Aims A 24 hm² permanent plot in Gutianshan National Nature Reserve provided a valuable case for association classification in evergreen broad-leaved forest. Our objectives were to divide the forest community into associations to provide a new classification of evergreen broad-leaved forest and introduce the algorithm of indicator value for species in associations. Indicator species previously could not be quantified.

Methods We used multivariate regression trees, based on topographic factors and species composition, for association classification. An indicator value was introduced to quantify the indicator species of associations. We named associations after the dominant species in the tree layer, followed by indicator species of lower tree layers.

Important findings The forest community was divided into three associations that not only reflect temporal and spatial disjunctions of the community, but also correspond with features of the basic unit of vegetation classification. The three associations are 1) Raphiolepis indica + Chimonanthus salicifolius―Eurya muricata + Syzygium buxifolium―Schima superba + Castanopsis eyrei Association; 2) Rhododendron simsii + Rhododendron mariesii―Quercus serrata var. brevipetiolata + Corylopsis glandulifera var. hypoglauca―Pinus massoniana + Castanopsis eyrei Association; and 3) Vaccinium carlesii + Camellia fraterna―Distylium myricoides + Neolitsea aurata―Schima superba + Castanopsis eyrei Association.

Aims Our objective was to understand seasonal and diurnal variations in CO₂ exchange of a grassland ecosystem by clarifying the carbon cycle and its affecting factors for a planted pasture ecosystem in the Sanjiangyuan Region of the Qinghai-Tibetan Plateau.

Methods We used the eddy covariance method to measure net ecosystem CO₂ exchange (NEE) and environmental factors in the planted pasture (Elymus nutans) ecosystem in 2006.

Important findings Daily maximum uptake and release of CO₂ were 6.56 and -4.87 g CO₂·m^-2·d^-1, respectively. Maximum rates of NEE uptake and release were -0.35 and 0.22 mg CO₂·m^-2·s^-1, respectively. Annual gross primary production (GPP) was 1 761 g CO₂·m^-2·a^-1, of which more than 90% was consumed by ecosystem respiration (R_eco). Annual NEE was -111 g CO₂·m^-2. In the growing season, maximum and minimum R_eco/GPP values were 90% in May and 79% in June, respectively. The Q₁₀ was 4.81, which is higher than in other ecosystems. The NEE was mostly influenced by photosynthetic photon flux density (PPFD), temperature and vapor pressure deficit (VPD). The R_eco was mainly affected by soil temperature at 5 cm depth (T_s).

Aims Net primary productivity (NPP) is a key parameter in vegetation growth and terrestrial ecosystem processes and plays an important role in carbon circulation. The relationship between NPP and climate is complicated and needed additional research. Our aim was to study this relationship in different time units and scales to uncover their interaction mechanism.

Methods Based on remotely-sensed estimated NPP calculated by light use efficiency model, the relationship between NPP and climatic indices (including precipitation, temperature, and effective precipitation and temperature) and three land surface humidity indices during 1982-2006, are assumed in Inner Mongolia. We considered land cover condition and time lag and accumulation effect of climate factors, using time lag correlation analysis, to uncover the interaction between NPP and climate.

Important findings Temperature related indices correlate poorly with annual NPP, and current year precipitation affects NPP the most. With month as the time unit, intra-annual monthly climatic factors are key factors influencing vegetation growth. In all vegetation types, intra-annual monthly climate indices could affect NPP in an effective time period of one month and so do NPP to climate. At the inter-annual level, monthly precipitation and humidity index affect NPP more than temperature related indices, which reveals that precipitation is the restricted climatic factor in this area with obvious accumulation effects. Areas with different vegetation types represent various relations between inter-annual monthly NPP and climatic indices.

Aims Our objectives were to illustrate inter-annual change of the productivity of three main vegetation types in the Liaohe Delta and to discover the driving factors resulting in the change of productivity.

Methods Principal component analysis, Pearson correlation analysis and partial correlation analysis were applied, based on data for 14-year yield of maize (Zea mays) and rice (Oryza sativa), 42-year productivity of common reed (Phragmites australis), and data on climatic factors, agricultural population, irrigation area and fertilizer use in the Liaohe Delta.

Important findings A slight increased yield of rice and maize was shown, but with obvious inter-annual fluctuation. However, a large increased yield of common reed was shown, but with slight inter-annual fluctuation. Climatic factors played an important role as the key factors for the inter-annual fluctuation of yield of maize and rice, while human factors (agricultural population, irrigation and fertilization) played a relatively small role. Both climatic factors and human factors (irrigation) played an important role in the inter-annual fluctuation of yield of common reed. Nevertheless, the three dominant vegetation types had different driving factors for their fluctuating yield. Annual hours of sunshine, annual precipitation and annual evaporation were identified as the mainly driving factors for the fluctuating yield of maize, rice and common reed, respectively.

