Community assembly mechanisms and succession processes significantly differ among treatments during the restoration of Stipa grandis - Leymus chinensis communities.

Understanding community assembly mechanisms is helpful to predict community dynamics. To explore which community assembly mechanism(s) drive(s) the grassland restoration in semi-arid region, we investigated the relationships between plant trait and species relative abundance (SRA), and estimated community functional diversity indices for each community under different treatments (enclosure, grazing and mowing treatment) in a restoration region of Stipa grandis - Leymus chinensis communities in the northern China from 2010 to 2012. There was a high fraction of significant relationships between trait value and SRA, suggesting that niche theory structured the grassland restoration in this region. The functional richness was higher and the functional divergence was lower in the enclosure community than that in the grazing or mowing community, and significantly positive plant height - SRA relationship was found in the enclosure community. These findings demonstrated that limiting similarity based on niche theory was more important in structuring the enclosure community and that environmental filtering based on niche theory played a more important role in driving the grazing or mowing community. Only the factor of year significantly affected the functional evenness (FEve), and the lowest FEve in 2011 implied that the relatively lower precipitation could enhance the effect of limiting similarity on community assembly in the semi-arid grassland.

Litter species diversity is more important than genotypic diversity of dominant grass species Stipa grandis in influencing litter decomposition in a bare field.

Studies have indicated that plant litter diversity can affect litter decomposition at both species diversity and genotypic diversity level within a species. However, the essence and relative importance of these two diversity levels on litter decomposition remain unknown. Here, two independent one-factor experiments, litter species diversity and litter genotypic diversity of the dominant species-Stipa grandis, were carried out to explore the effects of initial litter quality, litter composition and diversity on decomposition of mass, nitrogen (N), carbon (C) and phosphorus (P) simultaneously. The results showed that: (1) there were significant relationships between the initial litter N, C/N, lignin/N and the decomposition rate of N, between the initial litter P, N/P and the decomposition rate of P, and the litter composition significantly influenced litter mass, N, C and P remaining in both litter species and genotypic diversity experiments; and (2) litter species diversity significantly affected litter mass, N, C and P remaining, and non-additive relative mixture effects were mainly contributed by synergistic effects especially in 6-species mixtures; however, similar patterns were not found in litter genotypic diversity experiment. The present results emphasized that initial litter quality played the most important role in influencing litter decomposition of mass N, C and P, and suggested that litter species mixtures rather than litter genotypic mixtures of a dominant species could favor nutrient cycling in ecosystem of the semi-arid Inner Mongolia Steppe of China.

Effects of Epichlo endophytes of Achnatherum sibiricum on spore germination of arbuscular mycorrhizal fungi.

Endophytic fungi and arbuscular mycorrhizal (AM) fungi are important components of grassland ecosystem. Endophytes can reduce colonization rates of their host plants by AM fungi. In this study, Achnatherum sibiricum, infected by Epichlo sibiricum (Es) or E. gansuensis (Eg), was adopted as experimental material. The effect of Epichlo endophyte culture filtrate, root exudates and aqueous extracts from the leaves (including fresh and dead leaves) on the spore germination rates of AM fungi (Glomus mosseae and Glomus etunicatum) were evaluated. The results showed that culture filtration of Epichlo endophyte significantly inhibited the germination rate of AM fungi spores. Root exudates of infected plants only significantly inhibited the germination of G. etunicatum spores, and such effect was not related to the endophytic species. The leaf aqueous extracts had no significant effect on the germination rate of G. mosseae spores. Only the aqueous extract of Es-infected dead leaves significantly reduced the spore germination rate of G. etunicatum. In natural ecosystem, Epichlo endophytes are normally internally hosted in plants, which may affect the spore germination of AM fungi by affecting the root exudates of the host plants.

Phenotypic plasticity vs. local adaptation in quantitative traits differences of Stipa grandis in semi-arid steppe, China.

Whether plants are able to adapt to environmental changes depends on their genetic characteristics and phenotypic plastic responses. We investigated the phenotypic responses of 7 populations of an important dominant species in semi-arid steppe of China - Stipa grandis, and then distinguished which adaptive mechanism(s), phenotypic plasticity or local adaptation, was/were involved in this species to adapt to environmental changes. (1) All traits were significantly influenced by the interaction of population and growth condition and by population in each condition, and inter-population variability (CVinter) was larger in the field than in the common garden for 8/9 traits, indicating that both phenotypic plasticity and genetic differentiation controlled the phenotypic differences of S. grandis. (2) From a functional standpoint, the significant relationships between the values of traits in the common garden and the environmental variables in their original habitats couldn't support local habitat adaptation of these traits. (3) Low CVintra, low quantitative differentiation among populations (Q ST ), and low plasticity shown in the western populations indicated the very low adaptive potential of S. grandis to environmental changes. (4) From the original habitats to the common garden which is far away from S. grandis distribution region, positive phenotypic responses were found in several populations, indicating that some original habitats have become unfavorable for S. grandis.

