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This study was conducted to examine the effects of clipping and nutrient addition on plant traits of a dominant perennial forb species, Heteropappus altaicus (Willd.) Novopokr. (Compositae), at both the individual and population levels in a temperate steppe in northern China. A nested experimental design was used with clipping as the main factor and nutrient, including nitrogen (N), phosphorus (P) and both, addition as the second factor. The main effect of clipping reduced plant height, aboveground biomass (AGB) per plant, and pollen production per floret by 15.8, 34.3, 28.0% (all p < 0.05), respectively, but enhanced reproductive allocation and population density by 8 and 28.2% (both p < 0.05), respectively, suggesting contrary effects of clipping on H. altaicus traits at the individual and population levels. N addition significantly stimulated plant height, AGB per plant, reproductive allocation, pollen diameter, and pistil length, but decreased population density. The main effects of P addition also stimulated the plant traits at individual level, but did not change population traits. The significant interactions of clipping and nitrogen addition were observed on AGB per plant, pollen production, and population density. The differential responses of H. altaicus at the individual and population levels to clipping and nutrient addition indicate that the future dynamics of H. altaicus in the temperate steppe are uncertain and need long-term research to demonstrate. [ABSTRACT FROM AUTHOR]

Knowing the responses of arbuscular mycorrhizal (AM) fungi to warming and increased precipitation are critical for understanding how biodiversity is maintained and how the ecosystem functions under global climate-change scenarios in natural ecosystems. In this study, AM fungal communities were examined in a 6 year experiment with warming and increased precipitation, in a semiarid steppe in northern China. Only the increased precipitation, regardless of warming, significantly increased AM fungal extra-radical hyphal density, compared with the control treatment. AM fungal spore density was significantly increased by the combination of warming and increased precipitation, and increased precipitation-only treatments, but not by warming alone. A total of 36 operational taxonomic units (OTUs) of AM fungi were recovered by 454 pyrosequencing of 18S rDNA. Only increased precipitation, regardless of warming, significantly decreased AM fungal OTU richness and Shannon diversity index, and yet significantly increased AM fungal Bray-Curtis dissimilarity index, compared with the control treatment. AM fungal community composition was significantly affected by increased precipitation via water availability, but not by warming. Our findings demonstrated that the AM fungal community responded more strongly to water availability than to warming in the semiarid steppe ecosystem. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal fungi (AMF) play key roles in supporting ecosystem sustainability, stability and function, but little is known about how fertilization practices affect AMF abundance and community composition in the grassland ecosystems. In the present study, a field trial was established to examine the effects of 6 years of nitrogen (N) and phosphorus (P) fertilization on the community structure of AMF both in soils and plant roots in a typical temperate steppe in Inner Mongolia, northern China. The AMF small-subunit (SSU) rRNA genes were subjected to PCR, cloning, sequencing, and phylogenetic analyses. A total of 1554 sequenced SSU rRNA clones, including 919 clones from the soil and 635 clones from the roots, were analyzed. The 31 AMF sequence types belonging to Glomeromycota were identified: 17 to Glomus group A and 14 to Glomus group B. The experimental results indicated that N fertilization significantly altered the AMF communities in both soils and mixed roots but had no obvious influence on AMF abundance. However, P fertilization showed no significant influence on the AMF community structure, but induced a significant decrease in mycorrhizal colonization rate, arbuscule colonization and hyphal length density. Furthermore, N and P application showed significant interactions in affecting AMF species compositions in soils but not in roots. Generally the AMF diversity in the soil was higher than that in the roots. The study suggested that N fertilization predominantly altered AMF species composition, while P fertilization influenced AMF abundance in this steppe. [ABSTRACT FROM AUTHOR]