Aims Shortage of water resources is a key ecological problem facing the Loess Plateau. Therefore, it is critically important to understand and predict the coupling effects of landuse and climate variability on streamflow characteristics for integrated watershed management and ecological restoration. We used the typical meso-scale Qingshui River watershed located in middle reach of the Yellow River to examine the trend of annual streamflow and separate the effects of landuse change on streamflow from that of climate variability.

Methods The trend of annual streamflow, precipitation and potential evapotranspiration and their inflection points were analyzed and examined using the nonparametric Mann-Kendall test, Moving t-test technique and analysis of hopped parameter. Three phases of landuse for the watershed were obtained representing the original and dramatic landuse changes due to the watershed ecological restoration. Landuse in 1959 (original) was interpreted from the aerial photo image taken that year. Landuses in 1986 (Three Norths Shelterbelt Program) and 2007 (Three Norths and Land Conversion Program) were extracted and merged from four-season Landsat TM images by deploying Geomatica V8.2. The stream flow response to landuse and climatic variability was separated following the approach Milly and Dunne (2002) developed on the basis of water balance. In addition, the landuse and climate variability effects on the high, normal and low flow were examined by flow duration curve (FDC) analysis.

Important findings Streamflow decreased significantly during 1960 to 2005, with the inflection point in 1980. We estimated that streamflow reduction from 1980 to 2005 compared to 1960 to 1980 was attributable to landuse change (53.21%) and climate change (46.79%). Because precipitation had no significant trend and potential evapotranspiration significantly increased from 1960 to 2005, we concluded that the streamflow reduction was mainly due to the temperature-induced increase in potential evapotranspiration and evapotranspiration increase by increased forest landuse.

Aims Vegetation classification is an important topic in plant ecology, and many quantitative techniques for vegetation classification have been developed. The artificial neural network is a comparative new tool of data analysis. In this paper, self-organizing map (SOM) is applied to cluster analysis of mountain meadow data to determine whether SOM is suitable for classifying meadow vegetation.

Methods Data for 40 quadrats, 87 species, and six environment variables (elevation, slope, aspect, litter layer thickness, soil depth and soil density) from mountain meadow communities in the Sonshan Nature Reserve were analyzed. SOM was used to classify sample quadrats using importance values of species.

Important findings The trained SOM classified sample quadrats into seven groups: Saussurea nivea + Sanguisorba officinalis + Bupleurum chinensis, Sanguisorba officinalis + Artemisia annua + Vicia unijuga, Polygonum divaricatum + Sanguisorba officinalis + Carex rigescens, Carex rigescens + Sanguisorba officinalis + Saussurea nivea, Carex rigescens + Polygonum divaricatum + Rosa dahurica, Polygonum bistorta + Carex rigescens + Artemisia gmelinii and Carex rigescens + Saussurea iodostegia + Polygonum bistorta. The characteristics of community structure and species composition were significant. SOM classification and the dominant species enumeration in the meadow community data reflected the effects of elevation, slope, litter layer thickness and soil depth. SOM is suitable for classifying the mountain meadow communities and could be useful for assessing ecosystem quality and meadow community variations caused by environmental disturbances.

Aims Fine root surface area is important for nutrient and water uptake, but its seasonal dynamics remain poorly understood. Our objective was to investigate the seasonal dynamics of fine root surface area and its relation with the soil water content in Robinia pseudoacacia, Platycladus orientalis and Pinus tabulaeformis plantations.

Methods The study was conducted in Ansai County (36°30′ N, 108°51′ E), Shaanxi Province, China. Fine root surface area and soil water content were investigated by soil cores (300.0 cm depth, 6.8 cm diameter) taken in April, June, August and October 2007, at different horizontal distances (50, 100 and 150 cm) from the stem. Live root surface area and diameter were measured using the WinRHIZO root morphology and architecture measurement system. Fine root (≤2 mm) area density (surface area of root per unit soil volume, FRAD) was determined for every soil sample. The soil samples were oven-dried at 105 °C for 8 h and weighed to determine the soil water content by dry weight.

Important findings Throughout the study period, large variations in soil water content occurred in the 0-200 cm soil layer where 86.5%, 82.4% and 87.7% of the total fine root surface area were concentrated in the R. pseudoacacia, P. orientalis and P. tabulaeformis plantations, respectively. There was a significant positive correlation (p < 0.05) between vertical distribution of fine root surface area and soil water distribution in the profile. The model S = Ah^B(C + Dh + Eh² + Fh³) describes the fine root surface area vertical distribution of the plantations with R² > 0.85. The mean soil water content in all plantations changed in order of October > April > June > August. The highest value of fine root surface area was in June for R. pseudoacacia and P. tabulaeformis and in June and October for P. orientalis. There were differences in the seasonal dynamics of fine root surface area and soil water content. Of the water that the three plantations needed for growth, 87% came from precipitation, but there was no significant correlation (p < 0.05) between fine root surface area and soil water content. The study indicates that combined and integrated soil moisture, temperature, available nitrogen and genetic characteristics of tree species should be considered in research on seasonal dynamics of fine roots.

