Effect of grazing disturbance on floral display, pollen limitation and plant pollination efficiency in the desert steppe.

BACKGROUND: Grazing disturbance usually affects floral display and pollination efficiency in the desert steppe, which may cause pollen limitation in insect-pollinated plants. Effective pollination is essential for the reproductive success of insect-pollinated plants and insufficient pollen transfer may result in pollen limitation. Caragana microphylla Lam is an arid region shrub with ecological importance. Few studies have been conducted on how grazing disturbance influences pollen limitation and pollination efficiency of C. microphylla. Here, we quantify the effect of different grazing intensities on floral display, pollinator visitation frequency and seed production in the Urat desert steppe. RESULTS: In C. microphylla, supplemental hand pollination increased the seed set, and pollen limitation was the predominant limiting factor. As the heavy grazing significantly reduced the seed set in plants that underwent open-pollination, but there was no significant difference in the seed set between plants in the control plots and plants in the moderate grazing plots. Furthermore, there was a higher pollinator visitation frequency in plants in the control plots than in plants in the heavy grazing plots. CONCLUSIONS: We found that pollinator visitation frequency was significantly associated with the number of open flowers. Our findings also demonstrated that seed production is associated with pollinator visitation frequency, as indicated by increased seed production in flowers with higher pollinator visitation frequency. Therefore, this study provides insight into the effect of different grazing intensities on floral display that are important for influencing pollinator visitation frequency and pollination efficiency in desert steppes.

Annual Herbaceous Plants Exhibit Altered Morphological Traits in Response to Altered Precipitation and Drought Patterns in Semiarid Sandy Grassland, Northern China.

The frequency and intensity of extreme precipitation events and severe drought are predicted to increase in semiarid areas due to global climate change. Plant morphological traits can reflect plant responses to a changing environment, such as altered precipitation or drought patterns. In this study, we examined the response of morphological traits of root, stem, leaf and reproduction meristems of annual herbaceous species to altered precipitation and drought patterns in a semiarid sandy grassland. The study involved a control treatment (100% of background precipitation) and the following six altered precipitation treatments: (1) P(+): precipitation increased by 30%, (2) P(++): precipitation increased by 60%, (3) P(-): precipitation decreased by 30%, (4) P(--): precipitation decreased by 60%, (5) drought 1 (D1): 46-day drought from May 1st to June 15th, and (6) drought 2 (D2): 46-day drought from July 1st to August 15th. P(++) significantly increased root length, flower length-to-width ratio, both P(+) and P(++) significantly increased stem length and flower number in the plant growing seasons, while all of them decreased under P(-) and P(--). The annual herbaceous plants marginally increased the number of second-level stem branches and stem diameter in order to better resist the severe drought stress under P(--). P(+) and P(++) increased the root, stem, leaf, and flower dry weight, with the flower dry weight accounting for a larger proportion than the other aboveground parts. Under D2, the plants used the limited water resources more efficiently by increasing the root-to-shoot ratio compared with P(-), P(--) and D1, which reflects biomass allocation to belowground increased. The linear mixed-effects models and redundancy analysis showed that the root-to-shoot ratio and the dry weight of various plant components were significantly affected by morphological traits and altered precipitation magnitude. Our results showed that the herbaceous species have evolved morphological trait responses that allow them to adapt to climate change. Such differences in morphological traits may ultimately affect the growing patterns of annual herbaceous species, enhancing their drought-tolerant capacity in semiarid sandy grassland during the ongoing climate change.

Comparative effects of pollen limitation, floral traits and pollinators on reproductive success of Hedysarum scoparium Fisch. et Mey. in different habitats.

BACKGROUND: Reproduction in most flowering plants may be limited because of the decreased visitation or activity of pollinators in fragmented habitats. Hedysarum scoparium Fisch. et Mey. is an arid region shrub with ecological importance. We explored the pollen limitation and seed set of Hedysarum scoparium in fragmented and restored environments, and examined whether pollen limitation is a significant limiting factor for seed set. We also compared floral traits and pollinator visitation between both habitats, and we determined the difference of floral traits and pollinators influenced reproductive success in Hedysarum scoparium. RESULTS: Our results indicated that supplementation with pollen significantly increased seed set per flower, which is pollen-limited in this species. Furthermore, there was greater seed set of the hand cross-pollination group in the restored habitat compared to the fragmented environment. More visits by Apis mellifera were recorded in the restored habitats, which may explain the difference in seed production between the fragmented and restored habitats. CONCLUSIONS: In this study, a positive association between pollinator visitation frequency and open flower number was observed. The findings of this study are important for experimentally quantifying the effects of floral traits and pollinators on plant reproductive success in different habitats.

