Grassland Biodiversity Research Articles

Impact of exotic plantation on native Grassland Biodiversity: A 30-Year analysis in Tanzania’s southern highlands

Exotic trees have been introduced in various parts of the world for commercial and environmental reasons such as restoring degraded land and regulating the climate. Despite their economic benefits, they have been found to cause habitat loss and fragmentation, affect soil nutrient cycling, and deplete water quality and quantity. This study examined the extent of land use and land cover changes over the past 30 years, as well as the influence of exotic plant species on native grassland plant composition and diversity in Tanzania’s southern highlands. Drivers and the extent of changes were studied using Landsat imagery in 1990, 2000, 2010 and 2020. The study examined understory native plant species in 12 study sites, including grasslands as control sites near exotic plantations. The study used transects and rectangular plots to compare native plant species with those in exotic tree plantations. Trees with a stem diameter at breast height (DBH) of 10 cm or more were documented in 25 x 20 m plots, while shrubs with a DBH of 5 cm or more but less than 10 cm were recorded in 5 x 2 m sub-plots and grass as well as herbs were recorded in sub-sub plots of 2 x 0.5 m. The native plant composition and diversity were compared among exotic plantations (pine, eucalyptus and black wattle) and neighbouring grasslands. The generalised linear model (GLM) calculated the species abundance, while the native plant diversity in exotic plantations and grasslands was compared using a one-way analysis of variance (ANOVA). The study found that native species diversity is negatively impacted by exotic tree plantations, which displace natural grasslands (p < 0.05). Thus, wild medicinal plants, edible foods and habitats for flora and fauna, including pollinators, have decreased. The study recommends that afforestation and reforestation should emphasise native tree species for nature conservation.

Effects of species diversity on trait expression of the clonal herb Taraxacum officinale and its relation to genotype diversity and phenotypic plasticity.

Plant species respond to varying plant species diversity and associated changes in their abiotic and biotic environment with changes in their phenotype. However, it is not clear to what degree this phenotypic differentiation is due to genotype diversity within populations or phenotypic plasticity of plant individuals. We studied individuals of 16 populations of the clonal herb Taraxacum officinale grown in plant communities of different species richness in a 17-year-old grassland biodiversity experiment (Jena Experiment). We collected 12 individuals in each population to measure phenotypic traits and identify distinct genotypes using microsatellite DNA markers. Plant species richness did not influence population-level genotype and trait diversity. However, it affected the expression of several phenotypic traits, e.g. leaf and inflorescence number, maximum leaf length and seed mass, which increased with increasing plant species richness. Moreover, population-level trait diversity correlated positively with genotype richness for leaf dry matter content (LDMC) and negatively with inflorescence number. For several traits (i.e. seed mass, germination rate, LDMC, specific leaf area (SLA)), a larger portion of variance was explained by genotype identity, while variance in other traits (i.e. number of inflorescences, leaf nitrogen concentration, leaf number, leaf length) resided within genotypes and thus was mostly due to phenotypic plasticity. Overall, our findings show that plant species richness positively affected the population means of some traits related to whole-plant performance, whose variation was achieved through both phenotypic plasticity and genotype composition of a population.

Competition between alien and native species in xerothermic steno-Mediterranean grasslands: Cenchrus setaceus and Hyparrhenia hirta in Sicily and southern Italy

AbstractPerennial dry grassland communities, vital for plant biodiversity conservation in the Mediterranean, often harbor rare and endangered species. However, these habitats face threats, including the invasion of alien species. Cenchrus setaceus, a highly invasive grass, is spreading in the Mediterranean region. Historical records and observations document its establishment and invasiveness across various Italian regions. This study investigates the impact of C. setaceus on native grasslands dominated by Hyparrhenia hirta. We assessed the impact of C. setaceus invasion on plant biodiversity in Sicily and southern Italy, and we identified and characterized plant species’ composition using Ellenberg indicator values. The intention to analyze species richness, diversity, and ecological indicators is also emphasized. Starting from the use of the phytosociological method, multivariate analysis and Ellenberg indicator values to assess the impact of C. setaceus on grasslands composition were considered. There are several similarities and differences in diversity, floristic composition, and ecological traits between the two grassland types. A deep comparison with central European studies and evaluation of the impact of C. setaceus on species richness and community dynamics in Mediterranean habitats were concluded. Although C. setaceus is invading native grasslands, it does not drastically reduce species richness. The ecological implications of the invasion are explored, urging ongoing monitoring and collaborative efforts for effective conservation. The importance of interdisciplinary cooperation is highlighted to address the threat of invasive species and sustain the biodiversity of Mediterranean grasslands.