Aims In stylar polymorphous species, the morph ratios are maintained by negative frequency-dependent selection through disassortative mating. The spatial context of a population is of crucial importance to maintain this stylar polymorphism. Under particular circumstances, disassortative mating in such species may promote the evolution of a dimorphism by gender specialization. We asked whether flexistyly can promote sufficient disassortative mating, whether the female fitness of focal plant is affected by negative frequency-dependent selection at local level, and whether the two morphs in flexistylous plants differ in gender specialization.

Methods We used open-pollinated flexistylous Alpinia mutica to compare fertility in anaflexistylous, cataflexistylous and dimorphic arrays. Second, we used neighborhood models to investigate spatial distribution of morphs at local level within the population on reproductive output in the flexistylous, A. blepharaocalyx. We quantified the distribution of the morphs in terms of neighborhood morph bias. We then measured the effect of neighborhood morph bias on open-pollinated reproductive output. Third, the reproductive characters were examined in anaflexistylous and cataflexistylous morphs of A. blepharaocalyx. We assessed functional genders of two morphs based on their allocations associated with times-dependent mating opportunities and the mean number of seeds produced by anaflexistylous and cataflexistylous plants with morph frequency in the population.

Important findings Dimorphic arrays have higher female fertility than monomorphic arrays, demonstrating the flexistyly promotes inter-morph pollen transfer. Results from A. blepharaocalyx indicate that at the neighborhood scale, the two morphs have an aggregate distribution due to clonal growth. At this scale, focal plants showed no evidence of frequency-dependent total fruits and seeds per plant or seeds per flower. These results do not support frequency-dependent selection as a major mechanism affecting morph frequencies in A. blepharaocalyx within the context of this study. There are no significant differences between two morphs in flower and fruit characters. Functional gender analyses indicate that when illegitimate fertilization is negligible, the morphs are specialized in their later sexual functions, mediated by anaflexistylous morph through male fitness gained; however, when self- fertilization is included, the two morphs are both specialized in their female functions due to the lack of inbreeding depression in the formulas.

Aims Endophytes are found in the root systems of various plants and play beneficial roles in root growth and function maintenance, especially when plants are under biotic or abiotic stress. Xanthoceras sorbifolia is a unique woody plant that grows in the northern part of China and is resistant to cold and drought and highly tolerant to poor soil. Moreover, it is considered a promising candidate for bio-diesel and bio-lubricant production. Our objective was to investigate endophytes in the roots of X. sorbifolia. Results will help in the selection and development of bacterial fertilizer to improve the growth and yield of X. sorbifolia, which grows in marginal lands.

Methods We examined root systems of field-grown one- and two-year-old plants. After surface sterilization, endophytes were isolated with yeast-malt extract agar (YMA) and Ashby media respectively. Seven representative single colonies were selected according to their macro-morphology. After DNA extraction and purification, 16S rDNA PCRs were carried out with the universal bacterial primers. The PCR products were separated with electrophoresis, collected and purified. The 16S rDNA sequence similarity search of different bacteria was performed by Blast on NCBI against GenBank, and a similarity of 97% was set as the criterion for identity. Nitrogenase activity of the selected strains was assayed with ethylene production by GC.

Important findings The number and type of colonies on YMA medium were significantly more than those on Ashby medium, as YMA medium contains a small amount of nitrogen and is more suitable for bacteria growth. The number and species of endophytes in one-year-old X. sorbifolia roots were slightly more than those in two-year-old plants. This may be because the roots of one-year-old plants were as a whole younger than those of two-year-old plants and were more suitable for the infection and survival of endophytic bacteria. The main bacteria species isolated from the roots of one-year-old plants were Pantoea agglomerans, Agrobacterium tumefaciens and Klebsiella oxytoca, while those from two-year-old plants were of the Pseudomonas genus. Six of seven strains demonstrated nitrogenase activity, including the activity of 9.688 nmol·mg^-1·h^-1 in K. oxytoca, which is significantly higher than other strains. This report on endophytes of X. sorbifolia roots provides the basis for bacteria fertilizer strain selection.

Aims Our objectives were to detect the relationship between leaf carotenoid (Car) content and spectral reflectance characteristics and to recommend useful hyperspectral wavebands and hyperspectral indices for nondestructive and quick estimation of Car content in rice (Oryza sativa).

