to assess the influence of the Amazon River seasonal dynamic on floodplain lake morphology. The study area includes the Amazon River floodplain reach encompassed by the Madeira and Tapajós River confluences. Products from the Global Rain Forest Mapping (GRFM) and Moderate Resolution Imaging Spectroradiometer (MODIS) were used to derive variables such as lake size, shape and number. The main steps in the research were: data base implementation, legend definition, image processing (merge, segmentation, classification and edition), morphological mapping and quantitative assessment. Four classes of lacustrine morphology were defined in this study: circular/elliptical, elongated, composite, and dendritic. The result showed that 1) the lake class increased 18.38% from the low- to high-water period;2) there was a reduction in the total number of lakes from low to high water;3) the most common lake type was the circular/elliptical;and 4) better results were obtained integrating SAR and optical sensors.

Seasonal dynamics of fine root biomass, root length density, specific root length, and soil resource availability in a Larix gmelinii plantation

Fine root turnover is a major pathway for carbon and nutrient cycling in terrestrial ecosystems and is most likely sensitive to many global change factors.Despite the importance of fine root turnover in plant C allocation and nutrient cycling dynamics and the tremendous research efforts in the past,our understanding of it remains limited.This is because the dynamics processes associated with soil resources availability are still poorly understood.Soil moisture,temperature,and available nitrogen are the most important soil characteristics that impact fine root growth and mortality at both the individual root branch and at the ecosystem level.In temperate forest ecosystems,seasonal changes of soil resource availability will alter the pattern of carbon allocation to belowground.Therefore,fine root biomass,root length density(RLD)and specific root length(SRL)vary during the growing season.Studying seasonal changes of fine root biomass,RLD,and SRL associated with soil resource availability will help us understand the mechanistic controls of carbon to fine root longevity and turnover.The objective of this study was to understand whether seasonal variations of fine root biomass,RLD and SRL were associated with soil resource availability,such as moisture,temperature,and nitrogen,and to understand how these soil components impact fine root dynamics in Larix gmelinii plantation.We used a soil coring method to obtain fine root samples(≤2 mm in diameter)every month from May to October in 2002 from a 17-year-old L.gmelinii plantation in Maoershan Experiment Station,Northeast Forestry University,China.Seventy-two soil cores(inside diameter 60 mm;depth intervals:0-10 cm,10-20 cm,20-30 cm)were sampled randomly from three replicates 25 m×30 m plots to estimate fine root biomass(live and dead),and calculate RLD and SRL.Soil moisture,temperature,and nitrogen(ammonia and nitrates)at three depth intervals were also analyzed in these plots.Results showed that the average standing fine root biomass(live and dead)was 189.1 g·m^(-2)·a^(-1),50%(95.4 g·m^(-2)·a^(-1))in the surface soil layer(0-10 cm),33%(61.5 g·m^(-2)·a^(-1)),17%(32.2 g·m^(-2)·a^(-1))in the middle(10-20 cm)and deep layer(20-30cm),respectively.Live and dead fine root biomass was the highest from May to July and in September,but lower in August and October.The live fine root biomass decreased and dead biomass increased during the growing season.Mean RLD(7,411.56 m·m^(-3)·a^(-1))and SRL(10.83 m·g^(-1)·a^(-1))in the surface layer were higher than RLD(1474.68 m·m^(-3)·a^(-1))and SRL(8.56 m·g^(-1)·a^(-1))in the deep soil layer.RLD and SRL in May were the highest(10621.45 m·m^(-3) and 14.83m·g^(-1))compared with those in the other months,and RLD was the lowest in September(2198.20 m·m^(-3))and SRL in October(3.77 m·g^(-1)).Seasonal dynamics of fine root biomass,RLD,and SRL showed a close relationship with changes in soil moisture,temperature,and nitrogen availability.To a lesser extent,the temperature could be determined by regression analysis.Fine roots in the upper soil layer have a function of absorbing moisture and nutrients,while the main function of deeper soil may be moisture uptake rather than nutrient acquisition.Therefore,carbon allocation to roots in the upper soil layer and deeper soil layer was different.Multiple regression analysis showed that variation in soil resource availability could explain 71-73%of the seasonal variation of RLD and SRL and 58%of the variation in fine root biomass.These results suggested a greater metabolic activity of fine roots living in soil with higher resource availability,which resulted in an increased allocation of carbohydrate to these roots,but a lower allocation of carbohydrate to those in soil with lower resource availability.

