Background and Aims Shrublands is one of the major types of terrestrial ecosystems, which widely distributes from tropical to polar regions. Due to their largely distributional area in China, it is very important for us to exactly estimate their carbon storages and spatial distributions. Answers to the following questions were sought: (a) How much is the vegetation carbon storage of major shrublands in China? (b) How are their spatial distributions in China?
Methods Based on published biomass data in shrublands and 1∶4 000 000 digital vegetation map of China, carbon storage of major shrublands in China was estimated using the method of mean biomass carbon density for different shrublands types.
Key Results The carbon storage of six shrublands in China is 1.68±0.12 Pg C (1 Pg = 10¹⁵ g) with an total area of 15 462.64×10⁴ hm². The average vegetation carbon density is 10.88±0.77 Mg C·hm^-2, varying from 5.92 to 17.00 Mg C·hm^-2 for different shrubland types. The distribution of shrublands is spatially heterogeneous in the country. Shrublands in three provinces (Yunnan, Guizhou and Sichuan) in Southwest China occupies 23.5% of the total area and contributes to approximately one-third (32.6%) of the total carbon storage of six shrubland types in China due to favorable climeste and soil conditions. The area of six shrubland types in Inner Mongolia is the second largest among all the provinces. However, the vegetation carbon storage in Inner Mongolia shrublands is only 84.81 Tg C (1 Tg = 10¹² g), following that of Yunnan, Guizhou, Sichuan, Jiangxi, and Hunan. The probable reason is ascribed to its arid or semiarid climatic conditions. Although shrublands hold about 1.5 times the area of forests in China, the carbon storage of shrublands corresponds 27%-40% of forests because carbon density of shrublands accounts for only one-fifth of forests. Similarly, the proportion of vegetation carbon storage of shrublands to that of grasslands in China varies from 36% to 55% due to the different areas of grasslands used in previous studies.
Conclusions This study draw the following conclusions: (a) As important ecosystem types in China, shrublands hold large vegetation carbon storage, which is main component of China's vegetation carbon storage. (b) Because of different climatic and soil conditions, their distributions are spatially heterogeneous in China and The average vegetation carbon density varies greatly for different shrubland types.

Background and Aims Accurate estimates on the size of terrestrial organic carbon stocks are necessary for understanding their importance in regulating atmospheric CO₂ concentrations. In this paper, biomass and SOC contents in alpine grasslands (alpine steppe and alpine meadow) in Bayinbulak were estimated. In addition, the vertical distribution of belowground carbon was discussed. Our objectives were to (a) estimate biomass and SOC contents of two different alpine grasslands, (b) investigate the root distribution of two alpine grasslands, and (c) explore the vertical distribution of SOC of two alpine grasslands.
Methods SOC content was estimated by an improved method (integral arithmetic method). Based on continuous decrease of SOC density with soil depth, integral arithmetic method could estimate SOC content to a given soil depth.
Key Results There were significant differences in the biomass between the alpine steppe and alpine meadow; aboveground biomass of the alpine steppe was 71.4 g C·m^-2, whereas aboveground biomass of the alpine meadow was 94.9 g C·m^-2; belowground biomass of the two alpine grasslands was 1 033.5 and 1 285.2 g C·m^-2, respectively. No significant differences were found between integral arithmetic and traditional methods of estimating SOC contents. SOC contents of the alpine meadow was higher than in the alpine steppe; SOC contents in the two alpine grasslands was 25.7 and 38.8 kg·m^-2, respectively. Most of the root biomass of the two alpine grasslands was in the upper 40 cm of the soil profile, while SOC was concentrated in the top 60 cm. The two alpine grasslands had different root distributions; the percentage of root biomass in the top 20 cm averaged 76%-80% for the alpine steppe and alpine meadow. Alpine meadows had a deeper root profile with only 49% of the SOC in the upper 20 cm, whereas the alpine steppe had 55% of the total SOC in the top 20 cm.
Conclusions This study suggests that vegetation determines the vertical distribution of SOC through root: shoot ratio and its vertical root distribution.

Background and Aims Vegetation transect is an effective method to study the relationship between global change and terrestrial ecosystem. However there are few researches on biomass gradient characters of grassland vegetation and their environmental driving mechanism. The transect measurement was used in this study to analyze biomass gradient change of grassland vegetation in Inner Mongolia. The following questions were tried to answer: (a) How does grassland biomass change along with longitude and latitude as well as water and thermal gradients? (b) Which climate factors will produce pivotal effect to grassland biomass change? (c) How do climate factors control material production process of grassland ecosystem?
Methods The selection of 49 sample sites was principally defined by a 1 900 km long×150 km wide transect across the grasslands of Inner Mongolia. Aboveground and belowground biomasses were measured in the sample sites. The correlativity between biomass and climate factors was analyzed using China climate grid database which constructed by Chinese Ecosystem Research Network.
Key results Grassland biomass was found to be negatively correlated to mean annual temperature, ≥0 ℃ accumulated temperature, ≥10 ℃ accumulated temperature and annual hours of sunshine. Contrarily it was positively correlated with mean annual precipitation and mean annual relative humidity. Among climate factors, mean annual temperature and mean annual relative humidity effected grassland biomass the most obvious.
Conclusions Aboveground and belowground biomasses present visible change regulation along with longitude and latitude as well as climate gradients. Mean annual precipitation was shown as a key role to grassland biomass although its effect ways were complicated. The study suggested combined and integrated relationships of environment factors should be considered in researches of biomass forming and changing.

Background and Aims Artemisia ordosica is an important sand fixation plant in north China, whereas few studies were conducted on its population patterns. Population patterns of this species are therefore studied, and the aims are mainly: 1) how spatial scales are related to population patterns, 2) whether plant sizes effect population patterns, and 3) what roles environments play in the process of pattern formation?
Methods Two plots in the size of 50 m×50 m were established in the Mu Us sandy land, and all the A. ordosica plants were recorded and mapped. After that, the data were analyzed with the method of point pattern analysis.
Key results On the scales less than certain critical points, the population is usually characterized by non-random distribution (being clumped or regular), and their spatial association is considerably strong, but may be positive or negative. By contrast, if the scales enlarge beyond these points, the plants will disperse randomly, and their spatial association will loosen greatly. Small individuals are more likely to follow clumped distribution than those big ones. The spatial association between plants will turn from positive to negative if their size differences are enlarged increasingly. Unlike the A. ordosica plants growing in fixed sandy land, those plants in semi-fixed sandy land are easier to follow clumped distribution and associate with each other positively.
Conclusions Population patterns and spatial association of A. ordosica depend on spatial scales, individual sizes and environments, and so do their intra-specific relationships. If A. ordosica plants are transplanted into shifting sandy land for sand control and vegetation restoration, they ought to be arranged in the form of clumped distribution rather than regular distribution.

