Search

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.

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.

• 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.

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.

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

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.

Artemisia ordosica and Artemisia sphaerocephala seedlings were buried in sand to depths of 0, 0.25, 0.5, 0.75, 1 and 1.25 times the seedling height (H) and supplied with 2.5, 5.0, 7.5 and 10.0 mm of water every three days. For A. ordosica , the highest relative growth rate (RGR) and seedling height were achieved with 75 mm/month water supply and 0.5 H burial at 50 days, and the RGR decreased with 100 mm/month water supply. For A. sphaerocephala , the highest RGR was reached with 50 mm/month water supply and 0.5 H burial, but plants from this species had the greatest seedling height with 25 mm/month water supply and 0.75 H burial. A. ordosica and A. sphaerocephala have different proportions of their biomass in roots and shoots and thus are adapted to sandy environments in different ways. Partial sand burial significantly increased the RGR and growth height of the two Artemisia species, but complete burial lead to seedling death. Differences in the growth response to burial and moisture levels help explain why A. sphaerocephala is primarily found on drifting dunes and A. ordosica on semi-fixed and fixed dunes.

Picea mongolica W. D. Xu is an endemic and endangered species which is only found in semi-arid areas of northern China. It has been widely used as an afforestation tree in the establishment of the Three-North Shelterbelt System for its adaptation to arid soils and as a virescent tree in urban gardens and streets for its beautiful shape. Due to different microenvironments, P. mongolica populations may differentiate into many ecological groups with different adaptive abilities. Long-term adaptation to a dry environment makes P. mongolica differentiate into different ecotypes. Typical ecotypes are P. mongolica f. purpurea (Fp), P. mongolica f. rubra (Fr) and P. mongolica f. viridis (Fv). Our results show that cone size is clearly not uniform among different ecotypes; the largest cones are found in the Fv ecotype and the smallest in Fp. There were also distinct differences between these ecotypes in terms of height and length of squama. At the molecular level, the zymograms of peroxidase and lipase prove the existence of different ecotypes in P. mongolica. The results are useful for investigating and managing this rare spruce species in China.

Drought stress is one of the most important factors limiting the survival and growth of plants in the harsh karst habitats of southwestern China. Detailed knowledge about the ecophysiological responses of native plants with different growth forms to drought stress could contribute to the success of re-vegetation programs. Two shrubs, Pyracantha fortuneana and Rosa cymosa, and four trees, Broussonetia papyrifera, Cinnamomum bodinieri, Platycarya longipes and Pteroceltis tatarinowii, were randomly assigned to four drought treatments, i.e. well-watered, mild drought stress, moderate drought stress, and severe drought stress. Midday water potential, the maximum quantum efficiency of PSII photochemistry (Fv/Fm), pigments, osmotic solutes (soluble sugars and proline), cellular damages, and antioxidant enzymes (superoxide dismutase, catalase and peroxidase) were investigated. Drought stress significantly decreased pigments content, but increased the ratio of carotenoids to total chlorophylls in the studied species. After prolonged severe drought stress, the two shrubs exhibited higher Fv/Fm, less reductions of midday water potential, and lower increases of malondialdehyde content and ion leakage than the four trees. Prolonged severe drought stress largely decreased accumulations of osmotic solutes and activities of antioxidant enzymes in the four trees, but significantly increased proline content and superoxide dismutase activity in the two shrubs and peroxidase activity in P. fortuneana. The positive relationships were observed among activities of antioxidant enzymes, and between contents of osmotic solutes and activities of antioxidant enzymes. These findings suggested that the two shrubs had higher tolerance to severe drought stress than the four trees due to higher capacities of osmotic adjustment and antioxidant protection.

