Effects of Allelochemicals, Soil Enzyme Activities, and Environmental Factors on Rhizosphere Soil Microbial Community of Stellera chamaejasme L. along a Growth-Coverage Gradient

Allelochemicals released from the root of Stellera chamaejasme L. into rhizosphere soil are an important factor for its invasion of natural grasslands. The aim of this study is to explore the interactions among allelochemicals, soil physicochemical properties, soil enzyme activities, and the rhizosphere soil microbial communities of S. chamaejasme along a growth-coverage gradient. High-throughput sequencing was used to determine the microbial composition of the rhizosphere soil sample, and high-performance liquid chromatography was used to detect allelopathic substances. The main fungal phyla in the rhizosphere soil with a growth coverage of 0% was Basidiomycetes, and the other sample plots were Ascomycetes. Proteobacteria and Acidobacteria were the dominant bacterial phyla in all sites. RDA analysis showed that neochamaejasmin B, chamaechromone, and dihydrodaphnetin B were positively correlated with Ascomycota and Glomeromycota and negatively correlated with Basidiomycota. Neochamaejasmin B and chamaechromone were positively correlated with Proteobacteria and Actinobacteria and negatively correlated with Acidobacteria and Planctomycetes. Allelochemicals, soil physicochemical properties, and enzyme activity affected the composition and diversity of the rhizosphere soil microbial community to some extent. When the growth coverage of S. chamaejasme reached the primary stage, it had the greatest impact on soil physicochemical properties and enzyme activities.

Spatial Distribution and Influencing Factors of Soil Fungi in a Degraded Alpine Meadow Invaded by Stellera chamaejasme

Alpine meadow degradation causes a notable decrease in palatable grasses and an increase in forbs and toxic plants in recent decades. Stellera chamaejasme is one of the most serious toxic weeds, which exerts an increasing threat on alpine meadow in Qinghai–Tibetan Plateau. Combined DNA sequencing with geostatistics was applied to analyze a typical degraded meadow invaded by S. chamaejasme in Qinghai Province, China. The study aimed to determine the spatial variation of soil fungi and its interrelationship with the plant–soil environment. Alpha diversity and relative abundance of fungal phyla and classes showed moderate or strong spatial dependency and were structured in patches of 19–318 m, and taxonomic composition exhibited much higher spatial variability than alpha diversity. Compared to plant cover, the matching of patch size showed a closer spatial link between soil properties and fungal community. Community coverage, SOM, TN, TP, and TK positively correlated to fungal diversity and taxonomic composition; no direct correlation was found between S. chamaejasme coverage and fungal community. The result suggested significant but weak association between plant–soil properties and soil fungal community at local scale. Patchy pattern of S. chamaejasme may disturb spatial variations of soil properties and fungal community, since S. chamaejasme in higher coverage corresponded to lower TK content, which contributed to a decrease in fungal diversity indirectly.

Biogeographic Patterns of Leaf Stoichiometry and Adaption Strategy of Stellera Chamaejasme L. in Degraded Grasslands Across Northern China

Background: Plant leaf stoichiometry reflect its adaptations to environments. Leaf stoichiometry variations across different environments have been extensively studied among grassland plants, but little is known about intraspecific leaf stoichiometry, especially for widely distributed species, such as Stellera chamaejasme L. We present the first study on the leaf stoichiometry of S. chamaejasme, and evaluate their relationships with environmental variables by collecting S. chamaejasme leaf and soil samples from 29 invaded sites in the two plateaus of distinct environments [the Inner Mongolian Plateau (IM) and Qinghai-Tibet Plateau (QT)] in Northern China. Leaf C, N, P, and K and their stoichiometric ratios, and soil physicochemical properties were determined, together with climate information from each sampling sites. Results: Results showed that mean leaf C, N, P, and K concentrations were 498.60, 19.95, 2.15, and 6.57 g · kg-1, respectively; the C/N, C/P, and N/P ratios were 25.46, 246.22, and 9.84, respectively. Soil physicochemical properties of S. chamaejasme invaded area varied wildly, and few significant correlations between S. chamaejasme leaf ecological stoichiometry and soil physicochemical properties were observed. Except for C and N in leaves, the P and K had higher homeostasis than 1, between 4.17 and 13.21. Moreover, C and N content of S. chamaejasme leaves were unaffected by any climate factors. However, the correlation between leaf P and climate factors was significant in IM only, while leaf K in QT. Finally, partial least squares path modeling suggested that leaf P or leaf K were affected by different mechanisms in QT and IM regions. Conclusions: Our results indicated that S. chamaejasme tend to be insensitive to variation in soil nutrient availability, resulting in their broad distributions in China grasslands. Moreover, S. chamaejasme adapt to changing environments by adjusting its relationships with climate or soil factors to improve their chances of survival and spread in degraded grasslands.

