Calcareous Grassland Research Articles

Warmer and Poorer: The Fate of Alpine Calcareous Grasslands in Central Apennines (Italy)

Global change threatens alpine biodiversity and its effects vary across habitat types and biogeographic regions. We explored vegetation changes over the last 20 years on two Mediterranean alpine calcareous grasslands in central Apennines (Italy): stripped grasslands (EUNIS code E4.436) with Sesleria juncifolia growing on steep slopes, and wind edge swards (EUNIS code E4.42) with Carex myosuroides. Based on a re-visitation of 25 vegetation plots of 4 × 4 m, we assessed changes in overall and endemic plant species cover and richness by nonparametric Kruskal–Wallis test. We explored changes in structure and ecology using growth forms and Landolt indicators for temperatures. We identified species’ contribution to temporal changes using the similarity percentage procedure (SIMPER). The results evidenced a significant decline in all species cover and richness on both plant communities with a significant decline in alpine and endemic species and in hemicryptophytes with rosette and scapose ones on stripped grasslands, as well as a decline in subalpine and suffruticose chamaephytes species on wind edge swards. Such biodiversity loss, so far observed only in the warmest and Southern Mediterranean summits of Europe, is likely attributable to the combined effect of higher temperatures; the increase in the vegetative period; and the decrease in water availability, which is particularly severe in calcareous regions. Our study suggested the vulnerability of the analyzed alpine ecosystems to global change and the importance of monitoring activities to better understand vegetation trends and adaptation strategies in subalpine, alpine, and nival ecosystems.

Fallow deer foraging alone does not preserve the vegetation of traditionally sheep‐grazed calcareous grasslands

Abstract The goal of this study was to evaluate to what extent wild ungulates (fallow deer) can contribute to the maintenance of semi‐natural calcareous grasslands, which are a threatened habitat type (natura 2000 code *6210). In a 10‐year exclosure experiment, we tested the effects of ungulate foraging using three treatments: (A) control with combined foraging of herded sheep and wild fallow deer, (B) sheep exclosure with only deer foraging and (C) total exclosure with no foraging. Treatments not grazed by sheep (B, C) were characterized by significantly declining species numbers, litter accumulation and shrub encroachment. Despite high population densities, the effect of fallow deer alone (B) was weak: Succession of woody species was only partly inhibited, while annuals, short‐growing and rosette‐building plant species were strongly suppressed by litter accumulation. Only the combination of sheep and fallow deer foraging preserved vegetation structure and species richness and led to a promotion of target species. Synthesis and applications. We conclude that we need to continue the traditional land‐use forms such as sheep grazing in order to maintain calcareous grasslands. However, we should also raise our awareness for wild animals and analyse more in depth their potential contribution to the conservation management of open habitats.

Grazing conserves threatened carabid beetles in semi-natural calcareous grasslands better than mowing, especially at low intensities

Grazing conserves threatened carabid beetles in semi-natural calcareous grasslands better than mowing, especially at low intensities

Microclimate shapes vegetation response to drought in calcareous grasslands

AbstractQuestionsSemi‐natural grasslands have been shown to be relatively resilient to drought events, but there seems to be no uniform response of different grassland types or across species. The typical vegetation of calcareous grasslands, which are biodiversity hotspots in Europe, reportedly even profits from droughts. What was the response of their vegetation, considering different species groups, to the recent periods of intense summer droughts? How did differences in microclimate, such as between steep, south‐facing slopes (SSF) and flat or north‐facing slopes (FNF), affect species composition and drought response?LocationSemi‐arid calcareous grasslands (Mesobromion) in northwest Germany.MethodsIn 2019, we resurveyed 112 vegetation plots from 25 sites first established in 2008, after 11 exceptionally dry years. Species identities and cover were assessed in plots of 1 m2. We used linear mixed models to determine the effect of microclimate on species composition and drought response. Vegetation changes were visualised by non‐metric multidimensional scaling (NMDS).ResultsIn the initial survey in 2008, the species composition was significantly influenced by the microclimate, with positive effects of dry and warm conditions on SSF on character species. Phosphorus availability played an equally important, albeit contrasting, role. Vegetation change between 2008 and 2019 showed strong signs of the severe droughts. On SSF slopes, total species richness decreased, with negative trends for all species groups except ruderal species. Remarkably, this also affected the character species of dry grasslands. By contrast, dry conditions on FNF favoured an increase in total species richness and character species. However, eutrophication indicators increased here as well.ConclusionsWe conclude that sites with a dry and warm microclimate have to date had a positive, stabilising effect on the typical vegetation of calcareous grasslands. However, increasing droughts due to climate change pose a potential threat to the characteristic species composition, especially at sites with hot and dry microclimates.

