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Seed germination is a complex physiological process that can affect species establishment as well as vegetation restoration and dynamics; however, the germination characteristics of several key species used to combat desertification remain unclear. In light, temperature, and air humidity-controlled growth chambers, four different light treatments, five alternative temperature treatments, 11 levels of water potential, and five constant temperatures were set up to study the effects of light, temperature, and water stress on the completion of germination of Medicago sativa L., Astragalus adsurgens Pall., and Glycyrrhiza uralensis Fisch. The results showed that completion of germination of G. uralensis seeds occurred significantly less than that of M. sativa and A. adsurgens. Light intensity had no significant effect on the final germination percentage of M. sativa, A. adsurgens, and G. uralensis, but the germination rate under 100 and 400 μmol·m–2·s–1 light was significantly greater than that under 25 μmol·m–2·s–1. Temperature had no significant effect on the final germination percentage of these species’ seeds, and the germination rate was greater at 15/25 °C and 20/30 °C. The germination rate decreased as the water potential decreased. The germination results indicate that late spring is a suitable sowing time for G. uralensis to obtain optimal levels of completion of germination.

Plant salt tolerance is associated with a high rate of root growth. Although root growth is governed by cell wall and apoplastic pH, the relationship between these factors in the root elongation zone under salinity stress remains unclear. Herein, we assess apoplastic pH, pH- and expansin-dependent cell wall extensibility, and expansin expression in the root elongation zone of salt-sensitive (Yongliang-15) and -tolerant (JS-7) cultivars under salinity stress. A six-day 80 mM NaCl treatment significantly reduced apical root apoplastic pH in both cultivars. Using a pH-dependent cell wall extensibility experiment, we found that, under 0 mM NaCl treatment, the optimal pH for cell wall loosening was 6.0 in the salinity-tolerant cultivar and 4.6 in the salinity-sensitive cultivar. Under 80 mM treatment, a pH of 5.0 mitigated the cell wall stiffness caused by salinity stress in the salinity-tolerant cultivar but promoted cell wall stiffening in the salinity-sensitive cultivar. Salinity stress altered expansin expression and differentially affecting cell wall extensibility under pH 5.0 and 6.0. TaEXPA8 might be relative to cell wall loosening at pH 5.0, whereas TaEXPA5 relative to cell wall loosening at pH 6.0. These results elucidate the relationship between expansins and cell wall extensibility in the root elongation zone, with important implications for enhancing plant growth under salinity stress.

Two salt-sensitive (Yongliang-15, GS-6058) and two salt-tolerant (JS-7, Xinchun-31) wheat cultivars were used to investigate the extension, extensibility (viscoelastic parameters), and chemical composition of the cell walls in their root elongation regions (apical 10 mm-long root segments), under salinity stress. The elasticity of the root cell wall, indicated by E0, significantly decreased in the salt-sensitive cultivars, whereas the E0 in the salt-tolerant cultivars was maintained at the same level as that in the non-saline condition. Root extension and the differences among cultivars were largely dependent on elastic extension, which accounts for one-half to two-thirds of the total extension. Viscosity, indicated by η0, and the plastic extension of the root cell walls did not change across the treatments and cultivars. The significant decrease in cell wall elasticity in the root elongation region was one of the factors that depressed root growth in salt-sensitive cultivars under the saline condition. The well-maintained elasticity of salt-tolerant cultivars alleviated the depression of root growth by NaCl. Cell wall elasticity was positively correlated with the relative pectin and hemicellulose I contents and negatively correlated with the relative cellulose content. Under saline conditions, the relative hemicellulose II content did not change in the salt-sensitive cultivars; however, it decreased in the salt-tolerant ones. Thus, changes in chemical composition of the cell wall were correspond with the cell wall extensibility and root growth in wheat cultivars with different degrees of salt tolerance.

Evolutionary radiation is a widely recognized mode of species diversification, but its underlying mechanisms have not been unambiguously resolved for species-rich cosmopolitan plant genera. In particular, it remains largely unknown how biological and environmental factors have jointly driven its occurrence in specific regions. Here, we use Rhododendron, the largest genus of woody plants in the Northern Hemisphere, to investigate how geographic and climatic factors, as well as functional traits, worked together to trigger plant evolutionary radiations and shape the global patterns of species richness based on a solid species phylogeny. Using 3,437 orthologous nuclear genes, we reconstructed the first highly supported and dated backbone phylogeny of Rhododendron comprising 200 species that represent all subgenera, sections, and nearly all multispecies subsections, and found that most extant species originated by evolutionary radiations when the genus migrated southward from circumboreal areas to tropical/subtropical mountains, showing rapid increases of both net diversification rate and evolutionary rate of environmental factors in the Miocene. We also found that the geographically uneven diversification of Rhododendron led to a much higher diversity in Asia than in other continents, which was mainly driven by two environmental variables, that is, elevation range and annual precipitation, and were further strengthened by the adaptation of leaf functional traits. Our study provides a good example of integrating phylogenomic and ecological analyses in deciphering the mechanisms of plant evolutionary radiations, and sheds new light on how the intensification of the Asian monsoon has driven evolutionary radiations in large plant genera of the Himalaya-Hengduan Mountains.