Climate warming restructures seasonal dynamics of grassland soil microbial communities

Soil microbial community's responses to climate warming alter the global carbon cycle.In temperate ecosystems,soil microbial communities function along seasonal cycles.However,little is known about how the responses of soil microbial communities to warming vary when the season changes.In this study,we investigated the seasonal dynamics of soil bacterial community under experimental warming in a temperate tall‐grass prairie ecosystem.Our results showed that warming significantly(p=0.001)shifted community structure,such that the differences of microbial communities between warming and control plots increased nonlinearly(R^(2)=0.578,p=0.021)from spring to winter.Also,warming significantly(p<0.050)increased microbial network complexity and robustness,especially during the colder seasons,despite large variations in network size and complexity in different seasons.In addition,the relative importance of stochastic processes in shaping the microbial community decreased by warming in fall and winter but not in spring and summer.Our study indicates that climate warming restructures the seasonal dynamics of soil microbial community in a temperate ecosystem.Such seasonality of microbial responses to warming may enlarge over time and could have significant impacts on the terrestrial carbon cycle.

Seasonal dynamics of cyanobacteria and eukaryotic phytoplankton in a multiplereservoir recycling irrigation system

Background:Agricultural runoff recycling systems are manmade aquatic ecosystems of growing significance to global water sustainability,crop health,and production.This study investigated the seasonal dynamics of microbial community in a three-reservoir recycling irrigation system with a stepwise water flow and compared with that of an adjacent runoff-free stream.Runoff water from all production areas was captured in a sedimentation reservoir which overflowed to a transition reservoir then retention reservoir through a culvert.Stream water was pumped to replenish the reservoirs as needed during growing seasons.Results:16S rDNA PCR clone libraries of quarterly water samples from three reservoirs and one stream were sequenced,and 575 operational taxonomic units(OTUs)were identified and assigned to cyanobacteria,eukaryotic phytoplankton,and other bacteria.When compared to the stream,three reservoirs consistently had low microbial diversity.A distinct seasonal pattern of microbial community structure was observed for each reservoir and the stream.Stream was consistently dominated by other bacteria.Retention reservoir was dominated by cyanobacteria during the summer and fall and eukaryotic phytoplankton during the winter and spring.Sedimentation reservoir was dominated by cyanobacteria beginning in the spring but that dominance was altered when water was pumped from the stream from early spring to fall seasons.Transition reservoir had the greatest shift of microbial community structure,being dominated by other bacteria in the summer,cyanobacteria in the fall,and eukaryotic phytoplankton in the winter and spring.Water temperature and ammonium level were the two most important contributing factors to the seasonality of microbial community in these reservoirs.Conclusions:The three recycling irrigation reservoirs consistently had lower microbial diversity and distinct community structure when compared to the stream.These reservoirs were typically dominated by cyanobacteria during warm seasons and eukaryotic phytoplankton during cool seasons.This seasonal pattern was altered when water was pumped from the stream.The cyanobacteria dominance was associated with rising water temperature and ammonium level.These results highlight the importance of preventing agricultural runoff from entering natural waterways and water resources and provide a useful framework for further investigations into the ecological processes of this emerging ecosystem.

Seasonal dynamic changes in bacterial compositions in the Inner Mongolia desert steppe

Polymerase chain reaction-denaturing gradient gel electrophoresis(PCR-DGGE)technique was employed to examine the seasonal dynamic changes in bacterial community composition in the Inner Mongolia desert steppe using specific primers F954 and R1369.Bright and reproducible bands were sequenced,and the phylogenic tree was constructed.The results show that the bacterial community composition changed between different seasons.The specific bands were different between the sampling sites with light and heavy levels of degraded grassland.Three main types of bacteria constituting the microbial community in the Inner Mongolia desert steppe belonged to the α,γ and δ-sub phyla of Proteobacteria,Bacteroidetes and Acidobacteria.The unculturable bacteria accounted for 69%of the whole bacterial community of the Inner Mongolia desert steppe.

