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In nature some successful invasive plants grow faster and are better chemical defenders than native plants, which appears to contradict the conventional theory that plant growth and chemical defense are trade-offs in terms of the allocation of limited resources. Using greenhouse experiments we compared the growth, chemical defensive matters (condensed tannins and total phenolics) and energy-use strategies (construction cost and energy-use efficiency) of four highly noxious invasive plants to their congeneric or co-occurring native species in subtropical China. We hypothesized that the trade-offs between growth and chemical defense in invasive plants are alleviated, and this alleviation benefits from their high photosynthetic capacities and energy-use strategies. Our results showed that all the four invasive plants grew faster than their native counterparts, and three of them had higher condensed tannins and the remaining one had higher total phenolics, indicating the invasive plants achieved both faster growth and stronger chemical defense. Moreover, the growth rate positively related to condensed tannins but negatively to total phenolics in both invasive and native plants, indicating the chemical-specific pattern of the trade-offs. Our results demonstrate that the higher photosynthetic capacity and energy-use efficiency together with lower biomass construction cost facilitated the faster growth and stronger chemical defense in invasive plants, providing an insight for their chemical-specific trade-offs between growth and chemical defense.

Context The majority of ecological studies of roads have focused on their deleterious effects, and these preconceptions have hampered a full evaluation of the ecological functions of roads. As an integrated indicator, road width represents comprehensive effects, including anthropogenic and natural disturbances. Objectives We try to explore the different effects produced by various road widths by considering changes in forest vegetation and soil. Methods We selected six study forests spanning from Shandong Province in the north to Guangdong Province in the south of China, and we assessed the influences of wide and narrow roads on plant species diversity, biomass, and soil properties along transects running from the forest edges and adjacent forest interior. We used a “shape-dependent model” to explain the factors that determine the magnitude of road effects on forests. Results Three variables measured in this study changed significantly with increasing distance from the road to the forest interior along wide roads: tree biomass, herbaceous plant biomass, and soil pH. However, no measurable biological or environmental effects were found from narrow roads. The different shapes of glades in a forest may be one reason for the various effects caused by roads of different widths. Conclusions Forest roads of different widths may have quite different ecological effects. While wider roads with large glades tend to have substantial negative impacts, small-enough roads may cause little disturbance to the forest. This suggests that not all forest roads should be perceived as the same, and narrow roads may be compatible with forest conservation.

This study aims to verify the time-variant feature of American ginseng (AG) continuous cropping obstacles and to explore the factors impeding continuous cropping. We verified the feature with a plant-soil feedback pot experiment and then investigated the factors by comparing the properties of control soils that had not been previously used for growing ginseng (CS) with those of soils with a 10-year-crop-rotation cycle following the growth of AG (RS). It’s found that the survival rate of AG in RS was lower than that in CS. The RS had lower pH, available potassium content, and urease activity. Additionally, p-coumaric, p-hydroxybenzoic, vanillic, caffeic, and cinnamic acid levels were lower in RS than in CS, but salicylic acid levels showed the opposite pattern. RS had higher Rhodanobacter and lower Acidothermus, Sphingomonas relative abundances in bacterial community. It’s also found that many bacteria were substantially correlated with phenolic acids and soil physiochemical properties. Results indicate that even after 10-year crop rotation, the negative effects of prior continuous cropping of AG has not been eliminated. The growth of AG can be affected negatively with deterioration of soil physicochemical properties and with lower levels of phenolic acids which promote pathogen reproduction. Probiotics reduction also weighs. Moreover, biotic factors are interrelated with abiotic ones. Therefore, it can be inferred that the comprehensive change of soil properties is the main obstacle for continuous cropping.