Subtle Effects of Experimental Grassland Fragmentation on Density, Species Composition and Functional Dispersion of Gastropods

The fragmentation of continuous habitats has significant consequences for species and for the functional diversity of plant and animal communities. Fragmentation effects can be indirect, can occur at different spatial scales and may vary over years. Small fragmentation-related effects may only be detected in standardized, controlled field experiments accounting for the natural variation in environmental conditions and in remnants of habitat. Using a non-invasive trapping approach, we examined the responses of terrestrial gastropods (snails and slugs) to small-scale habitat fragmentation in a controlled experiment conducted in three species-rich, nutrient-poor calcareous grasslands in the Jura Mountains, Switzerland, over four years. We found site-specific differences in species richness, individual density, and species composition. Experimental grassland fragmentation did not significantly affect species richness or density, but affected functional dispersion (a measure of functional diversity) in the final year, indicating that fragmentation-related changes may occur with a time delay. Similarly, experimental fragmentation influenced the mean shell size of the snail assemblage and the proportions of individuals with certain life-history traits or habitat preferences in some years. The observed fragmentation effects were subtle and varied over time, underlining the importance of controlled field experiments.

Functional imbalance not functional evenness is the third component of community structure

It is generally assumed that functional richness, diversity and evenness are complementary and, taken together, describe different facets of the distribution of species and their abundances in functional space. However, although these three primary components of community structure are commonly accepted by most community ecologists, measures of functional evenness usually fail to properly capture the regularity of species abundances in functional space. In this paper we will use an underexplored decomposition of Rao’s index of functional diversity to introduce the notion of functional imbalance, an indicator of the strength of interaction between species abundances and their functional dissimilarities. Functional diversity always increases with increasing functional imbalance. Therefore, functional imbalance seems a more appropriate indicator of this facet of community structure than functional evenness. A worked example aimed at evaluating the influence of grazing on plant community structure showed that all proposed measures of functional imbalance were able to highlight the main functional changes of a dry calcareous grassland in Tuscany (Italy) following grazing exclusion.

Grassland type and presence of management shape butterfly functional diversity in agricultural and forested landscapes

Alteration of agricultural land use has led to a widespread loss of biodiversity in human-dominated landscapes. Degradation and gradual disappearance of natural and semi-natural habitats has become a global conservation problem. Together, intensive agriculture and the abandonment of extensively farmed areas endanger the wildlife of European landscapes. Our study aims to explore the complex processes that affect butterfly functional diversity and functional community composition in low-productive and threatened grasslands. We examined the functional characteristics of butterfly communities in response to three factors: habitat type (calcareous grassland vs. orchard meadow), management (managed vs. abandoned), and landscape context (forested vs. agricultural landscape). We surveyed butterflies of 20 calcareous grasslands and 20 orchard meadows in Central Germany. Both habitats are characterised by high structural diversity and extensive cultivation. To test the effects of our investigated variables, we selected six functional traits (overwintering, voltinism, wing length, diet, flight period, territoriality) for each butterfly species, and assigned values to them based on the literature. For our statistical analyses, we used single trait and multi-trait approaches. Our results showed that habitat type had the strongest filtering effect on butterfly functional traits of the three design variables. Functional diversity indices, such as functional richness and divergence values, were higher in calcareous grasslands than in orchard meadows. We found that calcareous grasslands are characterised by butterflies having more specialist traits (e.g., fewer food plants, fewer generations), which are favoured by grassland management and the vicinity of forests. Therefore, to maintain the threatened butterfly fauna of calcareous grasslands, extensive management should focus on these grasslands in forested landscapes. • Extensive management maintains higher butterfly diversity. • Both orchard meadows and calcareous grasslands harbour a valuable butterfly fauna. • Habitat type had the strongest filtering effect on butterfly functional traits. • Orchard meadows are characterised by butterflies with more generalist traits. • Calcareous grasslands are characterised by butterflies with more specialist traits.

