Methods We studied survival and biomass increase of plants subjected to 30, 60, 90, 120, 150 and 180 d submergence and in a control (no submergence). We measured total shoot length, total shoot number and total leaf number during the post-submergence recovery period.

Important findings Survival of the plants after long-term submergence was associated with their distribution pattern on riverbanks. Ficus tikoua, mainly occurring on high-elevation sites, died after 30 d submergence. Triarrhena sacchariflora, from intermediate-elevation sites, died after 150 and 180 d submergence. 90% and 100% of submerged plants of H. altissima and C. dactylon, respectively, survived after 180 d submergence. Submergence inhibited the growth of all plants, and the total biomass increase of each species was significantly lower than that of control plants. The aboveground biomass of all submerged plants decreased significantly. After 60 and 120 d submergence, the belowground biomass of T. sacchariflora decreased significantly, but that of H. altissimaand C. dactylon did not change during submergence. All surviving plants grew. After 30, 60 and 90 d submergence, the relative grown rate (RGR) in total shoot length of all submerged plants was not significantly different with that of control plants, but after 120, 150 and 180 d submergence, the RGR in total shoot length of submerged H. altissimaand C. dactylonwas higher than that of control plants. The RGR in total leaf number was always higher than that of control plants after all submergence durations. After long-term submergence, this might be an effective way for plants to generate more new leaves and accelerate photosynthesis.

Aims Hot-dry valleys in southwestern China are adverse habitats. The foliar antioxidant system of plants growing there must play an important role in protecting their photosynthetic apparatus against photo-oxidation. Our aim was to characterize the responses of the antioxidant system to seasonal changes of multiple abiotic stresses in two dominant tree species in the hot-dry valley of the Yuanjiang River, Yunnan.

Methods We chose two savanna species with different photosynthetic rates for study: the evergreen Cyclobalanopsis helferiana(oak) and drought-deciduous Terminthia paniculata(sumach). We examined changes of the two main antioxidants, ascorbate (ASC) and glutathione contents and the activities of all of the antioxidant enzymes of the water-water and ASC-glutathione cycle in these two species from the hot-rainy season to the chill-dry season and to the warm-dry season.

Important findings Both species showed the highest antioxidant activity in the chill-dry season; however, they had the highest activities of glutathione transferase and glutathione peroxidase in the subsequent warm-dry season. They had similar ASC and glutathione contents and activity of SOD, the initial enzyme of water-water cycle, but sumach displayed higher activities of most antioxidant enzymes in the water-water and ASC-glutathione cycles in all seasons compared to oak. Overall, sumach activated its antioxidant system more actively than oak, yet oak had more persistent antioxidant activity than sumach. Compared with activities of antioxidant systems of plants growing in other adverse conditions, the two study species have stronger antioxidant capacity, which is consistent with their absolutely lower contents of malondialdehyde in all seasons.

Aims Artemisia ordosica is important in vegetation succession in the Mu Us sandland of China. Little is known about the effects of AM fungi and water stress on A. ordosica under non-sterilized soil conditions. Our objective is to explore the effects of AM fungal colonization on growth and drought resistance ofA. ordosica.

Methods Glomus mosseae inoculums and the indigenous AM fungi in the rhizosphere of A. Ordosica were selected to study the effects of AM fungal colonization on growth and drought resistance ofA. ordosica. We used non-sterilized soil with two water contents: 75%-85% and 35%-45% of field moisture capacity.

Important findings Plant morphology and water content were not significantly affected by drought stress, but AM fungal colonization was seriously decreased. Leaf water retention capacity increased under water stress and the allocation of nitrogen and phosphorus to shoots was limited. The activity of superoxide dismutase (SOD) was relatively higher in the early stage of stress, and the activity of peroxidase (POD) was relatively higher in the later stage. AM fungal colonization percent and spore numbers were enhanced under the same water condition. Branch numbers and development of lateral roots, root/shoot ratio, water retention capacity, absorption of phosphorus and nutrients in roots were all improved by AM fungal colonization. Under AM fungal colonization, the contents of soluble sugar and malondialdehyde (MDA) were low, the soluble protein content did not change greatly and the activity of SOD and POD was improved. Therefore, drought resistance of A. ordosica was strengthened. There was a large discrepancy of promotion effects on A. ordosica under different soil conditions and AM fungal colonization. The effects of indigenous AM fungal colonization were better than the G. mosseae single colonization. Decline of AM infection rates might contribute to decreased plant water absorption capacity, and AM fungal colonization in the early stage of plant growth can improve the capacity for resistance to environmental drought stress at the middle-late growth stage.