Dynamics of dissolved organic carbon in the mires in the Sanjiang Plain,Northeast China

Mires in boreal area had proved to be an important dissolved organic carbon （DOC） reserve for the sensitivity to climate change and human interfering. The study was focused on the temporal and spatial dynamics and controlling factors of DOC in a seasonallywaterlogged mire （SLM） and perennially-waterlogged mire （PLM） in the Sanjiang Plain, Northest China. In the two mires, DOC concentrations in both surface water and upper soil strata experienced pronounced seasonal variation. DOC concentrations in the surface waters were the greatest and averagely was 47.82 in SLM and 34.84 mg/L and PLM, whereas that in soil water at 0.3-m depth had little difference （20.25 mg/L in SLM and 26.51 mg/L in PLM）. Results revealed that DOC concentrations declined 5-8 times vertically from the surface down to groundwater. DOC in the groundwater only was in a very small part with the average concentration of 5.18 mg/L. In relation to the surface water, DOC concentrations varied positively with temperature just before 8 August, and only in early spring and later autumn DOC concentrations exhibited identifiable spatial trends along with standing water depths in PLM. It was supposed that the influences from standing water depth took effect only in conditions of low temperature, and temperature should be the most powerful factor controlling DOC dynamics in the mires. Redox potential （Red） showed negative relationship with DOC values while total nitrogen （TN） and the majority of free ions in the soil solution exhibited no relationship. High soil TOC/TN ratio and low redox potentials also led to DOC accumulation in the mires in the Sanjiang Plain.

Seasonal variation in the three-dimensional structures of coastal thermal front off western Guangdong

The seasonal structure and dynamic mechanism of oceanic surface thermal fronts(STFs)along the western Guangdong coast over the northern South China Sea shelf were analyzed using in situ observational data,remote sensing data,and numerical simulations.Both in situ and satellite observations show that the coastal thermal front exhibits substantial seasonal variability,being strongest in winter when it has the greatest extent and strongest sea surface temperature gradient.The winter coastal thermal front begins to appear in November and disappears after the following April.Although runoff water is more plentiful in summer,the front is weak in the western part of Guangdong.The frontal intensity has a significant positive correlation with the coastal wind speed,while the change of temperature gradient after September lags somewhat relative to the alongshore wind.The numerical simulation results accurately reflect the seasonal variation and annual cycle characteristics of the frontal structure in the simulated area.Based on vertical cross-section data,the different frontal lifecycles of the two sides of the Zhujiang(Pearl)River Estuary are analyzed.

Dynamic Downscaling of Summer Precipitation Prediction over China in 1998 Using WRF and CCSM4

To study the prediction of the anomalous precipitation and general circulation for the summer（June–July–August） of1998, the Community Climate System Model Version 4.0（CCSM4.0） integrations were used to drive version 3.2 of the Weather Research and Forecasting（WRF3.2） regional climate model to produce hindcasts at 60 km resolution. The results showed that the WRF model produced improved summer precipitation simulations. The systematic errors in the east of the Tibetan Plateau were removed, while in North China and Northeast China the systematic errors still existed. The improvements in summer precipitation interannual increment prediction also had regional characteristics. There was a marked improvement over the south of the Yangtze River basin and South China, but no obvious improvement over North China and Northeast China. Further analysis showed that the improvement was present not only for the seasonal mean precipitation, but also on a sub-seasonal timescale. The two occurrences of the Mei-yu rainfall agreed better with the observations in the WRF model,but were not resolved in CCSM. These improvements resulted from both the higher resolution and better topography of the WRF model.

Spatial and temporal variability in vegetation cover of Mongolia and its implications

In this paper, we attempted to determine the most stable or unstable regions of vegetation cover in Mongolia and their spatio-temporal dynamics using Terra/MODIS Normalized Difference Vegetation Index （NDVI） dataset, which had a 250-m spatial resolution and comprised 6 periods of 16-day composited temporal resolution data （from 10 June to 13 September） for summer seasons from 2000 to 2012. We also used precipitation data as well as biomass data from 12 meteorological stations located in 4 largest natural zones of Mongolia. Our study showed that taiga and forest steppe zones had relatively stable vegetation cover because of forest characteristics and relatively high precipitation. The highest coefficient of variation （CV） of vegetation cover occurred frequently in the steppe and desert steppe zones, mainly depending on variation of precipitation. Our results showed that spatial and temporal variability in vegetation cover （NDVI or plant biomass） of Mongolia was highly dependent on the amount, distribution and CV of precipitation. This suggests that the lowest inter-annual CV of NDVI can occur dur- ing wet periods of growing season or in high precipitation regions, while the highest inter-annual CV of NDVI can occur during dry periods and in low precipitation regions. Although the desert zone received less precipitation than other natural zones of the country, it had relatively low variation compared to the steppe and desert steppe, which could be attributed to the very sparse vegetation in the desert.