Artemisia sphaerocephala and A. ordosica are two dominant shrub species in Mu Us sandy land (Inner Mongolia, China) and are widely used for vegetation restoration. However, there are two different conclusions about the effect of light on their germination: light promotes germination versus light inhibits germination. The aim of this study was to evaluate these two conclusions and relate the results to instances of failure of these two species to germinate well when air-dispersed in revegetation projects. The effects of fluctuating temperature, light/dark, source (population), position on mother plant, storage condition, and storage time were tested on germination of achenes of these two species. At low temperature, final percent germination (FPG) of achenes in dark and nearly dark conditions was significantly higher than those in light. At 10:20°C, achenes of both A. sphaerocephala and A. ordosica had higher FPG in dark than in light regardless of source, position on mother plants or storage condition. At suboptimum (5:15°C) and supraoptimal (25:35°C) temperatures, germination of A. sphaerocephala and A. ordosica achenes was inhibited in both light and darkness. It was concluded that light inhibits germination of A. sphaerocephala and A. ordosica achenes at low (10:20°C) temperature but not at high (15:25°C) temperature. Since the temperature in Mu Us sandy land is around 10:20°C in early June, when air sowing is done, achenes should germinate best when they are covered by a thin layer of sand.

It has been reported that elevated CO2 can enhance plant growth and water use, and that desert plants in particular will show the strongest response to rising atmospheric CO2 due to the strong water stress on these plants. In this study experiments were conducted to understand the responses of seedlings from four species, which are dominant in different successional stages in the semi-arid sandy grassland of central Inner Mongolia, to rising temperature and elevated CO2. Seedlings of the four species were grown for 8 weeks at two air temperatures and two CO2 concentration regimes in growth chambers. It was found that for the two Artemisia species and Hedysarum laeve elevated CO2 level resulted in increased relative growth rates (RGR) (6–12%), height increments (24–106%), net assimilation rates (20–45%) and water use efficiencies (WUE) (43–105%), and decreased transpiration (16–55%). For Caragana korshinskii, the elevated CO2 significantly increased the ratio of below ground to above ground biomass (16–23%), height increment (31–65%) and WUE (79–84%). At elevated CO2 level and the higher temperature, the two Artemisia species showed decreased RGR and height increments, while for, C. korshinskii and H. laeve increased RGR and height increments were observed. For A. sphaerocephala the higher temperature also resulted in increased WUE, but decreased WUE for the other three species. Obvious differences were observed between the two Artemisia species and C. korshinskii, with the Artemisia species characterized by higher RGR, lower ratio of below ground to above ground biomass and lower WUE. These findings should be applicable to similar shrub species located in other arid and semi-arid environments.

Artemisia ordosica Krasch. (Asteraceae) is the dominant psammophytic shrub species on the Ordos Plateau of northern China and is used for revegetation of semi-arid areas. Experiments were conducted to determine the effects of light intensity, constant temperature, alternating temperatures, and water potential on germination to determine why air-dispersed achenes fail to germinate well in the field. Achenes germinated within a wide alternating temperature window, except under the 5:15 °C (night:day) temperature regime in darkness. Final percent germination (FPG) was higher in darkness than in light at alternating temperature regimes, except under the 20:30 °C (night:day) temperature regime. Achenes subjected to a range of constant temperatures in the dark had high FPG over 76.8% except at 30 °C (8%). Photosynthetic photon flux densities (PPFD) of 100 and 400 µmol·m–2·s–1 significantly lowered FPG under a 10:20 °C (night:day) regime, while at 0–25 µmol·m–2·s–1 PPFD, the FPG was over 92%. Few achenes germinated at –1.4 MPa. The most suitable temperature for germination of achenes placed under water stress was 20 °C. The best timing for air dispersal is mid-May, so seeds would become covered with sand at a time when temperature and soil moisture conditions were optimal for germination.Key words: air dispersal, Artemisia ordosica, hydrothermal time, psammophytes, semi-arid regions, temperature.