Aims We studied protective enzyme activities and lipid peroxidation in wheat seedlings treated with different concentration of PEG6000 to determine the effects of He-Ne laser on wheat (Triticum aestivum)exposed to drought stress.

Method We treated 12-day-old, drought-stressed seedlings with 5%, 10% and 15% PEG6000 for 3, 6, 9, 12 and 15 days. After 3, 6, 9, 12 and 15 days of drought stress, a He-Ne laser was employed to irradiate seedlings of spring wheat for 0, 1 and 3 min. Leaves were sampled for various analyses.

Important findings He-Ne laser irradiation significantly decreased malondialdehyde (MDA) content and superoxide radical (O₂^-.) production rate and notably increased peroxidase (POD) enzyme activity and ascorbate (AsA) and glutathione (GSH) concentration in wheat seedlings exposed to moderate drought stress. We concluded that 3 min laser irradiation enhanced anti-drought characteristics of wheat seedlings treated with 5% or 10% PEG6000.

Aims Border cells and their secretory mucilage can form a layer over the surface of younger parts of roots to help form a “rhizosheath” protecting the root tip from biotic and abiotic stresses. Our objective was to investigate the ecological role of mucilage secretion strategies in response to Al exposure and absence.

Methods Soybean (Glycine max) ‘Zheqiu No. 2’ and ‘Zhechun No. 3’ were used in this study. Seedlings were aeroponically cultured in 0.2 mmol·L ^-1CaCl₂ solution, pH 4.5, containing 0, 100, 200, 300 or 400 µmol·L ^-1AlCl₃.Half of the seedlings were harvested after 24 h Al exposure and the other half continued to culture in the absence of Al³⁺. We measured percent viability of border cells, mucilage thickness and relative root elongation.

Important findings Percent viability of root border cells decreased with increasing external Al³⁺concentrations in both cultivars. Percent viability of ‘Zheqiu No. 2’ border cells decreased slightly after a 3-12 h treatment with 100, 200, or 400 µmol·L ^-1Al³⁺and then slightly increased with treatment time, whereas the same change in ‘Zhechun No. 3’ seedlings was noted at Al ³⁺concentrations of 300 and 400 µmol·L ^-1. Al³⁺induced a thicker mucilage layer around border cells of both cultivars, with a maximum of 17 µm after 24 h at 400 µmol·L ^-1Al³⁺. ‘Zheqiu No. 2’ border cells developed a thicker mucilage layer within 3-6 h in response to 100 and 200 µmol·L ^-1Al³⁺, while ‘Zhechun No. 3’ cells exhibited the same change after 12 h to 300 µmol·L ^-1Al³⁺. Relative root elongation of ‘Zheqiu No. 2’ exposed to 400 µmol·L ^-1Al³⁺was significantly higher than to 100-300 µmol·L ^-1Al³⁺treatment, while ‘Zhechun No. 3’ exhibited reduced relative root elongation after exposure to 100-400 µmol·L ^-1Al³⁺. With Al³⁺recovery treatment, ‘Zheqiu No. 2’ border cells developed a thinner layer of mucilage in the absence of Al ³⁺compared with Al³⁺exposure, while ‘Zhechun No. 3’ border cells continued to secrete a conspicuous layer of mucilage. Rapid induction of mucilage production exposure to Al ³⁺stress and abrupt halt by border cells is a specific response to Al³⁺stress and recovery for Al-resistant soybean cultivar.

Aims Our objective was to explore how temperature and light directly affect activity of violaxanthin de-epoxidase (VDE) in vitro and to clarify the relationship between VDE activity and xanthophyll cycle-dependant energy dissipation.

Methods We investigated VDE activities and energy dissipation in wheat leaves treated with different temperatures (4, 25, 38 and 45 ℃) combined with different light intensities (200, 500, 900 and 1 200 μmol·m ^-2·s^-1).

Important findings Maximum activity of VDE in wheat leaves appeared at 30 ℃, suggesting that this was the optimum temperature for VDE in vitro. Light intensity had no effects on VDE activity in wheat leaves in vitro. Compared with 25 ℃, 4 ℃ treatment exhibited no obvious effect on VDE activity; however, 38 ℃ treatment caused slight increase while 45 ℃ caused dramatic decrease in the VDE activity. With increasing light intensity, non-photochemical quenching (NPQ) and xanthophyll cycle-dependent energy dissipation (q_E) increased significantly. However, the ratio q_E/NPQ decreased slightly when the temperature increased from 4 ℃ to 38 ℃ and decreased significantly when the temperature was increased to 45 ℃. Under low and moderate light intensity, the VDE activity measured at treatment temperature was in agreement with the q_E/NPQ, which is a measure of the capacity of xanthophyll cycle-dependent energy dissipation.

