2019-03, Feng, Yanhao, Fouqueray, Timothée Donatien, van Kleunen, Mark

1.Darwin's naturalisation hypothesis posing that phylogenetic distance of alien species to native residents predicts invasion success, and Elton's diversity‐invasibility hypothesis posing that diversity of native communities confers resistance to invasion, are both rooted in ideas of species coexistence. Because the two hypotheses are inherently linked, the mechanisms underlying them may interact in driving the invasion success. Even so, these links and interactions have not been explicitly disentangled in one experimental study before.
2.To disentangle the links between the two hypotheses, we used 36 native grassland herbs to create greenhouse mesocosms with 90 grassland communities of different diversities, and introduced each of five herbaceous alien species as seeds and seedlings. We used phylogeny and four functional traits (plant height, specific leaf area, leaf size, seed mass) to calculate different measures of phylogenetic and functional distance and diversity. Specifically, we tested how the alien‐native distance (phylogenetic or functional) and the native diversity (phylogenetic or functional) affected each other in their effects on germination, seedling survival, growth and reproduction of the aliens.
3.Overall, our results supported both hypotheses. Multivariate functional distance based on four traits jointly had stronger positive effects than phylogenetic distance and the univariate ones based on each trait separately. Moreover, the aliens were more successful if they were more competitive by being taller and having larger leaves with a lower SLA than the native residents. Univariate functional diversity based on each trait separately had stronger negative effects than phylogenetic and multivariate functional diversity. Most importantly, we found that the effects of alien‐native phylogenetic and multivariate functional distance became stronger as diversity increased. Our analyses with single traits also showed that the strength of the effects of both alien‐native hierarchical functional distances (indicative of competitive inequalities) and absolute functional distances (indicative of niche differences) increased at higher diversities, where competition is more severe.
4.SynthesisOur study explicitly demonstrates for the first time how the mechanisms underlying the two classical invasion hypotheses interact in driving invasion success in grassland communities. This may help to explain some of the puzzling results of studies testing either of the two hypotheses.

2016, Liu, Yanjie, Dawson, Wayne, Prati, Daniel, Haeuser, Emily Sutton, Feng, Yanhao, van Kleunen, Mark

It is frequently assumed that phenotypic plasticity can be very advantageous for plants, because it may increase environmental tolerance (fitness homeostasis). This should, however, only hold for plastic responses that are adaptive, i.e. increase fitness. Numerous studies have shown shade-induced increases in specific leaf area (SLA), and there is wide consensus that this plastic response optimizes light capture and thus has to be adaptive. However, it has rarely been tested whether this is really the case.

2014, Feng, Yanhao, van Kleunen, Mark

Background and Aims
Recent studies have suggested that responses to shading gradients may play an important role in establishment success of exotic plants, but hitherto few studies have tested this. Therefore, a common-garden experiment was conducted using multiple Asian woody plant species that were introduced to Europe >100 years ago in order to test whether naturalized and non-naturalized species differ in their responses to shading. Specifically, a test was carried out to determine whether naturalized exotic woody species maintained better growth under shaded conditions, and whether they expressed greater (morphological and physiological) adaptive plasticity in response to shading, relative to non-naturalized species.

Methods
Nineteen naturalized and 19 non-naturalized exotic woody species were grown under five light levels ranging from 100 to 7 % of ambient light. For all plants, growth performance (i.e. biomass), morphological and CO2 assimilation characteristics were measured. For the CO2 assimilation characteristics, CO2 assimilation rate was measured at 1200 μmol m–2 s–1 (i.e. saturated light intensity, A1200), 50 μmol m–2 s–1 (i.e. low light intensity, A50) and 0 μmol m–2 s–1 (A0, i.e. dark respiration).

Key Results
Overall, the naturalized and non-naturalized species did not differ greatly in biomass production and measured morphological and CO2 assimilation characteristics across the light gradient. However, it was found that naturalized species grew taller and reduced total leaf area more than non-naturalized species in response to shading. It was also found that naturalized species were more capable of maintaining a high CO2 assimilation rate at low light intensity (A50) when grown under shading.

Conclusions
The results indicate that there is no clear evidence that the naturalized species possess a superior response to shading over non-naturalized species, at least not at the early stage of their growth. However, the higher CO2 assimilation capacity of the naturalized species under low-light conditions might facilitate early growth and survival, and thereby ultimately favour their initial population establishment over the non-naturalized species.

2016-11, Feng, Yanhao, Maurel, Noelie, Wang, Zhiheng, Ning, Lei, Yu, Fei-Hai, van Kleunen, Mark

Aim:
A major challenge in ecology is to understand how multiple causal factors, which may interact, drive success of non-native plants in new ranges. In this study we addressed the role of introduction history, climatic suitability, native range size, species traits and their interactions in the establishment of Chinese woody species in Europe.

Location:
China (native range), Europe (new range).

Methods:
We tested whether establishment of 449 Chinese woody species in Europe was associated with residence time (time since earliest planting), planting frequency, climatic suitability, native range size and species traits. We also considered possible nonlinear effects and interactions among these variables. For the 38 species that have established in Europe, we further tested whether these variables and interactions explained their establishment in multiple European countries.