Growth and photosynthetic responses of Fraxinus mandshurica seedlings to various light environments

To determine light requirement and adaptability of Fraxinus mandshurica seedlings, the seasonal variations of photosynthetic variables were measured in 3-year-old seedlings grown under four light levels （100%, 60%, 30%, and 15% of full sunlight） with a LI-6400 portable photosynthesis system. The leaf chlorophyll content, special leaf weight, annual height and basal diameter increment of seedlings were also observed. The maximum and minimum values of net photosynthetic rate, maximum rate of carboxylation, and maximum rate of electron transport of F. mandshurica seedlings were detected with 60% and 15% of full sunlight treatments, respectively. With the decrease of light level, both light saturation point and special leaf weight significantly declined （p 0.05）, but leaf chlorophyll content significantly increased （p 0.05）. Annual height and basal diameter increments of seedlings grown under 60% of full sunlight treatment were significantly greater than those of seedlings under other treatments （p 0.05）. It was concluded that F. mandshurica seedlings can adapt to a wide range of light environments from 15% to 100% of full sunlight by adjusting light saturation point, leaf chlorophyll content and special leaf weight. According to the maximum of relative growth, 60% of full sunlight treatment is the optimum light level for the growth of 3-year-old F. mandshurica seedlings.

Dynamic Effects of the South Asian High on the Ozone Valley over the Tibetan Plateau

In this study,the TOMS/SBUV（Total Ozone Mapping Spectrometer/Solar Backscatter Ultraviolet Radiometer） data and SAGE（Stratospheric Aerosol and Gas Experiment） II data were employed to calculate the monthly total zonal ozone deviations over the Tibetan Plateau and the 150-50-hPa zonal ozone variations.The results show that there is a significant correlation between the two,with a correlation coefficient of 0.977.From 150 to 50 hPa,the ozone valley over the Tibetan Plateau（OVTP） becomes the strongest based on the SAGE II data,and the South Asian high（SAH） is the most active according to the 40-yr reanalysis data of the European Centre for Medium-Range Weather Forecasts（ERA40）,so a correlation between the SAH and the OVTP may exist.The WACCM3（Whole Atmosphere Community Climate Model version 3） simulation results show that both SAH and OVTP could still present within 150-50 hPa with reduced strength even when the height of the Tibetan Plateau was cut down to 1500 m.It is also shown that the seasonal variation of SAH would result in a matched seasonal variation of the OVTP,which suggests a meaningful effect of SAH on the OVTP.Meanwhile,it is found that the atmospheric circulation would impose different effects on the OVTP,depending on the SAH＇s evolution stages and movement directions.At 150-50 hPa,as the SAH approaches the plateau,the SAH zonal（meridional） transport would make the OVTP deeper（shallower）,while the vertical transport of ozone produces a deeper（shallower） OVTP at the lower（higher） level;the combined dynamic effects lead to a weakened OVTP.When the SAH stabilizes over the plateau,the zonal（meridional） transport results in a shallower（deeper） OVTP while the vertical transport would create a deeper（shallower） OVTP at the middle（bottom and top） levels;the combined dynamic effects produce a deeper OVTP.As the SAH retreats from the plateau,the OVTP becomes deeper（shallower） under the zonal（meridional） effect or shallower under the vertical effect;the combined dynamic effects contribute to a deeper（shallower） OVTP at the middle（bottom and top） levels.The SAH would have a weak effect on the OVTP over the plateau when positioned over the tropical Pacific.

Study on the phenology of Chara vulgaris in Xin’an Spring, north China

The phenology of Chara vulgaris was studied.The specimens were collected four times from April 2004 to January 2005(one sampling per season).The water temperature,pH,dissolved oxygen,specific conductance,maximum width and maximum depth were monitored at every sampling time.Eighteen main morphological characteristics of the Chara vulgaris were also observed and measured under the microscope.The results showed that all the environmental factors had different seasonal patterns and some of the morphological characteristics had significant fluctuations,indicating differences in their seasonality.At the same time,some morphological characteristics were affected by the environmental parameters to some extent and the effect was primarily exhibited in its vegetative proportions;there was little effect on the sexual reproductive characteristics.Therefore,the relatively stable sexual reproductive characteristics can be used to identify the species.