Plant invasion alters movement behaviour in endangered butterflies but not their morphology or genetic variability

Invasions of alien plants often result in biodiversity loss and may impact the biology of native species. However, the effects of biological invasions on the behavioural responses of native species have rarely been investigated. We studied how the alteration of habitat due to the invasion of alien goldenrod (Solidago spp) affects a native butterfly, the scarce large blue Phengaris teleius, which is a flagship species for grassland biodiversity conservation. To better understand immediate responses in flight behaviour (daily movements, resting, and dispersal) to a new habitat, we performed observations of experimentally translocated butterflies of two origins (invaded vs. non-invaded habitats) to four different environments: invaded habitat, non-invaded habitat, invaded matrix, non-invaded matrix. Moreover, we tested whether the level of invasion may be related to the variation in morphological traits associated with flight (wing size, body mass) and genetic variability. Flight behaviour was affected by the high goldenrod cover and the sex of the butterflies, regardless of the butterflies’ origin. In the habitat and matrix invaded by goldenrod, the butterflies tended to display dispersal behaviour more often compared to the non-invaded ones. Flight distances were longest in the matrix with goldenrod and resting time was longest in habitats invaded by goldenrod. Analysis of morphological traits as well as eight microsatellite loci did not reveal significant differences in morphology or genetic variation among the populations studied.

The Effects of Infectious Diseases on the Consequences of Interspecific Competition in Grassland Communities

As infectious diseases have a severe impact on the individual survival and competitive ability of host species in grassland communities, competition between relevant species may have different consequences, potentially influencing the species composition of grassland communities and the functioning of grassland ecosystems. Understanding the impact of infectious diseases on competition is thus crucial for the health management of grassland ecosystems. How do infectious diseases affect the competitive coexistence of grassland plant species? In this study, by drawing on Tilman’s multispecies competition model and incorporating the spread characteristics of grassland plant diseases, we built three spatial competition models of two grass species subject to infectious diseases, and we analyzed the invasion conditions of infectious diseases and how they impact the population dynamics and competitive consequences of the species. Our model revealed the following: (1) Diseases with high transmission rates and low virulence are more likely to invade populations, while the presence of non-host species is detrimental to disease invasion. (2) Disease promotes the coexistence of competing species, breaking down the original competition–compromise trade-off mechanism for species coexistence and greatly expanding the range of parameters within which the two species can coexist. (3) Pathogen infections indirectly weaken the suppression of inferior species by dominant species, which is similar to the cascade effect seen in trophic interactions. Our findings highlight the importance of disease in species coexistence and grassland biodiversity maintenance.

Diversity Levels under Different Grazing Intensities in Semi-Wet Grasslands

The biodiversity of grasslands has been shaped by long-time interaction between natural processes and human activities, such as grazing. Traditional grazing management by animals contributes to the maintenance of high biodiversity in grasslands. However, changes in land use in recent years such as the abandonment of animal husbandry or intensification of grazing, pose a threat to grasslands biodiversity. The aim of the present study was to investigate the compositional and functional diversity in semi-humid grasslands of northern Greece under different grazing intensities. Three sites with similar vegetation and composition but different grazing intensities were selected in Taxiarchis University Forest of Mountain Holomontas. The three grazing intensities were (1) ungrazed, for more than 40 years, (2) moderate grazed, and (3) highly grazed. The ungrazed area showed an increase in vegetation cover and a decrease in bare ground. In comparison to grazed areas, the ungrazed one showed lower levels of grasses and legumes but higher abundances of woody and broad-leaved species. The highest values of all the studied diversity indices (Shannon–Wiener (H), Simpson Diversity Index, Jaccard, and species abundance) were recorded at moderate grazing intensity. Differences were recorded between the grazed and ungrazed areas in all of the quantitative traits (specific leaf area, leaf dry matter content, stem dry matter content, vegetative and reproductive plant height, leaf nitrogen, and phosphorus concentration). Protecting sensitive mountainous grasslands from both overgrazing and abandonment requires a balanced and sustainable management approach.