[Effects of methyl jasmonate treatments and endophyte infection on growth of Achnatherum sibiricum].

We used Achnatherum sibiricum, a native grass as test material and application of methyl jasmonate (MJ) to simulate herbivory, and compared the growth and physiological characters of endophyte-infected (EI) and endophyte-free (EF) plants. The results showed that MJ treatment significantly decreased the shoot growth, but significantly increased the concentrations of defensive substances such as total phenolic and lignin, and decreased the size of aphid population. Endophyte infection significantly increased the tiller number, total phenolic and lignin contents in the shoot. As for shoot biomass and total phenolic in the root, they were affected by MJ treatment. Without MJ treatment, no significant differences were found in shoot biomass or root phenolic content whether the plants were infected by endophyte or not. With MJ treatment, the shoot biomass was significantly lower and the shoot phenolic content was significantly higher in EI plants than in EF plants. Endophyte infection significantly increased resistance of the host plant to aphids, and the beneficial effect was enhanced by MJ treatments, after three applications with MJ, there were no aphids on EI plants. Overall, endophyte infection could alter the allocation pattern of the host plant between growth and defense, and MJ treatments further strengthened the defensive ability of the host plant at the cost of growth.

A tracer liquid image velocimetry for multi-layer radial flow in bioreactors.

BACKGROUND: This paper presents a Tracer Liquid Image Velocimetry (TLIV) for multi-layer radial flow in bioreactors used for cells cultivation of tissue engineering. The goal of this approach is to use simple devices to get good measuring precision, specialized for the case in which the uniform level of fluid shear stress was required while fluid velocity varied smoothly. METHODS: Compared to the widely used Particles Image Velocimetry (PIV), this method adopted a bit of liquid as tracer, without the need of laser source. Sub-pixel positioning algorithm was used to overcome the adverse effects of the tracer liquid deformation. In addition, a neighborhood smoothing algorithm was used to restrict the measurement perturbation caused by diffusion. Experiments were carried out in a parallel plates flow chamber. And mathematical models of the flow chamber and Computational Fluid Dynamics (CFD) simulation were separately employed to validate the measurement precision of TLIV. RESULTS: The mean relative error between the simulated and measured data can be less than 2%, while in similar validations using PIV, the error was around 8.8%. CONCLUSIONS: TLIV avoided the contradiction between the particles' visibility and following performance with tested fluid, which is difficult to overcome in PIV. And TLIV is easier to popularize for its simple experimental condition and low cost.

Diversity and taxonomy of endophytes from Leymus chinensis in the Inner Mongolia steppe of China.

Epichloë species and their anamorphic relatives in genus Neotyphodium are fungal symbionts of grasses ubiquitously existing in temperate regions all over the world. To date, 13 Epichloë species and 22 Neotyphodium species have been formally described, based on morphological characters and phylogenetic analyses. Leymus chinensis (Poaceae) is a dominant grass native to the Inner Mongolia steppe of China. Previously, it was reported to harbor endophytes, but little was known about these endophytes. To investigate their diversity and taxonomy, 96 fungal isolates were obtained from three field populations of L. chinensis. The isolates were classified into three morphotypes based on morphological characters and phylogenetic analyses of sequences of genes for ß-tubulin (tubB), translation elongation factor 1-α (tefA), and actin (actG). The dominant morphotype, morphotype I, was identified as a choke disease endophyte, Epichloë bromicola. This broadened the host range and phylogenetic definition of E. bromicola.

Potential antagonistic effects of nine natural fatty acids against Meloidogyne incognita.

Fatty acids, the essential components of life, were widely present in various seed cakes, gutter oil, and other resources. The objective of this study was to evaluate the potential antagonistic effects of nine fatty acids (FAs) against Meloidogyne incognita (root-knot nematodes). The results showed that butyric, caprylic, capric, lauric, myristic, palmitic, and oleic acids significantly reduced M. incognita reproduction, whereas cucumber (Cucumus sativus) biomass was not adversely affected by the tested FAs and was even significantly increased in several fatty acids treatments. All nine tested fatty acids showed apparent inhibitory effects on egg hatching on day 21, especially capric acid with which the hatching rate was reduced to 15.8% as compared to that using sterile distilled water. Caproic, caprylic, capric, lauric, myristic, and palmitic acids caused significantly higher mortality of the second-stage juvenile of M. incognita than the other three FAs, and both caprylic and capric acids resulted in approximately 50% mortality (2000 µmol/L) after a 24 h exposure. In conclusion, fatty acids showed the nematicidal effect differently, among which capric acid showed a strong nematicidal effect and might be a powerful active substance for integrated M. incognita management. Given the general nematicidal properties of FAs, farmers might utilize waste resources, such as oil seed cake, gutter oil, etc., containing various FAs or use pure FAs for effective M. incognita management.