Rationale In arid and semiarid grasslands where shrub encroachment usually occurs, water plays an important role and might control the process of shrub encroachment. Understanding how species adapt to different sandy environments can help explain the shrub encroachment process. Central methods Four different grades of shrub encroached grasslands were selected as follows: the Agriophyllum squarrosum community in shifting sandy land (SA), the Artemisia ordosica community in semifixed sandy land (SFA), the A. ordosica community in fixed sandy land (FA) and the Stipa bungeana community in fixed sandy land (FS), which are located on the Ordos Plateau (China) and were selected to analyze the dynamics of enzyme and osmotic adjustment compounds of species in different stages of shrub encroachment. Key results The results showed that from the community in shifting sandy land to the community in fixed sandy land, the average enzyme activities of species decreased and then increased; the malondialdehyde content increased, and the osmotic adjustment compounds increased (or increased and then decreased). The enzyme activities of grasses were significantly higher than those of shrubs. However, there were no significant differences in the malondialdehyde contents of grasses and shrubs. The proline and soluble protein contents of shrubs were significantly higher than those of grasses. The soluble sugar content of grasses was significantly higher than those of shrubs. The D values indicated that the drought resistance of the five species decreased as follows: S. bungeana in FS > S. bungeana in FA > Caragana korshinskii in FA > C. korshinskii in FS > A. ordosica in FS > A. squarrosum in SA > Artemisia sphaerocephala in SFA > A. sphaerocephala in SA > A. ordosica in FA > A. ordosica in SFA. Main conclusions The results suggest that the five dominant species in different shrub encroachment stages could enhance their drought resistance by upregulating the antioxidant system and osmotic adjustment in response to drought stress. S. bungeana had a higher drought resistance. For different plant functions, grass had a higher drought resistance than shrubs. It is concluded that S. bungeana can adapt to a drier environment; when the surface soil layer becomes dry, S. bungeana communities developed well due to its high drought ability. Compared to A. ordosica, the S. bungeana community can be a dominant community when human disturbance decreased in the Ordos Plateau.

In arid regions, fine roots turnover contributes directly to soil carbon and nutrient cycling. However, less information is available on how increasing agricultural activities influence tho...

Ex situ conservation plays an important role in maintaining global plant biodiversity and protects thousands of wild plants. Plant conservation in botanical gardens is an important part of ex situ conservation; however, little attention has been given to whether plant ecophysiological traits change and whether plant conservation goals are reached following ex situ conservation. In this study, tree and shrub plants were selected from Shanxi, Beijing of China and from Beijing Botanical Garden, and plants with good growth and similar ages were randomly selected to measure their light response curves, CO2 response curves with a portable photosynthesis system (Li-6400XT), relative chlorophyll contents using a chlorophyll meter (SPAD-502) and leaf water potential using a dew point water potential meter (WP4C). In comparison with cultivated plants, wild plants had higher water use efficiencies among all plants considered (by 92–337%) and greater light use efficiencies among some of plants considered (by 107–181%), while light response curves and CO2 response curves for wild plants were either higher or lower compared with cultivated plants. Ecological traits of wild and cultivated plants changed more as a result of habitat factors than due to plant factors. The initial slope of the light response curve, net photosynthetic rate at light saturation, light saturation point, maximum light energy utilization efficiency, maximum water use efficiency, leaf water content, and the leaf water potential of wild plants were larger or equal to those of cultivated plants, while dark respiration rate (by 63–583%) and light compensation point (by 150–607%) of cultivated plants were higher than those of wild plants. This research compared the ecophysiological traits of common green space plants cultivated in botanical gardens and distributed in different areas in wild environments. The response of plant ecophysiological traits to the changing environment has important theoretical and practical significance for wild plant conservation and urban green space system construction.

How large cosmopolitan plant genera survived great environmental changes and rediversified remains largely unknown. Here we investigated mechanisms underlying the rediversification of Rhododendron, the largest genus of woody plants in the Northern Hemisphere. Using 3437 orthologous nuclear genes, we reconstructed the first completely resolved and dated phylogeny of Rhododendron. We found that most extant species of Rhododendron originated by Neogene rediversification from Paleogene relicts during southern migration. The geographically uneven rediversification of Rhododendron led to a much higher diversity in Asia than in other continents, which was driven by two main environmental variables, i.e., habitat heterogeneity represented by elevation range and annual precipitation related to the Asian monsoons, and can be explained by leaf functional traits that show strong phylogenetic signals and correspond well with leaf-forms and geographical regions. Our study highlights the importance of integrating phylogenomic and ecological analyses in revealing the spatiotemporal evolution of species-rich cosmopolitan plant genera.

Tropical and subtropical forest ecosystems play an important role in the global carbon regulation. Although positive relationships between biodiversity and soil organic carbon (SOC) storage have been found in experimental grasslands, biodiversity effects on SOC storage in natural forests remain debated. Based on a large dataset from 523 forest inventory plots across subtropical forests in China, we tested the relationship between biodiversity and SOC storage and examined whether environmental conditions (temperature, precipitation, soil properties) and litter quantity (leaf litter and root biomass) and quality (leaf litter carbon to nitrogen ratio [leaf litter C/N]) had effects on SOC storage. Furthermore, we used linear mixed-effects models to test the relative effects of biodiversity, environmental conditions, and litter quantity and quality on SOC storage. We used structural equation models to test how these variables directly or indirectly affected SOC storage. We found that species diversity, together with climatic factors (mean annual temperature and mean annual precipitation), leaf litter C/N and root biomass determined SOC storage in subtropical forests at a large spatial scale. SOC storage was most strongly affected by climatic factors, followed by leaf litter C/N. Species diversity had both direct and indirect (through root biomass and leaf litter C/N) effects on SOC storage after accounting for environmental conditions. We also found that the positive diversity–SOC storage relationships were stronger in low and medium mean annual precipitation. Our findings highlight that higher species diversity can lead to higher SOC storage and therefore the conservation of biodiversity could play an important role in climate change mitigation.