Summer drought affects abundance of grassland grasshoppers differently along an elevation gradient

Abstract Orthoptera (hereinafter termed ‘grasshoppers’) are of great functional significance since they are the main arthropod consumers in grasslands and an important food source for medium‐sized insectivorous vertebrates. However, research investigating the effects of extreme weather events on the abundance of grasshoppers has lacked thus far. Here, we studied the effects of summer drought on grasshopper abundance in temperate semi‐natural grasslands with low land‐use intensity. We considered calcareous and mesic grasslands; per type, we randomly selected 27 plots. Our study revealed distinct differences in habitat characteristics between plots of calcareous and mesic grasslands. Overall, calcareous grasslands had a more heterogeneous and shorter vegetation than mesic grasslands. Consequently, species richness was higher in calcareous grasslands. By contrast, grasshopper abundance did not differ between the two types. Summer temperature was the key driver of grasshopper abundance. Abundance was lowest in grasslands that were situated at lower elevations with higher summer temperatures and that were characterised by the strongest effects of summer drought. Its influence even overrode the differences in habitat characteristics between calcareous and mesic grasslands. Extreme weather events, such as summer droughts, are expected to become more frequent due to global warming. Accordingly, suitable conservation strategies that increase the resistance and resilience of temperate semi‐natural grasslands and their insect assemblages against summer drought are highly needed. Based on our study, increasing habitat heterogeneity seems to be the most effective way to mitigate the negative effects of summer drought.

The Feasibility of Leaf Reflectance-Based Taxonomic Inventories and Diversity Assessments of Species-Rich Grasslands: A Cross-Seasonal Evaluation Using Waveband Selection

Hyperspectral leaf-level reflectance data may enable the creation of taxonomic inventories and diversity assessments of grasslands, but little is known about the stability of species-specific spectral classes and discrimination models over the course of a growing season. Here, we present a cross-seasonal dataset of seventeen species that are common to a temperate, dry and nutrient-poor calcareous grassland, which spans thirteen sampling dates, a week apart, during the spring and summer months. By using a classification model that incorporated waveband selection (a sparse partial least squares discriminant analysis), most species could be classified, irrespective of the sampling date. However, between 42 and 95% of the available spectral information was required to obtain these results, depending on the date and model run. Feature selection was consistent across time for 70 out of 720 wavebands and reflectance around 1410 nm, representing water features, contributed the most to the discrimination. Model transferability was higher between neighbouring sampling dates and improved after the “green-up” period. Some species were consistently easy to classify, irrespective of time point, when using up to six latent variables, which represented about 99% of the total spectral variance, whereas other species required many latent variables, which represented very small spectral differences. We concluded that it did seem possible to create reliable taxonomic inventories for combinations of certain grassland species, irrespective of sampling date, and that the reason for this could lie in their distinctive morphological and/or biochemical leaf traits. Model transferability, however, was limited across dates and cross-seasonal sampling that captures leaf development would probably be necessary to create a predictive framework for the taxonomic monitoring of grasslands. In addition, most variance in the leaf reflectance within this system was driven by a subset of species and this finding implies challenges for the application of spectral variance in the estimation of biodiversity.

The impact of environment on genetic and epigenetic variation in Trifolium pratense populations from two contrasting semi-natural grasslands.

Central European grasslands, such as calcareous grasslands and oat-grass meadows, are characterized by diverse environmental conditions and management regimes. Therefore, we aimed to determine potential differences in genetic and epigenetic variation patterns between the contrasting habitats and to identify the drivers of genetic and epigenetic variation. We investigated the genetic and epigenetic variation of the ecologically variable plant species Trifolium pratense L. applying amplified fragment length polymorphism and methylation-sensitive amplification polymorphism analyses. We observed low levels of genetic and epigenetic differentiation among populations and between habitat types. Genetic and epigenetic variations were not interdependent. Thus, genetic variation was significantly isolated by habitat dissimilarity, whereas epigenetic variation was affected by environment. More specifically, we observed a significant correlation of epigenetic diversity with soil moisture and soil pH (the latter potentially resulting in phosphorus limitation). Genetic variation was, therefore, affected more strongly by habitat-specific environmental conditions induced by land use-related disturbance and gene flow patterns, while epigenetic variation was driven by challenging environmental conditions.

