Epichloë Endophyte Enhanced Insect Resistance of Host Grass Leymus Chinensis by Affecting Volatile Organic Compound Emissions.

In plant-herbivore interactions, plant volatile organic compounds (VOCs) play an important role in anti-herbivore defense. Grasses and Epichloë endophytes often form defensive mutualistic symbioses. Most Epichloë species produce alkaloids to protect hosts from herbivores, but there is no strong evidence that endophytes can affect the insect resistance of their hosts by altering VOC emissions. In this study, a native dominant grass, sheepgrass (Leymus chinensis), and its herbivore, oriental migratory locust (Locusta migratoria), were used as experimental materials. We studied the effect of endophyte-associated VOC emissions on the insect resistance of L. chinensis. The results showed that endophyte infection enhanced insect resistance of the host, and locusts preferred the odor of endophyte-free (EF) leaves to that of endophyte-infected (EI) leaves. We determined the VOC profile of L. chinensis using gas chromatography-mass spectrometry (GC-MS), and found that endophyte infection decreased the pentadecane (an alkane) emission from uneaten plants, and increased the nonanal (an aldehyde) emission from eaten plants. The olfactory response experiment showed that locusts were attracted by high concentration of pentadecane, while repelled by high concentration of nonanal, indicating that Epichloë endophytes may increase locust resistance of L. chinensis by decreasing pentadecane while increasing nonanal emission. Our results suggest that endophytes can induce VOC-mediated defense in hosts in addition to producing alkaloids, contributing to a better understanding the endophyte-plant-herbivore interactions.

Infection by Endophytic Epichloë sibirica Was Associated with Activation of Defense Hormone Signal Transduction Pathways and Enhanced Pathogen Resistance in the Grass Achnatherum sibiricum.

Epichloë endophytes can improve the resistance of host grasses to pathogenic fungi, but the underlying mechanisms remain largely unknown. Here, we used phytohormone quantifications, gene expression analysis, and pathogenicity experiments to investigate the effect of Epichloë sibirica on the resistance of Achnatherum sibiricum to Curvularia lunata pathogens. Comparison of gene expression patterns between endophyte-infected and endophyte-free leaves revealed that endophyte infection was associated with significant induction of 1,758 and 765 differentially expressed genes in the host before and after pathogen inoculation, respectively. Functional analysis of the differentially expressed genes suggested that endophyte infection could activate the constitutive resistance of the host by increasing photosynthesis, enhancing the ability to scavenge reactive oxygen species, and actively regulating the expression of genes with function related to disease resistance. We found that endophyte infection was associated with induction of the expression of genes involved in the biosynthesis pathways of jasmonic acid, ethylene, and pipecolic acid and amplified the defense response of the jasmonic acid/ethylene co-regulated EIN/ERF1 transduction pathway and Pip-mediated TGA transduction pathway. Phytohormone quantifications showed that endophyte infection was associated with significant accumulation of jasmonic acid, ethylene, and pipecolic acid after pathogen inoculation. Exogenous phytohormone treatments confirmed that the disease index of plants was negatively related to both jasmonic acid and ethylene concentrations. Our results demonstrate that endophyte infection can not only improve the constitutive resistance of the host to phytopathogens before pathogen inoculation but also be associated with enhanced systemic resistance of the host to necrotrophs after C. lunata inoculation.

Aptamer-Engineered Natural Killer Cells for Cell-Specific Adaptive Immunotherapy.

Natural killer (NK) cells are a key component of the innate immune system as they can attack cancer cells without prior sensitization. However, due to lack of cell-specific receptors, NK cells are not innately able to perform targeted cancer immunotherapy. Aptamers are short single-stranded oligonucleotides that specifically recognize their targets with high affinity in a similar manner to antibodies. To render NK cells with target-specificity, synthetic CD30-specific aptamers are anchored on cell surfaces to produce aptamer-engineered NK cells (ApEn-NK) without genetic alteration or cell damage. Under surface-anchored aptamer guidance, ApEn-NK specifically bind to CD30-expressing lymphoma cells but do not react to off-target cells. The resulting specific cell binding of ApEn-NK triggers higher apoptosis/death rates of lymphoma cells compared to parental NK cells. Additionally, experiments with primary human NK cells demonstrate the potential of ApEn-NK to specifically target and kill lymphoma cells, thus presenting a potential new approach for targeted immunotherapy by NK cells.