Aims Oxidative stress is one of the responses of plants to salt stress, which causes the production of hydrogen peroxide (H₂O₂). Plants grafted on salt resistant rootstocks could improve their tolerance to salt stress because of the vigorous root system of rootstocks. However, little is known about the relationship between salt tolerance of grafted plants and the scavenging system of H₂O₂ under Ca(NO₃)₂ stress. Our objective was to investigate the mechanism and roles of ascorbate-glutathione metabolism system in salt tolerance of grafted eggplant under Ca(NO₃)₂ stress, including ascorbate pool, glutathione pool and the activities of antioxidant enzymes.

Methods We grafted cultivar ‘Suqi qie’ ( Solanum melongena) onto rootstock of ‘Torvum Vigor’ ( S. torvum), which is a salt tolerant cultivar introduced from Japan. We compared leaves of hydroponically-grown grafted and own-root eggplant seedlings grown under 80 mmol·L^-1Ca(NO₃)₂ stress for changes of antioxidant enzyme activities, contents of antioxidants in ascorbate-glutathione cycle metabolism and content of H₂O₂.

Important findings Under Ca(NO₃)₂ stress, H₂O₂ content increased in leaves of eggplant seedlings and was significantly lower in leaves of grafted seedlings than own-root seedlings. Also, activities of antioxidant enzymes (APX, DHAR and GR), regenerating rates of AsA and GSH and redox statuses (ratios of AsA/DHA and GSH/GSSG) were significantly higher in leaves of grafted seedlings than own-root seedlings. We concluded that grafted eggplant seedlings had efficient metabolism of ascorbate-glutathione cycle, which scavenged the H₂O₂ rapidly to alleviate the oxidative damage of Ca(NO₃)₂ stress; therefore, grafted seedlings had a stronger tolerance to salt stress.

Aims Litter fall acts as a connection between plants and soil and is the key in nutrient and energy cycling of forest ecosystems. Northeast (NE) China possesses one of the largest forest carbon stocks in the country; however, large scale litter fall patterns along environmental gradients in this region remain unclear. Our objective was to determine the relationship between litter production and climate indices, forest type and community structure for this region.

Methods Using data from 27 plots across NE China (recorded between 2004 and 2006 in Mt. Changbai, Mt. Mao’er, Liangshui and Genhe), we measured the litter fall for all major forest types in the region and statistically analyzed relationships between litter production and environmental factors.

Important findings Annual litter fall production averaged 2 337, 2 472, 3 130 and 4 146 kg·hm^-2for deciduous needleleaf forest, evergreen needleleaf forest, deciduous broadleaf forest and deciduous broadleaf and needleleaf mixed forest, respectively. Forest types differed greatly in composition of litter components. Mean proportions of leaf, branch and fruit for all forest types were 71%, 22% and 6%, respectively. Annual litter fall production was positively related to mean annual temperature (MAT; r=0.75, p<0.001), but was not significantly related to mean annual precipitation (MAP), forest type or community structure (p>0.05). Different litter fall components were controlled by different factors. Production of leaf litter was influenced by both MAT and forest type, and broadleaf forests showed a significantly higher leaf litter production than needleleaf forests with a similar climate. Branch litter production was mainly controlled by MAP and stand volume, while fruit litter production was affected by both forest type and MAP. Percentages of different litter components were mainly associated with MAP. Percentage of leaf litter was negatively correlated with MAP (r = -0.75, p<0.001), while percentage of branch litter showed a reverse pattern (r=0.68, p<0.001).

Aims Drought effects on terrestrial ecosystems are a key issue in global change research. This study was designed to 1) analyze effects of drought on carbon exchange in a subtropical coniferous plantation; 2) elucidate the sensitivity of carbon exchange to different degree of water deficit and the critical values when the ecosystem converts from carbon sink to source and 3) investigate the main factors that control ecosystem carbon exchange when drought occurs.

Methods The CEVSA2 model, which incorporated several significant modifications based on the CEVSA process-based ecosystem model and has been tested by using eddy covariance observation in different forest ecosystems, was parameterized by using site-specific ecophysiological measurements. Drought scenarios were designed to analyze effects on annual carbon budget and to elucidate the main control factors.

Important findings Drought decreases ecosystem production and carbon exchange significantly. Compared with simulation of no drought effect scenario, the droughts in 2003 and 2004 decrease annual net ecosystem production (NEP) by 63% and 47%, respectively. Ecosystem photosynthesis and respiration respond to drought differently, and the more rapid decrease of gross ecosystem production (GEP) than ecosystem respiration (Re) lead to the decrease of NEP when drought occurs. As daily average vapor pressure deficit (VPD) rises above 1.5 kPa, GEP, Re and NEP begin to decrease; When VPD rises above 2.5 kPa and relative soil water content (RSW; soil water content/saturated soil water content) decreases below 40%, the ecosystem converts from a carbon sink to source. Soil water deficit, which is the main factor controlling the ecosystem carbon exchange, accounts for 46% to the decrease of total annual NEP in 2003 and 2004, and atmospheric drought accounts for only 4%.