Background and Aims Sampling methods were essential in the process of studying plant population spatial distribution patterns. In early time, the population pattern research method which the ecologist used was generally simple. Some comprehensive research examples indicated the transect methods could not clearly present the spatial pattern in the vision. As a result of the spatial pattern complexity, there have not a measuring method to be possible clearly to express its complete characteristic or all information. So the authors presented a new method, photography orientation method, which based on point pattern analysis and GIS.
Methods The research was taken in a fenced plot of degraded typical steppe in the Xilingole League, Inner Mongolia, which had been monitored since 1983 by the Inner Mongolia Grassland Ecosystem Research Station of the Chinese Academy of Sciences. In this research, a community block of 10 m × 10 m was chosen and divided into four hundreds of 50 cm × 50 cm sub-blocks with bamboo chopsticks. All plants in the 400 sub-blocks were then pictured by a digital camera (Nikon D100) in order, and the growing positions of each plant individuals were accurately fixed in the pictures of sub-blocks by using GIS. The feasibility of this new method was examined by Wilcoxon signed ranks test.
Key Results The results showed the method was practicable. The working efficiency was largely enhanced and the research work could be done more delicately when the method was applied to measure population patterns of degraded typical steppe.
Conclusions This study suggests that using this method, the changes in population patterns, the life histories of plant individuals, and the interactions among species could be monitored dynamically; therefore the process of community succession could be probed from the aspect of population patterns.

Background and Aims Biological invasions, one of the three most pressing environmental problems, is an important component of global change and causes considerable environmental damage and economic losses to the invaded regions. Although China is a country heavily infested with invasive alien plants, factors influencing regional spatial patterns of these species are largely unknown.
Methods In order to explore the relationship between spatial patterns of invasive alien plants and environmental and anthropological factors, this study used multiple stepwise regression and canonical correspondence analysis to determine the effects of seven environmental variables (including area, latitude, longitude, mean temperature in January, mean temperature in July, annual precipitation, frost-free days) and seven anthropological factors (including number of foreign tourists, GDP, transport density, value of imported goods, area of nature conserve, rate of nature conserve, population density) on the number, density and spatial distribution of invasive alien plants in 32 provinces of China.
Key Results It was found that the number of invasive alien plant species decreased from the south to the north, which was largely determined by the frost-free days. The density of invasive plant species declined from the southeast coast inland to the northwest, which was best explained by transport density. In addition, about 50% of the variation in invasive alien species composition across provinces was accounted for by latitude.
Conclusions Our results suggest that both natural conditions and anthropological factors play important roles in shaping the patterns of plant invasions in China. These findings may help to understand ecosystem invasibility, and predict plant invasions on a regional scale, and hence have important implications for the management of invasive species.

Background and Aims The growing frequency and impact of biological invasions worldwide threaten biodiversity, ecosystem functioning, resource availability, national economies, and human health. Alternanthera philoxeroides is one of the most harmful invasive species and has caused great economic and ecological losses. This species has caused great harm to agriculture, fisheries, as well as to landscapes and native biodiversity, and, at times, has completely overrun and dominated an entire terrestrial ecosystem. It also can form dense tangled mats that float on the water surface of ponds or lakes and shade indigenous aquatic vegetation from sunlight, and thus replace native species. Previous studies have shown that A. philoxeroides can reduce the biodiversity of plants on paddy field ridges, but there have been no other studies on the effects of A. philoxeroides on biodiversity in other habitats. In this study, we conducted a survey of the species and their distributions in different weedy habitats that were invaded by A. philoxeroides in Nanjing during the spring and early summer season in order to interpret the relationship between its occurrence and the environments and elucidate the impact of its invasion on plant diversity.
Methods The abundance, coverage and frequency of each weed population were quantified using the square intercept method in 27 plots. The importance value of each weed was calculated as the sum of the relative abundance, relative coverage and relative frequency. We recorded 142 weed species that belonged to thirty-six families. The data were analysed using principal component analysis (PCA) in SPSS. Thirty-eight out of 142 weed species that had more than 20% frequency occurred in 27 samples were used in the analysis.
Key Results The results showed that the most important factors affecting the occurrence and distribution of weed species were the levels of human disturbance and the soil humidity. According to these two factors, all samples were divided into four groups. Group I included samples collected from experimental fields, and the dominant weed species were Capsella burss-pastoris, Veronica persica and Stellaria media. Group II included samples located in rape farmland which have high soil humidity, and the dominant weed species were Galium aparine var. tenerum, Conyza bonariensis, and Roegneria kamoji. Group III included samples located in public parks or under trees, and the dominant weed species were Vicia sativa, Beckmannia syzigachne, and Geranium carolinianum. The last group was mainly composed of samples distributed on wastelands and waysides which were non-managed or non-irrigated farmland, and the dominant weed species were Erigeron annuus, and Veronica arvensis. The change in the density of Alligator weed and other weeds in the different habitats were analysed. The results showed that the importance value of Alligator weed was high when the soil humidity was relatively high and the intensity of human disturbance was not too great, indicating that Alligator weed has a strong ability to adapt to different habitats. There were different dominants in the different plant communities, which means human disturbance and soil humidity had a key effect on the communities that were composed of a mixture of Alligator and other weeds. When species diversity indices of each group were compared, it was found that although species richness and Simpson's index increased slightly from group I to group IV, but the Shannon-Wiener index and the Pielou evenness index decreased with an increase in the average importance value of Alligator weed.
Conclusions These results indicated that the species composition of the weed community had changed, and the species diversity gradually decreased with increasing dominance of the invasive Alligator weed. These results clearly showed that the invasion of Alligator weed had a negative affect on biodiversity.

