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Invasive species can be the cause of severe problems for biodiversity, economy and human health. The cup plant (Silphium perfoliatum) is native to eastern North America and is increasingly cultivated in Germany as a new bioenergy crop. Its growth characteristics and autecology do not exclude a possible invasive potential. However, there are hardly any studies on this to date. In this study, habitat requirements for spontaneous colonization and establishment of the cup plant were investigated. Therefore, a 15 m radius around eleven cup plant fields in northern Bavaria (Germany) was examined. Data on cup plant colonization, habitat type, vegetation structure, ground cover, and further site conditions using the Ellenberg indicator values were collected and analyzed by logistic regression models. Spontaneously colonized cup plants were found in a wide range of habitats. Open habitats and human settlement areas were particularly suitable, especially field margins and agricultural paths. A portion of open soil of about 25% was preferentially colonized. Cup plants occurred predominantly within the first few meters of the field margin and increasingly around cup plant fields that have existed for a longer period. Favorable for the development of stems and thus for flowering, fruiting and establishing are warmer sites with a high herb layer. Individual plants that had developed a stem persist for several years and increased their stem number over time. The number of stem-developing individuals also increased over time. Thus, there exist an enormous potential for spread in the future. However, an invasive potential could not be confirmed based on the present study, because a threat of biodiversity was not proven. [ABSTRACT FROM AUTHOR]

Background: Impacts of invasive species on native communities are often difficult to assess, because they depend on a range of factors, such as species identity and traits. Such context-dependencies are poorly understood yet, but knowledge is required to predict the impact of invasions. Materials and methods: We assessed species- and developmental stage-specificity of competitive and allelopathic effects of the invasive plant Impatiens glandulifera on different developmental stages of four native plant species. While some studies have shown a reduction in plant growth caused by I. glandulifera, the magnitude of its impact is ambiguous. For our study we used seedlings and juveniles of I. glandulifera and the native target species Geum urbanum, Filipendula ulmaria, Urtica dioica, and Salix fragilis (seedlings only of the latter), which often co-occur with I. glandulifera in different habitats. Plants were grown in competition with I. glandulifera or treated with I. glandulifera leaf material, or 2-metoxy-1,4-naphtoquinone (2-MNQ), its supposedly main allelochemical. Results and conclusions: Overall I. glandulifera had a negative effect on the growth of all target species depending on the species and on the plant’s developmental stage. F. ulmaria was the least affected and U. dioica the most, and seedlings were less affected than juveniles. The species-specific response to I. glandulifera may lead to an altered community composition in the field, while growth reduction of seedlings and juveniles should give I. glandulifera an advantage in cases where plant recruitment is crucial. 2-MNQ led to minor reductions in plant growth, suggesting that it may not be the only allelopathic substance of I. glandulifera. Surprisingly, I. glandulifera was not fully tolerant to 2-MNQ. This autotoxicity could contribute to I. glandulifera population dynamics. We conclude that I. glandulifera reduces the growth of native vegetation and alters early successional stages without fully hindering it. [ABSTRACT FROM AUTHOR]

The lulo ( Solanum quitoense Lam.), an underutilized fruit crop originally from the Andes, is still widely unknown in Europe. Because of its delicious taste and high nutrition values it has high potential as greenhouse crop in Central Europe. But production of tropical crops in temperate regions might be limited by seasonal fluctuations in day length. Thus we studied lulo's reproductive development and yield in regard to seasonal photoperiod and supplemental lighting in winter. Therefore, we sow lulo seeds twice a year on 15 February and 20 June 2012 and grew them under natural light conditions so that bloom started in summer (natural long-day) and winter (natural short-day), respectively. Further lulos sown in June were exposed to an artificial long-day photoperiod as of 26 October 2012 (16 h day, ∼150 μmol m −2 s −1 photosynthetic active radiation). We confirmed that in lulo flower initiation and fruit set occurs throughout the year and timing is not significantly different between plants grown under long-day (natural, artificial) and those grown under short-day conditions. However, flower development is affected by photoperiod as first time from bud to fruit set and therefore harvest begin was accelerated at long-days. Second, portion of hermaphroditic flowers increased in andromonoecious lulo in natural, not artificial long-days probably due to higher light intensity. Summer blooming plants bore more fruits (15 fruits per plant) than winter blooming ones (10 fruits). Supplemental lighting in winter only increased fruit number to a comparable amount as in summer but not yield. Surprisingly, blooming and fruiting period was conspicuously longer when flowering started under natural conditions in winter and therefore lasted until spring. So regarding this whole blooming period total yield was even higher when plants were grown during winter without supplemental lighting. In conclusion, reproduction of lulo plants is not restricted to a certain seasonal day length indicating that this crop is suitable for year-round fruit production under greenhouse conditions in Central Europe. [ABSTRACT FROM AUTHOR]