Aims Evapotranspiration (ET) plays an important role in arid and semiarid temperate grassland where water availability is a major limiting factor for ecosystem functions. Understanding temporal variation of ET can help explain the surface-atmosphere interaction and its ecological function in grassland ecosystems. Partitioning total ET into its components of evaporation from soil (E) and transpiration from plants (T) is important for understanding the biotic and abiotic factors that control water balance. Our objectives were to simulate the seasonal and interannual variations of ET and its components, analyze the contribution of the components to ETand analyze influencing factors.

Methods We used flux data derived from eddy covariance technology over Inner Mongolia steppe (43°32′ N, 116°40′ E), measuredLAIand MODIS data from 2003 to 2005 and parameterized VIP (Vegetation interface processes) model to simulate ET of the grassland. The results were validated using half-hourly latent heat fluxes (LE) and net radiation (R_n) estimated from eddy covariance measurements.

Important findings VIP model can effectively simulate latent heat fluxes of the grassland (R²=0.80). In 2003 and 2004, precipitation (P) was near average and annual ET was 337 and 338 mm, respectively, which were greater than P. In the drier year of 2005, annual ET was 223 mm, which was higher than P. On average, E andT made relatively equivalent contributions to ET. About 83% of annual EToccurred during the growing season. Ewas the primary component of ET before June and was exceeded by Tafter that. The monthly totals of both ET and Treached maxima in July and August. Total ETduring July and August accounted for 43% of the annual amount. ETwas strongly correlated with LAI and moderately correlated with P. E changed little during the growing season, and the difference in ET was accounted for T.

Aims Betula utilis andAbies faxoniana are two typical, important plants in timberline ecotone in subalpine regions of western Sichuan, China. Their responses in phenology, growth and leaf and branch traits to simulated global warming can be studied using the open-top chamber (OTC) method. The main purposes of our experiment are to determine how two species change their phenology, whether shoot growth is enhanced and whether responsive patterns of deciduous and evergreen species are consistent. We reported the second year’s responses of plants to the OTC treatment.

Methods During the 2007 growing season, we observed phenological events (bud break, leaf expansion and defoliation) and measured branch and leaf growth rates, traits and distribution patterns. Microclimate data between OTCs and control plots (CK) were automatically recorded at 15-minute intervals. We analyzed phenological events, leaf area, branch length, etc. for OTCs and CKs by the Mann-Whitney U-test. Specific leaf area (SLA) was analyzed by the Wilcoxon’s signed ranks test.

Important findings Air temperature at vegetation height (1.2 m) increased by 2.9 ^oC during the growing season, and soil temperature at 5 cm depth did not differ between OTC and CK throughout the growing season. Abies faxonianashowed earlier bud break in the OTC, and B. utilishad extended foliage period and individual leaf longevity in the OTC. Elevated temperature resulted in higher leaf and branch growth rates and basal diameter relative growth rates for both species. There were significant differences in SLA and leaf size for B. utilisbetween the OTC and the CK. Different responses (positive, negative or no effects) were found in branch length, branch number and leaf distribution pattern for both species. Therefore, evergreen conifer and deciduous broad-leaved species differ in their responses to warming.

Aims The subalpine coniferous forests in eastern Qinghai-Tibet Plateau provide a natural laboratory for studying effects of climate warming on terrestrial ecosystems. Research on differences between tree species in their responses to experimental warming can provide insights into their regeneration behavior and community composition under a future warmer climate.

Methods We used open-top chamber (OTC) to determine short-term effects of two levels of air temperature (ambient and warmed) and light (full light and ca. 10% of full light regimes) on the early growth and physiology of Betula albo-sinensis and Abies faxonianaseedlings.