Background and Aims Niche fitness of Artemisia halondendron population, that fixes shifting and semi-fixed sandy soils in Horqin sandy land, rarely has been explored. This study addresses 1) spatial and temporal differences in niche fitness and composite vigor and 2) limiting factors of niche fitness in different habitats.
Methods Mathematical models were adapted to calculate composite vigor index (CVI) and niche fitness values of a population of A. halondendron inhabiting shifting, semi-fixed, and fixed sandy lands. Data on CVI and niche fitness were collected by measuring height, size of canopy, branches, and biomass of individuals, as well as soil moisture content, nutrient content, and bulk density.
Key Results CVI was remarkably low on fixed sandy land, indicating that the ecological function of the population was weakened. Composite niche fitness values for different soils during the growing season ranked: semi-fixed > fixed > shifting sandy land. Moisture fitness values ranked: shifting > semi-fixed > fixed sandy land. As the soil moisture content changed, the limiting layer also changed. It was 15-30 cm in the different sandy lands in July, but with the infiltration of rain water, the layer deepened to 45-60 cm in August. In September, it was 30-45 cm in semi-fixed and fixed sandy lands, but remained 15-30 cm in shifting sandy land. The limiting factors in different habitats were different: soil organic matter content was limiting on shifting sandy land and soil moisture content was limiting on semi-fixed and fixed sandy lands.
Conclusions This study indicated that soil moisture content and nutrient content affected composite niche fitness. The relationship of soil moisture content and nutrient content directly influences composite niche fitness. Their ratio could reflect the importance of organic matter to fine roots, and the population could adapt to the ratio by adjusting the growth of fine roots.

Background and Aims In hilly Loess region, Artemisia scoparia is always the dominator in the early abandoned field communities. It may be replaced by Agropyron cristatum or Heteropappus altaicus or Stipa bungeana in next succession stage when no disturbance occurs. In order to study the direction of Artemisia scoparia community succession under different standing conditions, we conducted transplant experiments to test the intraspecfic and interspecfic competition of Artemisia scoparia in river terrace and northern mound land and, at the same time, its morphological traits were investigated.
Methods In the experiments, nine species (three coexisting species, five later sere species and Artemisia scoparia itself) were chosen and transplanted as test species, but due to the low survival of two species, only seven species were analyzed to test the relative competition ability to phytometer Artemisia scoparia under different standing conditions.
Key Results The results show that the individuals tend to be miniaturized, i.e., its communities are composed mainly of small-sized individuals and competition can change the morphological traits. The unit biomass competition intensity is better than total competition intensity in explaining plants' relative competitive ability when local conditions and plant size are considered. Under the northern mound land and the lowest river terrace, late-successional and perennials species have higher competitative ability than early-successional and annual plants, suggesting that the competition of late- against early-successional species is one of the driving force to succession. Comparison of the competition between the seven test species and the unit biomass of Artemisia scoparia, the northern mound land ranks the first, lower river terrace the second and the lowest terrace the third, suggesting that intensive competition occurs more severely in poor growing conditions. There is significant difference in the ability of competition between the test species and Artemisia scoparia from the lowest river terrace to the northern mound land, suggesting that the ranks of the competition ability may vary depending on standing conditions.
Conclusions As competition is one of the decisive factors in constructing plant community, the shift or variation of competition ability between coexisting species and sere species may result in different community structure and dynamics, so it changes the direction and pathway of succession under different standing conditions.

Background and Aims The reproductive characteristics of fig species in the understory of tropical rainforest are rarely explored until now. Ficus cyrtophylla in Xishuangbanna tropical rainforest was chosen for a case study. We'd like to answer the following questions in this paper: 1) who is the pollen vector for F. cyrtophylla, 2) what reproductive characteristics does F. cyrtophylla have, and 3) compared with other fig species reported, what does F. cyrtophylla share with them and what is F. cyrtophylla different from them?
Methods An integrative approach combining investigation of the fig tree's phenology and its pollinator's behavior with Kruskal-Wallis tests and Mann-Whitney U tests was adopted. Data on the fig's phenology were collected by observing the sampled trees once a week from August 2004 to August 2005. The pollinator's behavior was observed at a dissecting microscope (OLMPUS-SZX12) in our lab.
Key results The results showed Blastophaga sp. was the only species-specific pollinator for F. cyrtophylla, and the passive pollinator only could produce their offspring within its figs. The range of the pollinator number trapped in the gall fig and seed fig cavity were both 0-5, and the majority (about 78.45% of gall fig and 84.25% of seed fig) had only one,other cases were very rare. For F. cyrtophylla, the fig trees were ever-green, and a little variation occurred in the quantity of the leaves. On the population level, they could continuously produce the figs year-round, synchrony within the single tree but asynchrony among the trees. The functional male tree's fruiting presented much more asynchrony than the female ones. There were two fruiting peaks in a year, November and April-May, respectively, and every tree could produce 2-3 crops in the whole year. Under the natural conditions,the mean number of galls and pollinators in every gall fig were respectively 147.32±62.61 and 110.94±62.82, the sex ratio of pollinators was 0.143 9±0.131 6, the ratio of galls per fig was 64.13%±19.89%, the mean number of seeds per seed fig was 231.44±74.25, and the ratio of seeds per fig was 85.72%±14.19%.
Conclusions The two partners in this symbiosis performed many high co-adaptations in many aspects, for example, between the pollination behavior and A/O ratio. Compared with those fig species reported until now, the reproductive ecology of F. cyrtophylla was different from them, which maybe suggest that various fig species in different geographic environment and those species with different life form in the same environment might adopt different reproductive strategies to stabilize their mutualism.

Background and Aims In Horqin sandy land, vegetation degradation usually occurs in improper management regimes under fragile conditions, e.g. clearing and grazing. However, few information is available about the effects of grazing and enclosing on the structure and performance of soil seed banks in the semi-arid desert environment. Therefore, a field experiment was conducted in grazed and enclosed grasslands to examine the structure and performance of soil seed banks.
Methods In late March 2003, three parallel 200-m line transects (20 m apart) were established in two experimental sites, grazed and enclosed grasslands. For each transect, 20 sampling points were set up at 10-m intervals, and a soil sample of 5 cm in depth and 20 cm × 20 cm in dimension was collected from each sampling point. All soil samples were transported to the laboratory in open plastic bags and chopped and sieved (mess width is 0.2 mm) soon. The sieved soil samples were placed in plastic germination pots (33 cm in diameter and 12 cm in depth) and spread evenly to form an approximately 1 cm thick layer in individual pots. Pots were placed in an unheated greenhouse for seed germination. Pots were watered daily with a very fine nozzle in the afternoon. Emergent seedlings were identified to species and carefully removed from the pots. Seed germination and seedling identification were carried out continuely in the following three months. However, some unidentifiable seedlings remained longer in the pots until they were identified. The density of the existing seed bank was expressed as the number of viable seeds per square meter. At each site, the frequency of species in the soil seed bank was determined in terms of the 60 sampling points or the 60 quadrats.
Key Results The study was conducted in grazed and enclosed grasslands to examine the relationship between density and composition of soil seed bank and vegetation in Horqin sandy land, Inner Mongolia. The results showed that there were 22 and 30 plant species in seed banks in the grazed and enclosed grasslands, respectively. In the grazed and enclosed grasslands, the seed bank density were 20 657±3 342 and 16 149±1 900 viable seeds·m^-2, respectively, with annual herbaceous plants dominating in both sites (occupied 99% and 98%, respectively) Shannon-Wiener index and richness of the grazed grassland were 0.836 3 and 4.954 9, respectively, which were distinctly lower than those in the enclosed grassland (0.968 2 and 7.226 0), suggesting negative impacts of grazing on seed bank diversity. Seed bank density strongly related to the standing vegetation density in both grazed and enclosed grasslands (p<0.001), indicating the standing vegetation density increased with the increase of seed bank density. Differences in seed bank density accounted for 78% and 58% of the variance of standing vegetation density in grazed and enclosed communities, respectively.
Conclusions Our results showed that adoption of enclosure management practice significantly increased density and species diversity of the seed bank, compared with the grazed grassland. Therefore, reseeding, enclosure and other management steps should be used to speed up the restoration process of the degraded grassland.