Self-Assembled Aptamer-Nanomedicine for Targeted Chemotherapy and Gene Therapy.

Chemotherapy is the mainstream treatment of anaplastic large cell lymphoma (ALCL). However, chemotherapy can cause severe adverse effects in patients because it is not ALCL-specific. In this study, a multifunctional aptamer-nanomedicine (Apt-NMed) achieving targeted chemotherapy and gene therapy of ALCL is developed. Apt-NMed is formulated by self-assembly of synthetic oligonucleotides containing CD30-specific aptamer and anaplastic lymphoma kinase (ALK)-specific siRNA followed by self-loading of the chemotherapeutic drug doxorubicin (DOX). Apt-NMed exhibits a well-defined nanostructure (diameter 59 mm) and stability in human serum. Under aptamer guidance, Apt-NMed specifically binds and internalizes targeted ALCL cells. Intracellular delivery of Apt-NMed triggers rapid DOX release for targeted ALCL chemotherapy and intracellular delivery of the ALK-specific siRNA induced ALK oncogene silencing, resulting in combined therapeutic effects. Animal model studies reveal that upon systemic administration, Apt-NMed specifically targets and selectively accumulates in ALCL tumor site, but does not react with off-target tumors in the same xenograft mouse. Importantly, Apt-NMed not only induces significantly higher inhibition in ALCL tumor growth, but also causes fewer or no side effects in treated mice compared to free DOX. Moreover, Apt-NMed treatment markedly improves the survival rate of treated mice, opening a new avenue for precision treatment of ALCL.

Both evenness and dominant species identity have effects on litter decomposition.

Exploring how interactions between species evenness and dominant species identity affect litter decomposition processes is vital to understanding the relationship between biodiversity and ecosystem functioning in the context of global changes. We carried out a 127-day litter decomposition experiment under controlled conditions, with interactions of four species evenness types (high, medium, low and single species) and three dominant species identity (Leymus chinensis, Serratula centauroides, Artemisia capillaris). After collecting the remaining litter, we estimated how evenness and dominant species identity affected litter mass loss rate, carbon (C) loss rate, nitrogen (N) loss rate and remaining litter C/N directly or indirectly, and assessed relative mixture effects (RMEs) on litter mass loss. The main results are shown as follows. (1) By generalized linear models, litter mass loss rate was significantly affected by evenness after 69-day decomposition; N loss rate was affected by dominant species identity after 69-day decomposition, with treatment dominated by Serratula centauroides being at least 9.26% higher than that dominated by any of other species; and remaining litter C/N was affected by the interactions between evenness and dominant species identity after 30-, 69- and 127-day decomposition. (2) Twenty-three out of 27 RMEs were additive, and dominant species identity showed a significant effect on RMEs after 127-day decomposition. (3) By confirmatory path analyses, litter mass loss rate was affected by dominant species identity directly after 127-day decomposition, and by both species evenness and dominant species identity indirectly which was mediated by initial litter functional dispersion (FDis) after 30- and 69-day decomposition; remaining litter C/N was affected by evenness indirectly which was mediated by initial litter FDis after 127-day decomposition. These findings highlight the importance of evenness and dominant species identity on litter decomposition. The study provides insights into communities during retrogressive successions in semi-arid grasslands in the context of global changes.

An ultra pH-sensitive and aptamer-equipped nanoscale drug-delivery system for selective killing of tumor cells.

