Epichloë endophytes can improve the resistance of host grasses to pathogenic fungi in grasslands. However, little is known about the mechanisms involved. We investigated the mechanisms underlying the effect of Epichloë sibirica on the resistance of Achnatherum sibiricum to Curvularia lunata by metabolomics approaches. The results demonstrated that before and after pathogen inoculation, 58 and 157 differential metabolites (DMs) were respectively induced by endophytes. Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses of DMs showed that amino acids and phenols were mostly accumulated by endophytic infection. Integrated transcriptome and metabolomics KEGG analysis revealed that plant hormone signal transduction was significantly enriched. After measurement, we found that endophytic infection increased jasmonic acid (JA) concentration before pathogen inoculation and increased ethylene (ET) and pipecolic acid concentration after pathogen inoculation. Exogenous phytohormones treatment verified that endophytes improved the disease resistance of A. sibiricum by promoting JA and ET accumulation. In phenylpropanoid synthetic pathway, the endophytes promoted the accumulation of ferulic acid, p-coumaroylagmatine, and feruloylputrescine which was related to resistance against plant disease. Overall, our research suggests that Epichloë endophytes presumably trigger induced systemic resistance of the hosts to pathogenic fungi via activating JA/ET signaling pathways and promoted antimicrobial phenol accumulation in hosts.

Understanding community restoration state and the corresponding assembly mechanism is helpful to assess the restoration measures and predict community dynamics. We collected plots by shrub cover (low, medium and high) in three Caragana mircophylla shrub-encroached grasslands which were fenced since 1979, 1983, and 2003 (fencing duration) in the northern China, to explore the effect of fencing duration and shrub cover on the community restoration by vegetation investigation and phylogenetic approach. There were significant differences in community composition among different fencing duration or shrub cover treatments. Species richness in the site of fencing since 1979 or in the plots of high shrub cover was relatively higher than that in any other sites or plots. By phylogenetic analysis, functional traits were phylogenetically convergent. Based on the standardized effect sizes of mean pairwise distance (SESMPD) ranged from -1.96 to 1.96 in six out of nine plots, which suggested that stochastic processes dominated community assembly. SESMPD were lower than -1.96 in the rest three plots which indicated that competitive exclusion drove community assembly. These results indicated that the increase of fencing duration or shrub cover could enhance competitive exclusion. The present findings highlighted the importance of shrub in influencing the community composition and community assembly, supporting that shrub-encroached grassland is another stable state in the semi-arid northern China. Therefore, it is essential to distinct shrub-encroached grassland from degraded grasslands when formulating relevant conservation and management measures in the semi-arid regions.

Aims How plant-plant interactions vary with the changes of biotic and abiotic factors has debated for a long time among ecologists. The aim of this study was to explore how different neighbors influenced the responses of the intensity and importance of competition on Stipa grandis and S. krylovii to the change of soil nutrition condition. Methods The seedlings of the target species, S. grandis and S. krylovii, were grow alone and in two-species mixtures with different neighbors under two soil nutrition treatments. For each target species, we measured the biomass, root: shoot ratio, intensity and importance of competition and nutrition-addition effect. Important Findings We founded that the competition responses were mediated by the identities of neighbors and target species. (1) When in mixture with Leymus chinensis, both intensity and importance of competition negatively increased with the increase of soil nutrition. The competition importance was significantly negative on S. grandis under both soil nutrition treatments and on S. krylovii under the high soil nutrition treatment, supporting Grime’s theory. (2) When in S. grandis – S. krylovii mixture system, the competition inhibition decreased while competition importance showed no significant effects on both target species with the increase of soil nutrition, indicating competitive reduction. (3) When in mixture with Agropyron cristatum, the competition intensity significantly influenced by the interaction between target species and soil nutrition, suggesting competitive change along the soil nutrition gradient. The competition importance was significantly negative on S. grandis under the low soil nutrition treatment and on S. krylovii under the high soil nutrition treatment. Ultimately, our results demonstrate that the identities of both target and neighbor species influenced the responses of intensity and importance of competition to the change of soil nutrition condition. Several mechanisms potentially contributed to these different competition effects on different target species.

Understanding community assembly mechanism is essential for us to predict community dynamics and restoration process in the context of intensive human activities. In this study, we aimed to explore how the removal of shrub canopy influenced the community assembly in shrub-encroached grassland by both trait-based and phylogenetic approaches. We carried out an experiment of shrub canopy removal with three frequencies (no removal, removal once and twice a year) in a shrub-encroached grassland in China. We investigated community species composition under each treatment and collected plant functional traits for each species. We calculated the standard effect size (SES) of phylogenetic and trait-based functional diversity based on null model analysis to determine the dominant community assembly process. By phylogenetic analysis, the random process drove the community assembly, being independent of the removal frequencies and locations; while by trait-based approach, random process dominated the assembly in communities under ‘no removal’ treatment beneath shrub and under ‘removal twice a year’ treatment in shrub-interspace when using some certain single traits, and the limiting similarity process dominated the assembly in the rest communities. Removal of shrub canopy twice a year released more niches which promoted the performance of herbaceous species beneath shrub and promoted the settlement of annuals in shrub-interspace. Compared with phylogenetic analysis, the results of trait-based approach were more sensitive to the human activities. All these findings indicated that removal of shrub canopy twice a year would be an effective way for the restoration of shrub-encroached grassland.