Following plant community assembly in semi-natural European grasslands by analyzing environmental factors vs. history effects

Characteristics used to categorize plant species into functional groups for their effects on ecosystem functioning may also be relevant to higher trophic levels. In addition, plant and consumer diversity should be positively related because more diverse plant communities offer a greater variety of resources for the consumers. Thus, the functional group composition and richness of a plant community may affect the composition and diversity of the herbivores and even higher trophic levels associated with that community. We tested this hypothesis by sampling arthropods with a vacuum sampler (34 531 individuals of 494 species) from an experiment in which we manipulated plant functional group richness and composition. Plant manipulations included all combinations of three functional groups (forbs, C 3 graminoids, and C 4 graminoids) removed zero, one, or two at a time from grassland plots at Cedar Creek Natural History Area, MN. Although total arthropod species richness was unrelated to plant functional group richness or composition, the species richness of some arthropod orders was affected by plant functional group composition. Two plant characteristics explained most of the effects of plant functional groups on arthropod species richness. Nutritional quality, a characteristic related to ecosystem functioning, and taxonomic diversity, a characteristic not used to designate plant functional groups, seemed to affect arthropod species richness both directly and indirectly. Thus, plant functional groups designated for their effects on ecosystem processes will only be partially relevant to consumer diversity and abundance.

Summary1. Many rangelands evolved under an interactive disturbance regime in which grazers respond to the spatial pattern of fire and create a patchy, heterogeneous landscape. Spatially heterogeneous fire and grazing create heterogeneity in vegetation structure at the landscape level (patch contrast) and increase rangeland biodiversity. We analysed five experiments comparing spatially heterogeneous fire treatments to spatially homogeneous fire treatments on grazed rangeland along a precipitation gradient in the North American Great Plains.2. We predicted that, across the precipitation gradient, management for heterogeneity increases both patch contrast and variance in the composition of plant functional groups. Furthermore, we predicted that patch contrast is positively correlated with variance in plant functional group composition. Because fire spread is important to the fire–grazing interaction, we discuss factors that reduce fire spread and reduce patch contrast despite management for heterogeneity.3. We compared patch contrast across pastures managed for heterogeneity and pastures managed for homogeneity with a linear mixed effect (LME) regression model. We used the LME model to partition variation in vegetation structure to each sampled scale so that a higher proportion of variation at the patch scale among pastures managed for heterogeneity indicates patch contrast. To examine the relationship between vegetation structure and plant community composition, we used constrained ordination to measure variation in functional group composition along the vegetation structure gradient. We used the meta‐analytical statistic, Cohen’s d, to compare effect sizes for patch contrast and plant functional group composition.4. Management for heterogeneity increased patch contrast and increased the range of plant functional group composition at three of the five experimental locations.5. Plant functional group composition varied in proportion to the amount of spatial heterogeneity in vegetation structure on pastures managed for heterogeneity.6. Synthesis and applications. Pyric‐herbivory management for heterogeneity created patch contrast in vegetation across a broad range of precipitation and plant community types, provided that fire was the primary driver of grazer site selection. Management for heterogeneity did not universally create patch contrast. Stocking rate and invasive plant species are key regulators of heterogeneity, as they determine the influence of fire on the spatial pattern of fuel, vegetation structure and herbivore patch selection, and therefore also require careful management.

Summary 1. The benefits of plant functional group and plant species diversity for sustaining primary productivity have been extensively studied. However, few studies have simultaneously explored potential benefits of plant species and functional group richness and composition for the delivery of other ecosystem services and their dependency on resource availability. 2. Here, we investigated in soils of different fertility the effects of plant species and functional group richness and composition on carbon (C) and nitrogen (N) stocks in vegetation, soil and soil microbes and on CO2 exchange and the loss of C and N from soil through leaching. We established plant communities from a pool of six mesotrophic grassland species belonging to one of three functional groups (C3 grasses, forbs and legumes) in two soils of contrasting fertility. We varied species richness using one, two, three or six species and one, two or three functional groups. 3. After 2 years, vegetation C and N and soil microbial biomass were greater in the more fertile soil and increased significantly with greater numbers of plant species and functional group richness. The positive effect of plant diversity on vegetation C and N coincided with reduced loss of water and N through leaching, which was especially governed by forbs, and increased rates of net ecosystem CO2 exchange. 4. Soil C and N pools were not affected by the number of plant species or functional group richness per se after 2 years, but were enhanced by the presence and biomass of the legumes Lotus corniculatus and Trifolium repens. 5. Synthesis. Collectively, our findings indicate that changes in plant species and functional group richness influence the storage and loss of both C and N in model grassland communities but that these responses are related to the presence and biomass of certain plant species, notably N fixers and forbs. Our results therefore suggest that the co‐occurrence of species from specific functional groups is crucial for the maintenance of multifunctionality with respect to C and N storage in grasslands.