Understanding the response of vegetation to a changing global climate is important. The relationships among 33 topographic, soil and climatic variables and 74 vegetation assemblages were analyzed b...

Understanding the mechanisms of how environmental factors limit species distribution along environmental gradients is a central question in ecology. This study aimed to understand species acclimation in view of photosynthetic parameters in an arid mountainous region. We measured some photosynthetic parameters and light and CO 2 photosynthesis response curves for all plant communities with seven dominant species in 13 sites along an elevation gradient in the Qilian Mountains in arid northwestern China. The results showed that species in xerothermic environments had low maximum rate of carboxylation (Vcmax) (14.5 μmol m -2 s -1 ) and maximum rate of electron transport (Jmax) (22.7 μmol m -2 s -1 ), high light compensation points (60.0 μmol m -2 s -1 ) and light saturation points (1150.7 μmol m -2 s -1 ), high dark respiration rates (5.3 μmol m -2 s -1 ), and high maximum photosynthetic rates (Amax) (18.1 μmol m -2 s -1 ) compared with species in mesic environments. Photosynthesis parameters did not vary with temperature, precipitation, and altitude in different communities dominated by the same species, Picea crassifolia. However, some photosynthesis parameters varied with temperature, precipitation, and altitude in communities dominated by species other than spruce at different elevations. Selected photosynthesis parameters could be used to measure species adaptation to environmental gradients in arid mountain regions.

In view of the increase in global warming and carbon dioxide (CO2) concentrations, it is essential to investigate the influences of climate change on plant growth and water use in arid and semi-arid grassland species. Experiments were conducted to understand the ecophysiological response of four indigenous species to elevated CO2 in the semi-arid sandy grassland of central Inner Mongolia. Seedlings of the four species were grown for 8 weeks at four different consistently elevated CO2 concentrations in the environment-controlled growth chambers. All four elevated CO2 concentrations (400, 800, 1200, 1600 ppm) were found to result in decreased stomatal conductance (26–86%), decreased transpiration rate (21–80%), increased shoot water potential (1–42%) and increased water use efficiency (WUE) (10–412%) for two Artemisia species and Caragana korshinskii. Under our experimental conditions, the two Artemisia species and C. korshinskii would benefit more than Hedysarum laeve from exposure to elevated CO2 in terms of higher shoot water potential and WUE combined with lower stomatal conductance and transpiration rate. The results indicate that in a warmer, CO2-enriched future atmospheric environment, WUE in semi-arid grasslands may be higher than previously expected. Our findings will provide information for screening appropriate species for restoration of the degraded sandy grasslands in semi-arid areas under future climate change scenarios.

The reproductive stages of the life cycle are crucial in explaining the distribution patterns of plant species because of their extreme vulnerability to environmental conditions. Despite reported evidence that seed germination is related to habitat macroclimatic characteristics, such as mean annual temperature, the effect of this trait in controlling plant species distribution has not yet been systematically and quantitatively evaluated. To learn whether seed germination can predict species distribution along altitude gradients, we examined germination data of 36 Rhododendron species in southeastern Tibet originating from contrasting altitudes, habitats, plant heights, seed masses, and phylogenies. Germination varied significantly with altitude, habitat, plant height, and phylogeny and was higher in the light than in the dark. Germination percentage was highest at 10:20°C in the light and 15:25°C in the dark. As altitude increased, germination percentages first rose and then decreased, being highest at 3,500–4,000 m. Germination percentage and rate were highest on rocky slopes, increasing as seed mass and plant height rose. Variations in germination percentage and rate were not significant at subgenera, section, and subsection levels, but they were significant at species level. The results suggested that the relationship between germination and altitude may provide insights into species distribution patterns. Further, germination patterns are a result of long‐term evolution as well as taxonomic constraints.

Shrub encroachment has been a key phenomenon in arid and semi-arid grasslands over the last century. However, little research has been dedicated to vegetation dynamics in the abandoned croplands, which are surrounded by shrub-encroached grasslands. In this study, several abandoned croplands in Ruanliang and Yingliang in the Ordos Plateau were selected, and the biomass, coverage, density, root pattern, and plant litter dynamics were studied. The results showed that: (1) The abandoned croplands in Ruanliang experienced three community types, including weeds community, the subshrub Artemisia ordosica community, and the perennial grass community, while the abandoned croplands in Yingliang experienced three community types, including weeds community, perennial Stipa bungeana with Artemisia frigida community, and S. bungeana community. (2) The important value for the annual or biennial grass in abandoned croplands in Ruanliang declined during the restoration process, for the perennial grass it increased, and for the subshrub it first increased and then went down to zero. In Yingliang abandoned croplands, however, the perennial grass remained dominant during the succession process. (3) The root of A. ordosica in Ruanliang abandoned croplands was mainly distributed in soil depths of 0–30 cm; the root of the perennial grass was mainly in the 0–20 cm range, and S. bungeana was found at soil depths of 0–5 cm. To restore to a natural vegetation state, about 20 years would be needed to recover the total biomass, and 10 years would be needed to restore the vegetation coverage in Ruanliang abandoned croplands. For Yingliang abandoned croplands, about 15 and 20 years would be needed to restore the total biomass and vegetation coverage, respectively, to a state of natural vegetation.