Vertical distribution of soil seed bank and the ecological importance of deeply buried seeds in alkaline grasslands.

BackgroundSoil seed banks play a central role in vegetation dynamics and may be an important source of ecological restoration. However, the vast majority of seed bank studies examined only the uppermost soil layers (0–10 cm); hence, our knowledge on the depth distribution of seed bank and the ecological significance of deeply buried seeds is limited. The aim of our study was to examine the fine-scale vertical distribution of soil seed bank to a depth of 80 cm, which is one of the largest studied depth gradients so far. Our model systems were alkaline grasslands in East-Hungary, characterised by harsh environmental conditions, due to Solonetz soil reference group with Vertic horizon. We asked the following questions: (1) How do the seedling density and species richness of soil seed bank change along a vertical gradient and to what depth can germinable seeds be detected? (2) What is the relationship between the depth distribution of the germinable seeds and the species traits?MethodsIn each of the five study sites, four soil cores (4 cm diameter) of 80 cm depth were collected with an auger for soil seed bank analysis. Each sample was divided into sixteen 5-cm segments by depth (320 segments in total). Samples were concentrated by washing over sieves and then germinated in an unheated greenhouse. Soil penetration resistance was measured in situ next to each core location (0–80 cm depth, 1-cm resolution). We tested the number and species richness of seedlings observed in the soil segments (N = 320), using negative binomial generalized linear regression models, in which sampling layer and penetration resistance were the predictor variables. We ran the models for morphological groups (graminoids/forbs), ecological groups (grassland species/weeds) and life-form categories (short-lived/perennial). We also tested whether seed shape index, seed mass, water requirement or salt tolerance of the species influence the vertical distribution of their seed bank.ResultsGerminable seed density and species richness in the seed bank decreased with increasing soil depth and penetration resistance. However, we detected nine germinable seeds of six species even in the deepest soil layer. Forbs, grassland species and short-lived species occurred in large abundance in deep layers, from where graminoids, weeds and perennial species were missing. Round-shaped seeds were more abundant in deeper soil layers compared to elongated ones, but seed mass and ecological indicator values did not influence the vertical seed bank distribution. Our research draws attention to the potential ecological importance of the deeply buried seeds that may be a source of recovery after severe disturbance. As Vertisols cover 335 million hectares worldwide, these findings can be relevant for many regions and ecosystems globally. We highlight the need for similar studies in other soil and habitat types to test whether the presence of deep buried seeds is specific to soils with Vertic characteristics.

Machine‐learning algorithms predict soil seed bank persistence from easily available traits

AbstractQuestionSoil seed banks (SSB), i.e. pools of viable seeds in the soil and on its surface, play a crucial role in plant biology and ecology. Information on seed persistence in soil is of great importance for fundamental and applied research, yet compiling data sets on this trait still requires enormous efforts. We asked whether the machine‐learning (ML) approach could be used to infer and predict SSB properties of a regional flora based on easily available data.LocationEighteen calcareous grasslands located along an elevational gradient of almost 2000 m in the Bavarian Alps, Germany.MethodsWe compared a commonly used ML model (random forest) with a conventional model (linear regression model) as to their ability to predict SSB presence/absence and density using empirical data on SSB characteristics (environmental, seed traits and phylogenetic predictors). Further, we identified the most important determinants of seed persistence in soil for predicting qualitative and quantitative SSB characteristics using the ML approach.ResultsWe demonstrated that the ML model predicts SSB characteristics significantly better than the linear regression model. A single set of predictors (either environment, or seed traits, or phylogenetic eigenvectors) was sufficient for the ML model to achieve high performance in predicting SSB characteristics. Importantly, we established that a few widely available SSB predictors can achieve high predictive power in the ML approach, suggesting a high flexibility of the developed approach for use in various study systems.ConclusionsOur study provides a novel methodological approach that combines empirical knowledge on the determinants of SSB characteristics with a modern, flexible statistical approach based on ML. It clearly demonstrates that ML can be developed into a key tool to facilitate labor‐intensive, costly and time‐consuming functional trait research.