Impact of floral characters, pollen limitation, and pollinator visitation on pollination success in different populations of Caragana korshinskii Kom.

Caragana korshinskii Kom. has a significant function in desert-grassland revegetation in arid regions. Plant reproduction in arid regions can be restricted due to inadequate pollen receipt and reduced pollen transfer. An assessment of pollination success as a result of pollen limitation and pollinator visitation in various C. korshinskii populations is presently lacking. We thus tested three different treatments (pollen addition, control, and procedural control) to elucidate how pollen limitation affects seed numbers per flower in C. korshinskii. We also determined the effect of pollinator visit frequency on seeds per flower. Our results demonstrated that there was a higher proportion of open flowers and mature fruits in the managed population than in the natural population. Pollen addition significantly increased seed number per flower, and pollen limitation was determined to be a significant limiting factor in seed production. Furthermore, Apis mellifera was determined to be the principal pollinator, and pollinator visitation frequency was significantly correlated with open flower number. Our findings also demonstrated that pollinator visitation rate and seed production were positively correlated. Management and pollinator visitation could affect seed production, which may explain the higher seeds per flower in the managed population compared with the natural population.

Comparative pollen limitation and pollinator activity of Caragana korshinskii Kom in natural and fragmented habitats.

In many flowering plants, fragmented habitats may affect pollen limitation, pollinator behavior, and plant-pollinator interactions. Pollen limitation may decrease plant reproduction due to low levels of pollen transfer and inadequate pollen receipt. However, how fragmented habitats affect the pollen limitation and pollinator activity of Caragana korshinskii Kom. still needs further study. We designed a pollen supplementation treatment to understand how pollen limitation affects seed set. We calculated the visiting patterns and frequency of pollinators in different habitat types (natural and fragmented) to determine the effect of fragmented habitats on pollinator activity and on the pollination success of a desert-grassland shrub. Our results demonstrated that pollen supplementation was found to significantly increase seed set per flower, which is pollen-limited in the studied species. Moreover, the pollen limitation index in fragmented habitats was increased compared to that of natural habitats. Apis mellifera was found to be the dominant pollinator, with more pollinators and a higher visitation frequency of A. mellifera found in natural habitats compared to fragmented habitats. Our results showed that pollen limitation intensity was significantly correlated with the pollinator visitation frequency in the both habitats. Outcrossing was dominant in the breeding system, and insect pollination played a critical role in outcrossing. We found that fragmented habitats could affect pollinator activity, which might reduce pollen dispersal among flowers and the probability of outcrossing in the studied habitats.

Pollinator activity and pollination success of Medicago sativa L. in a natural and a managed population.

Medicago sativa L. is an important cash crop in the arid region of northwest China. Pollinator activity is an essential aspect of pollination success, but the relationships between pollinator visitation rate and seed set still need further study of M. sativa. We investigated the following characteristics of M. sativa in natural and managed populations: floral traits, pollinator activity, and breeding system. Our results indicated the management could affect the number of flowers produced; however, there was no detectable effect on the seed set per flower. We found the percentage of seeds among pollinated flowers in the managed population was significantly higher than that in the natural population. Moreover, the increase in the proportion of pollinated flowers could significantly increase seed set per flower, and pollinator visitation rate was the important limiting factor for seed set in both populations. Andrena lebedevi Popov was found to be the most frequent pollinator in both populations. Outcrossing was dominant in the breeding system and insect pollination played an important role in outcrossing. Our study suggested that proper management (artificial selection) could promote pollination success of M. sativa.

Effect of pollen and resource limitation on reproduction of Zygophyllum xanthoxylum in fragmented habitats.

