Ondřej Mudrák

Interactions of the Hemiparasitic Species Rhinanthus minor with its Host Plant Community at Two Nutrient Levels

For root hemiparasites, host plants are both the source of water and nutrients below-ground, but competitors for light above-ground. Hemiparasites can reduce host biomass, and in this way considerably affect the whole plant community. To investigate these effects, we carried out two experiments in an oligotrophic meadow with a native population of Rhinanthus minor. In the first experiment, removal of R. minor was combined with fertilization in a factorial design, and in the second one, we manipulated R. minor density by thinning. The presence of R. minor decreased the biomass of its host community, mostly by suppressing grasses. In this way, the species was able to counterbalance the effect of fertilization, which increased community biomass and in particular that of grasses. Neither the presence of R. minor nor fertilization affected the total number of species or the Shannon-Wiener diversity index (H’) of the host community. However, H’ of grasses was higher and H’ of forbs (non-leguminous dicots) was lower in the presence of R. minor. Reduction of grasses by R. minor favored mainly the dominant forb Plantago lanceolata, which partly acquired the role of a competitive dominant. Effects of R. minor on community diversity seem to be highly dependent on the relative sensitivities of dominant and subordinate species. Fertilization increased the mortality of seedlings, resulting in a lower number of flowering plants. However, surviving individuals on average produced more flowers. Thinning resulted in lower mortality of R. minor plants. This indicates that intraspecific competition in R. minor populations results in negative density dependence.

Applying the dark diversity concept to nature conservation

Linking diversity to biological processes is central for developing informed and effective conservation decisions. Unfortunately, observable patterns provide only a proportion of the information necessary for fully understanding the mechanisms and processes acting on a particular population or community. We suggest conservation managers use the often overlooked information relative to species absences and pay particular attention to dark diversity (i.e., a set of species that are absent from a site but that could disperse to and establish there, in other words, the absent portion of a habitat-specific species pool). Together with existing ecological metrics, concepts, and conservation tools, dark diversity can be used to complement and further develop conservation prioritization and management decisions through an understanding of biodiversity relativized by its potential (i.e., its species pool). Furthermore, through a detailed understanding of the population, community, and functional dark diversity, the restoration potential of degraded habitats can be more rigorously assessed and so to the likelihood of successful species invasions. We suggest the application of the dark diversity concept is currently an underappreciated source of information that is valuable for conservation applications ranging from macroscale conservation prioritization to more locally scaled restoration ecology and the management of invasive species.

Changes in the functional trait composition and diversity of meadow communities induced by Rhinanthus minor L.

Rhinanthus minor L. is a root hemiparasite with known effects on community productivity and species composition. It is unclear, though, how these effects operate on functional trait composition and functional diversity. To fill this gap we established an experiment in a meadow community with a natural Rhinanthus population, where Rhinanthus presence (removal vs no removal) was manipulated under fertilized and unfertilized conditions. We assessed the biomass of individual species at the scale where plant individuals interact, in 20 cm × 20 cm plots. The community trait composition was characterized by community weighted means (CWM) and Rao’s quadratic entropy (as an index of functional diversity). Given the expected differences in the response to Rhinanthus parasitism, these parameters were computed for the whole community, for grasses (Poaceae family) and for forbs (non-leguminous dicots) separately. Generally, the species favoured by Rhinanthus were those with low competitive ability (with a low height, a low capacity for clonal growth, a taproot during the whole lifecycle, were monocyclic and had low leaf dry matter content). Rhinanthus increased functional diversity for clonality, which indicated a better coexistence of species with various capacities for clonal growth. CWM and functional diversity of grasses were not affected. Among the forbs, Rhinanthus mainly suppressed the tall, clonal species without a taproot (those which are functionally similar to grasses). Fertilization also affected CWM and functional diversity, but without significant interaction with Rhinanthus. We conclude that functional traits highlight the processes by which Rhinanthus affects vegetation structure and species coexistence.

Adventitious sprouting enables the invasive annual herb Euphorbia geniculata to regenerate after severe injury

Euphorbia geniculata, an annual weed of arable land native to America and invasive in subtropical and tropical regions, is able to regenerate from seeds and is also able to produce adventitious buds on the hypocotyl. Whether sprouting from adventitious buds represents a mechanism for surviving severe injury, and whether this ability is crucial for species invasion is, however, not known. The significance of such sprouting was investigated with a field survey and a pot experiment. Among 897 plants in 25 field populations surveyed in Indonesia, only a few exhibited marks of injury and sprouting from adventitious buds. When seeds were collected from 12 of the populations and used in a pot experiment, however, the seedlings were able to survive severe injury (removal of all tissue above the hypocotyl) by sprouting from adventitious buds on the hypocotyl and were able to set seed, although they produced less vegetative and generative (flowers and fruits) biomass than control plants. Growth but not fitness of plants in the pot experiment was population specific but neither growth characteristic correlated with disturbance level assessed in the field. Although the pot experiment indicates that E. geniculata can cope with severe injury by adventitious sprouting from the hypocotyl, the survey data are inconsistent with the hypothesis that such adventitious sprouting is important for the plant’s invasion in tropical regions.