Carbonate-Induced Chemical Reductants Are Responsible for Iron Acquisition in Strategy I Wild Herbaceous Plants Native to Calcareous Grasslands.

Significant progress has been made in understanding Strategy I iron (Fe) acquisition using crop/model plants under controlled conditions in laboratories. However, plant species native to calcareous soils may have evolved unique strategies for adaptation to high carbonate/pH-induced Fe deficiency. Until now, little information is available on the Fe acquisition mechanisms in these plants. Here, we explored the Fe acquisition mechanisms in wild dicot species native to calcareous grasslands, by monitoring the Fe nutrition-related rhizosphere processes in field and greenhouse conditions. Most of these wild species displayed comparable shoot Fe concentration to those of crops, and some dicots actually accumulated very high shoot Fe. However, these species did not exhibit ferric reductase oxidase (FRO)-dependent Strategy I responses to Fe deficiency, including visual rhizosphere acidification and increased Fe3+ reduction. In contrast, chemical reductants exuded by roots of dicots were responsible for Fe3+ reduction in these wild plants. These features were not observed in the FRO-dependent Strategy I crop plant cucumber. Neither leaf chlorophyll nor shoot/root Fe was depressed by 10% CaCO3 application in all the examined wild species. Furthermore, their root exudation was significantly activated by CaCO3, leading to an increased Fe3+ reduction. We show that chemical reductant-mediated Fe3+ reduction occurs preferentially in these wild dicots and that these mechanisms are not sensitive to high soil carbonate/pH. Our findings support that Fe acquisition in Strategy I wild plants native to calcareous soils is substantially different from the enzyme-dependent system of Strategy I plants.

Effects of local climate and habitat heterogeneity on breeding-bird assemblages of semi-natural grasslands

The intensification of agricultural land-use, abandonment and afforestation have caused severe loss and degradation of nutrient-poor, semi-natural grasslands across Europe. Calcareous grasslands have an outstanding value for nature conservation due to their highly diverse flora and fauna, including birds. However, knowledge of environmental factors driving the composition of bird communities in calcareous grasslands is still scarce. The aim of our study was to compare the breeding-bird assemblages of calcareous grasslands and the second most common semi-natural grassland type in the study area (Diemel Valley, Central Germany), mesic grasslands, along an elevation (climate) gradient. For each grassland type, we randomly selected 27 square-shaped plots with a size of 5 ha each and a cover of the focal grassland type of at least 50% within the plot. Our study revealed that both the number and density of threatened species of breeding birds were higher in plots of calcareous grasslands than in those of mesic grasslands. Based on multivariable generalised linear mixed-effects models, the most important predictors of overall species richness and density of breeding birds in plots of calcareous grasslands were the area of juniper-rich calcareous grassland and Shannon habitat diversity. By contrast, the number and density of threatened species were in both grassland types mainly driven by breeding-season temperature. Heterogeneous, juniper-rich calcareous grasslands seem to be a key habitat for bird assemblages with high species richness and density. These grasslands usually consisted of small-scale habitat mosaics providing suitable nesting sites and foraging grounds in close proximity. By contrast, mesic grasslands had rather homogeneous swards and shrubs or trees were normally restricted to the edges of the grassland patches. Based on our study, increasing habitat heterogeneity at the landscape scale and within grasslands is the key to enhancing species richness and density of breeding birds.