Background and Aims The study area is located on the eastern Qinghai-Tibetan Plateau (101°-103° E, 34°-35°70' N). The altitude ranges from 2 900 m to 4 000 m, and the climate is cold and humid with an annual rainfall of 450-780 mm, which is mainly distributed in July, August and September. Mean annual air temperature is 1.8 ℃ with -10.7 ℃ in January and 11.7 ℃ in July, and average annual frost days are no less than 270 d. The grassland types include mainly alpine meadow (59.32%), brushy meadow (33.39%), woodland meadow (0.32%), saline meadow (0.15%), swampy meadow (5.61%) and upland grass (1.21%). The vegetation belongs to typical alpine meadows, and the species composition of the plant community is dominated by many monocotyledons and various dicotyledons. The capacity of seed germination and seedling establishment determines partially the regeneration of plant communities of the grassland. However, there is few germination data. Accordingly, we have undertaken a major study of the gramineous species of the alpine meadow. A comparison of the germination biology of many species will provide an ecological context for subsequent studies of field distribution.
Methods Seeds were collected from as many sources as possible to get an adequate representation of the whole community from July to October in 2003. Enveloped seeds were spread on tables at room temperatures(about 15 ℃)until dried and threshed by hand through screens. The experiment of germination started on March 3, 2004. For each species 50 seeds were placed in Petri-dishes on filter paper moistened with distilled water in a growth chamber with a 12-h day at 25 ℃ and a 12-h night at 5 ℃. This temperature regime has relevance to field conditions: it approximates the mean daily maximum and minimum temperature in 5 cm deep soil from May to August. The percentage of seeds germinated was recorded every day. Newly emerged seedlings were removed from the Petri-dishes and seeds were regularly watered with distilled water. A seed was considered germinated when the length of the emerged radicle was equal to the length of seed. Germination was judged to be complete when no further germination occurred for five successive days. The remaining ungerminated seeds were checked for viability by soaking in water at 30 ℃ for 2 h, removing the seed coats and sliting open the seeds, then soaking the embryos in 0.1% tetrazomium chloride for 4 h at 30 ℃. In viable seeds embryos were stained pink. The amount of germination was then calculated as a percentage of the total number of viable seeds and rate of seed germination as the number of seeds germinating each day expressed as a percentage of the final germination. In this study, we make use of 4 indices: percent germination, days to first germination, germination period and days to 50% germination.
Key Results Of the 54 species examined, the following 26 species exceeded 80% germination: Achnatherum inebrians, Agrostis alba, A. sp1., A. stolonifera, Aneurolepidium dasystachys, Arundinella anomala, Bromus tectorum, Deschampsia caespitosa, Deyeuxia scabrescens, D. sp., Elymus dahuricus, E. tangutorum, Festuca sinensis ,Helictotrichon leianthum, Mellica scabrosa , Orinus kokonorica, Poa schoenites, P. sinattenuata, P. botryoides, P. poophagorum, P. pratensis, Ptilagrostis dichotoma, P. mongholica, P. roshevitsiana, Roegneria nutans and R. stricta. The following 11 species had 60%-80% germination: Achnatherum sibiricum, A. splendens, Brachypodium sylvaticum, Bromus magnus, B. sinensis, Deyeuxia arundinacea, Gramineae sp., Helictotrichon tibeticum, Ptilagrostis junatovii, Stipa capillacea and S. przewalskyi. The following 8 species had 40%-60% germination: Agrostis hugoniana, Brachypodium sp., Festuca ovina, F. rubra, Helictotrichon sp2., Poa declinata, Roegneria kokonorica and Stipa aliena. The following 5 species had 20%-40%germination: Aristida triseta, Helictotrichon schellianum, H. sp1., Koeleria cristata and Oryzopsis munroi and the following 4 species had values of less than 20%: Stipa purpurea, Agrostis sp2., Stipa penicillata var. hirsuta and A. trinii; 14 species, Achnatherum inebrians, A. splendens, Agrostis alba, Aneurolepidium dasystachys, Arundinella anomala, Brachypodium sp., Bromus tectorum, Elymus dahuricus, E. tangutorum, Mellica scabrosa, Orinus kokonorica, Poa sinattenuata, Ptilagrostis mongholica and Roegneria nutansbegan, began to germinate within 3-5 days; 29 species, Poa schoenites, Achnatherum sibiricum, Agrostis sp2., A. stolonifera, Brachypodium sylvaticum, Bromus magnus, B. sinensis, Deschampsia caespitosa, Deyeuxia arundinacea, D. sp., Festuca ovina, F. rubra, F. sinensis, Gramineae sp., Helictotrichon sp2., H. tibeticum, Koeleria cristata, Oryzopsis munroi, Poa botryoides, P. declinata, P. poophagorum, P. pratensis, Ptilagrostis junatovii, P. roshevitsiana, Roegneria kokonorica, R. stricta, Stipa aliena, S. capillacea and Stipa penicillata var. hirsuta, began to germinate within 6-8 days; 10 species, Agrostis hugoniana, A. sp1., A. trinii, Aristida triseta, Deyeuxia scabrescens, Helictotrichon leianthum, H. schellianum, H. sp1., Ptilagrostis dichotoma and Stipa przewalskyi, began to germinate within 9-10 d; and only Stipa purpurea exceeded 10 d. For species such as Stipa purpurea, Achnatherum inebrians, Agrostis alba, A. sp1., A. sp2., A. stolonifera, Aneurolepidium dasystachys, Aristida triseta, Arundinella anomala, Elymus dahuricus, E. tangutorum, Helictotrichon schellianum, H. sp1., Mellica scabrosa, Poa poophagorum and P. sinattenuat (16 species), the germination period was short (1-7 d); 28 species, Poa schoenites, Achnatherum splendens, Agrostis hugoniana, A. trinii, Brachypodium sp., Bromus magnus, B. sinensis, B. tectorum, Deschampsia caespitosa, Deyeuxia arundinacea, D. scabrescens, D. sp., Festuca ovina, F. rubra, F. sinensis, Gramineae sp., Helictotrichon leianthum, H. tibeticum, Koeleria cristata, Orinus kokonorica, Oryzopsis munroi, Poa botryoides, P. declinata, P. pratensis, Roegneria kokonorica, R. nutans, Stipa capillacea and Stipa penicillata var. hirsuta, had the germination period of 8-14 d; and 10 species, Achnatherum sibiricum, Brachypodium sylvaticum, Helictotrichon sp2., Ptilagrostis dichotoma, P. junatovii, P. mongholica, P. roshevitsiana, Roegneria stricta, Stipa aliena and S. przewalskyi, germinated over a longer period (15-21 d);for species such as Poa sinattenuata, Achnatherum inebrians, Agrostis alba, Aneurolepidium dasystachys, Arundinella anomala, Brachypodium sp., Bromus tectorum, Elymus dahuricus, E. tangutorum, Mellica scabrosa and Roegneria nutans (11 species), germinated 50% within 1-7 d, while Poa schoenites, Achnatherum splendens, Agrostis hugoniana, A. sp1, A. stolonifera, Bromus magnus, B. sinensis, Deschampsia caespitosa, Deyeuxia arundinacea, D. scabrescens, D. sp., Festuca ovina, F. rubra, F. sinensis, Gramineae sp., Helictotrichon leianthum, H. tibeticum, Orinus kokonorica, Poa botryoides, P. declinata, P. poophagorum, P. pratensis, Ptilagrostis mongholica, P. roshevitsiana, Roegneria kokonorica, R. stricta and Stipa capillacea (27 species) germinated 50% within 8-14 d; and the time to 50% germination of Achnatherum sibiricum, Brachypodium sylvaticum, Ptilagrostis dichotoma, P. junatovii and Stipa przewalskyi exceeded 14 d, but 11 species, Agrostis sp2., A. trinii, Aristida triseta, Helictotrichon schellianum, H. sp1., H. sp2., Koeleria cristata, Oryzopsis munroi, Stipa aliena, S. purpurea and Stipa penicillata var. hirsuta, failed to germinate 50% after the experiment.
Conclusions These species showed four germination patterns: rapid (e.g. Achnatherum inebrians and Agrostis alba), slow (e.g. Achnatherum sibiricum and Stipa przewalskyi), intermediate (e.g. Deschampsia caespitosa and Orinus kokonorica) (percent germination >50%) and low germination (e.g. Oryzopsis munroi and Stipa purpurea) (percent germination <50%).The experiment illustrated that the gramineous species of the alpine meadow on the eastern Qinghai-Tibetan Plateau are heterogeneous in their germination characteristics. Nevertheless, knowledge of other factors (e.g. light, temperature and storage methods) influencing germination is needed before we can fully understand the relationships between germination characteristics and field distribution.