Limitations on pollen and resources may significantly affect plant reproduction in fragmented habitats. In this study, phenology and pollinator frequency and activity were investigated to estimate the role of pollinators in Zygophyllum xanthoxylum reproduction, and this species is ecologically important in northwest China. In addition, the relative impact of restrictive amounts of pollen and resources on the seed set per flower was evaluated. It was found that adding pollen boosted the size of the seed set per flower, but had no significant effect on the number of flowers. By contrast, the addition of resources increased flower numbers as well as had a slight impact on the seed set per flower. These results indicate the amount of available pollen is a limiting factor for reproductive success. Moreover, Apis mellifera was identified as the most effective pollinator of Z. xanthoxylum, and there were more overall pollinators and visitations in the control than in the fragmented habitats. Furthermore, the limitations in pollen were more restrictive in the fragmented area than in the control. This was due to increased pollinator visitations in the control that could ameliorate the effects of lower pollen levels. When there is a limited availability of suitable pollinators, self-pollination is critical in fragmented habitats. Z. xanthoxylum has reproductive strategies that aid in adapting to harsh environments, including protogyny and delayed selfing.

Effects of sand burial on the survival and growth of two shrubs dominant in different habitats of northern China.

Plants that grow in dune ecosystems always suffer from sand burial. Shrubs play implications on the healthy functioning of dune ecosystems due to control blowing sand. However, the survival and growth responses of shrubs to sand burial remain poorly understood. The survival rate and seedling height of two shrubs (Artemisia halodendron and Lespedeza davurica) along with the soil properties under different burial depths were examined in order to reveal the causing ecophysiological attributes of sand burial on shrubs in the desertified region. It was found that A. halodendron can survive a burial depth of 6 cm greater than its seedling height, which is a dominant shrub in mobile dunes with intense burial, whereas a burial depth equivalent to three fourths of its seedling height is detrimental to L. davurica, which is dominant in fixed dunes with less burial. The reasons for the shrub death under sand burial were associated with the physical barrier to vertical growth and the reduction in photosynthetic area. In conclusion, A. halodendron can facilitate the stabilization of mobile dunes because of their high tolerance to the frequent and intensive sand burial, while L. davurica can be beneficial for the recovery process because of their higher survival rates under shallow burial following restoration of mobile dunes.

Effects of habitat disturbance on the pollination system of Ammopiptanthus mongolicus (Maxim) Cheng f. at the landscape-level in an arid region of Northwest China.

Ammopiptanthus mongolicus is an ecologically important species in the arid region of Northwest China. Habitat disturbance can significantly affect plant mating success and ultimately species viability. Pollen limitation of plant reproduction occurs in many plant species, particularly those under habitat disturbance. However, previous investigations have demonstrated differences in pollen limitation between conserved and disturbed sites. We compared the phenology, pollen limitation, pollinators and breeding system of both sites to determine whether habitat disturbance has generated changes in these plant components. We found that the species differed in four aspects. First, blooming duration and flowering peak were longer in the disturbed site than in the conserved site. Second, A. mongolicus can be pollen-limited and pollen limitation was more intense in the conserved site than in the disturbed site. Third, Anthophora uljanini was found to be a frequent pollinator in the conserved site, while Apis mellifera was the most effective and frequent flower visitor. More pollinator visits were recorded in the disturbed site, which could explain the differences in reproductive success. Finally, seed set was higher in the disturbed site than in the conserved site. We found that outcrossing was dominant in both sites and that agamospermy and self-pollination played complementary roles to ensure reproduction. Differences in flower production influenced by artificial selection and pollinator type explain the different seed set in both sites, whereas habitat disturbance cause changes differences in the pollination process and limits pollen flow. The balance between artificial management and mating success is crucial to analysis of the pollination process and manipulation of A. mongolicus population size.

Responses of soil fungal community to the sandy grassland restoration in Horqin Sandy Land, northern China.

Sandy grassland restoration is a vital process including re-structure of soils, restoration of vegetation, and soil functioning in arid and semi-arid regions. Soil fungal community is a complex and critical component of soil functioning and ecological balance due to its roles in organic matter decomposition and nutrient cycling following sandy grassland restoration. In this study, soil fungal community and its relationship with environmental factors were examined along a habitat gradient of sandy grassland restoration: mobile dunes (MD), semi-fixed dunes (SFD), fixed dunes (FD), and grassland (G). It was found that species abundance, richness, and diversity of fungal community increased along with the sandy grassland restoration. The sequences analysis suggested that most of the fungal species (68.4 %) belonged to the phylum of Ascomycota. The three predominant fungal species were Pleospora herbarum, Wickerhamomyces anomalus, and Deconica Montana, accounting for more than one fourth of all the 38 species. Geranomyces variabilis was the subdominant species in MD, Pseudogymnoascus destructans and Mortierella alpine were the subdominant species in SFD, and P. destructans and Fungi incertae sedis were the dominant species in FD and G. The result from redundancy analysis (RDA) and stepwise regression analysis indicated that the vegetation characteristics and soil properties explain a significant proportion of the variation in the fungal community, and aboveground biomass and C:N ratio are the key factors to determine soil fungal community composition during sandy grassland restoration. It was suggested that the restoration of sandy grassland combined with vegetation and soil properties improved the soil fungal diversity. Also, the dominant species was found to be alternative following the restoration of sandy grassland ecosystems.