[Features of calcium crystals and calcium components in 54 plant species in salinized habitats of Tianjin].

Plant calcium (Ca) is composed of dissociated Ca2+ and easily soluble, slightly soluble, and hard soluble combined Ca salts. The hard soluble Ca salts can often engender Ca crystals. To understand the Ca status in different growth form plants in salinized habitats, 54 plant species were sampled from the salinized habitats in Tianjin, with the Ca crystals examined by microscope and the Ca components determined by sequential fractionation procedure. More Ca crystals were found in 38 of the 54 plant species. In 37 of the 38 plant species, drusy and prismatic Ca oxalate crystals dominated, whereas the cystolith of Ca carbonate crystal only appeared in the leaves of Ficus carica of Moraceae. The statistics according to growth form suggested that deciduous arbors and shrubs had more Ca oxalate crystal, liana had lesser Ca oxalate crystal, and herbs and evergreen arbors had no Ca oxalate crystal. From arbor, shrub, liana to herb, the concentration of HCl-soluble Ca decreased gradually, while that of water soluble Ca was in adverse. The concentration of water soluble Ca in herbs was significantly higher than that in arbors and shrubs. This study showed that in salinized habitats, plant Ca crystals and Ca components differed with plant growth form, and the Ca oxalate in deciduous arbors and shrubs played an important role in withstanding salt stress.

[Effects of root-knot nematodes on cucumber leaf N and P contents, soil pH, and soil enzyme activities].

A pot experiment was conducted to study the effects of inoculation with root-knot nematodes on the cucumber leaf N and P contents, and the rhizospheric and non-rhizospheric soil pH and enzyme activities. The rhizospheric soil pH didn't have a significant decrease until the inoculation rate reached 6000 eggs per plant. With the increase of inoculation rate, the leaf N and P contents, rhizospheric soil peroxidase activity, and rhizospheric and non-rhizospheric soil polyphenol oxidase activity all decreased gradually, rhizospheric soil catalase activity was in adverse, non-rhizospheric soil pH decreased after an initial increase, and non-rhizospheric soil catalase activity had no regular change. After inoculation, rhizospheric soil urease activity decreased significantly, but rhizospheric and non-rhizospheric soil phosphatase activity and non-rhizospheric soil peroxidase activity only had a significant decrease under high inoculation rate. In most cases, there existed significant correlations between rhizospheric soil pH, enzyme activities, and leaf N and P contents; and in some cases, there existed significant correlations between non-rhizospheric soil pH, enzyme activities, and leaf N and P contents.

[Characteristics of Stipa grandis growth and reproductive biomass allocation at different hill position of Xilingol grassland, Inner Mongolia].

An investigation was conducted on the vegetative and reproductive biomass allocation of Stipa grandis at the hill-top and hill-foot of Xilingol grassland, and relatedness- and factor analyses were made to study the effects of hill position on the S. grandis seed biomass. Significant differences were observed in the vegetative and reproductive growth of S. grandis plants at the hill-top and hill-foot. At hill-foot, the height and number of non-flowering S. grandis ramets increased by 24.69% and 35.37%, respectively, the number of flowering ramets increased by 102.97%, the vegetative, reproductive, and total biomass increased by 44.14%, 95.59% and 47.45%, respectively, and the 100-grain mass increased by 25.00%, as compared with those at hill-top. The seed biomass of S. grandis at hill-top was mainly affected by soil moisture content, while that at hill-foot was mainly affected by soil pH. Hill position induced the differentiation of soil moisture and N contents, and made the S. grandis at the fertile hill-foot allocating more energy to its sexual reproduction.

Taxonomy, diversity and origins of symbiotic endophytes of Achnatherum sibiricum in the Inner Mongolia Steppe of China.

We sampled five Achnatherum sibiricum populations and documented the distribution and abundance of endophytes. In total, 438 fungal isolates were obtained. They were classified into 11 morphotypes based on growth rate and morphological characters including colonial morphology, the production of conidiogenous cells, conidial size and dimension on potato dextrose agar medium. Both tub2 and actG sequences identified only a single product in all representative isolates from three dominant morphotypes. All sequences fell in the same main clade, including Neotyphodium gansuense and Neotyphodium gansuense var. inebrians from another Achnatherum species in North China, Achnatherum inebrians, and Neotyphodium guerinii from European grasses Melica ciliate and Melica transsilvanica. Based on both morphological and phylogenetic analyses, isolates in morphotype I were described as representing a novel Neotyphodium species, Neotyphodium sibiricum sp. nov. Isolates in both morphotype II and III were identified as representing N. gansuense. Both tub2 and actG sequences suggested that N. sibiricum and N. guerinii were probably derived from a common Epichloë ancestor.