Summary Artemisia sphaerocephala is widely used for vegetation rehabilitation, but its germination is very low after air seeding of achenes. We explored effects of light, temperature and water stress on germination. Results show that both final percent germination and germination rate were increased by temperature increment, with the highest values occurring at 15: 25°C (night: day) in dark and 20: 30°C under light. Light inhibited germination, especially at lower alternating temperatures (5: 15°C and 10: 20°C). The alternating temperature window for germination was slightly narrower under light than in dark, and germination was slower under light than in dark across the temperature range. Achenes incubated in the dark and at constant temperatures had over 80% germination at 10 to 25°C, with an optimum at 20°C. Under dark and 25μmol m-2 s-1 light flux density at 10: 20°C, final percent germination was over 94%, but if the light flux density was increased to 100 and 400 μmol m-2 s-1, final percent germination was significantly lower (64% and 38% respectively). However, achenes could keep their germination capacity for a long time (over 50 days) and germinate well after going back to the dark. Germination was also lower under water stress and few achenes germinated at -1.4 MPa. This was more pronounced at high and low temperatures. Given these findings and the prevailing climatic characteristics, the most suitable time for air seeding of achenes may be mid-May.

Agriophyllum squarrosum (L.) Moq. (Chenopodiaceae), a pioneer species of natural succession in semi-arid regions of China, is widely used for vegetation rehabilitation by air seeding. Experiments were conducted to determine the effects of light intensity and photoperiod, as well as constant and alternating temperatures, on germination to improve the technology of air seeding. Seed of A. squarrosum rarely (–2·s–1) photoperiod. Under dark conditions there was a high final percent seed germination (>90%), except for 71.8% final percent seed germination at 5/15 °C. Constant temperature conditions were associated with lower seed germination (–2·s–1) at 10/20 °C. There was no significant difference in final percent germination when seeds were exposed to 400, 100, or 25 µmol m–2 s–1 for 2 h daily. Final percent germination and germination rate deceased rapidly when the photoperiod was increased under 400 µmol·m–2·s–1. Only 49.2% of seeds germinated after 3 d. Because of the deleterious effect of light on germination, air seeding in late May is recommended.Key words: Agriophyllum squarrosum, air seeding, alternating temperature, constant temperature, light, semi-arid regions.

Caragana korshinskii Kom. is a very important shrub species for vegetation rehabilitation in northern China for its high ecological and economic values. Experiments were conducted to determine its germination responses to (i) different temperature regimes under light and/or dark conditions, (ii) different light intensities, and (iii) different water potentials combined with varied constant temperatures. Under alternating temperatures (from 5:15 to 25:35°C), final percent germinations of Caragana korshinskii were quite similar. In dark conditions, constant temperatures resulted in lower final percent germinations than alternating temperatures. At a controlled temperature regime of 10:20°C, neither final percent germinations nor germination rates showed significant differences among varied light intensities. As water potentials were reduced from 0 (distilled water) to −0.6 MPa, final percent germinations increased slightly and reached the peak at approximately −0.6 MPa, however, the increment was not significant. Beyond −0.6 MPa, further water potential reduction led to decreased final percent germinations and few seeds could germinate at −1.4 MPa. Water stress also strongly inhibited germination at very high or low temperatures. The experimental results suggested that middle May might be a suitable time for aerial seeding for this species.

Tree peony flowers are edible and traditional Chinese medicine materials. In the present study, 26 flavonoids were identified and quantified in yellow flowers of tree peony by high-performance liquid chromatography with diode array detector (HPLC-DAD) and by HPLC-electrospray ionization-mass spectrometry (HPLC-ESI-MS). Seventeen of them were first reported in flowers of tree peony, and glycosides of kaempferol, luteolin, and apigenin as well as isosalipurposide were the main flavonoids investigated. Furthermore, the petal extracts showed high antioxidant activity according to DPPH*, ABTS*(+), and OH* scavenging assays and ferric reducing antioxidant power assay. There were significant correlations between antioxidant activity and both the total polyphenol content (determined by Folin-Ciocalteu method) and the total content of quercetin, kaempferol, and luteolin glycosides. This work is valuable for elucidation of phenolic composition in tree peony flowers and for further utilization of them as functional food and medicine materials.