Deep learning-based detection of indicator species for monitoring biodiversity in semi-natural grasslands

Deep learning (DL) has huge potential to provide valuable insights into biodiversity changes in species-rich agricultural ecosystems such as semi-natural grasslands, helping to prioritize and plan conservation efforts. However, DL has been underexplored in grassland conservation efforts, hindered by data scarcity, intricate ecosystem interactions, and limited economic incentives. Here, we developed a DL-based object-detection model to identify indicator species, a group of vascular plant species that serve as surrogates for biodiversity assessment in high nature value (HNV) grasslands. We selected indicator species Armeria maritima, Campanula patula, Cirsium oleraceum, and Daucus carota. To overcome the hurdle of limited data, we grew indicator plants under controlled greenhouse conditions, generating a sufficient dataset for DL model training. The model was initially trained on this greenhouse dataset. Then, smaller datasets derived from an experimental grassland plot and natural grasslands were added to the training to facilitate the transition from greenhouse to field conditions. Our optimized model achieved remarkable average precision (AP) on test datasets, with 98.6 AP50 on greenhouse data, 98.2 AP50 on experimental grassland data, and 96.5 AP50 on semi-natural grassland data. Our findings highlight the innovative application of greenhouse-grown specimens for the in-situ identification of plants, bolstering biodiversity monitoring in grassland ecosystems. Furthermore, the study illuminates the promising role of DL techniques in conservation programs, particularly as a monitoring tool to support result-based agri-environment schemes.

Common soil history is more important than plant history for arbuscular mycorrhizal community assembly in an experimental grassland diversity gradient

The relationship between biodiversity and ecosystem functioning strengthens with ecosystem age. However, the interplay between the plant diversity - ecosystem functioning relationship and Glomeromycotinian arbuscular mycorrhizal fungi (AMF) community assembly has not yet been scrutinized in this context, despite AMF’s role in plant survival and niche exploration. We study the development of AMF communities by disentangling soil- and plant-driven effects from calendar year effects. Within a long-term grassland biodiversity experiment, the pre-existing plant communities of varying plant diversity were re-established as split plots with combinations of common plant and soil histories: split plots with neither common plant nor soil history, with only soil but no plant history, and with both common plant and soil history. We found that bulk soil AMF communities were primarily shaped by common soil history, and additional common plant history had little effect. Further, the steepness of AMF diversity and plant diversity relationship did not strengthen over time, but AMF community evenness increased with common history. Specialisation of AMF towards plant species was low throughout, giving no indication of AMF communities specialising or diversifying over time. The potential of bulk soil AMF as mediators of variation in plant and microbial biomass over time and hence as drivers of biodiversity and ecosystem relationships was low. Our results suggest that soil processes may be key for the build-up of plant community-specific mycorrhizal communities with likely feedback effects on ecosystem productivity, but the plant-available mycorrhizal pool in bulk soil itself does not explain the strengthening of biodiversity and ecosystem relationships over time.

Environment and management jointly shape the spatial patterns of plant species diversity of moist grasslands in the mountains of Northeastern Yunnan

Grasslands account for about a quarter of the Earth’s land area and are one of the major terrestrial ecosystems, with significant ecological and economic value. The influence of environmental factors and management types on grassland biodiversity has garnered considerable attention. This study investigated how patterns of species richness are influenced by geographical distance, environmental gradients, and management type in the grasslands of northeastern Yunnan, China. We used structural equation modeling to disentangle the impacts of environment and management on phylogenetic community structure, and partial Mantel tests to estimate the roles of dispersal limitation and environmental filtering on taxonomic and phylogenetic beta diversity of three types of grasslands. Our results show that taxonomic alpha diversity increased in grazed grasslands and decreased in mowed grasslands, compared with protected grasslands. However, the phylogenetic structure of both grazed and mowed grassland communities was clustered, whereas that of protected communities was random. Moreover, both grazing and mowing significantly reduced the taxonomic and phylogenetic beta diversity of grasslands, with the lowest values observed in mowed grasslands. Both taxonomic and phylogenetic beta diversity were dominated by species turnover under different management types. The taxonomic and phylogenetic beta diversities of protected and grazed grasslands were simultaneously affected by environmental filtering and dispersal limitation, with the later playing a stronger role. In addition, mowing and related management measures had a stronger filtering effect on grassland community structure, as reflected by changes in community composition.