Results:
Establishment of the 449 species in Europe was positively associated with residence time, planting frequency and climatic suitability. Except residence time, these factors were also positively associated with establishment of the 38 species in multiple countries. None of the traits tested had statistically significant main effects on establishment in Europe, but, for the established species, longer flowering period and having compound leaves were positively associated with establishment in multiple countries. The positive association between establishment in Europe and residence time was stronger for evergreen than for deciduous species. In addition, evergreens, unlike deciduous species, showed a positive association between establishment in Europe and fruiting duration. Moreover, establishment in multiple countries was positively associated with planting frequency for species with compound leaves but not for species with simple leaves, and the association between the establishment and fruiting duration changed from negative to moderately positive as climatic suitability increased.

Main conclusions:
Introduction history and climatic suitability explain most of the variation in establishment, and modulate the role of species traits, such as leaf retention, leaf type and fruiting duration.

2015, Song, Yuan, Liu, Lijun, Feng, Yanhao, Wei, Yunzhu, Yue, Xiule, He, Wenliang, Zhang, Hua, An, Lizhe

Chilling (0-18°C) and freezing (<0°C) are two distinct types of cold stresses. Epigenetic regulation can play an important role in plant adaptation to abiotic stresses. However, it is not yet clear whether and how epigenetic modification (i.e., DNA methylation) mediates the adaptation to cold stresses in nature (e.g., in alpine regions). Especially, whether the adaptation to chilling and freezing is involved in differential epigenetic regulations in plants is largely unknown. Chorispora bungeana is an alpine subnival plant that is distributed in the freeze-thaw tundra in Asia, where chilling and freezing frequently fluctuate daily (24 h). To disentangle how C. bungeana copes with these intricate cold stresses through epigenetic modifications, plants of C. bungeana were treated at 4°C (chilling) and -4°C (freezing) over five periods of time (0-24 h). Methylation-sensitive amplified fragment-length polymorphism markers were used to investigate the variation in DNA methylation of C. bungeana in response to chilling and freezing. It was found that the alterations in DNA methylation of C. bungeana largely occurred over the period of chilling and freezing. Moreover, chilling and freezing appeared to gradually induce distinct DNA methylation variations, as the treatment went on (e.g., after 12 h). Forty-three cold-induced polymorphic fragments were randomly selected and further analyzed, and three of the cloned fragments were homologous to genes encoding alcohol dehydrogenase, UDP-glucosyltransferase and polygalacturonase-inhibiting protein. These candidate genes verified the existence of different expressive patterns between chilling and freezing. Our results showed that C. bungeana responded to cold stresses rapidly through the alterations of DNA methylation, and that chilling and freezing induced different DNA methylation changes. Therefore, we conclude that epigenetic modifications can potentially serve as a rapid and flexible mechanism for C. bungeana to adapt to the intricate cold stresses in the alpine areas.

2016-07, Feng, Yanhao, van Kleunen, Mark

2015, Feng, Yanhao

Due to intensive human activities across the globe, a vast number of alien plants are introduced to new biogeographical areas. A major theme in ecology is to understand why only some of them manage to become established and further invasive in new ranges, where they threaten biodiversity and ecosystem functioning. This is a challenging theme because plant invasion is a complex process occurring across ecological scales at different invasion stages. In this thesis, I explored both regional- and local-scale drivers of alien plants establishment and invasion success using dataset analysis, and common-garden and greenhouse experiments.
First, I explored how regional-scale establishment success and spread of 449 Chinese woody species in Europe were interactively associated with a broad range of factors. I found that the establishment success and spread significantly increased with residence time (only in spread), planting frequency and climatic suitability. Although none of species traits had significant main effects on the establishment, having a longer flowering period and compound leaves favored the spread of established species. The role of some traits (fruiting duration, leaf retention and leaf type) in the establishment and/or spread was dependent on other factors (residence time, planting frequency, climatic suitability and other species traits). These findings explicitly show how the role of some factors in the invasion process is context-dependent.
Second, I explored whether the ability of alien woody plants to cope with shading explained their regional-scale establishment success. Overall, the established and non-established species did not differ greatly in biomass production, morphological characteristics and CO2 assimilation, across five light intensities (from 100% to 7% of ambient light). However, the established species grew taller and reduced total leaf area more than the non-established ones in response to shading. Furthermore, the established species maintained a greater low-light CO2-assimilation capacity under shading. Overall, these differences were small, and therefore I conclude that the response to shading is not important for the successful establishment of alien woody plants.
Last, I explored local-scale direct and indirect interactions among alien and native plant species. In particular, I tested whether a native species that is phylogenetically closely related rather than distantly related to an alien species can directly suppress the alien, and as a consequence can indirectly reduce competitive effects of the alien on other co-occurring native species. Overall, competition was more severe between more closely-related alien species and native species, although this pattern was partly dependent on the regional-scale commonness of the alien. However, the presence of distantly-related rather than closely-related native species indirectly offset strong competitive effects of alien species on target native species. These interactions were explained by functional traits (e.g. plant height, SLA, leaf area ratio, root length ratio and shoot weight ratio) rather than by phylogenetic/functional distances of the interacting species. This implies that functional traits could help to disentangle complex interactions among plants.
To sum up, my thesis explored different mechanisms across ecological scales in the process of plant invasions. My findings may shed lights on the future studies to systematically integrate regional-scale processes (by considering complex interactions among various factors) with local-scale processes, such as adaptation to local environments and species interactions to ultimately explain and predict success of alien plants outside their native ranges.