Nanotechnology has often been applied in the development of targeted drug-delivery systems for the treatment of cancer. An ideal nanoscale system for drug delivery should be able to selectively deliver and rapidly release the carried therapeutic drug(s) in cancer cells and, more importantly, not react to off-target cells so as to eliminate unwanted toxicity on normal tissues. To reach this goal, a selective chemotherapeutic is formulated using a hollow gold nanosphere (HAuNS) equipped with a biomarker-specific aptamer (Apt), and loaded with the chemotherapy drug doxorubicin (DOX). The formed Apt-HAuNS-Dox, approximately 42 nm in diameter, specifically binds to lymphoma tumor cells and does not react to control cells that do not express the biomarker. Through aptamer-mediated selective cell binding, the Apt-HAuNS-Dox is internalized exclusively into the targeted tumor cells, and then released the DOX intracellularly. Of note, although the formed Apt-HAuNS-Dox is stable under normal biological conditions (pH 7.4), it appears ultrasensitive to pH change and rapidly releases 80% of the loaded DOX within 2 h at pH 5.0, a condition seen in cell lysosomes. Functional assays using cell mixtures show that the Apt-HAuNS-Dox selectively kills lymphoma tumor cells, but has no effect on the growth of the off-target cells in the same cultures, indicating that this ultra pH-sensitive Apt-HAuNS-Dox can selectively treat cancer through specific aptamer guidance, and will have minimal side effects on normal tissue.

Biostable ssDNA aptamers specific for Hodgkin lymphoma.

As a "chemical antibody", oligonucleotide aptamers can specifically bind to their target molecules. However, clinical potential of aptamers in disease diagnosis is not yet fully explored. Using a tumor cell-based selection protocol, we developed single-stranded DNA aptamers for Hodgkin lymphoma (HL) tumor cells. The aptamers specifically bound to HL cells with a high affinity, reaching maximal cell binding at 10 nM final concentration. Importantly, the aptamers were able to selectively detect HL cells and did not react to other tumor or blood cells in mixed samples, indicating that the aptamers can be used as a specific probe for in vitro analysis of HL cells. Moreover, due to the inherent properties of DNA, the aptamers were stable in human serum, suggesting potential for in vivo detection of HL tumor cells.

Intraspecific trait variation and adaptability of Stipa krylovii: Insight from a common garden experiment with two soil moisture treatments.

Understanding patterns of intraspecific trait variation can help us understand plant adaptability to environmental changes. To explore the underlying adaptation mechanisms of zonal plant species, we selected seven populations of Stipa krylovii, a dominant species in the Inner Mongolia Steppe of China, and evaluated the effects of phenotypic plasticity and genetic differentiation, the effects of climate variables on population trait differentiation, and traits coordinated patterns under each soil moisture treatment. We selected seeds from seven populations of S. krylovii in the Inner Mongolia Steppe, China, and carried out a soil moisture (2) × population origin (7) common garden experiment at Tianjin City, China, and measured ten plant traits of S. krylovii. General linear analyses were used to analyze how soil moisture and population origin affected each trait variation, Mantel tests were used to analyze population trait differentiation-geographic distance (or climatic difference) relationships, regression analyses were used to evaluate trait-climatic variable relationships, and plant trait networks (PTNs) were used to evaluate traits coordinated patterns. Both soil moisture and population origin showed significant effects on most of traits. Aboveground biomass, root-shoot ratio, leaf width, specific leaf area, and leaf nitrogen (N) content were significantly correlated with climate variables under the control condition. Specific leaf area and leaf N content were significantly correlated with climate variables under the drought condition. By PTNs, the hub trait(s) was plant height under the control condition and were aboveground biomass, root length, and specific leaf area under the drought condition. This study indicates that both phenotypic plasticity and genetic differentiation can significantly affect the adaptability of S. krylovii. In addition, soil moisture treatments show significant effects on trait-climate relationships and traits coordinated patterns. These findings provide new insights into the adaptive mechanisms of zonal species in the semiarid grassland region.

Endophytic infection increases the belowground over-yielding effects of the host grass community mainly by increasing the complementary effects.