[Extraction of Adipogenic Secretory Factors: a Comparison Between Adherent Culture and Suspension Culture].

OBJECTIVE: To optimize the extraction method of secretory factors from adipose tissue explant (SFAE) in vitro. METHODS: SFAE were obtained through adherent culture (SFAE-A) and suspension culture (SFAE-S) and concentrated by filtration and centrifugation. The yield of SFAE was compared using BCA protein detection kit. P3 adipose-derived stem cells (ADSCs) were induced with equal amount of SFAE for 7-13 d, before the state of adipogenesis between suspension culture and adherent culture was compared by microscope observation and oil red O staining. RESULTS: The average amount of SFAE yielded from adherent culture and suspension culture did not show significant difference. While the yield of SFAE from suspension culture was consistent at 8. 7 mg per gram of adipose tissue, the adherent culture generated an inconsistent result in the four repeat experiments, ranging from 7. 3 mg to 12. 4 mg per gram of adipose tissue. Moreover, ten more flasks and better distribution were needed for adherent culture to acquire an equal amount of SFAE in comparison with suspension culture. SFAE from both adherent and suspension culture promoted the adipogenesis of P3 adipose-derived stem cells. No differences on the adipogenic effect were found between the two extraction methods. CONCLUSION: Secretory factors from adherent culture and suspension culture have the same adipogenesis effect. Suspension culture can save time and labor. The most important advantage of suspension culture is its stable yield of SFAE.

[Germination and seedling growth of Artemisia halodendron under different incubation environments].

Artemisia halodendron is a dominant species in mobile and semi-mobile dunes of Horqin Sand Land. To investigate the germination character and seedling growth under different temperature and light conditions, the germination rate, germination index and growth of radicle and plumule were measured after treatments in laboratory and heating cabinet incubations. In the laboratory the light and temperature were near to nature condition, while in the heating cabinet it was kept at 25 degrees C with varying durations of light supply, including 24-, 12- and 0-hour light per day. Germination rate (66.6%) and germination index (19.1%) under laboratory condition were both significantly lower than in the heating cabinet (P < 0.05). In the heating cabinet, the germination rate under 0-hour light was 70.2%, which was insignificantly lower (P > 0.05) than under 12- and 24-hour light conditions (both 73.4%), and the germination index under 24-hour light was 28.2%, which was significantly (P < 0.05) lower than under 0- and 12-hour light conditions (31.3% and 30.8%, respectively). Radicle and plumule growth responded to light more readily than the seed germination rate and germination index during the process of germination, and the radicle growth was inhibited by darkness while promoted by light, and the plumule lengths under 0- and 12-hour light conditions were 2.81 cm and 1.51 cm, respectively, significantly higher than under 24-hour light (1.21 cm) and natural condition (1.27 cm). It was concluded that temperature was a main factor in seed germination, and seedling growth was mainly influenced by light regime.

[Effects of environmental factors on litter decomposition in arid and semi-arid regions: A review].

Litter decomposition is one of the important biochemical processes in arid and semi-arid regions, and a key component of regional nutrient turnover and carbon cycling, which is mainly affected by climate, litter quality, and decomposer community. In order to deeply understand the relationships between litter decomposition and environmental factors in arid and semi-arid regions, this paper summarized the research progress in the effects of abiotic factors (soil temperature, precipitation, and ultraviolet-B radiation) and biotic factors (litter quality, soil microbial and animal composition and community structure) on the litter decomposition in these regions. Among the factors, precipitation and ultraviolet-B radiation are considered to be the main limiting factors of litter decomposition. In arid and semi-arid regions, precipitation can significantly increase the litter decomposition rate in a short term, while the photo-degradation induced by ultraviolet-B radiation, due to the strong and long-term radiation, can increase the decomposition rate of terrestrial litter. Litter quality, soil microbial and animal composition and community structure are mainly affected by the type of ecosystems in a long term. However, the affecting mechanisms of these environmental factors on litter decomposition are still not very clear. It was suggested that the future litter ecological research should be paid more attention to the interaction of environmental factors under climate change, the variations of litter decomposition at different spatial scales, and the establishment of litter decomposition models in relation to the synergistic interactions of multiple factors.