The Indian mock strawberry [ Duchesnea indica (Andrews) Focke] is an invasive plant in several regions of central Europe and Germany. In order to explore its competitive ability, we compared it with the native woodland strawberry ( Fragaria vesca L.) by growing it alone as well as in intra- or inter-specific competition in a pot experiment under greenhouse conditions. Nutrient solution was added several times at two nitrogen (N) levels. One addition involved 15N labelling to determine whether the competition of both plant species depends on their ability to acquire N from soil. Duchesnea had a higher biomass production than Fragaria when grown in nutrient-rich soil, both in competition and as a solitary plant. Under N-poor conditions, root interference could change this superiority due to limited soil space. After 65 days of growth, total plant dry weight, total N content and 15N content in the plant tissues were determined. The results show that the predominance of Duchesnea in biomass production was confirmed at high, but not at low N availability. The assimilate partitioning strategy of Duchesnea differs from that of Fragaria: the former generally had a higher shoot-to-root ratio. The N content in shoots and roots was affected only by N addition but not by competition or species. Duchesnea allocated more N to the leaves, Fragaria to the roots. The amount of 15N taken up was nearly equal for both species. In relation to root biomass, Duchesnea had a higher specific uptake rate at low N addition because of the higher root biomass in Fragaria. The roots of Fragaria and Duchesnea did not affect each other when grown together. We conclude that the invasive potential of Duchesnea is only poorly related to the N uptake rate or to better root competition for N. In N-rich environments, however, Duchesnea is highly competitive because of the preferred investment in shoot biomass. Therefore, environments with increased N deposition, i.e. from anthropogenic sources, could promote the invasive potential of Duchesnea. [ABSTRACT FROM AUTHOR]

Silage maize (Zea mays L.) intensification to maximise biomass production increases greenhouse gas emissions, accelerates climate change and intensifies the search for alternative bioenergy crops with high carbon (C) sequestration capacity. The perennial cup‐plant (Silphium perfoliatum L.) not only serves as a viable bioenergy source but may also be a promising soil C conservator. However, the dynamics of soil organic C (SOC) under the C3 cup‐plant, exposed to moderate drought conditions, that reduces growth rate without causing crop failure, compared with the drought‐tolerant C4 maize, remains unexplored. Here, we investigated in a lysimeter experiment the effects of moderate drought stress on crop growth and soil CO2 efflux under cup‐plant and silage maize compared with well‐watered conditions. Soil CO2 efflux along with root and shoot biomass, soil moisture and temperature as well as SOC and nitrogen (N) were measured over three consecutive years. Irrespective of the watering regime, cup‐plant induced a greater soil CO2 efflux (16% and 23% for 2020 and 2021, respectively), which was associated with higher root and shoot biomass compared with silage maize suggesting a substantial contribution of the roots to total soil CO2 efflux. In addition, soil CO2 efflux correlated negatively with soil dissolved N and positively with microbial C:N imbalance suggesting that low soil N availability influences soil CO2 efflux through processes related to N‐limitation such as N‐mining. Strikingly, moderate drought had no effect on soil CO2 efflux and C content and microbial biomass C, but increased dissolved organic C and microbial biomass N in both crops suggesting a complex interplay between C availability, N‐limitation and microbial adaptation under these conditions. Although cup‐plant increased soil CO2 efflux, the observed higher root and shoot biomass even under moderate drought conditions suggests a similar soil C management as silage maize; however, this still requires longer‐term investigation. [ABSTRACT FROM AUTHOR]