Introduction: Increases in plant species diversity may increase the community diversity effect and produce community over-yielding. Epichloë endophytes, as symbiotic microorganisms, are also capable of regulating plant communities, but their effects on community diversity effects are often overlooked. Methods: In this experiment, we investigated the effects of endophytes on the diversity effects of host plant community biomass by constructing artificial communities with 1-species monocultures and 2- and 4-species mixtures of endophyte-infected (E+) and endophyte-free (E-) Achnatherum sibiricum and three common plants in its native habitat, which were potted in live and sterilized soil. Results and discussion: The results showed that endophyte infection significantly increased the belowground biomass and abundance of Cleistogenes squarrosa, marginally significantly increased the abundance of Stipa grandis and significantly increased the community diversity (evenness) of the 4-species mixtures. Endophyte infection also significantly increased the over-yielding effects on belowground biomass of the 4-species mixtures in the live soil, and the increase in diversity effects on belowground biomass was mainly due to the endophyte significantly increasing the complementary effects on belowground biomass. The effects of soil microorganisms on the diversity effects on belowground biomass of the 4-species mixtures were mainly derived from their influences on the complementary effects. The effects of endophytes and soil microorganisms on the diversity effects on belowground biomass of the 4-species communities were independent, and both contributed similarly to the complementary effects on belowground biomass. The finding that endophyte infection promotes belowground over-yielding in live soil at higher levels of species diversity suggests that endophytes may be one of the factors contributing to the positive relationship between species diversity and productivity and explains the stable co-existence of endophyte-infected Achnatherum sibiricum with a variety of plants in the Inner Mongolian grasslands.

The relative importance of drought stress and neighbor richness on plant-plant interactions shifts over a short time.

Exploring how plant-plant interactions between species and their neighbors vary with biotic and abiotic factors is vital to understanding community assembly mechanisms in the context of global changes. In this study, using a dominant species (Leymus chinensis (Trin.) Tzvel.) in the semiarid Inner Mongolia steppe as the target species and ten other species as neighbors, we carried out a microcosm experiment to evaluate how drought stress, neighbor richness and season affected the relative neighbor effect (Cint) (the ability to reduce growth of target species). The factor of season interactively affected the effect of drought stress or neighbor richness on Cint. In the summer, drought stress decreased Cint directly and indirectly by decreasing SLA hierarchical distance and neighbor biomass. In the subsequent spring, drought stress increased Cint, and neighbor richness increased Cint directly and indirectly by increasing neighbor community functional dispersion (FDis) and neighbor biomass. Specifically, SLA hierarchical distance was positively associated with neighbor biomass, while height hierarchical distance was negatively associated with neighbor biomass in both seasons, which increased Cint. These findings show that the relative importance of drought stress and neighbor richness on Cint shifted over seasons, which provides strong empirical evidence of how plant-plant interactions respond to changes in biotic and abiotic factors in the semiarid Inner Mongolia steppe over a short-term time. Furthermore, this study provides novel insight into community assembly mechanisms in the context of climatic aridity and biodiversity loss in semiarid regions.

Comparative Research on Metabolites of Different Species of Epichloë Endophytes and Their Host Achnatherum sibiricum.

Achnatherum sibiricum can be infected by two species of fungal endophytes, Epichloë gansuensis (Eg) and Epichloë sibirica (Es). In this study, the metabolites of Eg, Es, and their infected plants were studied by GC−MS analysis. The results showed that the metabolic profiles of Eg and Es were similar in general, and only six differential metabolites were detected. The direct effect of endophyte infection on the metabolites in A. sibiricum was that endophyte-infected plants could produce mannitol, which was not present in uninfected plants. Epichloë infection indirectly caused an increase in the soluble sugars in A. sibiricum related to growth and metabolites related to the defense against pathogens and herbivores, such as α-tocopherol, α-linolenic acid and aromatic amino acids. Epichloë infection could regulate galactose metabolism, starch and sucrose metabolism, tyrosine metabolism and phenylalanine metabolism of host grass. In addition, there was a significant positive correlation in the metabolite contents between the endophyte and the host.

Soil moisture and species richness interactively affect multiple ecosystem functions in a microcosm experiment of simulated shrub encroached grasslands.

Understanding relationships between biodiversity and ecosystem functions (BEF) and the way in which ecosystem functions respond to changing climatic conditions or community composition is useful for predicting ecological consequences of global changes. However, how soil moisture condition, plant species richness interactively affect ecosystem functions in shrub-encroached grasslands is poorly understood. We conducted a soil moisture × species richness microcosm experiment using semi-arid grassland species with a N-fixing shrub Caragana microphylla Lam. as the dominant species to evaluate how soil moisture and plant species richness affected ecosystem functions directly or indirectly via regulating community functional structure, such as community-weighted mean values (CWM) and functional dispersion (FDis). Soil moisture and species richness interactively affected soil functions (soil C-, N-, P cycles and soil multifunctionality), with greater species richness buffering the adverse effects of soil drought. Soil moisture and species richness showed opposite effects on FDis but similar effects on CWM. FDis mediated the indirect effect of soil moisture and species richness on ecosystem functions, while CWM only mediated the indirect effect of soil moisture. More specifically, both soil moisture and plant species richness were negatively associated with soil P cycle, and the CWMPC1 contributed by traits related to resource-conservative strategy was positively associated with soil N cycle. Species richness showed a positive direct effect on total shoot biomass, which was mainly contributed by the complementarity effect of neighbor species richness. This study provides strong empirical support of how biomass and soil nutrient cycles respond to the changes of soil moisture and plant species richness in C. microphylla shrub-encroached grasslands, and insights on the mechanisms underlying the interactive effects of soil condition and community species composition on multiple ecosystem functions in N-fixing shrub encroached grasslands in semi-arid grassland regions.