[Effects of different afforestation types on soil faunal diversity in Horqin Sand Land].

In order to deeply understand the effects of afforestation on the soil faunal diversity in mobile sand land, an investigation was conducted on the community structure of soil animals in the mobile sand land and its adjacent about 30 years old forest land and shrub land in Hrqin Sand Land. Afforestation on the mobile sand land had remarkable effects on the soil properties, especially the soil environment in shrub land, in which, the soil water content, pH, and nutrient contents were improved. In the three lands investigated, a total of 485 individuals belonging to 11 soil animal groups were collected, among which, Acarina and Collembola were the dominant groups, Corrodentia was the common group, and the others were of rare groups. From the mobile sand land to shrub land to forest land, the soil faunal density decreased, group richness and Shannon index increased, and evenness declined, but no significant differences were observed in these indices among these three lands. It was suggested that afforestation on mobile sand land could improve the soil environment and enhance soil faunal diversity, but there was a limitation to take 30 years old plantations as test objects to investigate the effects of afforestation on soil faunal diversity in mobile sand land.

[Ecological effect of plant root exudates and related affecting factors: a review].

The formation of plant root exudates is a vital physiological phenomenon in the metabolic processes of plant, and an important link of material turnover in "plant-soil" system. To study the plant root exudates is of significance in understanding the matter and energy flow, carbon and nitrogen balance, and improvement of primary production in terrestrial ecosystems. This paper reviewed the ecological effect of plant root exudates, such as the effect on plant physiological processes, soil microorganisms, soil matter turnover, and degradation of soil organic contaminants, and summarized the related affecting factors, including soil heavy metals and nutrient contents, soil moisture, light, and heat conditions, plant gene type, soil microorganisms, and input of exogenous organic contaminants. Based on the present research status of plant root exudates, the future research directions about the objects, methods, and effect assessment were prospected.

[Leaf nitrogen and phosphorus stoichiometry in typical desert and desertified regions, north China].

Characteristics of leaf nitrogen and phosphorus stoichiometry at regional scale is key factors to understand spatial pattern, forecast change trends and reveal responses of terrestrial ecosystem to global change. In this study, pattern of leaf nitrogen and phosphorus of 214 plants was investigated to elucidate their relationships with rainfall and temperature in typical desert and desertified regions of northern China. The results showed that average leaf nitrogen concentration, average leaf phosphorus concentrations, and leaf N/P of 214 species are (24.45 +/- 8.1) mg/g, (1.74 +/- 0. 88) mg/g, 15.77 +/- 7.5 in these regions of northern China, respectively. Compared with other studies at global, national or regional scale, leaf nitrogen and phosphorus concentrations are significantly higher in this study (p < 0.001). However, leaf N/P didn't show any significant differences with other studies. This implies that leaf N/P is generally well-constrained. One-way ANOVA analysis showed that leaf N, P, and N/P varied significantly among trees, shrubs, graminoids, and forbs. Leaf N concentration in shrubs, forbs and leaf P concentration in forbs are averagely higher than those in other life-forms, respectively. This implies that nutrient use strategies are significantly different among plant life-forms. There are no significant differences in leaf nitrogen concentration among each typically desert and desertified region. However, Leaf phosphorus concentration and leaf N/P are significantly different among each typically desert and desertified regions. Leaf phosphorus concentrations are relatively high in Kerqin Sand Land and Mowuso Sand Land. Leaf N/P of most species in Talimu basin, Zhunger Basin, and Alashan is higher than 16, and lower than 14 of most species in Kerqin Sand land. This means that nutrient constraining in different regions varies greatly. Correlations analysis showed that leaf N, P, and N/P are significantly correlated with annual precipitation, but not significantly correlated with annual mean temperature in desert and desertified regions of northern China.

[Community structure and diversity of soil arthropods in naturally restored sandy grasslands after grazing].