Reversing expansion of Calamagrostis epigejos in Carpathian mountain grasslands by mowing and application of hemiparasitic Rhinanthus alectorolophus

AbstractQuestionsThe expansion of Calamagrostis epigejos poses a significant threat to the biodiversity of mountain grasslands. We asked whether grasslands dominated by C. epigejos can be restored through mowing and the application of hemiparasitic Rhinanthus alectorolophus.LocationCarpathian Violion caninae alliance mountain grassland close to Vrchslatina, Veporské vrchy Mts, Slovakia.MethodsWe conducted a before–after control–impact experiment in a grassland entirely dominated by C. epigejos: six blocks, each with four treatment combinations: (i) mowing once in summer, (ii) mowing in summer and autumn, (iii) mowing in summer and seed sowing of R. alectorolophus, (iv) mowing in summer and autumn along with seed sowing of R. alectorolophus. We monitored the above‐ground biomass of C. epigejos, R. alectorolophus, the combined above‐ground biomass of other species, and the vegetation composition annually from 2014 to 2017. Linear mixed‐effect models and redundancy analysis (RDA) were employed to analyze the effects of the treatments on C. epigejos and community parameters.ResultsSowing established R. alectorolophus at the plots mown twice in the first year, but its density strongly declined in subsequent years. R. alectorolophus and mowing twice significantly reduced C. epigejos biomass and herb layer cover. They also increased community evenness and the ratio between other species and C. epigejos biomass with a more pronounced effect on the plots where R. alectorolophus was applied. Mowing twice led to increased species richness, evenness, the number of target grassland species and their proportion in the community. R. alectorolophus had an additional positive impact on community evenness and the proportion of target species. RDA identified R. alectorolophus as the main driver of the directional community change triggered by the experimental treatments.ConclusionMowing twice per season proves to be an efficient restoration management strategy for mountain grasslands dominated by C. epigejos. Sowing R. alectorolophus, however, may be employed as an additional measure to accelerate the decline of C. epigejos at the outset of the restoration process and enhance community structure and composition.

Detecting flowers on imagery with computer vision to improve continental scale grassland biodiversity surveying

Abstract Large‐scale biodiversity monitoring is essential for assessing biodiversity trends, yet traditional surveying methods are limited in the spatial/temporal scale they can cover. Recent technological developments have led to computer vision‐based species identification tools, such as the Pl@ntNet application. Increasing accuracy of such algorithms presents an opportunity of integrating computer vision into larger monitoring schemes and could lead to automating ground‐based evidence provision related to agri‐environmental measures (e.g. flower strips, field margins). However, images from surveys or farmer declarations do not live up to the standards of current applications. In order to integrate these automated methods into biodiversity monitoring, more generalized models are needed. We create a dataset using 500 manually delineated images of vegetation patches in European grasslands taken during the Land Use/cover Area Survey (LUCAS) grassland module. We train the Faster R‐CNN model to detect and extract individual flower objects. Using this model, we extract the abundance of flowers in an image, analyse their colour distribution, and use the Pl@ntNet application to identify the species of the individual flowers detected. The best model reaches precision and recall of 0.89/0.61 and predicts 1377 flowers on the 100 test images distributed between 10 colours. Using Pl@ntNet, only 52 flowers were identified with a certainty score above 0.5 due to the limitations in image size and quality. Of these flowers, 30% were correctly automatically identified at the species level and 42% at the genus level. The results show that we can automatically extract valuable information on floral abundances, colours, and sizes from images of vegetation patches, though in most cases better images are needed for species identification. Despite limitations with image quality, integrating this workflow into large‐scale monitoring could speed up the sampling process and allow for better spatial and temporal data on floral diversity and abundance.

Exploring the effects of habitat management on grassland biodiversity: A case study from northern Serbia.