Background and Aims Ammopiptanthus monglicus, endemic to the semi-arid desert region of central Asia, is an endangered evergreen leguminous shrub. Having difficulties to recruit into its original habitat, A. mongolicus population is experiencing difficulties in regeneration, and the area it ever possessed is shrinking. It is included in the China Red Data Book of Endangered Plant as the third-class protected plant. Despite the importance of seed germination characteristics in developing an adequate understanding of both primary and secondary colonization processes, there still not a few previous studies on the germination of A. mongolicus. To get a comprehensive understanding about the germination characteristics and seedling performance of A. mongolicus, experiments were, therefore, conducted to define the optimum environmental condition for germination. Further, the seed size effects on the seedling performance is also investigated here.
Methods In order to find out optimal temperature for soaking, Seeds were soaked in water of 21.5 (room temperature), 40, 60, 80, 90 ℃ for 5 minutes respectively. Treated seeds were placed on moistened filter papers in 11cm diameter Petri dishes, then, transferred into a laboratory incubator at 28 ℃. To test the germination response of the seed to the environmental temperature, seeds presoaked in 60 ℃ hot water were put into incubator under 15, 20, 25, 30, 35, 40 ℃ for germination, respectively. In the case of container seedling culture, presoaked seed were sowed with different cultural media, sandy soil, clay loam, mixed soil (sand soil mixed with clay loam at the ratio of 1∶1). Attempt to answer the question that whether the seeds with different size will differ in seedling performance, seeds were categorized into three groups according to the their diameter, those less than 5 mm, those between 5 and 6 mm, and those that of more than 6 mm. Pretreated seeds of its respective size were sowed into the raised seedbed separately. Observations on the seedlings survival rate, leaf width, leaf number, and plant height were recorded almost twice a month.
Key Results Seeds presoaked in water at 60 ℃, gave the highest germination vigor that 56.4% seeds were germinated within one day's incubation at 28 ℃. The optimal temperature for hypocotyl and radicle elongation of seedling is 25 ℃ to 30 ℃, lower than that for seed germination initiation (30 ℃). Temperature above 40 ℃ would likely have a detrimental effect on seedling growth in the germination test, it cause the hypocotyl and radical tissue damage and eventually decay of the seedlings. Interestingly, the percentage of abnormal seedlings with tightly twisted radicle and split tip, which are less likely to survive in the seedbed, were just 5.2%-8.6% under the temperature of 30 ℃ to 40 ℃, greatly less than that of 28.1% under the temperature of 15 ℃. In the case of container seedling culture, sixty three percent seedlings emerged out of the sand soil within 7 days, while in clay loam only 11%. Compared with seedlings emerged from the smaller one, seedlings emerged from seeds with size more than 5 mm tend to be stronger and growing more vigorous than the smaller one during the early stages of growth. This trend is further evidenced by the weak and high susceptibilities to pathogen and continuous death of seedlings from the smaller seeds within the 70 days growth. Seedlings from larger seeds took only about 57 days to attain a constant survival rate of more than 56.3%, while seedlings from the smaller ones took more than 70 days to attain 35.4% and still on a decreasing trend.
Conclusions Extremely high or low temperature have a detrimental effect on germination and seedlings performance of A. mongolicus shortly after the germination initiation, despite the fact that their adult counterpart have a extremely high tolerance to the hardness of its environment. This is accordance with our filed observation that very few seedlings or saplings were seen in the natural habitat. Soaking in hot water between 40 ℃ to 60 ℃ did promote the germination rate of A. mongolicus, and decrease the percentage of remaining hard-coated seeds. Seeds less than 5 mm in diameter showed reductions in seedling quality and seedling performance suggests that seeds with different size may have significant impacts on future community composition in the prospect habitat and should be treated discriminatingly in nursery and re-introduction activity.