Taking the Naiman Desertification Research Station under Chinese Academy of Sciences as a base, an investigation was conducted on the community structure of soil arthropods in the naturally restored sandy grasslands after different intensity grazing disturbance, with the effects of vegetation and soil on this community structure approached. In the non-grazing grassland, soil arthropods were rich in species and more in individuals, and had the highest diversity. In the restored grassland after light grazing, soil arthropods had the lowest evenness and diversity. In the restored grassland after moderate grazing, the individuals of soil arthropods were lesser but the major groups were more, and the evenness and diversity were higher. In the restored grassland after heavy grazing, the individuals of soil arthropods were more but the major groups were lesser, and the diversity was higher. Plant individuals' number, vegetation height and coverage, and soil alkalinity were the main factors affecting the soil arthropod community in naturally restored grasslands after different intensity grazing disturbance. It was implied that after 12-year exclosure of grassland, soil arthropod community could be recovered to some degree, while grazing disturbance had long-term negative effects on the arthropod community.

[Soil condensation water in different habitats in Horqin sandy land: an experimental study].

Weighing method was adopted to study the formation time and the amount of soil condensation water in four habitats (mobile sandy land, fixed sandy land, farmland, and Mongolian pine forest land) in Horqin Sandy Land in August 2007. The soil condensation water began to form at 20:00-22:00, increased gradually at 22:00-4:00, and began to evaporate after 4:00. In the four habitats, soil condensation water was mainly formed in 0-9 cm layer, and the amount was the greatest in 0-3 cm layer, accounting for 40% of the total. The soil condensation water also formed in 9-30 cm layer, but in very small amount. There was a greater difference in the mean daily amount of soil condensation water in 0-3 cm layer in the four habitats, with the sequence of fixed sandy land > mobile sandy land > farmland > Mongolian pine forest land, which indicated that the habitat with better vegetation condition was not benefit the formation of soil condensation water. The mean daily amount of soil condensation water in 0-30 cm layer was 0.172 mm in fixed sandy land, 0.128 mm in Mongolian pine forest land, 0.120 mm in mobile sandy land, and 0.110 mm in farmland.

[Challenge to the desertification reversion in Horqin Sandy Land].

Analyses of the changes in desertified land area, water resource availability, land use, and plant productivity in Horqin Sandy Land in recent 50 years showed that from 1950 to the late 1980s, the land desertification in Horqin Sandy Land had a rapid expansion, but reversed since then. The annual runoff of Xiliaohe River decreased consistently, and in 1999, the middle reach at Tongliao section was dried up. In recent 20 years, the water table of Xihu Lake was decreased by about 10 m, and dried up in 2001. The above-ground biomass of grasslands decreased from 520 g x m(-2) in 1937 to 197 g x m(-2) in 2005. The main cause of these results was the change of land use pattern, i. e., the overuse of water resources for re-vegetation or cropland irrigation. Water resources reduction was the major challenge to the desertification reversion in Horqin Sandy Land.

[Effects of vegetation cover on physical and chemical properties of bio-crust and under-layer soil in Horqin Sand Land].

To understand the effects of different vegetation cover on the bio-crust and its under-layer soil in Horqin Sand Land, the bio-crust and 0-5 cm soil samples in Artemisia frigida, Salix microstachya, Populus simonii, and Pinus sylvestris var. mongolica stands were collected, and their physical and chemical properties were studied. After fifteen years enclosure protection and vegetation establishment, the flowing sand dune in most natural and artificial vegetation sites was covered with bio-crusts. The coverage degree of the crust was 50%-80%, with a thickness of 1-2 cm. In S. microstachya stand, the crust thickness, hardness, and organic matter and nutrient contents were the highest, followed by in P. sylvestris var. mongolica stand, and in A. frigida and A. frigida stands. Moss crust had higher thickness, hardness, and organic matter and nutrient contents than lichen crust. Comparing with those in flowing sand land, the physical and chemical properties of under-layer soil in test stands were improved obviously, the improvement degree being higher under moss crust than under lichen crust, and higher in S. microstachya and P. sylvestris var. mongolica stands than in A. frigida and P. simonii stands. Vegetations with moderate height and rich branches and leaves were more helpful to the development of bio-crust and the improvement of under-layer soil, because they could reduce wind velocity and accumulate more dust and litters, and the development of moss crust was more favorable than lichen crust to the improvement of its under-layer soil.