Important findings The OTC manipulation increased mean air temperature and soil surface temperature by 0.51 ℃ and 0.33 ℃, respectively, under the 60-year plantation and 0.69 ℃ and 0.41 ℃, respectively, under the forest opening. Warming generally increased the growth, biomass accumulation and advanced physiological processes for seedlings of both species. In response to warming, both species allocated relatively more biomass to foliage and had significantly decreased root/shoot ratios (R/S), which might provide tree species an adaptive advantage when other environmental factors are not limiting. Warming may enhance photosynthesis in the two seedlings by increasing efficiency of PSⅡ in terms of increase inF_v/F_m, photosynthetic pigment concentrations and apparent quantum yield (Φ). However, the effects of warming on seedling growth and physiological performance varied by light conditions and species. For B. albo-sinensis seedlings, the effects of warming were pronounced only under full-light conditions, while the growth and physiological responses of A. faxoniana seedlings to warming were found only under low-light conditions. Competitive and adaptive relationships between the two species may be altered as a result of response differences to warming manipulation. The short-term beneficial impact of warming on the early growth and development of the two species suggests that global warming may lead to changes in regeneration dynamics and species composition in subalpine coniferous forest ecosystems.

Aims Ficus hispida is a common pioneer tree species in the tropical secondary forests of Xishuangbanna, China. Our objective was to determine effects of light and temperature on seed germination of F. hispida to understand its response to forest microenvironments.

Methods Our experiments were carried out in incubator with 14 h light/10 h dark treatments. Experiments to test the effects of temperature on germination were conducted at 35/25, 35/20, 30/20, 25/15 and 30 ℃ under fluorescent light. Neutral-density black plastic film was used to determine the effect of light intensity on germination at 30 ℃. Tests of the effects of R/FR ratio on germination were set at 23/20 and 30 ℃, and R/FR ratio gradients were created by filtering incandescent light through 2, 4 and 6 layers of green plastic film.

Important findings The seeds of F. hispida were photoblastic, germinating only in light. R/FR ratio significantly influenced seed germination, followed by temperature and light intensity. Germination could be induced by very low PPFD though delayed. Although the final germinations in all temperature treatments under fluorescent light were >96%, mean time to germinate differed among temperature treatments. Seed germination at 0.42 R/FR ratio was inhibited at 23/20 ℃, while much higher and earlier germination was recorded at 30 ℃. In addition, an R/FR ratio of 0.34 significantly inhibited germination at 30 ℃.

Aims Land-use and land-cover changes are important in the study of global change. Our objective is to understand the impact of topography on land use and cover change in Xishuangbanna, Southwest China, from 1976 to 2007.

Methods Based on GIS techniques, we used six periods of Landsat MSS/TM/ETM images and 1:50 000 digital elevation model (DEM) to analyze patterns of land use and cover change and transfer rates as affected by topography.

Important findings The magnitude, pace and spatial reach of land use and cover changes in Xishuangbanna were unprecedented. The most significant changes were a decrease of forest area from 13 193 to 8 336 km²and an expansion of area of rubber plantations from 249 to 2 256 km²at low elevation. Topographic features, especially elevation and slope, exerted significant influence on the distribution pattern, intensity and velocity of land use and cover changes. Changes varied along elevation gradients, slope gradients and aspects. Forest cover continuously decreased below 1 600 m, while the upper limit of rubber plantations increased continuously from 1 000 to 1 400 m and was dominant between 400 and 1 000 m. Farmland was dominant below 600 m and decreased rapidly with increasing elevation. Along all slope gradients, forest cover decreased gradually, while rubber plantation increased, but shrubland and dry land first increased and then decreased. Rubber plantations and farmland were mainly on gentle slopes, while forest occupied the majority of steep slopes. After 1988, rubber plantation cover was unchanged below slopes of 5˚, but continuously expanded above slopes of 5˚. Aspect had large influence on the distribution pattern of cash crops and agricultural land. Rubber plantations on south aspects rapid expanded in comparison to a trend of general increase on north aspects, where forests reached a maximum and dry lands a minimum. Economic interests and population growth lead to excessive deforestation and reclamation in this region. Especially in recent years, the continuous conversion of forests to both rubber plantations and tea gardens has yielded negative effects which have led to further fragmentation affecting the biodiversity and security of natural ecosystems. For local sustainable development, the government must control the expansion of rubber plantations into forest and higher elevations, safeguard relatively intact of tropical ecosystems and manage land sustainably over the long term.

Aims Dominant tree species control the structure and function of forest ecosystems. Delimiting plant functional types (PFTs) based on dominant tree species, therefore, can assist in understanding the functional, structural framework and species distributions of an ecosystem. Straddling the subtropical and warm-temperate zones of the Funiu Mountain National Natural Reserve, East China, is representative of north-south climatic transition zones. The tree layer is composed mainly of a few dominant species whose abundances vary along altitudinal gradients.

Methods Using community ecology techniques, we sampled the north and south slopes of Funiu Mountain. We calculated species importance values for 37 tree species and identified dominant species. χ²tests, together with association coefficient and percentage co-occurrence, were used to measure interspecific associations of the dominant tree species. PFTs were defined according to interspecific associations and altitudinal distributions of the dominant species.