Background and Aims The fungal endophytes in grasses grow intercellularly and systemically in aboveground plant tissues. Vertically transmitted asexual endophytes (Neotyphodium) forming asymptomatic infections of cool-season grasses have been repeatedly derived from sexual species (Epichloı) that abort host inflorescences. The phylogenetic distribution of seed-transmitted endophytes is strongly suggestive of cocladogenesis with their hosts. Endophytes are considered plant mutualists: they receive nutrition and protection from the host plant while the host plant may benefit from enhanced competitive abilities and increased resistance to herbivores, pathogens, and various abiotic stresses. Most studies of grass-endophyte associations have been undertaken with two economically important plant species, Lolium perenne and Festuca arundinacea. The interactions between endophytes and other grasses in natural plant communities, however, are seldom concerned. Much less attention has been paid to native grasses in Inner Mongolia Steppe, which lies in the north of China and is an important part of Steppe in Eurasia, and only limited published symbiosis studies are available in this natural ecosystem. Thereby, a more comprehensive view of the ecology, diversity of endophytes and their interactions with host plants becomes essential.
Methods Our research of grass (Achnatherum sibiricum) associated with Neotyphodium endophyte (a new grass-endophyte association) was carried out in the Inner Mongolia Steppe, China. Twenty-seven endophyte strains were isolated from four A. sibiricum populations including Hulingol (H), Xi Ujimqin Qi (X), Inner Mongolia Grassland Ecosystem Research Station of the Chinese Academy of Sciences (IMGERS-CAS) (I), and the Leymus chinensis plot of the IMGERS-CAS (L), respectively. Colony morphology, growth rate on potato dextrose agar (PDA) and conidial measurements of isolates were used to characterize diversity of endophytes hosted by A. sibiricum. The genetic polymorphisms of Neotyphodium species from the four A. sibiricum populations were also analyzed using random amplified polymorphic DNA (RAPD) markers.
Key Results Four morphological groups of Neotyphodium species and five individual morphological types were described based on the colony morphology, growth rate, and conidial shape and size. A total of 463 bands were obtained using 20 RAPD primers, of which 461 bands were polymorphic. A total of 93 unique loci were obtained, accounting for 20.1% of the total amplified loci. Nei's diversity index (h) and Shannon's diversity index (I) were 0.238 and 0.387, respectively. In the four populations (H , X , I, and L), the value of h was 0.122 0, 0.180 4, 0.146 3 and 0.210 7, respectively. The four populations may be ranked in a descending order as L > X > I > H, and the I of the four populations had a similar trend. The fixation index (F_ST), the coefficient of gene differentiation (G_ST), and the genetic differentiation (Hsp-Hpop)/Hsp (estimated by Shannon's diversity index) were 0.205 1, 0.300 4, and 0.355 0, respectively. The genetic variation of Neotyphodium species mainly existed within populations. Genetic similarities within each population were found to be in the range of 0.647 9-0.943 8 in similarity, and the average genetic distance among the four populations was 0.285 8, varying from 0.057 8 to 0.433 9. Clustering analysis based on Nei's unbiased genetic distance and UPGMA method showed that there were seven distinct RAPD genetic groups.
Conclusions The high incidence of endophytic infection in A. sibiricum was indicative that the presence of the endophyte gave the grass a competitive advantage over non-infected grasses. The study also indicated that there were higher genetic diversity based on morphological and RAPD results, and that there were relatively high genetic variations among the four populations and higher genetic differentiation of Neotyphodium sp. within a geographical region. Most of the genetic groups were related to geographical origins of the strains. The dendrogram of genetic distance matched rather well with the morphological data, as reflected by the four morphotypes.

Background and Aims The water source area of the middle line project for transferring water from south to north is in the interface of Henan, Hubei and Shaanxi Provinces, the largest source of freshwater in Asia. Economic development of the area surrounding the Danjiangkou Reservoir will affect water quality. The objective of this study is to develop methods for monitoring biological resources, including annual changes of plankton in the reservoir, in order to provide a scientific base for sustainable exploitation, protection of biological resources, regulations for water resource protection, and establishment of a database for long-term ecological research on the middle line project.
Methods Water samples were collected using standard methods at three points of Qushou, Kuxin and Dashiqiao from March 2003 to August 2005, for biological, physical, and chemical analyses. Qualitative samples were collected using 25 phytoplankton networks, and taxa were identified by ordinary microscopes. Quantitative samples were collected using bottles and were fixed in Lugol's medium. Samples were condensed and counted in the laboratory under light microscopy with a phytoplankton counter frame. Algal diversity was calculated using Margalef and Menkinick diversity indices.
Key Results Samples contained 96 species and varieties, 63 genera, and 8 divisions of phytoplankton; diatoms were the most important component, followed by green algae and blue green algae (cyanobacteria). Cell densities exhibited seasonal changes, with maximum values in summer and minimum values in winter. Investigation of phytoplankton from three recent years showed an average annual density of algae of 109.33×10⁴ cells·L^-1 at low water level, and no pollution of indicator species was detected in the water sources. Application of diversity indices to assessment of water quality showed the d, α value, and differences among the different sample sites were small. There were only small differences in water quality nutrition status.
Conclusions Water quality indicated mesotrophy and middle nutrition status. This study provides a scientific base for long-term ecological research on biological resources and for policy development for ecological environmental protection. It will have an important effect on the water quality on the middle line project.