Grasslands represent a biodiversity hotspot in the European agricultural landscape, their restoration is necessary and offers a great opportunity to mitigate or halt harmful processes. These measures require a comprehensive knowledge of historical landscape changes, but also adequate management strategies. The required data was gathered from the sand grasslands of northern Serbia, as this habitat is of high conservation priority. This area also has a long history of different habitat management approaches (grazing and mowing versus unmanaged), which has been documented over of the last two decades. This dataset enabled us to quantify the effects of different measures across multiple taxa (plants, insect pollinators, and birds). We linked the gathered data on plants, pollinators, and birds with habitat management measures. Our results show that, at the taxon level, the adopted management strategies were beneficial for species richness, abundance, and composition, as the highest diversity of plant, insect pollinator, and bird species was found in managed areas. Thus, an innovative modelling approach was adopted in this work to identify and explain the effects of management practices on changes in habitat communities. The findings yielded can be used in the decision making as well as development of new management programmes. We thus posit that, when restoring and establishing particular communities, priority needs to be given to species with a broad ecological response. We recommend using the decision tree as a suitable machine learning model for this purpose.

Cumulative nitrogen enrichment alters the drivers of grassland overyielding

Effects of plant diversity on grassland productivity, or overyielding, are found to be robust to nutrient enrichment. However, the impact of cumulative nitrogen (N) addition (total N added over time) on overyielding and its drivers are underexplored. Synthesizing data from 15 multi-year grassland biodiversity experiments with N addition, we found that N addition decreases complementarity effects and increases selection effects proportionately, resulting in no overall change in overyielding regardless of N addition rate. However, we observed a convex relationship between overyielding and cumulative N addition, driven by a shift from complementarity to selection effects. This shift suggests diminishing positive interactions and an increasing contribution of a few dominant species with increasing N accumulation. Recognizing the importance of cumulative N addition is vital for understanding its impacts on grassland overyielding, contributing essential insights for biodiversity conservation and ecosystem resilience in the face of increasing N deposition.

How to successfully improve the biodiversity of city grasslands?

Urban grasslands (UG) are among the most common types of urban green areas. They are usually species poor, and spontaneous plant migration, which can increase biodiversity, is limited. To improve the range of ecosystem services provided by UG, various seed mixtures are applied during the establishment and restoration of UG. These mixtures vary in content, quality, and cost. High-quality seed mixtures are expensive and are usually only available in small amounts. Meanwhile, alternative methods of seed introduction (e.g., fresh hay application, seeds harvested by brush) have not been well studied in UG restoration, and inexpensive commercial mixtures could have low quality and lead to poor restoration outcomes. Here, we tested the effectiveness of different seed sources to create high-quality UG at two study sites. Based on the results, all seed addition methods increased the species richness of restored grasslands. The outcome of seed addition was satisfactory regardless of differences in residual vegetation species composition and soil properties between the sites. The species richness on plots that received a commercial mixture of flower meadow plants dedicated to pollinators decreased after overwintering. The alternative seed sources (fresh hay and seed incidentally collected during mowing) yielded grassland quality that was comparable to that on plots that received high-quality mixtures with known seed origin (a seminatural meadow mixture and a mixture with the addition of grasses).

Plant diversity and community age stabilize ecosystem multifunctionality.

It is well known that biodiversity positively affects ecosystem functioning, leading to enhanced ecosystem stability. However, this knowledge is mainly based on analyses using single ecosystem functions, while studies focusing on the stability of ecosystem multifunctionality (EMF) are rare. Taking advantage of a long-term grassland biodiversity experiment, we studied the effect of plant diversity (1-60 species) on EMF over 5 years, its temporal stability, as well as multifunctional resistance and resilience to a 2-year drought event. Using split-plot treatments, we further tested whether a shared history of plants and soil influences the studied relationships. We calculated EMF based on functions related to plants and higher-trophic levels. Plant diversity enhanced EMF in all studied years, and this effect strengthened over the study period. Moreover, plant diversity increased the temporal stability of EMF and fostered resistance to reoccurring drought events. Old plant communities with shared plant and soil history showed a stronger plant diversity-multifunctionality relationship and higher temporal stability of EMF than younger communities without shared histories. Our results highlight the importance of old and biodiverse plant communities for EMF and its stability to extreme climate events in a world increasingly threatened by global change.

Precipitation variation: a key factor regulating plant diversity in semi-arid livestock grazing lands.