Methods Four field experiments with different nitrogen application rates and rice cultivars were conducted at different eco-sites over three years. Time-course measurements were taken on hyperspectral reflectance of 350- 2 500 nm and Car content in four top leaves. We calculated the simple ratio spectral index (SR (λ1, λ2)) and normalized difference spectral index (ND (λ1, λ2)) with all combinations of two wavelengths (λ1 and λ2 nm) as well as other indices sensitive to Car, and analyzed the relationships between Car content to single wavelength reflectance and these spectral indices.

Important findings Spectral reflectance varied with Car content, and the sensitive wavebands mostly occurred at green and red edge regions. The SR indices using reflectance around 723 nm combined with near infrared reflectance (NIR) or the ND indices using reflectance around 713 nm combined with NIR could be used to estimate leaf Car content in rice, among which the SR (723, 770) and ND (770, 713) have the best performance, with determination of coefficients (R²) of 0.897 and 0.898, respectively. Tests with an independent dataset showed that R² values between observed and predicted Car content with SR (723, 770) and ND (770, 713) were 0.856 and 0.858, with root meansquare error (RMSE) as 0.072, and relative error (RE) as 11.9% and 12.0%, respectively, which indicated that Car content in top leaves of rice could be predicted effectively with these two indices.

Flooding causes substantial stress for terrestrial plants, particularly if the floodwater completely submerges the shoot. The main problems during submergence are shortage of oxygen due to slow diffusion rates of gases in water and unfavorable conditions of light and carbon dioxide supply. Collectively, these factors lead to loss of biomass and eventually death of the submerged plants. The survival of plants is closely related to carbohydrates, the substrate for respiration. There are two major aspects of the correlation of plants flooding adaptability and carbohydrates. First, there are morphological and physiological responses of terrestrial plant species that enable the positive effects of carbohydrates on underwater plant performance: plants usually elongate or reduce underwater elongation and maintain a higher level of root carbohydrates that facilitates survival. Second, plants change the expression of hormone, enzyme and gene, adjusting carbohydrate metabolism to flooding. The research advances in concentration of carbohydrates upon morphological and physiological changes and hormone, enzyme and gene expression to submergence are summarized.

In this paper, stamen movement is defined as the movement of stamens with their own energy, either automatically or stimulated by pollinator or other forces, except the forced movement of stamen under the pressure of pollinators. Four main types of stamen movements are classified: stimulated, simultaneous and slow, quick and explosive and cascade. Stimulated movement is normally caused by touching of visiting insects, which can enhance the contact probability of anther/pollen with pollinators or promote contact of anther with self pistil. Simultaneous and slow movement can alter the extent of herkogamy and modify reproductive patterns, and in some plants the stamen can move the anther directly to the self stigma to promote autogamy. Quick and explosive movement can release the pollen rapidly to the air or adhere to visiting insects to promote wind and/or insect dispersal of pollen grains. In cascade movement-in Ruta graveolens (Rutaceae), Tropaeolum majus (Tropaeolaceae), and plants of Loasaceae and Parnassiaceae - the stamens can move one by one and anthers dehisce individually when positioning at the center of flowers. The adaptive significances of cascade movement have not been studied, but, according to ‘pollen presentation theory’, cascade movement can alter the herkogamy and control the pace of pollen presentation and distribute pollen among pollinators by either packaging or dispensing mechanisms, which can greatly enhance pollen removal efficiency. Furthermore, the interferences between stamens and pistil and among individual stamens can be decreased as a result of obvious herkogamy and spatial separation of each stamen caused by cascade movement. In Ruta graveolens, all the stamens move together to the center of flower after the cascade movement, this two-time, multiple-direction stamen movement probably is the most complex stamen movement presently known. Future emphasis in the field of stamen movement should include 1) the effects of stamen movement, especially the cascade movement, on sexual interference and interference among individual stamens, 2) the interaction of stamen movement with dichogamy (temporal separation of male and female funtion) and herkogamy (spatial separation of anthers and stigma), both of which can be modified by stamen movement and 3) the physiology and development of stamen movement.

The symbiosis between leguminous plants and rhizobia leads to the formation of a novel root organ, the nodule. In mature nodules, rhizobia provide the host plant with ammonium, which is produced through bacterial nitrogen fixation. The symbiotic interactions involve the perception of bacterial signaling factors called Nod factors (NFs) by plant host, the NF signaling pathway, the formation of infection threads and the development of nodule in the cortex. Although this nodule formation is beneficial for host plants to secure a nitrogen resource, overproduction of nodules could deleteriously affect plant growth. Legume plants avoid this by utilizing a negative feedback regulation known as autoregulation of nodulation (AON), in which earlier formed nodules suppress further nodulation through shoot-root communication. We summarize nodule formation and types and highlight recent studies on the molecular basis underlying NF signaling cascade, AON and effects of environmental nitrogen conditions on nodulation. We also discuss current research problems and reflect on the future of this field.