Intraspecific more than interspecific diversity plays an important role on Inner Mongolia grassland ecosystem functions: A microcosm experiment.

Biodiversity changes in terrestrial communities continue in the context of global changes. However, the interactive effects of the changes in diversity at inter- and intraspecific levels as well as cascading effects from plant to soil microorganisms on ecosystem functioning under climate changes remains largely unexplored. Using grassland species in the semi-arid Inner Mongolia Steppe, we conducted a microcosm experiment to assess how drought treatment (non-drought and drought conditions), species diversity (2, 4, and 7 species) and genotypic diversity of the dominant species Leymus chinensis (1, 3, and 6 genotypes) affected ecosystem functions directly or indirectly via regulating plant community functional structure [community-weighted mean (CWM) and functional dispersion (FDis)] and soil microbial diversity (Shannon-Wiener index). Drought treatment, species and genotypic diversity significantly and interactively affected soil N, P cycle and soil multifunctionality as well as soil microbial diversity. Drought treatment significantly affected biomass, soil C cycle, CWM and soil microbial diversity. Species diversity significantly affected soil N cycle, CWM and FDis, and genotypic diversity significantly affected all soil functions and soil microbial diversity. CWM regulated the responses of all ecosystem functions except soil N cycle to the changes in soil moisture and species diversity, which supports the mass ratio hypothesis. The cascading effect from genotypic diversity to soil microbial diversity was significant on belowground biomass but not on any of the other ecosystem functions observed in this study. These findings highlight the importance of genotypic diversity of the dominant species L. chinensis in affecting belowground ecosystem functioning as well as soil microbial diversity, which should not be ignored for grassland protection and management. This study provides further insights into biodiversity and ecosystem functioning mechanisms in semi-arid grasslands in the context of global climate changes.

A nanocomplex that is both tumor cell-selective and cancer gene-specific for anaplastic large cell lymphoma.

BACKGROUND: Many in vitro studies have demonstrated that silencing of cancerous genes by siRNAs is a potential therapeutic approach for blocking tumor growth. However, siRNAs are not cell type-selective, cannot specifically target tumor cells, and therefore have limited in vivo application for siRNA-mediated gene therapy. RESULTS: In this study, we tested a functional RNA nanocomplex which exclusively targets and affects human anaplastic large cell lymphoma (ALCL) by taking advantage of the abnormal expression of CD30, a unique surface biomarker, and the anaplastic lymphoma kinase (ALK) gene in lymphoma cells. The nanocomplexes were formulated by incorporating both ALK siRNA and a RNA-based CD30 aptamer probe onto nano-sized polyethyleneimine-citrate carriers. To minimize potential cytotoxicity, the individual components of the nanocomplexes were used at sub-cytotoxic concentrations. Dynamic light scattering showed that formed nanocomplexes were ~140 nm in diameter and remained stable for more than 24 hours in culture medium. Cell binding assays revealed that CD30 aptamer probes selectively targeted nanocomplexes to ALCL cells, and confocal fluorescence microscopy confirmed intracellular delivery of the nanocomplex. Cell transfection analysis showed that nanocomplexes silenced genes in an ALCL cell type-selective fashion. Moreover, exposure of ALCL cells to nanocomplexes carrying both ALK siRNAs and CD30 RNA aptamers specifically silenced ALK gene expression, leading to growth arrest and apoptosis. CONCLUSIONS: Taken together, our findings indicate that this functional RNA nanocomplex is both tumor cell type-selective and cancer gene-specific for ALCL cells.