Soil water sources for shrub encroachment in arid and semiarid regions have not been fully understood. This study used stable δ2H and δ18O isotope ratios of plants, soil water and precipitation, coupled with proportional similarity index of species to identify relations between shrub encroachment and water sources for four shrub and grass species at various shrub encroachment stages in a semiarid grassland of Inner Mongolia. We found that shallow rooted grasses (Agriophyllum squarrosum and Stipa bungeana) predominantly used shallow soil water (0–20 cm) during growing season. In contrast, deeply-rooted semi-shrubs (Artemisia ordosica and Artemisia sphaerocephala) used middle and deep soil water in July but shallow and middle soil depth water in May and September. Plants competition for soil water in different shrub encroachment stages were different depending on plant water use sources. The highest plant competition existed in the A. ordosica community in semi-fixed sandy land, followed by A. squarrosum community in shifting sandy land, A. ordosica community in fixed sandy land, and S. bungeana community in fixed sandy land. Competition for soil water and differences of water use sources of grass and shrub species were crucial in driving shrub encroachment in semiarid grasslands. Communities dominated by A. ordosica were not stable, with an increase in surface soil water availability, the dominance was replaced by S. bungeana. Our findings on the linkage between plant water use sources and patterns and shrub encroachment shall help future arid and semiarid grassland management under changing climate conditions.

Shrub encroachment occurs worldwide, especially in arid and semiarid grasslands. Changes in soil water in different layers affect the process of shrub encroachment. Understanding the biological and physiological responses of plant species to shrub encroachment is essential for explaining shrub encroachment. The dominant species in six typical plant communities changed from Stipa bungeana Trin. to Artemisia ordosica Krasch., representing different shrub-encroached grasslands. The gravimetric soil water content (SWC) and enzyme and osmotic adjustment compounds of the dominant species across shrub encroachment stages and growing seasons were measured to explain the shrub encroachment. Results showed that SWC decreased and then increased during the growing seasons. With the process of shrub encroachment, SWC first increased, then decreased. With increasing soil depth, SWC increased or decreased. Across seasons with decreasing SWC, enzyme activity decreased and then increased, and malondialdehyde content and osmotic adjustment compounds increased. With the process of shrub encroachment, enzyme activity, malondialdehyde content and osmotic adjustment compounds increased or decreased. The two dominant species (S. bungeana and A. ordosica) enhanced their drought resistance abilities by regulating their antioxidant systems and osmotic adjustment compounds when soil water in a specific layer was not over the threshold. We recommend increasing the clay content to increase the water holding capacity in the surface soil layer to restore the zonal vegetation of S. bungeana.

It is generally assumed that plants can respond to varying degrees of physical damage by growth compensation via resprouting, and resprouting is a key functional trait in many species. Few studies have investigated how grass and shrub species distributed in moving dunes and semifixed dunes in semiarid areas respond to the combined effects of temperature and shoot removal. Medicago sativa, Artemisia ordosica, and Artemisia sphaerocephala plants were grown in a glasshouse for 8 weeks at air temperatures of 10/20°C, 12.5/22.5°C, 15/25°C, and 17.5/27.5°C (night/day) and were subjected to treatments of removing all leaves (LR), removing all leaves followed by cutting at half the plant height (HC), and removing all aboveground tissue (WC). The species, temperature, and damage extent had significant effects on the shoot number, leaf mass ratio, leaf area ratio and ratio of belowground to aboveground dry matter, and the species had a significant effect on the net assimilation rate, specific leaf area, and total biomass. The three species grew well under the HC and LR treatments, and high temperatures (15/25°C and 17.5/27.5°C) significantly promoted the regrowth of the three species. Medicago sativa grew faster than the two Artemisia species. Medicago sativa can be used for fertilizing or vegetation restoration in unimportant conservation areas, and the two Artemisia species can be effectively used for vegetation restoration in the Mu Us Sandland. Due to the low labor costs and the local climate conditions, plants should be clipped before the beginning of the main growing season (end of May or early June) to ensure rapid growth.

Tropical and subtropical forest ecosystems play an important role in the global carbon regulation. Despite increasing evidence for effects of biodiversity (species diversity, functional diversity and functional dominance), stand structural attributes, stand age and environmental conditions (climate and topography) on tree carbon storage, the relative importance of these drivers at large scale is poorly understood. It is also still unclear whether biodiversity effects on tree carbon storage work through niche complementarity (i.e. increased tree carbon storage due to interspecific resource partitioning) or through the mass-ratio effect (tree carbon storage regulated by dominant traits within communities). Here we analyze tree carbon storage and its drivers using data of 480 plots sampled across subtropical forests in China. We use multiple regression models to test the relative effects of biodiversity, stand structural attributes, stand age and environmental conditions on tree carbon storage, and use a partial least squares path model to test how these variables directly and/or indirectly affect tree carbon storage. Our results show that tree carbon storage is most strongly affected by stand age, followed by climate, biodiversity and stand structural attributes. Stand age and climate had both direct and indirect (through species diversity, functional dominance and stand structural attributes) effects. We find that tree carbon storage correlates with both species diversity and functional dominance after stand age and environmental drivers are accounted for. Our results suggest that niche complementarity and the mass-ratio effect, not necessarily mutually exclusive, both play a role in maintaining ecosystem functioning. Our results further indicate that biodiversity conservation might be an effective way for enhancing tree carbon storage in natural, species-rich forest ecosystems.