Important findings Four dominant tree species (Quercus variabilis, Q. glandulifera, Q. acutidentata, Pinus armandi) formed the basis of four PFTs: Ⅰ. Q. variabilis, Q. aliena, Aldizzia kalkora, Castanea seguinii (under 1 000 m); Ⅱ. Q. glandulifera, Platycarya strobilacea, Pistacia chinensis (1 100-1 400 m); Ⅲ. Q. acutidentata, Carpinus cordata, Toxicodendron vernicifluum (1 400-1 800 m) and Ⅳ. Pinus armandi, P. tabulaeformis, Abelia biflora, Betula platyphylla, B. albo-sinensis (above 1 800 m). These PFTs differ in many morphological traits such as leaf size and phellem (cork) thickness, Further eco-physiological studies are required to better understand these differences.

Aims Stipa purpurea steppe is one of the most important ecosystems in source regions of Changjiang (Yangtse) and Huanghe (Yellow) Rivers. Our objective was to determineStipa purpureacommunity characteristics.

Methods Typical Stipa purpurea communities distributed in Maduo, Qumalai and Tongde of Qinghai Province were selected as three sampling locations and sampled using 33 sampling lines for a total of 330 samples. Analyses used PCORD, SPSS and EXCEL software.

Important findings Species composition of the investigated community was simple, with 96 species grouped into 58 genera and 23 families. North Temperate genera were dominant. We identified three associations: Stipa purpurea+Potentilla bifurcaassociation (Ⅰ),Stipa purpurea +Carex parva association (Ⅱ), andStipa purpurea+Poa indattenuata association (Ⅲ). These associations have different characteristics that are analyzed in this paper. Comparability analysis show that association Ⅰ is much more similar to association Ⅱ than Ⅲ, but the importance value ofS. purpureais much higher than any other species in all associations. The community distribution of S. purpureasteppe is heterogeneous at coarse scale and regionally homogeneous at fine scale. The correlations are all significant among evenness, Simpson, Shannon-Wiener indices and latitude. The curves of evenness, Simpson and Shannon-Wiener indices changed similarly in samples. Species diversity for the associations was Ⅱ>Ⅲ>Ⅰ.

Aims Our purpose is to examine changes in community composition and niche characteristics of dominant species in an artificial plant community in the wind-breaking and sand-fixing forest in the lower reaches of the Tarim River, Xinjiang, China. Findings will provide a case for sustainable management of artificial plant communities in desert inland river basins.

Methods Using representative plots, we sampled 24 locations for species diversity, community structure and interspecific relationships from August 2004 to June 2007. Dominant species were identified based on species’ Importance Index in the communities. Niche breadth and overlap were calculated and analyzed using Simpson’s and Pianka’s methods.

Important findings Community composition between planted and existing communities changed in the seven years. Species diversity increased over four years and then decreased, and community structure became more complex. After four years, the invasion of native species changed the artificial community into an artificial-natural plant community, with changes in dominant species. Niche breadths of dominant species were Phragmites communis>Karelinia caspica>Calligonum caput-medusae>Elaeagnus angustifolia>P. euphratica>Tamarix ramosissima>Haloxylon ammodendron>H. glomeratus.The niche overlap value between C. caput-medusae and P. euphratica was the largest among dominant species. At the present stage of community succession, there is no relationship between niche breadth and niche overlap of dominant species, which shows that there is competition among plants and high spatial heterogeneity of environmental resources.

Aims Estimating species potential distribution based on observed occurrence records in combination with environmental variables is very important for conservation of rare and endangered species. Pseudotaxus chienii, endemic to southeastern China, is a relic species with a restricted distribution. Our object is to use the specimen records to study the distribution of P. chienii and estimate the potential distribution with the climate data.

Methods Diva-Gis software is used to describe the distribution and abundance of P. chienii with altitude layer and land vegetation layer. Bioclim and Domain models embed in the Diva-Gis software are used to estimate the potential distribution of P. chieniiwith the specimen occurrence and bioclimate data.

Aims Our objective was to investigate population quantitative characteristics and dynamics of Tsuga tchekiangensis, which is listed as a Chinese national third protective plant with a small geographic distribution in subtropical forests of Jiulongshan Nature Reserve, Zhejiang Province, China.

Methods Ten plots (20 m × 20 m) were investigated along different ridges from low to high altitude. We developed a static life table of T. tchekiangensis population based on the population life table and theory of survival analysis. Survivorship curves, mortality rate, killing power, survival rate, cumulative mortality rate, mortality density and hazard rate were determined, and population dynamics were analyzed using spectral analysis.