The impact of invasive species is often difficult to assess due to species × ecosystem interactions. Impatiens glandulifera heavily invaded several habitat types in Central Europe but its impact on native plant communities is rated ambiguously. One reason could be that the impact differs between habitat types or even between environmentally heterogeneous patches (micro-habitats) within one habitat type. In the present study a vegetation survey was performed within heterogeneous riverside habitats in Germany investigating the impact of I. glandulifera on native vegetation in dependence of environmental conditions. The vegetation was recorded in summer and spring because of seasonal species turnover and thus potentially different impact of the invasive plant. We found that the cover of I. glandulifera depended on environmental conditions resulting in a patchy occurrence. I. glandulifera did not have any impact on plant alpha-diversity but reduced the cover of the native vegetation, especially of the dominant species. This effect depended on micro-habitat and season. The native vegetation was most affected in bright micro-habitats, especially those with a high soil moisture. Not distinguishing between micro-habitats, plant species composition was not affected in summer but in spring. However, environmental conditions had a higher impact on the native vegetation than I. glandulifera. We conclude that within riparian habitats the threat of I. glandulifera to the native vegetation can be rated low since native species were reduced in cover but not excluded from the communities. This might be due to patchy occurrence and year-to-year changes in cover of I. glandulifera. The context-dependency in terms of micro-habitat and season requires specific risk assessments which is also an opportunity for nature conservation to develop management plans specific to the different habitats. Particular attention should be given to habitats that are bright and very wet since the effect of I. glandulifera was strongest in these habitats. [ABSTRACT FROM AUTHOR]

Biological invasions are one of the major threats to biodiversity worldwide and contribute to changing community patterns and ecosystem processes. However, it is often not obvious whether an invader is the "driver" causing ecosystem changes or a "passenger" which is facilitated by previous ecosystem changes. Causality of the impact can be demonstrated by experimental removal of the invader or introduction into a native community. Using such an experimental approach, we tested whether the impact of the invasive plant Impatiens glandulifera on native vegetation is causal, and whether the impact is habitat‐dependent. We conducted a field study comparing invaded and uninvaded plots with plots from which I. glandulifera was removed and plots where I. glandulifera was planted within two riparian habitats, alder forests and meadows. A negative impact of planting I. glandulifera and a concurrent positive effect of removal on the native vegetation indicated a causal effect of I. glandulifera on total native biomass and growth of Urtica dioica. Species α‐diversity and composition were not affected by I. glandulifera manipulations. Thus, I. glandulifera had a causal but low effect on the native vegetation. The impact depended slightly on habitat as only the effect of I. glandulifera planting on total biomass was slightly stronger in alder forests than meadows. We suggest that I. glandulifera is a "back‐seat driver" of changes, which is facilitated by previous ecosystem changes but is also a driver of further changes. Small restrictions of growth of the planted I. glandulifera and general association of I. glandulifera with disturbances indicate characteristics of a back‐seat driver. For management of I. glandulifera populations, this requires habitat restoration along with removal of the invader. [ABSTRACT FROM AUTHOR]

Gentianella bohemica Skalický (Gentianaceae) is a critically endangered species endemic to the Bohemian Massif in the border region of Germany, Czechia and Austria. It consists of a restricted number of extremely scattered populations which are known to form distinct genetic groups. The objective of this work was to test for differences in the floral scent between Gentianella bohemica and Gentianella germanica and within these two species among populations, and to test for a correlation of scent and genetic similarity among the populations of G. bohemica . Floral scent was collected from the inflorescences/plants of eight flowering populations of G. bohemica and three populations of G. germanica using dynamic headspace methods, followed by GC/MS analyses. Both species emitted several aromatic and terpenoid compounds and multivariate analyses revealed differences in scent between the two species and within species among G. bohemica populations. Volatile components overlapped as expected for closely related species but floral scent was taxon-specific. Floral scent differentiation among G. bohemica populations was in high congruence with the genetic differentiation suggesting that scent differences among populations have a genetic basis and showing that scent is a suitable chemotaxonomic marker in this species. [ABSTRACT FROM AUTHOR]