Background and Aims Canopy stomatal conductance is considered as a sensitive parameter of forest ecosystem in responding to environmental changes and can be used to monitor the impacts of water stress, air pollution, trace gas and other environmental factors on forest function. Sap flow of an Acacia mangium forest was measured to scale up stand transpiration and canopy stomatal conductance. It aimed at understanding water use of A. mangium forest in different environmental water conditions and its responses to soil moisture change at an ecosystem level.
Methods The Granier's thermal dissipation probes were applied to monitor sap flow of 14 sample trees in an Acacia mangium forest in hilly land of South China. The sap flow data were used to calculated whole-tree and stand transpiration, and to estimate mean canopy stomatal conductance (G_c) by combing with synchronous measurement of environmental factors.
Key Results Sap flux density (J_s) and whole-tree transpiration (E_t) were obviously affected by tree morphological features. Even though there were less individual trees with large diameter at breast height (DBH) in the sample plot, they comprised relatively larger proportions of total sapwood area and transpiration of the forest. Daily variations of J_s and E_t were mainly controlled by photosynthetically active radiation (Q_o) and vapor pressure deficit (D). Soil moisture (θ) had greater effects on J_s and E_t of trees with larger DBH than on those trees with smaller DBH. The differences of J_s and E_t across individuals reduced with decreasing θ. The highest stand transpiration (E) occurred in July when the radiation and hydrothermal condition were favorable, whereas the reduced water supply in soil during the time period of September-November resulted in lower E value and its sensitivity to D. G_c responded to major environmental factors in a similar way with E. Long-term lower θ would significantly decreased G_c, which would cause reduction in E.
Conclusions Mature A. mangium forest can maintain a vigorous transpiration under sufficient radiation and hydrothermal conditions, but could not stand well under long-term stress of soil moisture. Granier's probes have the potential to accurately estimate stand transpiration, canopy conductance and their responses to environmental factor, extending the temporal and spatial scales in studying the ecological process of forest ecosystem.

Background and Aims Phytoremediation is an important method for restoring bare soil or slag; however, the physiological traits of plants used for revegetation are poorly known, even though such traits are important to successful remediation. This study was carried out on oil shale waste in Maoming City, Guangdong Province to screen for tree species with high photosynthetic potential, appraise the ability of these plants to acclimatize to oil shale waste, and provide valuable information for ecological restoration of similar waste sites.
Methods Diurnal variation of photosynthesis was measured for 12 tree species in summer and winter, using portable photosynthetic equipment (LI-6400, LI-COR, Inc., USA). Other parameters such as transpiration, stomatal conductance, relative humidity, etc. were measured simultaneously, and water use efficiency (WUE) was calculated as net photosynthesis divided by transpiration.
Key Results There were large seasonal differences in all parameters, with values of net photosynthesis, transpiration, and stomatal conductance higher in summer than winter (60.9%, 77.7% and 85.7%, respectively), but WUE higher in winter than in summer (26.8%-77.2%). Diurnal variation of net photosynthesis also exhibited seasonal differences. Many tree species exhibited a bimodal peak in summer and a unimodal peak in winter; however, Cinnamomum camphora was unimodal in both seasons; Terminalia bellirica, Tristania confertam, and Tectona grandis were bimodal in both seasons; and Syzygium cumini was bimodal in winter and unimodal in summer. Trees with higher mean net photosynthetic rate in both winter and in summer should be more useful for phytoremediation than species with high net photosynthetic rate in only one season. Accordingly, net photosynthetic rate, which synthesizes all parameters examined, should be considered the most important parameter to appraise the ability of plants to acclimatize.
Conclusions According to mean net photosynthetic rates in both winter and summer, the sequence of photosynthesis efficiency of the 12 tree species tested was: Acacia auriculiformis, Terminalia bellirica, Cassia siamea, Gmelina arborea, Tectona grandis, Tristania conferta, Cinnamomum camphora, Ormosia pinnata, Ilex rotunda, Syzygium cumini, Peltophorum ptetocarpum and Pterygota alata.

Background and Aims Making nitrogen (N) recommendations without knowing the N supply capability of a soil can lead to inefficient use of N and potential pollution of the ground water. Conventional soil test techniques are destructive and time consuming. Remote sensing of canopy reflectance has the capacity of non-destructive and rapid estimating crop N status, and could be potentially used in evaluating soil N supply status.
Methods Thus, rice (Oryza sativa) canopy reflectance spectra and soil available N content (NH⁺₄-N+NO^-₃-N) of different straw and N treatments were measured at key development stages of rice at two sites with different soil types and rice varieties. All possible normalized difference vegetation indices (NDVI) and ratio vegetation indices (RVI) composed by two bands, and some hybrid vegetation indices such as SAVI (soil adjusted vegetation index), TSAVI (transformed soil adjusted vegetation index) were calculated. Then the correlations between these VIs and soil available N were analyzed and the best regression equation was also investigated.
Key Results The correlations of soil available N content and canopy reflectance were negative at visible band, while positive at near infrared bands during the whole growing cycle. NDVI and RVI were well correlated with soil available N content, with the best stage of tillering and the best indices of the combination of 870, 1 220 nm and 560, 710 nm. Relationship between soil available N content and the best vegetation indices screened at tillering stage were influenced by soil background. While TSAVI was proved to be the best choice for removing the effect of soil background, and the relationship was consistent at two sites, with the best regression equation in exponential form. TSAVI calculated with the best band combinations screened in this study can improve the relationship, especially for the TSAVI calculated with 870 and 710 nm, with the decision coefficient (R²) increased from 0.46 to 0.60. At the heading and filling stage, the ratios of vegetation index and new SAVI calculated by 1 220 and 760 nm were well related to soil available N content independent of sites.
Conclusions Our observations suggest that evaluating soil N status at rice growing stage of with canopy reflectance spectra is feasible, but more research still need to be conducted to test and improve the soil N prediction model.

Background and Aims Arsenic (As) exists ubiquitously in our environment and in various forms that can be harmful to human beings as well as agricultural crops. In order to study mechanisms of carbon and nitrogen metabolism in flue-cured tobacco, Nicotiana tabacum, contaminated by arsenic, a systematic experiment was conducted on the farm of Henan Agricultural University, Zhengzhou, China.
Methods Five arsenic treatment levels (0, 5, 20, 40, 60 mg·kg ^-1 (added as sodium arsenate Na₃AsO₄·12H₂O)) were used to determine the effects of arsenic toxicity on carbon and nitrogen metabolism and on the yield and quality of potted (400 mm×340 mm) flue-cured tobacco plants (Nicotiana tabacum L. cv. ‘Yunyan 85’).
Key Results The results showed that arsenic toxicity inhibited assimilation and transformation of carbon, decreased chlorophyll content and photosynthetic rates, and caused the accumulation of soluble sugar content during the whole growth period, and the decrease of starch content during the last part of the growing period. Arsenic toxicity also altered nitrogen metabolism and resulted in a decrease in nitrogen assimilation capacity during the early growing stage. Nitrate-reductase (NR) activity, and protein and total nitrogen content were decreased compared with the control. Nitrogen transformations resulted in an increase in the content of the free amino acids and activity of glutamate-pyruvate transaminase (GPT), an accumulation of protein and total nitrogen during the middle and late growth stages, but a decrease in nicotine content during the whole growing period. The results also showed that arsenic toxicity lowered tobacco yields and their economic value, Although the sugar-nitrogen ratio and the increase of the total content of soluble sugars related to carbon-nitrogen metabolism was beneficial, the decrease of nicotine content and the increase of the content of protein and total nitrogen, as well as high sugar-nicotine and nitrogen-nicotine ratios were not favorable for the formation of leaves with high chemical quality.
Conclusions Arsenic toxicity had significant effects on carbon and nitrogen metabolism during the whole growing period, and lowered yield and economic value of flue-cured tobacco. Besides, it was unfavorable for the formation of leaves with high chemical quality, and led to an accumulation of arsenic in the leaves. Therefore, it was suggested that flue-cured tobacco not be planted in arsenic contamination regions.