Theories and models attempt to explain how and why particular plant species grow together at particular sites or why invasive exotic species dominate plant communities. As local climates change and human‐use degrades and disturbs ecosystems, a better understanding of how plant communities assemble is pertinent, particularly when restoring grassland ecosystems that are frequently disturbed. One such community assembly theory is priority effects, which suggests that arrival order of species into a community alters plant–plant interactions and community assembly. Theoretically, priority effects can have lasting effects on ecosystems and will likely be altered as the risk of invasion by exotic species increases. It is difficult to predict how and when priority effects occur, as experimental reconstruction of arrival order is often difficult in adequate detail. As a result, limited experimental studies have explored priority effects on plant community assembly and plant invasions. To determine if and how priority effects affect the success of invasive species, we conducted a greenhouse study exploring how the arrival order of an invasive grass, Bromus tectorum, affects productivity and community composition when grown with native grasses. We found evidence for priority effects, as productivity was positively related to dominance of B. tectorum and was greater the earlier B. tectorum arrived. This suggests that priority effects could be important for plant communities as the early arrival of an invasive species drastically impacted the productivity and biodiversity of our system at the early establishment stages of plant community development.

IntroductionBiodiversity loss and climate change have been determined as major global drivers affecting ecosystems and their functioning. In this context, drought was shown to have negative effects on ecosystems by disrupting ecological processes, which could be buffered in more biodiverse systems. Many studies, however, focus on effects on aboveground communities of single drought events, while dynamics of soil-borne communities are still widely unclear, despite their important roles in ecosystem functioning.MethodsTo elucidate the effect of recurrent summer drought periods on fungal communities in a long-term grassland biodiversity experiment, roof shelters were installed on grassland plots ranging in plant species richness from 1 to 16 species and plant functional group richness (1-4 groups) and composition. After 9 years of summer droughts, bulk soil was sampled and used for Illumina sequencing of the ITS2 and SSU genes to characterize the total fungal and arbuscular mycorrhizal fungal (AMF) communities, respectively.ResultsWe found shifts of AMF and total fungi community structures caused by recurrent drought and plant species richness, but no buffering of drought effects by plant diversity. Alpha-diversity (VT or ASV richness) of both AMF and total fungi increased with plant species richness but was not significantly affected by drought. Even though drought overall had minimal long-lasting effects, we found Diversispora and Paraglomus among the AMF and Penicillium among total fungal communities to be more abundant after the drought treatment. AMF communities were affected by the presence of individual plant functional groups, reacting stronger to presence of legumes under drought, while total fungal interaction with plant communities were similar under drought as control. AMF α-diversity differed between plant functional groups in control conditions but was independent of plant community composition under drought. In contrast, total fungi α-diversity was increased by presence of herbs and legumes only under drought.DiscussionFrom our results, we conclude that recurring moderate summer droughts do not strongly affect soil fungal communities. All shifts can be explained by indirect effects through the plant community and its top-down effect on soils altered by drought. Further, AMF are not less affected than total fungal communities, but rather respond differently by interacting more strongly with legumes in response to drought. Consequently, not plant species richness, but plant functional composition, dominates in shaping fungal communities under recurrent droughts.