A direct comparison of the effects and mechanisms between species richness and genotype richness in a dominant species on multiple ecosystem functions.

Both species (interspecific) richness and genotype (intraspecific) richness of dominant species have significant effects on ecosystem functioning directly or indirectly by regulating plant community functional structure. However, the similarities and differences of the effects between inter- and intraspecific levels are poorly understood. In this study, we selected the main species in the semi-arid Eurasian typical steppe as study objects and simultaneously carried out a species richness experiment and a genotype richness experiment of Stipa grandis which is one of the dominant species in this region. We investigated how plants at each of the two richness levels affected multiple ecosystem functions (biomass, soil C, N and P cycles) directly and indirectly by regulating community functional structure, including community-weighted mean trait values (CWM) and functional dispersion (FDis). Both species richness and genotype richness showed significant direct effects on soil P cycle, and FDis significantly mediated the responses of aboveground biomass and soil N cycle to the changes of species richness and the response of belowground biomass to the changes of genotype richness in S. grandis. CWM showed significant effects on biomass in the species richness experiment and soil nutrient cycles in the genotype richness experiment, independently of the levels of plant richness. These findings provide experimental insights of intraspecific richness effects into the relationships between biodiversity and ecosystem functioning, and highlight the importance of conserving the intraspecific diversity of dominant species in the semi-arid steppe regions.

Using oligonucleotide aptamer probes for immunostaining of formalin-fixed and paraffin-embedded tissues.

For tissue immunostaining, antibodies are currently the only clinically validated and commercially available probes. Aptamers, which belong to a class of small molecule ligands composed of short single-stranded oligonucleotides, have emerged as probes over the last several decades; however, their potential clinical value has not yet been fully explored. Using cultured cells and an RNA-based CD30 aptamer, we recently demonstrated that the synthetic aptamer is useful as a specific probe for flow cytometric detection of CD30-expressing lymphoma cells. In this study, we further validated the use of this aptamer probe for immunostaining of formalin-fixed and paraffin-embedded lymphoma tissues. Using CD30 antibody as a standard control, we demonstrated that the synthetic CD30 aptamer specifically recognized and immunostained tumor cells of classical Hodgkin lymphoma and anaplastic large cell lymphoma, but did not react with background cells within tumor sites. Notably, the CD30 aptamer probe optimally immunostained lymphoma cells with lower temperature antigen retrieval (37 vs 96°C for antibody) and shorter probing reaction times (20 vs 90 min for antibody) than typical antibody immunostaining protocols. In addition, the CD30 aptamer probe showed no nonspecific background staining of cell debris in necrotic tissue and exhibited no cross-reaction to tissues that do not express CD30, as confirmed by a standard CD30 antibody staining. Therefore, our findings indicate that the synthetic oligonucleotide CD30 aptamer can be used as a probe for immunostaining of fixed tissue sections for disease diagnosis.

Using an RNA aptamer probe for flow cytometry detection of CD30-expressing lymphoma cells.

Aptamers are small molecular ligands composed of short oligonucleotides that bind targets with high affinity. In contrast to antibodies, as synthetic oligonucleotides, aptamers have lower production costs and elicit no antigenic reactions. Therefore, aptamers are potential agents for disease diagnosis and treatment. In this study, we validate a fluorescently labeled RNA aptamer, which has been reported to bind specifically to mouse CD30 proteins in solution, for human CD30 protein recognition on intact cells. The aptamer probe was tested with cultured anaplastic large cell lymphoma and Hodgkin's lymphoma cells that express high levels of CD30. Flow cytometry and fluorescence microscopy showed specific and sensitive binding of the aptamer probe to CD30-expressing lymphoma cells at low concentrations (0.3 nM). Studies performed on multiple cell lines and nuclear cells from healthy donors confirmed that the CD30 aptamer and anti-CD30 antibody, the standard clinical probe, recognized the same set of cells. The potential application of multicolor flow cytometry analysis using the CD30 aptamer probe and antibodies was also shown. In conclusion, the developed CD30 aptamer probe could act as a replacement and/or a supplement for antibodies in the diagnosis of the CD30-expressing lymphomas.

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.

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.

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.