Background and Aims We examined the effect of acid-alkaline concentrations in media on growth rate and nutrient uptake of a red macroalga, Gracilaria lemaneiformis, which has a rapid growth rate, rapid nutrient uptake rate, and high agar content. We address the following questions: 1) can the culture media be kept relatively stabilized, 2) what organic compound best buffers pH, and 3) how does the compound buffer the media and affect growth of the alga?
Methods Utilizing the dark-light bottles method, we selected a suitable zwitterionic organic compound from seven reagents (barbitone, borate, HEPES, TRIS, MOPS, TAPS, POPSO) that did not inhibit photosynthetic production of dissolved oxygen (DO), did not increase depletion of DO in respiration, and adjusted acid-alkaline balance in the culture media. We examined the effects of each buffer on growth rate (SGR) of G. lemaneiformis, measured diurnal and weekly variations of pH and dissolved inorganic carbon (DIC), and determined CO₂ concentrations according to pH and DIC. We integrated these with the growth rate of G. lemaneiformis, to investigate the mechanisms of growth and carbon uptake.
Key Results POPSO was the zwitterionic organic compound that best met our objectives. During the diurnal experiment of POPSO's effect on algal growth, pH rose continuously during the light cycle, contrary to DIC; however, high concentration of POPSO can buffer this fluctuation. During the one-week experiment, according to results of the diurnal experiment, pH values and DIC at the beginning and end of the light cycle indicated that lower concentrations of POPSO (0 and 5 mmol·L^-1) did not buffer pH fluctuations, but higher concentrations (>15 mmol·L^-1) suitably stabilized pH values and leveled off DIC content in the media. Ambient CO₂ concentration determined algal growth rates, with the relationship between SGR of G. lemaneiformis and ambient CO₂ concentration similar to a Michaelis-Menton kinetics equation. The saturated concentration of CO₂ was 5.25 μmol·L^-1, and the maximum growth rate of the alga was 10.11%·d^-1.
Conclusions This study determined that POPSO is a suitable organic compound to buffer G. lemaneiformis culture media. A possible mechanism is that, under relative stabilization of acid-alkaline media, HCO^-₃and CO^2-₃(components of DIC), transformed into CO₂ and accelerated growth rate of the alga.

The relationship between plant and pollinator is considered as a mutualism because plant benefits from the pollinator's transport of male gametes. Nectar robbers are frequently described as cheaters in the plant-pollinator mutualism, because it is assumed that they obtain a reward (nectar) without providing a service (pollination). Nectar robbers are birds, insects, or flower visitors that remove nectar from flowers through a hole pierced or bitten in the corolla. Nectar robbing represents a complex relationship between animals and plants. Whether plants benefit from the relationship is always the controversial part in earlier studies. This paper is to review the recent literatures on nectar robbing and attempt to acquire an expanded understanding of the ecological and evolutionary roles that robbers play. Understanding the effects of nectar robbers on the plants that they visited and other flower visitors is especially important when one considers the high rates of robbing that a plant population may experience and the high percentage of all flower visitors that nectar robbers make to some species.
There are two standpoints in explaining why animals forage on flowers and steal nectar in an illegitimate behavior. One is that animals can only get food in illegitimate's way because of the mismatch of the morphologies of animals' mouthparts and floral structure. The other point of view argues that nectar robbing is a relatively more efficient, thus more energy-saving way for animals to get nectar from flowers. This is probably associated with the difficulty of changing attitudes that have been held for a long time. In the case of positive effect, the bodies of nectar robbers frequently touch the sex organs of plants during their visiting to the flowers and causing pollination. The neutral effect, nectar robbers' behavior may destruct the corollas of flowers, but they neither touch the sex organs nor destroy the ovules. Their behavior don't affect the fruit sets or seed sets of the hosting plant. Beside the direct impacts on plants, nectar robbers may also have an indirect effect on the behavior of the legitimate pollinators. In some circumstances, the change in pollinator behavior could result in improved reproductive fitness of plants through increased pollen flow and out-crossing.

Plants have evolved many adaptive mechanisms to cope with heavy metal stress, including governing uptake of heavy metal ions, detoxification by chelation, intracellular sequestration and cellular homeostasis to minimize the damage from exposure to nonessential metal ions. Mycorrhizae, root exudates and cellular membranes are three key factors that regulate heavy metal uptake. Ectomycorrhizae can significantly enhance the heavy metal tolerance of the host plant, and root exudates reduce the absorption of heavy metal ions by changing the pH and redox state of rhizsphere as well as chelation. However, the molecular mechanisms of these processes are not yet clear. The trans-membrane transporters have been fully researched and have been either identified or isolated. Many genes are involved, such as the ZIP (ZRT IRT related proteins) family, natural resistance associated macrophage proteins (Nramp) and P_1B-type ATPase family were discovered and cloned in recent years. The primary chelators of heavy metals in plants are metallothioneins (MTs), phytochelatins (PCs), organic acids and amino acids. They alleviate the toxicity of metal ions in plants by chelation. MT-like genes encoding MTs and genes encoding γ-glutamyl-cysteine synthetase have been cloned. Gene expression in tested plants has demonstrated the role of genes in tolerance to heavy metals. Genes of phytochelatins synthetase (PCs) helping synthesis of PCs, i.e. γ-Glu-Cys, also have been cloned. The nicotianamine gene, an amino acid involved in biosynthesis of muginetic acids, has been shown to contribute to tolerance and hyperacumulation to heavy metals. ABC-type (ATP-binding cassette) transporters and CDF (cation diffusion facilitators) as well as other trans-membranes transporters help to sequester the heavy metals in vacuoles. The genes governing these transporters have been cloned and expressed in plants, which show to contribute to heavy metal adjustment. Plants with heavy metal tolerance have developed pertinent genes or functional proteins in these aspects. In recent years, we have increased our understanding of the molecular mechanisms of plant heavy metal tolerance and have used plants in the remediation of heavy metal contamination. Understanding molecular mechanisms of plant heavy metal tolerance might be a key step for heavy metal remediation.