Land use/cover and vegetation patterns are influenced by many ecological factors. However, the effect of various factors on different classification systems and different levels of the same system is unclear. We conducted a redundancy analysis with 10 landscape metrics and ecological factors in four periods (1986–2005/2007, 1991–2005/2007, 1996–2005/2007, 2001–2005/2007) to explore their effects on the land use/cover system, vegetation group and vegetation type, and formation and subformation levels of the vegetation classification system in the Jing-Jin-Ji region. Soil, temperature and precipitation from 1986–2005, 1991–2005, and 2001–2005 were the important causal factors, and anthropogenic disturbance and atmospheric factors in 1996–2005 were causal factors at the land use/cover level. The total explained variance from 1996–2005 and 2001–2005 was higher than that from 1986–2005 and 1991–2005 at the land use/cover level. Causal factors and the variance explained by causal factors at the vegetation group, vegetation type, and formation and subformation levels were similar but different in the land use/cover system. Geography, soil and anthropogenic disturbance were the most important causal factors at the three vegetation levels, and the total explained variance from 2001–2007 was higher than that from 1986–2007, 1991–2007, and 1996–2007 at the three vegetation levels. In environmental research, natural resource management and urban or rural planning, geographic factors should be considered at the vegetation group, vegetation type and formation and subformation levels while atmospheric and temperature factors should be considered at the land use/cover level.

Background Simulating vegetation distribution is an effective method for identifying vegetation distribution patterns and trends. The primary goal of this study was to determine the best simulation method for a vegetation in an area that is heavily affected by human disturbance. Methods We used climate, topographic, and spectral data as the input variables for four machine learning models (random forest (RF), decision tree (DT), support vector machine (SVM), and maximum likelihood classification (MLC)) on three vegetation classification units (vegetation group (I), vegetation type (II), and formation and subformation (III)) in Jing-Jin-Ji, one of China’s most developed regions. We used a total of 2,789 vegetation points for model training and 974 vegetation points for model assessment. Results Our results showed that the RF method was the best of the four models, as it could effectively simulate vegetation distribution in all three classification units. The DT method could only simulate vegetation distribution in units I and II, while the other two models could not simulate vegetation distribution in any of the units. Kappa coefficients indicated that the DT and RF methods had more accurate predictions for units I and II than for unit III. The three vegetation classification units were most affected by six variables: three climate variables (annual mean temperature, mean diurnal range, and annual precipitation), one geospatial variable (slope), and two spectral variables (Mid-infrared ratio of winter vegetation index and brightness index of summer vegetation index). Variables Combination 7, including annual mean temperature, annual precipitation, mean diurnal range and precipitation of driest month, produced the highest simulation accuracy. Conclusions We determined that the RF model was the most effective for simulating vegetation distribution in all classification units present in the Jing-Jin-Ji region. The RF model produced high accuracy vegetation distributions in classification units I and II, but relatively low accuracy in classification unit III. Four climate variables were sufficient for vegetation distribution simulation in such region.

Due to significant decreases in precipitation in northern China, knowledge of the response of seed germination and plant growth characteristics to key limiting factors is essential for vegetation restoration. We examined seed germination under different temperatures and water potentials, and we examined seedling growth under different amounts of water supply. Experiments were carried out in automatic temperature‐, humidity‐, and light‐controlled growth chambers. Under low water potentials, the final germination percentages of four herbaceous species were high, while seed germination of the shrub species Caragana microphylla was significantly inhibited. Under the different water supply amounts, seedlings of Agropyron cristatum allocated more biomass to the root and had a higher growth rate than those of Elymus dahuricus and C. microphylla. In light of these results and drier environmental conditions (annual mean precipitation is 366 mm, which falling mainly between June and August), potential selections for revegetation of different landscapes include the following: A. cristatum for shifting sand dunes, the establishment of the pioneer species Agriophyllum squarrosum, C. microphylla for semifixed sand dunes, E. dahuricus for fixed sand dunes, and Melilotus suaveolens and Medicago sativa for cultivation.

Precipitation is a key environmental factor determining plant community structure and function. Knowledge of how community characteristics and leaf stoichiometric traits respond to variation in precipitation is crucial for assessing the effects of global changes on terrestrial ecosystems. In this study, we measured community characteristics, leaf stoichiometric traits, and soil properties along a precipitation gradient (35–209 mm) in a desert ecosystem of Northwest China to explore the drivers of these factors. With increasing precipitation, species richness, aboveground biomass, community coverage, foliage projective cover (FPC), and leaf area index (LAI) all significantly increased, while community height decreased. The hyperarid desert plants were characterized by lower leaf carbon (C) and nitrogen/phosphorus (N/P) levels, and stable N and P, and these parameters did not change significantly with precipitation. The growth of desert plants was limited more by N than P. Soil properties, rather than precipitation, were the main drivers of desert plant leaf stoichiometric traits, whereas precipitation made the biggest contribution to vegetation structure and function. These results test the importance of precipitation in regulating plant community structure and composition together with soil properties, and provide further insights into the adaptive strategy of communities at regional scale in response to global climate change.