Livestock presence impacts plant biodiversity (species richness) in grassland ecosystems, yet extent and direction of grazing impacts on biodiversity vary greatly across inter-annual periods. In this study, an 8-year (2014-2021) grazing gradient experiment with sheep was conducted in a semi-arid grassland to investigate the impact of grazing under different precipitation variability on biodiversity. The results suggest no direct impact of grazing on species richness in semi-arid Stipa grassland. However, increased grazing indirectly enhanced species richness by elevating community dominance (increasing the sheltering effect of Stipa grass). Importantly, intensified grazing also regulates excessive community biomass resulting from increased inter-annual wetness (SPEI), amplifying the positive influence of annual humidity index on species richness. Lastly, we emphasize that, in water-constrained grassland ecosystems, intra-annual precipitation variability (PCI) was the most crucial factor driving species richness. Therefore, the water-heat synchrony during the growing season may alleviate physiological constraints on plants, significantly enhancing species richness as a result of multifactorial interactions. Our study provides strong evidence for how to regulate grazing intensity to increase biodiversity under future variable climate patterns. We suggest adapting grazing intensity according to local climate variability to achieve grassland biodiversity conservation.

Grass Evolutionary Lineages Can Be Identified Using Hyperspectral Leaf Reflectance

AbstractHyperspectral remote sensing has the potential to map numerous attributes of the Earth’s surface, including spatial patterns of biological diversity. Grasslands are one of the largest biomes on Earth. Accurate mapping of grassland biodiversity relies on spectral discrimination of endmembers of species or plant functional types. We focused on spectral separation of grass lineages that dominate global grassy biomes: Andropogoneae (C4), Chloridoideae (C4), and Pooideae (C3). We examined leaf reflectance spectra (350–2,500 nm) from 43 grass species representing these grass lineages from four representative grassland sites in the Great Plains region of North America. We assessed the utility of leaf reflectance data for classification of grass species into three major lineages and by collection site. Classifications had very high accuracy (94%) that were robust to site differences in species and environment. We also show an information loss using multispectral sensors, that is, classification accuracy of grass lineages using spectral bands provided by current multispectral satellites is much lower (accuracy of 85.2% and 61.3% using Sentinel 2 and Landsat 8 bands, respectively). Our results suggest that hyperspectral data have an exciting potential for mapping grass functional types as informed by phylogeny. Leaf‐level hyperspectral separability of grass lineages is consistent with the potential increase in biodiversity and functional information content from the next generation of satellite‐based spectrometers.

Grazing exclusion jeopardizes plant biodiversity effect but enhances dryness effect on multifunctionality in arid grasslands

Grassland biodiversity is vital for the provision of multiple ecosystem functions, termed ecosystem multifunctionality. As an effective practice of grassland management, grazing exclusion is widely used to restore the ecosystem multifunctionality of degraded grasslands, but it might not be always beneficial for conserving grassland biodiversity. Moreover, when grazing is excluded, it remains unknown whether grassland biodiversity promotes multifunctionality. Here, we conducted a field experiment of grazing exclusion along a gradient of climatic aridity across four major grassland types in the arid grasslands of northern China. We determined the effects of grazing exclusion on biodiversity and multifunctionality, and further investigated how grazing exclusion could modify biodiversity-multifunctionality relationships. We found that grazing exclusion increased soil fungal diversity, but had negligible effects on plant species richness and soil bacterial diversity. The effects of grazing exclusion on multifunctionality varied among grassland types: it promoted multifunctionality only in less arid grasslands. Importantly, multifunctionality was positively associated with plant species richness under grazing, but this positive association disappeared under grazing exclusion. In addition, we showed that climatic aridity affected multifunctionality indirectly through its negative effect on plant species richness under grazing, whereas such effect disappeared under grazing exclusion. Furthermore, aridity weakly reduced multifunctionality under grazing, and its negative effect was strengthened under grazing exclusion. Our results suggest that grazing exclusion restrains the capacity of plant biodiversity to sustain multiple ecosystem functions, and moreover, aggravates the negative influences of climatic dryness on ecosystem multifunctionality. Our findings illustrate the value of grazing for maintaining biodiversity-multifunctionality relationships and for mitigating the impacts of climate change in arid grasslands.