A new brood-pollination mutualism between Stellera chamaejasme and flower thrips Frankliniella intonsa

Background Brood pollination mutualism is a special type of plant-pollinator interaction in which adult insects pollinate plants, and the plants provide breeding sites for the insects as a reward. To manifest such a mutualism between Stellera chamaejasme and flower thrips of Frankliniella intonsa, the study tested the mutualistic association of the thrips life cycle with the plant flowering phenology and determined the pollination effectiveness of adult thrips and their relative contribution to the host’s fitness by experimental pollinator manipulation. Results The adult thrips of F. intonsa, along with some long-tongue Lepidoptera, could serve as efficient pollinators of the host S. chamaejasme. The thrips preferentially foraged half-flowering inflorescences of the plants and oviposited in floral tubes. The floral longevity was 11.8 ± 0.55 (mean ± se) days, which might precisely accommodate the thrips life cycle from spawning to prepupation. The exclusion of adult thrips from foraging flowers led to a significant decrease in the fitness (i.e., seed set) of host plants, with a corresponding reduction in thrips fecundity (i.e., larva no.) in the flowers. Conclusions The thrips of F. intonsa and the host S. chamaejasme mutualistically interact to contribute to each other’s fitness such that the thrips pollinate host plants and, as a reward, the plants provide the insects with brooding sites and food, indicating the coevolution of the thrips life cycle and the reproductive traits (e.g., floral longevity and morphology) of S. chamaejasme.

Study on Gas Chromatographic Fingerprint of Essential Oil from Stellera Chamaejasme Flowers and Its Repellent Activities against Three Stored Product Insects

The objective of this study was to establish the chromatographic fingerprints of the essential oil (EO) from Stellera chamaejasme flowers collected from various natural sites by gas chromatography (GC) combined with chemometric methods. The EO was obtained by hydrodistillation, and its chemical composition was analyzed by gas chromatography−mass spectrometry (GC−MS). Most components were identified as ketones and the relatively high-content components were fitone (38.973%), n-hentriacontane (5.807%), myristic acid (4.944%) and phytol (3.988%). In addition, the repellent activities of the EO from S. chamaejasme flowers and its four main chemical compounds were evaluated against three stored product pests (Tribolium castaneum, Lasioderma serricorne, Liposcelis bostrychophila) for the first time. In this work, the EO and the four chemical compounds showed a repellent effect against three storage pests after 2 and 4 h exposure. The experimental method and repellent activity of S. chamaejasme flower EO could provide a basis for the development of botanical pesticide and the utilization of the rich plant resources of S. chamaejasme in the future.

Leaf Elemental Stoichiometry of Stellera Chamaejasme L. in Response to Environmental Factors in Degraded Grasslands Across Northern China

Plant leaf stoichiometry reflect its adaptations to environments. Leaf stoichiometry variations across different environments have been extensively studied among grassland plants, but little is known about intraspecific leaf stoichiometry, especially for widely distributed species, such as Stellera chamaejasme L. In order to evaluate the biogeographical drivers for leaf elemental stoichiometry in S. chamaejasme, leaf and soil samples were collected from 29 invaded sites in the two plateaus of distinct environments [the Inner Mongolian Plateau (IM) and Qinghai-Tibet Plateau (QT)] in Northern China. Leaf C, N, P, and K and their stoichiometric ratios, and soil physicochemical properties were determined. Results showed that mean leaf C, N, P, and K concentrations were 498.60, 19.95, 2.15, and 6.57 g kg-1, respectively; the C/N, C/P, and N/P ratios were 25.46, 246.22, and 9.84, respectively. Only leaf K was significantly different between the two environments studied. Soil physicochemical properties of S. chamaejasme invaded area varied wildly, suggesting this wide ranging species tend to be insensitive to variation in soil nutrient availability. C and N content of S. chamaejasme leaves were unaffected by any environmental factors. However, the stoichiometric homeostasis of P and K was observed. The correlation between leaf P and climate factors was significant only in IM, while leaf K was significantly related to climate factors only in QT. Partial least squares path modeling suggested that soil exerted a significant effect on LP and climate affected leaf P and K both directly and indirectly in QT, while LP appeared to be limited mainly by climatic factors via direct ways and LK was not affected significantly by any environmental factors in IM. This study evaluated the S. chamaejasme leaf elemental stoichiometry and their relationships with environmental variables, which can help understand the plant biogeographic patterns and adaption strategy in degraded grasslands in China.

Soil Microbial Differences under Unpalatable Stellera Chamaejasme and Neighboring Palatable Elymus Nutans in Alpine Meadows

Stellera chamaejasme L. is a fast-spreading unpalatable poisonous plant that grows in the alpine grasslands of the Qinghai-Tibetan Plateau (QTP). The impacts of unpalatable plant species spread on animal health and plant community have been well studied, but studies into their effects on belowground organisms and processes are rare. We carried out a soil metabarcoding study using Illumina MiSeq sequencing to investigate whether the soil bacteria and fungi communities of Stellera are different to the soil microbiome of neighboring palatable grass Elymus nutans Griseb. Total carbon and nitrogen, the ratio of carbon to nitrogen, ammonium nitrogen, and microbial biomass carbon were all significantly greater in Stellera soil compared to Elymus soil, while no significant differences were observed for gravimetric soil moisture, pH or nitrate nitrogen. There were no significant differences in bacterial and fungal abundance between Stellera and Elymus soil. The bacterial species richness was significantly lower in Stellera soil but no significant difference was observed for fungal species richness. The beta diversity and community composition of bacteria and fungi were markedly different between soils. The presence of bacterial phyla Actinobacteria and Verrucomicrobia, and fungal phyla, Basidiomycota and Glomeromycota, were significantly greater under Stellera soil. This study demonstrated that the spread of undesirable unpalatable plants can potentially disrupt existing plant-soil-microbe associations with potential consequences for grassland soil biodiversity and ecosystem functioning.