The selection of certain indicators is critical to undertake ecological risk assessments of long-term oil pollution and other environmental changes. The indicators should be easily and routinely monitored, be sensitive to pollution, respond to pollution in a predictable manner, and match the spatial and temporal scales of investigations. To compare the effectiveness of indicators for the long-term risk assessments, this study investigated the multiple ecological effects of chronic oil pollution on the plant community dominated by reed (Phragmites australis). The physiology, growth and reproduction of reed, together with the composition and productivity of the reed community, were measured around oil wells that have operated for approximately 10 years in the Yellow River Delta, eastern China. The predictive power of each indicator was evaluated using the coefficients of determination (R-2) of linear regression models established for each indicator and soil Total Petroleum Hydrocarbons (TPH) concentration. The sensitivities of indicators were evaluated by comparing slopes of new established regression lines using standardized data. The top three indicators in terms of predictive power were leaf length, width and number, followed by the Shannon Wiener index, Pielou evenness index and Simpson's diversity index. Community aboveground biomass, foliar projective coverage and species richness showed predictive power lower than those of the three diversity indexes, but higher than those of leaf net photosynthetic rate, reed height, aboveground biomass and vertical projective coverage of reed plants. Leaf transpiration, chlorophyll concentration and reed stem density showed no significant linear response to elevated soil TPH concentration. In terms of sensitivity, the top three biological indicators were Pielou evenness index, Simpson's diversity index and Shannon Wiener index, followed by community vertical projective coverage, community aboveground biomass, and species richness. Leaf number, length and width were moderately sensitive, followed by reed coverage, aboveground biomass and height. The sensitivity of net photosynthetic rate was the lowest. The predictive power and sensitivities of indicators were compared in terms of their spatial and temporal scales. In conclusion, scale can be used to facilitate the selection of indicators, and the combination of different indicators may yield improved understanding of the various effects of elevated soil TPH concentration at the different biological levels. (C) 2014 Elsevier Ltd. All rights reserved.

• Floral color is a key reproductive character, often associates with environmental adaptation, and undergoes human intervention. A large number of Rhododendron species spread widely with various flower colors, which makes a good model for flower coloration. The chromatic features and anthocyanin compositions of 30 species from seven subgenera were systematically analyzed. • The Royal Horticultural Society Color Chart and CIE L*a*b* system were employed to describe and investigate flower colors. The UPLC-PDA/ESI-MSn system was used to identify and quantify anthocyanins in petal extracts. • The flower colors of 30 Rhododendron species were categorized into four groups—red, purplish pink, purple and white. Seven anthocyanins were identified and quantified in petals, including delphinidin, cyanidin and malvidin 3-O-arabinoside-5-O-glucosides, cyanidin 3,5-di-O-glucoside, 3-O-galactoside and 3-O-arabinoside, and delphinidin 3-O-glucoside. The red-flowered species mainly contained cyanidin monoglycosides and had much higher total anthocyanin contents than purplish pink- and purple-flowered species. Purplish pink- and purple-flowered species had similar anthocyanin types and contents. The chromatic differences were significant among groups, except the purplish pink and purple groups. Statistical analysis showed that Cy3Gal and Cy3Arb are characteristic for red-flowered species, and Mv3Arb5G and Dp3Arb5G play important roles in purple coloration; their contents were major components that greatly affected the chromatic parameters. In total, 21 flavonols derivates were identified. However, total flavonols content and copigmentation index showed no significant difference or correlation among /with color groups, suggesting that flavonols might not play a major role in coloration. • These results enhance our knowledge of the biochemical basis of flower coloration in Rhododendron species, and will lay a foundation for genetic variation study and aid the breeding of cultivars with novel flower colors. This article is protected by copyright. All rights reserved.

The distribution of plant species and relationships between species and soil factors in the east central part of Gurbantunggut Desert was studied to provide more insight into the flora and determine differences in vegetation across various parts of the desert. Two-way Cluster Analysis showed that the vegetation in the area could be divided into three groups, the first group was dominated by the shrub species, Ephedra przewalskii and the grass species, Carex physodes mainly in areas of flat grounds and gentle slopes; the second group was dominated by C. physodes, Artemisia songorica and A. xerophytica mainly on the slope of sand dunes and the third group was dominated by the shrub species, Haloxylon persicum mainly on the top of sand dunes. There was no difference in plant density between Groups 1 and 2 but there was a significant decrease in Group 3. Soil water under vegetation Group 3 was much lower than that in the other two groups at all soil depths. The EC, organic matter, total P and soluble Na, Ca and Mg varied very similarly with soil water. Canonical correspondence analysis (CCA) satisfactorily assessed the species-soil relations in the area. The distribution of plant species was strongly correlated with the soil factors of water content, organic matter, EC and nutrients. The variations in species occurrence explained by the three CCA axes were about 70%, indicating that some explanatory site variables may exist outside our studied parameters. Soil texture is suggested to be included in future studies to improve the explanation of CCA.

To investigate the mechanisms and potential for the remote sensing of phenanthrene-induced vegetation stress, we measured field canopy spectra, and associated plant and soil parameters in the field controlled experiment in the Yellow River Delta of China. Two widely distributed plant communities, separately dominated by reed (Phragmites australis) and glaucous seepweed (Suaeda salsa), were treated with different doses of phenanthrene. The canopy spectral changes of plant community resulted from the decreases of biomass and foliar projective coverage, while leaf photosynthetic pigment concentrations showed no significance difference among treatments. The spectral response to phenanthrene included a flattened red edge, with decreased first derivative of reflectance. The red edge slope and area consistently responded to phenanthrene, showing a strong relationship with aboveground biomass, coverage and canopy pigments density. These results suggest the potential of remote sensing and the importance of field validation to correctly interpret the causes of the spectral changes.