Is spectral pixel-to-pixel variation a reliable indicator of grassland biodiversity? A systematic assessment of the spectral variation hypothesis using spatial simulation experiments

Covering 30%–40% of the terrestrial surface, grasslands are important hosts of biodiversity, crucial for nutrient cycles and carbon sequestration. However, these ecosystems face a pressing threat in the form of biodiversity loss, which can disrupt their functioning and resilience. Addressing this challenge requires effective monitoring of biodiversity changes on large scales. Remote sensing emerges as a valuable tool in this endeavour, enabling the assessment of grassland biodiversity through the analysis of vegetation patterns, species composition, and ecosystem health over extensive areas.According to the spectral variation hypothesis (SVH), the link between pixel-to-pixel spectral variation and species diversity in remote sensing images can be used to retrieve plant diversity based on spectral data. Nevertheless, the transferability of the proposed relation across ecosystem types, seasons and spatial resolutions remains unclear. The absence of comprehensive data has hindered systematic assessments of the SVH so far, which would ideally incorporate coherent sets of diversity estimates from remote sensing data and in-situ plant diversity measurements.With this study, we present a combined approach that brings together trait data from field measurements, simulations of spatial species distributions and radiative transfer models for a systematic and in-depth analysis of the SVH in temperate grasslands. Based on simulated grassland communities with different diversity levels, we assessed the spectral-to-species diversity relationship across (1) three temperate grassland types, (2) three seasons and, (3) five spatial resolutions (from 10 m to 0.2 m pixel size). We used the mean Euclidean distance and Rao’s Q as measures for spectral diversity and different biodiversity indices to describe the species and trait diversity of the simulated grassland communities.Based on 45000 simulated grassland communities in five different spatial resolutions, we found that the spectral-to-species diversity relationship is not stable across grassland types and seasons, despite the spectral diversity metric used. Correlations with spectral diversity were inconsistent for the different applied diversity indices and no single index outperformed the others. Spectral diversity was mainly driven by the spatial resolution (i.e. pixel size) of the image and not by species richness (SR) or functional trait diversity (FD) per se. Our results further underline that the link between SR and FD is not always prominent in plant communities and the basic assumption of the SVH is fulfilled only under certain conditions. Consequently, we argue that FD, which is an important driver of the spectral signature of a plant community, is not inevitably linked to the number of present species in an image. We conclude that the interplay of SR and FD is crucial for the expression of the spectral-to-species diversity relationship. This study clearly underlines the context-dependency of the SVH and we point out that, although of promising value for distinct ecosystems, it is not universally applicable in grasslands.

Elevated CO2 interacts with nutrient inputs to restructure plant communities in phosphorus-limited grasslands.

Globally pervasive increases in atmospheric CO2 and nitrogen (N) deposition could have substantial effects on plant communities, either directly or mediated by their interactions with soil nutrient limitation. While the direct consequences of N enrichment on plant communities are well documented, potential interactions with rising CO2 and globally widespread phosphorus (P) limitation remain poorly understood. We investigated the consequences of simultaneous elevated CO2 (eCO2 ) and N and P additions on grassland biodiversity, community and functional composition in P-limited grasslands. We exposed soil-turf monoliths from limestone and acidic grasslands that have received >25 years of N additions (3.5 and 14 g m-2 year-1 ) and 11 (limestone) or 25 (acidic) years of P additions (3.5 g m-2 year-1 ) to eCO2 (600 ppm) for 3 years. Across both grasslands, eCO2 , N and P additions significantly changed community composition. Limestone communities were more responsive to eCO2 and saw significant functional shifts resulting from eCO2 -nutrient interactions. Here, legume cover tripled in response to combined eCO2 and P additions, and combined eCO2 and N treatments shifted functional dominance from grasses to sedges. We suggest that eCO2 may disproportionately benefit P acquisition by sedges by subsidising the carbon cost of locally intense root exudation at the expense of co-occurring grasses. In contrast, the functional composition of the acidic grassland was insensitive to eCO2 and its interactions with nutrient additions. Greater diversity of P-acquisition strategies in the limestone grassland, combined with a more functionally even and diverse community, may contribute to the stronger responses compared to the acidic grassland. Our work suggests we may see large changes in the composition and biodiversity of P-limited grasslands in response to eCO2 and its interactions with nutrient loading, particularly where these contain a high diversity of P-acquisition strategies or developmentally young soils with sufficient bioavailable mineral P.