Functional Traits in a Species-Rich Grassland and a Short-Term Change in Management: Is There a Competition-Colonization Trade-Off?

The species richness of grasslands generally cannot be fully restored after changes in management. Some species with small statures and basal leaf rosettes can be lost forever. The same species, however, seem to possess the traits necessary for successful re-colonization – they produce small, easily dispersable seeds, numerous seedlings and have lasting seed banks. We tested the hypothesis that plants in species-rich grasslands can be characterized by a negative correlation between their competitive ability and potential for generative regeneration, i.e. by a competition-colonization trade-off. An analysis of the traits of 95 grassland species supported this hypothesis. We then conducted a manipulative experiment in three different meadow communities in the Bílé Karpaty Mts. The experiment involved characterizing species traits during periods of different grassland management regimes in the years 1997–2000 and comparing these with the original management regime, which was restored between 2000 and 2003. We found out that the hypothesis only holds true for the pooled dataset for all three communities. When the individual meadow communities were analyzed separately, plant traits other than those responsible for the competition-colonization trade-off appear to be characteristic of responsive species, e.g. shoot lifespan or phenology. Our results imply that despite the general trade-offs found in large comparative studies, the plant response in a specific community is constrained by the local species pool.

Time lags in functional response to management regimes – evidence from a 26 year field experiment in wet meadows

Questions (i) How does functional composition and diversity respond to different timings and frequencies of mowing or fallow treatment? (ii) To which species assembly and related ecosystem processes do these developments correspond? (iii) What is the time course of these developments, and do they reach a stable state? Location North-western Germany Methods In 1987, a field experiment in nine wet meadow sites formerly exploited as fertilized meadows or pastures was established with four management treatments: (i) mowing twice a year in June/July and in September, (ii) mowing once a year in June/July, (iii) mowing once a year in September, and (iv) leaving fallow except shrub removal. Vegetation was recorded at least every second year and the functional composition (community weighted means) and diversity (Raos quadratic entropy) were analysed in the course of the experiment. We selected eight plant functional traits (Canopy height, SLA, LDMC, Seed mass, Shoot cyclicity, Clonal Index, Onset of flowering, Leaf distribution) capturing the main plant life strategies. Results Temporal changes, fluctuations and divergences between treatments could be observed in both functional composition and diversity. In particular, the vegetation of the fallow treatment showed strong competition for light and a higher investment into internal nutrient cycling. Over time, all treatments respond towards more stressful conditions due to generally less intensive management compared with the former management and respective nutrient depletion, leading to a more nutrient retentive and patch holding strategy and little investment into competitive seedlings. High competition and loose abiotic filters in the fallow treatment led to a niche separation in foliar traits. Mowing on the other hand enforced a divergence of reproduction mechanisms. Conclusion We detected long-term fluctuations and ongoing changes in functional composition and diversity even after 26 years. Especially early succession was characterized by a transient loss of functional diversity, caused by strong time lags in immigration and extinction of species. Our findings stress the importance of long-term experimental studies to avoid precarious misinterpretations. This article is protected by copyright. All rights reserved.

Seasonality promotes grassland diversity: Interactions with mowing, fertilization and removal of dominant species

Current biodiversity declines in species‐rich grasslands are connected with the cessation of management, eutrophication and the expansion of dominant grass species. One of the theoretical mechanisms limiting biodiversity loss is the ability of subordinate species to avoid competitive exclusion by seasonal niche separation from dominant species. Here, we explore how seasonality underpins the maintenance of diversity in temperate meadows under different management regimes and competition intensities in relation to species functional traits. We studied eight different communities in a long‐term meadow experiment that manipulated mowing, fertilization and dominant species (Molinia caerulea) removal. In each community, species‐specific trait and biomass data were taken five times during the year to test whether seasonal variation in species composition and functional strategies enable species to coexist. Mown unfertilized meadows exhibited pronounced seasonal variations in community composition and structure, linked to differences in resource‐use strategies between mid‐summer dominants and the spring and autumn subordinates. Higher specific leaf area and foliar nitrogen concentration in the fast‐growing dominants, and increased water use (δ¹³C) and nutrient acquisition (δ¹⁵N) efficiency in resource‐retentive subordinates, best predicted their temporal niche separation. Seasonal segregation of species with contrasting strategies increased after mowing cessation, and the resulting summer dominance of Molinia. Conversely, the seasonal dynamics were markedly reduced by fertilization, promoting tall grasses over sedges and forbs throughout the entire year, thereby decreasing the overall taxonomic and functional diversity. When Molinia was removed the compositional changes during the season became less pronounced, being significant only in mown unfertilized plots. Synthesis. Seasonal shifts in community composition reduced the competitive interactions and promoted the coexistence of dominant and subordinate species. Seasonality reversed the negative mid‐summer diversity‐productivity relationship with a positive one during the spring and autumn, and seasonality only prevented diversity loss in unfertilized conditions possibly because competition is most intense in summer. In fertilized meadows, subordinate species are not able to escape competitive exclusion by shifting their phenological peaks to the spring or autumn periods because asymmetric competition is intense over the entire growing season. Studying seasonal dynamics is key to understanding the maintenance of grassland diversity under ongoing land use change.