Soil microbial communities resistant to changes in plant functional group composition

Question:Which are the plant functional groups responding most clearly to agricultural disturbances? Which are the relative roles of habitat availability, landscape configuration and agricultural land use intensity in affecting the functional composition and diversity of vascular plants in agricultural landscapes?Location:25 agricultural landscape areas in seven European countries.Methods:We examined the plant species richness and abundance in 4 km × 4 km landscape study sites. The plant functional group classification was derived from the BIOLFLOR database. Factorial decomposition of functional groups was applied.Results:Natural habitat availability and low land use intensity supported the abundance and richness of perennials, sedges, pteridophytes and high nature quality indicator species. The abundance of clonal species, C and S strategists was also correlated with habitat area. An increasing density of field edges explained a decrease in richness of high nature quality species and an increase in richness of annual graminoids. Intensive agriculture enhanced the richness of annuals and low nature quality species.Conclusions:Habitat patch availability and habitat quality are the main drivers of functional group composition and plant species richness in European agricultural landscapes. Linear elements do not compensate for the loss of habitats, as they mostly support disturbance tolerant generalist species. In order to conserve vascular plant species diversity in agricultural landscapes, the protection and enlargement of existing patches of (semi‐) natural habitats appears to be more effective than relying on the rescue effect of linear elements. This should be done in combination with appropriate agricultural management techniques to limit the effect of agrochemicals to the fields.

Plant functional composition and species diversity affect soil C, N, and P during secondary succession of abandoned farmland on the Loess Plateau

Biodiversity–ecosystem functioning experiments have shown that plant species and functional group richness are important drivers of grassland productivity, but the impact that plant order of arrival (i.e. priority effects) has on grassland overyielding and its drivers (complementarity and dominance effects) has been overlooked so far. Using species‐specific plant biomass data collected in mixture and monoculture plots of a grassland field experiment (Jülich Priority Effect experiment) that manipulated the order of arrival of three plant functional groups (forbs, grasses and legumes), we quantified net biodiversity effects (overyielding) as well as complementarity and dominance effects in mixtures one and 2 years after sowing. In this experiment, priority effects were created by sowing one functional group 6 weeks before the two others. First, we tested whether plant order of arrival affected overyielding, complementarity and dominance effects. Second, we investigated whether the magnitude of net biodiversity, complementarity and dominance effects was dependent on the strength and direction of priority effects. We found that complementarity and dominance effects were affected by plant order of arrival during community assembly. In addition, we found that moving from negative to positive priority effects increased grassland overyielding, mainly via increased complementarity effects. These results highlight the need to combine biodiversity and assembly approaches in future ecosystem functioning research, as this will increase the predictive power of community ecology in conservation and ecological restoration. A free Plain Language Summary can be found within the Supporting Information of this article.

Producing grassland herbage with high yield and good nutritive value is a prerequisite of an efficient ruminant livestock production. Due to climate change, precipitation patterns are expected to vary and the frequency of extreme weather events like droughts are supposed to increase. Productive grassland requires a particularly sufficient and regular water supply during the growing season. Thus, grassland production, yield stability and nutritive value will be affected by drought. Because of this, adaptation strategies are necessary to ensure a sustainable future herbage production from grassland. Increasing plant biodiversity has been proposed as a way to improve ecosystem functions like productivity and nutritive value in grassland. There is an ongoing discussion on species richness' reactions to stress, especially drought stress, and on how productivity, nutritive value and water utilization are affected. Other investigations have stressed species identity and composition of functional groups as important factors for productivity and nutritive value. We, therefore, conducted a drought stress experiment in a vegetation hall from July 2009 to June 2011. The climatic conditions followed the normal seasonal pattern with frost in winter and higher temperatures in summer. Different drought stress conditions were performed over three periods in two growing seasons. Drought stress was induced by temporarily ceasing the watering of the containers after initial watering while soil water availability could be controlled. We chose productive agricultural species of temperate grasslands. Plants were sown in monoculture and three- and five-species mixtures and included the three functional groups legume (Trifolium repens L.), grass (Lolium perenne L., Dactylis glomerata L.) and forb (Plantago lanceolata L., Taraxacum officinale F.H. Wigg. agg.). This range of species number has been shown to affect productivity in biodiversity experiments. Effects of species richness and functional composition on yield, yield stability, water utilization and nutritive value (crude protein, water-soluble carbohydrates, neutral detergent fibre and acid detergent fibre) were examined. As indicators for the performance of yield and particularly agronomic water use efficiency (relation of yield and water use), we used nitrogen yield and concentration of swards as well as signatures of δ13C under not limited water supply and drought. Furthermore, in 2009, we conducted a short term field experiment at the experimental farm of the University of Goettingen at Relliehausen on old grassland. Here, influence of drought and species richness on yield and water utilization were also investigated. Our data show that drought stress lowered production and influenced water utilization. Both increased with the severity of the stress. Agronomic water use efficiency was unchanged or slightly increased under moderate stress but decreased under strong drought stress. Nitrogen yield and concentration were suitable indicators for agronomic water use efficiency while δ13C was less appropriate. Agronomic water use efficiency was increased by nitrogen. There was no or minor immediate impact of drought on nutritive value. Seasonal effects on nutritive value were more distinct. Generally, yield decrease of grassland herbage seems to be more important than changes in nutritive value. Species richness did not influence nutritive value or yield stability over the growing season. The occasional positive influence of species richness on yield and agronomic WUE and decrease of the influence under drought could be explained by a sampling effect. Well performing but drought sensitive legume increased with species richness. There was a hint that species richness also increased the rapidity of water use. Results of the field experiment support these data concerning drought effects, yield and water utilization. The “insurance hypothesis” that species richness can stabilize ecosystem functioning against environmental changes could not be confirmed. But functional groups composition of swards was an important determinant of performance in both unlimited water supply and drought stress. Especially legume had a positive influence on yield, agronomic water use efficiency and crude protein concentration but increased water use and seasonal variability. Grass stabilized yield and water use and increased water-soluble carbohydrates and fibre components while yield and agronomic water use efficiency decreased under the nitrogen limited conditions of our experiment. The functional group forb showed quite similar results regarding yield and water utilization but increased crude protein. Our results indicate that the predicted increase of droughts will reduce production and lead to a change in water utilization in productive grassland. Alteration in nutritive values will not be as important as decrease in yield. The investigated species richness seems to be less important than functional composition of grassland swards for production, water utilization and nutritive value. Thus, to cope with future climate change, an adapted sward composition might be one possibility to ensure ruminant livestock production from grassland.