Xanthoceras sorbifolium, a tree species endemic to northern China, has high oil content in its seeds and is recognized as an important biodiesel crop. The plant is characterized by late-acting self-incompatibility (LSI). LSI was found to occur in many angiosperm species and plays an important role in reducing inbreeding and its harmful effects, as do gametophytic self-incompatibility (GSI) and sporophytic self-incompatibility (SSI). Molecular mechanisms of conventional GSI and SSI have been well characterized in several families, but no effort has been made to identify the genes involved in the LSI process. The present studies indicated that there were no significant differences in structural and histological features between the self- and cross-pollinated ovules during the early stages of ovule development until 5 days after pollination (DAP). This suggests that 5 DAP is likely to be a turning point for the development of the selfed ovules. Comparative de novo transcriptome analysis of the selfed and crossed ovules at 5 DAP identified 274 genes expressed specifically or preferentially in the selfed ovules. These genes contained a significant proportion of genes predicted to function in the biosynthesis of secondary metabolites, consistent with our histological observations in the fertilized ovules. The genes encoding signal transduction-related components, such as protein kinases and protein phosphatases, are overrepresented in the selfed ovules. X. sorbifolium selfed ovules also specifically or preferentially express many unique transcription factor (TF) genes that could potentially be involved in the novel mechanisms of LSI. We also identified 42 genes significantly up-regulated in the crossed ovules compared to the selfed ovules. The expression of all 16 genes selected from the RNA-seq data was validated using PCR in the selfed and crossed ovules. This study represents the first genome-wide identification of genes expressed in the fertilized ovules of an LSI species. The availability of a pool of specifically or preferentially expressed genes from selfed ovules for X. sorbifolium will be a valuable resource for future genetic analyses of candidate genes involved in the LSI response.

In this study we aimed to determine whether a sequential distribution pattern along an aridity gradient is related to seed germination and seedling emergence of three Caragana species. The study tested the adaptive abilities of these species to major sandy environment factors including soil water potential, precipitation amount, and sand burial depth. The rank order of tolerance to drought and sand burial of the three species is C. korshinskii>C. intermedia>C. microphylla. The amount of precipitation and sand burial depth appear to be the main selective forces responsible for the geographical distribution of these species., Environmental tolerance of a species has been shown to correlate positively with its geographical range. On the Ordos Plateau, three Caragana species are distributed sequentially along the precipitation gradient. We hypothesized that this geographical distribution pattern is related to environmental tolerances of the three Caragana species during seed germination and seedling emergence stages. To test this hypothesis, we examined seed germination under different temperature, light and water potentials, and monitored seedling emergence for seeds buried at eight sand depths and given different amounts of water. Seeds of C. korshinskii germinated to high percentages at 5 : 15 to 25 : 35 °C in both light and darkness, while those of C. intermedia and C. microphylla did so only at 15 : 25 and 25 : 35 °C, respectively. Nearly 30 % of the C. korshinskii seeds germinated at −1.4 MPa at 20 and 25 °C, while no seeds of the other two species did so. Under the same treatments, seedling emergence percentages of C. korshinskii were higher than those of the other two species. The rank order of tolerance to drought and sand burial of the three species is C. korshinskii > C. intermedia > C. microphylla. The amount of precipitation and sand burial depth appear to be the main selective forces responsible for the geographical distribution of these species.

Hedysarum fruticosum is one of the common species for combating desertification in the semi-arid area of China, mainly because of its ability of efficient regeneration from seed and quick clonal growth. In this study, experiments were conducted to determine the effects of light intensity, constant temperature, alternating temperature and water potential (generated by PEG) on seed germination of H. fruticosum. It was found that under alternating temperature regimes, final percent germination increased from 87.2% to 99.2% when temperature increased from 5:15°C (night:day) to 10:20°C, then decreased with increasing temperature; germination could not take place at all under 25:35°C conditions in a 14h (215μmol m − 2 s − 1 ) photoperiod. Under dark conditions there was a similar final percent germination to that under light. The germination pattern under constant temperature conditions was similar to that under alternating temperature, and there were no significant differences in final percent germination and germination rate between alternating and constant temperature. Under varying light intensities, final percent germination of H. fruticosum showed no significant differences, with values always above 74.4%. When water potentials were reduced, final percent germination decreased dramatically, and few seeds could germinate at − 0.2MPa. The germination rate showed a pattern similar to that of final percent germination with changing water potentials. Based on the experimental results and environmental conditions in the study area, H. fruticosum seeds should be dispersed from early to mid-May so that germination requirements can be fulfilled and higher germination is possible.