Management of upland calcareous grasslands for target vascular plant community impacts upon abundance but not diversity of non-target bryophytes

Management of upland calcareous grasslands for target vascular plant community impacts upon abundance but not diversity of non-target bryophytes

Assessing Population Genetic Status for Designing Plant Translocations

Assisted gene flow interventions such as plant translocations are valuable complementary techniques to habitat restoration. Bringing new genetic variants can contribute to increasing genetic diversity and evolutionary resilience, counteract inbreeding depression and improve plant fitness through heterosis. Large, highly genetically variable populations are usually recommended as sources for translocation. Unfortunately, many critically endangered species only occur as small populations, which are expected to show low genetic variation, high inbreeding level, paucity of compatible mates in self-incompatible species, and increased genetic divergence. Therefore, assessment of population genetic status is required for an appropriate choice of the source populations. In this paper, we exemplify the different analyses relevant for genetic evaluation of populations combining both molecular (plastid and nuclear) markers and fitness-related quantitative traits. We assessed the genetic status of the adult generation and their seed progeny (the potential translocation founders) of small populations of Campanula glomerata (Campanulaceae), a self-incompatible insect-pollinated herbaceous species critically endangered in Belgium. Only a few small populations remain, so that the species has been part of a restoration project of calcareous grasslands implementing plant translocations. In particular, we estimated genetic diversity, inbreeding levels, genetic structure in adults and their seed progeny, recent bottlenecks, clonal extent in adults, contemporary gene flow, effective population size (Ne), and parentage, sibship and seed progeny fitness variation. Small populations of C. glomerata presented high genetic diversity, and extensive contemporary pollen flow within populations, with multiple parentage among seed progenies, and so could be good seed source candidates for translocations. As populations are differentiated from each other, mixing the sources will not only optimize the number of variants and of compatible mates in translocated populations, but also representativeness of species regional genetic diversity. Genetic diversity is no immediate threat to population persistence, but small Ne, restricted among-population gene flow, and evidence of processes leading to genetic erosion, inbreeding and inbreeding depression in the seed progeny require management measures to counteract these trends and stochastic vulnerability. Habitat restoration facilitating recruitment, flowering and pollination, reconnecting populations by biological corridors or stepping stones, and creating new populations through translocations in protected areas are particularly recommended.

Soil Seed Bank Persistence Across Time and Burial Depth in Calcareous Grassland Habitats.

Seed persistence in the soil is crucial for population dynamics. Interspecific differences in soil seed mortality could be a mechanism that may stimulate species coexistence in herbaceous plant communities. Therefore, understanding the levels and causes of seed persistence is vital for understanding community composition and population dynamics. In this study, we evaluated the burial depth as a significant predictor of the temporal dynamics of soil seed persistence. We suppose that species differ in this temporal dynamics of soil seed persistence according to burial depth. Furthermore, we expected that burial depth would affect soil seed persistence differently concerning the species-specific type of dormancy, light, and fluctuating temperature requirements for germination. Seeds of 28 herbaceous species of calcareous grasslands were buried in the field into depths of 1, 5, and 10 cm under the soil surface. Seed viability was tested by germination and tetrazolium tests several times for three years. Species-specific seed traits—a type of dormancy, light requirements and alternating temperature requirements for germination, and longevity index—were used for disentangling the links behind species-specific differences in soil seed persistence. Our study showed differences in soil seed persistence according to the burial depth at the interspecific level. Generally, the deeper the buried seeds, the longer they stayed viable, but huge differences were found between individual species. Species-specific seed traits seem to be an essential determinant of seed persistence in the soil. Seeds of dormant species survived less and only dormant seeds stayed viable in the soil. Similarly, seeds of species without light or alternating temperature requirements for germination generally remained viable in the soil in smaller numbers. Moreover, seeds of species that require light for germination stayed viable longer in the deeper soil layers. Our results help understand the ecosystem dynamics caused by seed reproduction and highlight the importance of a detailed long-term investigation of soil seed persistence. That is essential for understanding the fundamental ecological processes and could help restore valuable calcareous grassland habitats.