Important findings There were abundant young but fewer old individuals. Population structure fluctuated. The survival curve of the population was Deevey type Ⅱ. Two peaks of mortality rate and killing power existed in the lifespan: the 5th and 15th age class periods. The population survival rate of T. tchekiangensis decreased monotonically, whereas the cumulative mortality rate increased monotonically. Meanwhile, the cumulative mortality rate significantly increased during the 13th age class period, up to 98%. Four survival functional curves showed that the T. tchekiangensis population grew stably at young age, decreased very quickly in middle age and declined in old age. Spectral analysis of the population showed that there was a marked periodic fluctuation in the process of natural regeneration.

Aims ‘Black soil land’ grassland on the Tibetan Plateau results from degradation of Kobresia alpine meadow and has many weeds and poisonous plants. This disturbed grassland forms in small bottomland patches. There are no studies of community spatial patterns, relationships and scale patterns of adult plants and seedlings are important to explaining the formation of this secondary weed community.

Methods We selected a typical ‘black soil land’ community of about 30 m × 50 m in the headwaters of the Yellow River and used 100 sample plots (50 cm × 50 cm) to investigate number and density of adults and seedlings (determined by pulling) by species. Spatial heterogeneity of the community and the similarity between adult plants and seedlings were analyzed by semi-variance, fractal dimension, spatial correlation spatial autocorrelation, etc.

Important findings Species number of adult plants is highly spatially heterogeneous and plant density homogeneous at large scales. Species number of seedlings is highly spatially heterogeneous at small scales, and its density is highly spatially heterogeneous at large scales. Seedlings have high density in areas of micro-topography and gaps of adult plants, where seedlings grow and establish in empty ecological niches. The ‘black soil land’ community regenerates and recruits in vegetation gaps. The generation of ‘black soil land’ community depends on high density of seedlings of weeds and poisonous plants, and its generation capability is strong. According to our results, the ‘black soil land’ secondary community becomes more stable without interference. We suggest that human management be used to decrease the stability of the ‘black soil land’ weed community and restore alpine meadow.

Aims When interconnected ramets of clonal plants grow under reciprocal patches in terms of the availabilities of different resources, they likely specialize morphologically and functionally to exploit locally abundant resource(s) more efficiently. This phenomenon is known as division of labor. Patchy contrast is a critical component that partially determines the occurrence and magnitude of division of labor. We investigate the effect of patchy contrast on intraclonal division of labor and test the hypothesis that the magnitude of division of labor is positively correlated with patchy contrast. We also examine the association between adaptive plasticity and division of labor.

Methods We subjected connected ramet pairs of Potentilla anserina to reciprocal patchy environments with four levels of patchy contrasts, which were formed by providing ambient daylight but altering soil nutrient level for one ramet within each pair and providing a high soil nutrient level but changing light regime for the other. We measured shoot height, leaf area and shoot and root biomass. To quantify the magnitude of division of labor, we proposed an index based on root/shoot ratio (R/S) of ramets, namely, the ratio of difference between ramets in R/S to the sum of them.

Important findings Shoot height and leaf area of P. anserina were highly plastic in response to local light availability, and such plasticity ultimately resulted in better ability to acquire scarce light resource, instead of abundant resource as predicted according to the rule of division of labor. This contradiction was probably due to the fact that the locally adaptive plasticity of shoot height and leaf area in response to local light environment took precedence over ramet specialization and division of labor, which was realized primarily by regulating biomass partitioning. The magnitude of division of labor peaked at the intermediate level of patch contrast and decreased both at the higher and lower levels. This pattern was likely an ultimate consequence of cost-benefit tradeoffs of ramet specialization. In conclusion, only when the benefits outweigh the costs at a certain patchy contrast, does division of labor occur, and there likely is an optimum patchy contrast that maximizes the division of labor. But under higher patchy contrast than the optimum one, division of labor may decrease as consequence of increased risks.

Aims Current-year shoots (twigs) are the most active compartment in plants. Biomass allocation within twigs is an important parameter categorizing plant life history strategies. Our objective was to explain variation in leaf size among habitats and why small-leaved species are more likely to be seen in severe habitats than large-leaved species.

Methods Effects of twig size on biomass allocation among lamina, stem, and petiole and on lamina supporting efficiency were estimated using standardized major axis estimation. Correlation between parameters was examined using the phylogenetically independent comparative method.

Important findings Fractional lamina mass was found to be independent of twig size, but allometric relationships were found between stem mass and petiole mass and between lamina area and stem mass. Petiole mass increased disproportionally with stem mass, while lamina area failed to keep pace with the increase in stem mass. Species with smaller twigs and smaller leaves may be advantageous in lamina area supporting efficiency over their counterparts.