Seed mass and morphology are plant life history traits that influence seed dispersal ability, seeding establishment success, and population distribution pattern. Southeastern Tibet is a diversity center for Rhododendron species, which are distributed from a few hundred meters to 5500 m above sea level. We examined intra- and interspecific variation in seed mass and morphology in relation to altitude, habitat, plant height, and phylogeny. Seed mass decreased significantly with the increasing altitude and increased significantly with increasing plant height among populations of the same species. Seed mass differed significantly among species and subsections, but not among sections and subgenera. Seed length, width, surface area, and wing length were significantly negative correlated with altitude and significantly positive correlated with plant height. Further, these traits differed significantly among habitats and varied among species and subsection, but not among sections and subgenera. Species at low elevation had larger seeds with larger wings, and seeds became smaller and the wings of seeds tended to be smaller with the increasing altitude. Morphology of the seed varied from flat round to long cylindrical with increasing altitude. We suggest that seed mass and morphology have evolved as a result of both long-term adaptation and constraints of the taxonomic group over their long evolutionary history.

Our objectives were to determine the influence of salinity on root cell wall composition in soya beans and the possible mechanism of salt tolerance. Two soya bean cultivars, Touzan 69 (salt sensitive) and Dare (salt tolerant), were selected as experimental material for comparison. Root growth was clearly inhibited by salinity in both cultivars, but Touzan 69 showed more severe reductions in root length than Dare. In the 0–5 mm root segment (from root tip), the total cell wall sugar content of Touzan 69 decreased considerably due to salinity as were the pectin, hemicellulose and cellulose fractions. In Dare, NaCl treatments only caused a slight decrease in the pectin fraction and no marked change in hemicellulose and cellulose fractions. Without salt treatment, the pectin fraction accounted for about 40 % and cellulose for 30 % of cell wall composition in the 0–5 mm root segment; in the 5–10 segment (from root tip), pectin and cellulose accounted for 27 % and 45 % in Touzan 69, and 34 % and 38 % in Dare. The percentage of pectin decreased and that of cellulose increased in the 5–10 mm root segment compared with the 0–5 mm segment. This indicates that pectin largely regulates cell growth, as the 0–5 mm region is considered the elongation zone of soya bean roots. Salt treatment decreased the percentage of pectin, but increased that of cellulose across root zones of the two cultivars, suggesting that salt presence may increase cell wall rigidity, and thus, inhibits root growth. Dare was able to maintain its main root cell wall substances, an apparent advantage for root cell growth that may overall improve its salt tolerance. Also, the less reduction in cell wall uronic acid was of some benefit in the positive regulation of root cell growth in Dare. The changes in cell wall composition, especially the pectin content had a close relation with the regulation of root growth. The difference in salt tolerance between the two tested cultivars can partly be explained on the basis of these changes in response to salinity. Sugar compounds in each cell wall constituent and their functions in ion transport as well as the relationship between root cell wall and soya bean salt tolerance need to be further investigated.

Soil-plant water relations are crucial for understanding the mechanisms by which plants adapt to their environments. An experiment was conducted to understand the responses of 4 dominant psammophyte shrub species to different sandy environments. Pots were filled with tap water or sand, and pots planted with different species and filled with sand with and without pot covers were kept in 4 growth cabinets at 15/25 °C and with a water supply of 75 mm per month. Soil water content; dry weights of roots, shoots, and leaves; and leaf area were measured. The relative growth rate (0.039-0.042 g g-1 day-1) was higher for the 2 Artemisia Krasch. species and lower for Caragana korshinskii Kom. and Hedysarum laeve Maxim. (0.016-0.023 g g-1 d-1). The final soil water content of the 2 Artemisia species (1.3%-2.7%) was lower than that of H. laeve and C. korshinskii (14.7%-18.4%). Soil water content increased from the top of the profile to deeper levels for H. laeve and C. korshinskii. However, for the 2 Artemisia species, soil water was lower in the deeper profile compared with the upper profile. Considering water consumption, the 2 Artemisia species were similar while C. korshinskii and H. laeve were similar; this result was different from our hypothesis.

Warming, watering and elevated atmospheric CO₂-concentration effects have been extensively studied separately; however, their combined impact on plants is not well understood. In the current research, we examined plant growth and physiological responses of three dominant species from the Eurasian Steppe with different functional traits to a combination of elevated CO₂, high temperature, and four simulated precipitation patterns. Elevated CO₂ stimulated plant growth by 10.8-41.7 % for a C₃ leguminous shrub, Caragana microphylla, and by 33.2-52.3 % for a C₃ grass, Stipa grandis, across all temperature and watering treatments. Elevated CO₂, however, did not affect plant biomass of a C₄ grass, Cleistogenes squarrosa, under normal or increased precipitation, whereas a 20.0-69.7 % stimulation of growth occurred with elevated CO₂ under drought conditions. Plant growth was enhanced in the C₃ shrub and the C₄ grass by warming under normal precipitation, but declined drastically with severe drought. The effects of elevated CO₂ on leaf traits, biomass allocation and photosynthetic potential were remarkably species-dependent. Suppression of photosynthetic activity, and enhancement of cell peroxidation by a combination of warming and severe drought, were partly alleviated by elevated CO₂. The relationships between plant functional traits and physiological activities and their responses to climate change were discussed. The present results suggested that the response to CO₂ enrichment may strongly depend on the response of specific species under varying patterns of precipitation, with or without warming, highlighting that individual species and multifactor dependencies must be considered in a projection of terrestrial ecosystem response to climatic change.