Changes in resource availability can alter plant growth, the influence of plants on soil characteristics, and, ultimately, plant–soil feedback (PSF). Previous studies often show that invasive plants can outperform native plants under high but not low resource conditions. However, it remains unclear whether under low resource conditions, invaders can outperform natives in the long term by generating more positive or less negative PSFs. Using three non-native invasive and three non-invasive native annual Asteraceae plants, we conducted a two-phase pot experiment, where in the first, conditioning generation plants were grown to induce changes in soil characteristics, and in the second, bioassay generation plants were regrown to evaluate how they respond to these soils. Half of the pots received a nutrient addition treatment in the conditioning generation. We found significant species-specific effects of conditioning on most of the soil characteristics, and some soil characteristics were significantly correlated with bioassay generation biomass of a subset of species, but neither species nor invasive or native status affected bioassay generation biomass. All invasive species generated neutral PSFs across soil nutrient conditions. The native Emilia sonchifolia tended to condition the soil that favored its own growth more than others, and under low nutrient conditions, the native Eclipta prostrata conditioned the soil that disfavored its own growth more than others. These results indicate that invaders may not outperform natives through PSFs under low resource conditions, and increasing resource availability may change the types of PSFs for some native but not invasive plants.

L., an exotic plant that is widely distributed in China, is harmful to native ecosystems; however, little is known about its effects on soil microbial communities. Therefore, we investigated the effects of R. typhina on soil bacterial communities by 16S rRNA gene sequencing and compared the effects of R. typhina and native (Rhus chinensis Mill.) and non-invasive exotic species (Amorpha fruticosa L. and Robinia pseudoacacia L.) on soil bacterial communities via a greenhouse experiment. R. typhina decreased the diversity of the soil bacterial community compared with R. chinensis, and A. fruticosa. R. typhina soil was characterized by more Actinobacteria and lesser Proteobacteria and Acidobacteria than the other soils. Among Actinobacteria members, there was a difference in the relative abundance of Nocardioides and Streptomyces, and this could be advantageous for the growth of R. typhina. However, there was no significant difference in the soil bacterial community structure associated with R. typhina and other species. Moreover, the concentrations of total carbon, potassium, and nitrate were found to be the major soil factors influencing the relative abundance of soil bacteria.

Due to increasing globalization and human disturbance, plant invasion has become a worldwide concern. Soil characteristics associated with the vegetation of recipient communities affect plant invasion success to a great extent. However, the relative importance of soil biotic and abiotic factors of different recipient communities in resisting plant invasion is not fully understood. We hypothesized that natural forest soils can better resist plant invasion than can plantation soils, that the allelopathic legacy of resident trees in soil plays a role in resisting invasive plants, and that late-successional soils have a strong effect. We examined the effects of soil and litter collected from four natural forests at successional stages and one Robinia pseudoacacia Linn. plantation in eastern China on the growth of Phytolacca americana L., which is a highly invasive species across China, and explored the individual effects of soil nutrients, allelochemicals, and soil microbes. We found that allelopathic activity of natural forest soils can effectively resist P. americana invasion, and that low level of nutrients, especially of phosphorus, in the soils might be potential limiting factors for the plant growth. The profound conditioning of soil resources by exotic R. pseudoacacia based on tree traits (including allelopathy) facilitated further P. americana invasion. Allelochemicals from forest litter inhibited the germination of P. americana seeds, but pH played a major role in P. americana growth when these substances entered the soil. However, we have no evidence that late-successional forest soils exhibit strong allelopathy toward P. americana. The present study will help to further our understanding of the mechanism of community resistance to invasion.

Exotic plant invasion alters the structure and coverage of terrestrial vegetation and affects the carbon (C) stocks in ecosystems. Previous studies have shown the increases in the C stocks with increasing invasive plants, but these results remain contentious. Soil microbial communities are usually altered by plant invasion, which potentially influences the C cycling underground. We hypothesized that the plant invasion-caused dynamic changes in soil microbes would lead to the corresponding change in soil C accumulation. Using greenhouse experiments we simulated different invader intensities through varying the relative abundance of invasive species Mikania micrantha and its co-occurring native species Paederia scandens. By analyzing 13C-phospholipid fatty acid we found the invasive M. micrantha assimilated more 13C and transferred faster the fixed 13C through different tissues to soils, as compared to native P. scandens. Soil microbial components, i.e., i15:0, 16:0, 10Me16:0, 18:1w9c and 18:2w6,9 were mainly using the photo-assimilated 13C. In addition, we found a hump-shaped relationship between soil net 13C accumulate rate and rhizosphere microbial biomass, indicating that the soil C accumulation may be either enhanced or reduced in invaded ecosystems, depending on microbe abundance.