Aims The North Yellow Sea is a typical model for marine ecologic systems of the North Temperate Zone. Over the past decade, much non-biological research had been done in multidisciplinary projects. Our aims were to provide basic biological information for marine picoplanktonic study.

Methods Water samples were collected from 80 stations in the North Yellow Sea in August 2006 and immediately fixed in situwith paraformaldehyde (final concentration: 1%). After treatment for 15 to 20 min, samples were transferred into liquid nitrogen for deep freezing and then stored in -80 ^oC for laboratory analysis. Picophytoplankton was examined using epifluorescence microscopy, and the components, distribution and diurnal variations of picophytoplankton in the sea were analyzed.

Important findings Two groups of picophytoplankton were found, Synechococcus (Syn) and picoeukaryotes (Euk). Phycoerythrin-rich Synechococcus (PE cells) dominated Syn in abundance (1.76×10⁵cells∙ml^-1on average) and phycocyanin-rich Synechococcus (PC cells) were less abundant (only contributed 5.48% of Syn abundance). Syn and Euk were more abundant in northern Rongcheng Bay than other areas. There was extremely low Syn abundance in the Cold Water Mass of the North Yellow Sea at 30-m depth and 2-m depth above the bottom, whereas no low Euk abundance in the Cold Water Mass. In vertical distribution, Syn abundances at surface and 10-m depth were higher than at 30-m depth and 2-m depth above the bottom; however, no significant vertical changes in Euk concentration were found. There were no significant variations in both the Syn and Euk abundances at different depths in daytime and nighttime.

Aims Water use efficiency (WUE) and drought tolerance of crops are important in arid and semiarid areas. Our objective was to investigate the effects of root pruning at the regreening stage on drought tolerance and WUE of winter wheat (Triticum aestivum) in late growing stage.

Methods We manipulated root size by root pruning regreening plants grown in pots. In a light root pruning treatment, we partially cut off the secondary lateral roots along one side of the plant. In a heavy root pruning treatment, we partially cut off the secondary lateral roots along four sides of the plant. Control plants (CK) were left intact.

Important findings Both the root pruning treatments reduced the root system significantly, but their root/shoot ratio remained similar. The values of chlorophyll fluorescence parameters, i.e., the maximum photochemical efficiency of PSⅡ (F_v/F_m), PSⅡ potential activity (F_v/F_o), effective PSⅡ quantum yield (Φ_PSⅡ), apparent rate of photosynthetic electron transport (ETR), coefficient of photochemical quenching (q_P) and coefficient of non-photochemical quenching (NPQ), were significantly higher in both treatments than the control 8 days after withholding water at anthesis. This means that root pruning improved drought tolerance of wheat, resulting in improved photosynthetic capability. Light root pruning had no significant effects on grain yield under wet condition, but improved yield under moderate drought stress. Therefore, light root pruning wheat produced a higher index of drought resistance compared with the control. Light root pruning improved WUEof wheat under two water conditions. Heavy root pruning did not improve WUE or the index of drought resistance due to a reduced shoot density and grain yield. The study showed that reducing root size moderately through breeding or agricultural measures would be beneficial to improving drought tolerance and WUEin winter wheat.

Quantitative palaeovegetation reconstruction is an important topic in studies of past global changes. Biomisation, an effective method of quantitatively reconstructing palaeovegetation, can translate pollen records into biome assignments based on defining biome types in terms of characteristic plant functional types and using a standard numerical method to calculate the affinity scores of pollen spectra. This review briefly introduces the history of Biomisation, its working processes and current problems. The world’s palaeovegetation patterns in the Mid-Holocene (MH) and at the last glacial maximum (LGM) including China have successfully been reconstructed using this technique. Results showed that the Arctic forest limit was shifted slightly north during the MH in some sectors, but not in all. Northern temperate forest zones were generally shifted greater distances north. Temperate deciduous forests in Europe were greatly extended into the Mediterranean region as well as to the north. Steppe encroached on forest biomes in interior North America, but not in central Asia. Enhanced monsoons extended forest biomes in China inland and Sahelian vegetation (e.g., steppe, xerophytic woods/scrubs and tropical dry forest ) into the Sahara, while the African tropical rain forest was also reduced. Cold and dry conditions at LGM, however, favored extensive tundra and steppe. These biomes intergraded in northern Eurasia. Northern hemisphere forest biomes were displaced southward. Boreal evergreen forests (taiga) and temperate deciduous forests were fragmented, while European and East Asian steppes were greatly expanded. Tropical moist forests (i.e., tropical rain forest and tropical seasonal forest) in Africa were reduced. In south-western North America, desert and steppe were replaced by open confiner woodland.