Soil enzyme activity plays an important role in the conversion of soil organic carbon into inorganic carbon, which is significant for the global carbon cycle. In this study, we investigated the soil enzyme activities of two ligninolytic enzymes (peroxidase and polyphenol oxidase) and five non-ligninolytic enzymes (α-1,4-glucosidase (AG); β-1,4-glucosidase (BG); N-acetyl-β-glucosaminidase (NAG); β-D-cellobiosidase (CBH); and β-xylosidase (BXYL)) in four plant communities of the Sangong River basin in Fukang, North Xinjiang, China. The four typical plant communities were dominated by Haloxylon ammodendron, Reaumuria soongonica, Salsola passerina, and Tamarix rarmosissima, respectively, with saline soils of varied alkalinity. The results showed that the soil peroxidase activity decreased seasonally. The activities of the five non-ligninolytic enzymes decreased with increasing soil depths, while those of the two ligninolytic enzymes did not show such a trend. In the four plant communities, BG had the highest activity among the five non-ligninolytic enzymes, and the activities of the two ligninolytic enzymes were higher than those of the four non-ligninolytic ones (AG, NAG, CBH, and BXYL). The community of H. ammodendron displayed the highest activity with respect to the two ligninolytic enzymes in most cases, but no significant differences were found among the four plant communities. The geometric mean of soil enzyme activities of the four plant communities was validated through an independently performed principal component analysis (PCA), which indicated that different plant communities had different soil enzyme activities. The correlation analysis showed that soil polyphenol oxidase activity was significantly positively correlated with the activities of the five non-ligninolytic enzymes. The soil pH value was positively correlated with the activities of all soil enzymes except peroxidase. Soil microbial carbon content also showed a significant positive correlation (P

Adverse climate change attributed to elevated atmospheric carbon dioxide concentration (CO2) and increased temperature components of global warming has been a central issue affecting economic and social development. Climate change, particularly global warming, imposes a severe impact on the terrestrial ecosystem. Elevated CO2, drought, and high temperature have been extensively documented individually; however, relatively little is known about how plants respond to the interaction of these factors. To summarize current knowledge on the response of plants to global change factors, we focus on the interactive effects of CO2 enrichment, warming, and drought on plant growth, carbon allocation, and photosynthesis. Stimulation due to elevated CO2 might be suppressed under other negative climatic/environmental stresses such as drought, high temperature, and their combination. However, elevated CO2 could alleviate deleterious effects of moderate drought via reducing stomatal conductance, altering leaf surface, and regulating gene expression. High CO2 levels and rising temperatures may result in opposite responses in plant water use efficiency. Stimulation of plant growth due to elevated CO2 for C3 species occurs regardless of water conditions, but only under a water deficit for C4 species. The positive effect of elevated CO2 on C4 species is derived mainly from the improved water status. Plant adaptive or maladaptive responses to multivariate environments are interactive; thus, researchers need to explore the ecological underpinnings involved in such responses to the multiple factors involved in climate change.

Clarifying the persistence time of seedlings of dominant species under continual drought will help us understand responses of ecosystems to global climate change and improve revegetation efforts. Drought tolerance of four dominant psammophytic shrub species occurring in different environments was studied in the semi-arid areas of Inner Mongolian grasslands. Seedlings of Hedysarum laeve, Caragana korshinskii, Artemisia sphaerocephala and Artemisia ordosica were grown under four air temperature regimes (night/day: 12.5/22.5°C, 15/25°C, 17.5/27.5°C and 20/30°C) within climate (air temperature and humidity) controlled, naturally lit glasshouses with a night/day relative humidity of 70%/50%. Pots were watered to field capacity for each temperature treatment. Soil water condition was monitored by weighting each pot every day using an electronic balance. Date of seedling death for each treatment was recorded and the dead plants were harvested. Plant dry weights were determined after oven drying at 80°C for 3 days. Two Artemisia species had higher growth rates than H. laeve and C. korshinskii, and the growth of all four species increased with increasing temperatures. The two Artemisia species had the highest leaf biomass increment, followed by C. korshinskii, and then H. laeve. Shoot biomass increment was higher for A. ordosica and C. korshinskii, intermediate for A. sphaerocephala and lowest for H. laeve. C. korshinskii had the highest root biomass increment. The final soil water content at death for all four species varied from 1% to 2%. C. korshinskii, A. sphaerocephala, H. laeve and A. ordosica survived for 25–43, 24–41, 26–41, and 24–37 days without watering, respectively. C. korshinskii, A. sphaerocephala, H. Laeve, and A. ordosica seedlings survived longer at the lowest temperatures (12.5/22.5°C) than at the highest temperatures (20/30°C) by 18, 17, 15 and 13 days, respectively. Increased climatic temperatures induce the death of seedlings in years with long intervals between rainfall events. The adaptation of seedlings to droughts should be emphasized in revegetation efforts in the Ordos Plateau, Inner Mongolia.

Vegetation patterns and spatial organization are influenced by the changing environmental conditions and human activities. However, the effect of environment on vegetation at different vegetation classification levels has been unclear. We conducted an analysis to explore the relationship between environment and vegetation in the land use/land cover (LULC), vegetation group, vegetation type, and formation and subformation levels using redundancy analysis with seven landscape metrics and 33 environmental factors in the upper reaches of the Heihe River basin in an arid area of China to clarify this uncertainty. Atmospheric counter radiation was the most important factor at the four levels. The effect of soil was the second determinant factor at three levels (except in vegetation formation and subformation level). The number of variables whose relationship to vegetation reached significant levels varied from 26 to 28, and 20 variables were the same at all four levels. The factors affecting vegetation were basically the same at vegetation group level and vegetation‐type level. It was sufficient to analyze the relationship between environmental and vegetation patterns only in LULC, vegetation group and vegetation formation and subformation level in mountainous regions; different factors should be considered at different vegetation levels.