The response of soil respiration to different N compounds addition in a saline–alkaline grassland of northern China

AbstractThe increase in atmospheric nitrogen (N) deposition has profound effects on soil respiration (SR). However, the responses of SR to the addition of different N compounds, particularly in saline–alkaline grasslands remain unclear. A 3-year controlled field experiment was conducted to investigate the responses of SR to different N compounds (NH4NO3, (NH4)2SO4 and NH4HCO3) during the growing seasons in a saline–alkaline grassland located in the agro-pastoral ecotone of northern China. Our results demonstrated that SR showed a bimodal pattern and a significant interannual difference that was regulated by air or soil temperature and precipitation. Nitrogen addition had a significant effect on SR, and the effect of N addition on SR varied yearly, which was related to seasonal precipitation. The mean SR across 3 years (2017–2019) was increased by 19.9%, 13.0% and 16.6% with the addition of NH4NO3, (NH4)2SO4 and NH4HCO3, respectively. The highest effect of NH4NO3 addition on SR across 3 years was ascribed to the highest aboveground net primary production, belowground net primary production (BNPP) and soil NO3− concentrations. SR (C loss) was significantly increased while plant productivity (C input) did not significantly change under NH4HCO3 addition, indicating a decrease in C sequestration. In addition, BNPP was the main direct factor influencing SR in this saline–alkaline grassland, and soil salinization (e.g. soil base cations and pH) indirectly affected SR through soil microorganisms. Notably, NH4NO3 addition overestimated the response of SR to N addition, and different N compounds should be considered, especially in saline–alkaline grassland.

Geographical variation of floral scents in generalist entomophilous species with variable pollinator communities

Abstract Floral scents are considered major attractants for pollinator species and scent composition is likely to be under pollinator‐mediated selection. Relatively, few studies have investigated geographical variation in floral scents in plant species with generalist pollination, and little is known about the mechanism behind this variation, often interpreted as the result of local adaptation to pollinators without considering phenotypic plasticity. One possible way to investigate this question is to compare floral bouquets both in natural populations and in populations reared under controlled conditions. We compared the identity and proportions of volatile organic compounds (VOCs), collected on plants both in the field and in the greenhouse, emitted by four generalist plant species found in six calcareous grasslands distributed along an environmental and diversity gradient. We recorded pollinator visits in the field to document geographical variation of pollinator communities associated with each plant species. We then analysed the relation between VOCs and pollinator variation using a redundancy analysis (RDA). We found that VOC composition differed among species and among populations, but also between field and greenhouse. The RDA showed a significant effect of the variation in pollinator communities associated with the variation in the VOCs emission, even after removing potential confounding effects, suggesting some stability in the compounds attractive to a given pollinator species. However, only one species showed significant geographical differences among populations tested in both conditions, suggesting local genetic adaptation. Another species showed geographical variation in VOC proportion in the field, but these results were not confirmed by the greenhouse extractions, suggesting an effect of phenotypic plasticity. Our findings suggest that geographical variation of floral scent may, in some cases, be genetically based and possibly explained by pollinator‐mediated selection, even in generalist pollinated species, which represent the large majority of pollination systems. However, our results also showed significant phenotypic plasticity, suggesting that studies of floral volatiles must be conducted in natural populations to obtain a representative picture of the signal that can be potentially perceived by pollinators. A free Plain Language Summary can be found within the Supporting Information of this article.

Limestone quarries are the most important refuge for a formerly widespread grassland butterfly

Abstract Calcareous grasslands have an outstanding value for nature conservation. However, during the last century, they have suffered from severe area loss, fragmentation and degradation. Here, we studied the influence of macroclimate, landscape quality and habitat quality on populations of the Silver‐studded Blue, Plebejus argus, in calcareous grasslands and limestone quarries in a Central European landscape. Our study revealed that limestone quarries, especially those being actively managed, are the most important refuge for P. argus. Originally, the species was common in calcareous grasslands across the study area. More recently, however, patch occupancy was five times higher at quarries compared to calcareous grasslands and mean adult abundance nearly four times higher at occupied quarries than at occupied grasslands. The key driver of patch occupancy and adult abundance was a high abundance of the host plant. Adult abundance, additionally, increased with a sparse vegetation and a high cover of bedrock. The deterioration of habitat quality due to abandonment and decreasing grazing intensity has resulted in a strong decline of P. argus in calcareous grasslands. In contrast, quarries exhibit a very low successional speed due to their shallow soils. Hence, they are characterised by a high habitat quality for P. argus, i.e. dense stands of the host plant L. corniculatus, which grow on skeletal soils providing warm microclimatic conditions. Preserving limestone quarries with their early‐successional stages is of crucial importance for the conservation of P. argus.