Earthworms increase plant biomass more in soil with no earthworm legacy than in earthworm‐mediated soil, and favour late successional species in competition

Summary As ecosystem engineers, earthworms greatly affect plant communities. They create persistent soil structures enriched by nutrients that improve the conditions for plant growth and modify competition between plant species. We therefore hypothesized that earthworm activity would be more important in early stages of the primary succession, when the soil is not modified by earthworms, than in the late stages of the succession, when the soil is already improved by earthworms. On the other hand, earthworms also affect plants via many other effects such as seed predation or excreting hormone-like compounds, which could make earthworm presence important in late successional soil. To explore earthworm effects on plant community succession, we performed a laboratory microcosm experiment without and with earthworms (Lumbricus rubellus and Aporrectodea caliginosa), with early successional plants (Poa compressa, Medicago lupulina, and Daucus carota) and late successional plants (Arrhenatherum elatius, Lotus corniculatus, and Plantago lanceolata), and with soil previously unaffected by earthworms (young soil) and soil substantially affected by earthworms (developed soil). These soils were taken from the early and late successional post-mining sites of the Sokolov coal mining district (northwest Czech Republic). When both early and late successional plants were grown separately, earthworms increased plant biomass proportionally more in the young soil than in the developed soil, indicating that earthworm activity is more important in undeveloped than in developed soil. When early and late successional plants were competing each other, the biomass of the early successional plants was reduced. In the young soil the reduction was independent of earthworm presence. In the developed soil the reduction was promoted by the earthworms. Late successional plants profited from the reduction of early successional plants and increased their biomass. This increase was promoted by the earthworm presence. Our results indicate that the direct effects of earthworm presence on plants decrease during succession because of the cumulative effects of earthworm activity on soil conditions. Such ecosystem engineering effects favor late successional competitors and therefore promote the replacement of species during succession. This article is protected by copyright. All rights reserved.

Reversing expansion of Calamagrostis epigejos in a grassland biodiversity hotspot: hemiparasitic Rhinanthus major does better job than increased mowing intensity

Questions Can hemiparasitic Rhinanthus major originating from a local population suppress the competitive clonal grass Calamagrostis epigejos and reverse its expansion in species-rich semi-natural grasslands? Does sowing seeds of R. major facilitate restoration of target meadow vegetation? Is R. major more beneficial for biodiversity restoration/conservation than increased mowing intensity, a conventional measure to suppress C. epigejos? Location Certoryje National Nature Reserve, Bile Karpaty (White Carpathians) Protected Landscape Area, Czech Republic. Methods We conducted a before-after-control-impact (BACI) experiment in meadow patches heavily infested by C. epigejos: eight blocks, each containing four plots with four treatment combinations: (i) traditional management, i.e. mowing once in summer, (ii) mowing in summer and autumn (iii) mowing in summer and seed sowing of R. major (iv) mowing in summer and autumn and seed sowing of R. major. Aboveground biomass of C. epigejos and vegetation composition of each of the plots were monitored every year from 2013 to 2016. To assess the effects of treatments, we analyzed biomass production of C. epigejos, herb layer cover and vegetation composition. Results Both the sowing R. major and an additional autumn meadow cut significantly suppressed C. epigejos. Their effects were additive and of comparable size. Both treatments also had significant but markedly different effects on community composition. R. major facilitated directional community composition change towards the regional Brachypodio-Molinetum meadows. By contrast, increased mowing intensity significantly decreased frequency of threatened species, which however may have also been influenced by R. major. Conclusions Sowing of autochtonous R. major seeds was demonstrated as an efficient tool to suppress C. epigejos and facilitate community restoration. It can be combined with an additional meadow cut to further accelerate the decline of the grass. The additional cut should however be used as a short term practice (1-2 years) only to minimize potential negative effects of its long-term application on some threatened plant species. The effects of R. major are comparable to those of R. alectorolophus reported previously. As a species occurring naturally in species-rich dry grasslands, R. major has a broader and longer-term application potential than R. alectorolophus in ecological restoration and conservation of these communities. This article is protected by copyright. All rights reserved.