Ethylene evolution changes in tilted Fraxinus mandshurica Rupr. var. japonica maxim. seedlings in relation to tension wood formation.

The effects of ethylene on tension wood formation were studied in 3-year-old Fraxinus mandshurica Rupr. var. japonica Maxim. seedlings in two separate experiments. In experiment 1, ethylene evolution of buds and stems was measured using gas chromatography after 0, 2, 4, 7, 14, and 21 d of treatment; in experiment 2, both aminoethoxyvinylglycine (AVG) and AgNO3 were applied to the horizontally-placed stems, and the cell numbers on sites of applications were measured after 40 d. Ethylene evolution from buds was found to be much greater in tilted seedlings than in upright ones. The cell numbers of wood fibers in shoots and 1-year-old stems were reduced in treatments with 12.5 x 10(-7)micromol/L AVG, 12.5 x 10(-8)micromol/L AVG, and 11.8 x 10(-8)micromol/L AgNO3; whereas the horizontal and vertical diameters were reduced by treatment of 12.5 x 10(-7)micromol/L AVG. Ethylene evolutions of shoots and 1-year-old stems were inhibited greatly in comparison with the control by applying 12.5 x 10(-7)micromol/L AVG. The formation of a gelatinous layer of wood fibers was affected by neither AVG nor AgNO3 application. These results suggest that ethylene regulates the quantity of wood production, but does not affect G-layer formation in F. mandshurica Rupr. var. japonica Maxim. seedlings.

Influence of nitrogen fertilizer and endophyte infection on ecophysiological parameters and mineral element content of perennial ryegrass.

An experiment was designed to determine the effect of the fungal endophyte Neotyphodium lolii on the growth, physiological parameters and mineral element content of perennial ryegrass (Lolium perennel L.), when growing at two N supply levels. Endophyte infection had a significant positive effect on both shoot and root growth of ryegrass, but this difference was only significant in the high N supply treatment. At high N supply, endophyte-infected (EI) plants accumulated more soluble sugar in the sheath and the root than endophyte-free (EF) plants. Endophyte infection affected mineral element concentrations in the root more than in the shoot. We found a significant effect of endophyte infection on B, Mn and Mg in the root, but significant effect was only found on B in the shoot. EI plants tended to accumulate less B in the shoot at both N levels, but accumulated more B, Mn and Mg in the root at low N levels. The difference of growth parameters in different periods was significant. The content of soluble sugar and crude protein in the sheath were also dependent on the growth stages of both EI and EF plants.

Genetic diversity and population differentiation of the dominant species Stipa krylovii in the Inner Mongolia Steppe.

Random amplified polymorphic DNA was used to assess the level of genetic diversity and genetic structure of Stipa krylovii (Gramineae), an important dominant species in the northern grasslands of China. Genetic diversity was low within S. krylovii populations, and diversity at the population level was associated with precipitation and cumulative temperature variations. There was much genetic differentiation among populations and among habitats as well. A Mantel test indicated no significant correlation between genetic distance and geographic distance of populations. A nonmetric multidimensional scaling analysis revealed some spatial relationships among the 90 individuals in a two-dimensional plot. Habitat fragmentation and degradation throughout the geographic range of S. krylovii could account for the low genetic diversity and high genetic differentiation of the species. Such information will be useful for conservation managers trying to plan an effective strategy to protect this important species.

Heavy metal accumulation of urban domestic rubbish compost in turfgrass by EDTA chelating.

Seven kinds of heavy metal accumulation of rubbish compost in turfgrass by EDTA chelating were investigated. With EDTA application, heavy metal accumulation by two species of turfgrass was increased significantly. The enrichment coefficients of Lolium perenne L(L) and Festuca arundinacea L(F) to Cr reached 9.45 and 6.15 respectively. In the range of EDTA dosages given, heavy metal accumulation in turfgrass increased with increasing EDTA level. There were significant differences in remediation of different metals by applying EDTA. L had high ability to accumulate Cr, Cd, Ni and Zn, showing better remediation to heavy metals of rubbish compost. In contrast, F showed high ability to accumulate Cr, Ni, Cu and Zn. Low EDTA level increased aboveground net primary production (ANP) of turfgrass, but EDTA would considerably inhibit it when EDTA was higher than 20 mmol/kg. The results demonstrated that the optimum dosage of EDTA for remediating heavy metals in rubbish compost by turfgrass was between 10 mmol/kg and 20 mmol/kg.