Ecosystems are faced with high rates of species loss which has consequences for their functions and services. To assess the effects of plant species diversity on the nitrogen (N) cycle, we developed a model for monthly mean nitrate (NO3-N) concentrations in soil solution in 0–30 cm mineral soil depth using plant species and functional group richness and functional composition as drivers and assessing the effects of conversion of arable land to grassland, spatially heterogeneous soil properties, and climate. We used monthly mean NO3-N concentrations from 62 plots of a grassland plant diversity experiment from 2003 to 2006. Plant species richness (1–60) and functional group composition (1–4 functional groups: legumes, grasses, non-leguminous tall herbs, non-leguminous small herbs) were manipulated in a factorial design. Plant community composition, time since conversion from arable land to grassland, soil texture, and climate data (precipitation, soil moisture, air and soil temperature) were used to develop one general Bayesian multiple regression model for the 62 plots to allow an in-depth evaluation using the experimental design. The model simulated NO3-N concentrations with an overall Bayesian coefficient of determination of 0.48. The temporal course of NO3-N concentrations was simulated differently well for the individual plots with a maximum plot-specific Nash–Sutcliffe Efficiency of 0.57. The model shows that NO3-N concentrations decrease with species richness, but this relation reverses if more than approx. 25 % of legume species are included in the mixture. Presence of legumes increases and presence of grasses decreases NO3-N concentrations compared to mixtures containing only small and tall herbs. Altogether, our model shows that there is a strong influence of plant community composition on NO3-N concentrations.

ABSTRACTQuestionThe order of arrival of plant species during community assembly can affect how species interact with each other. These so‐called priority effects can have strong implications for the structure and functioning of plant communities. However, the extent to which the strength, direction, and persistence of priority effects are modulated by weather conditions during plant establishment (“year effects”) is not well known.LocationNiederhaverbeck, Bispingen, Germany.MethodsWe present the first results from a field experiment initiated in 2020 in Northern Germany to test how plant functional group (PFG) order of arrival and the year of initiation of an experiment interactively affect the structure and functioning of nutrient‐poor dry acidic grasslands, both above and below ground. To do this, we established the same experiment, manipulating the order of arrival of forbs, grasses, and legumes on the same site, but in different years representing different weather conditions.ResultsWe found that time since establishment was a stronger driver of plant community composition than PFG order of arrival and year of initiation. PFG order of arrival effects on plant diversity evolved over time and depended on the year of initiation of an experiment. Year of initiation, not PFG order of arrival, was the strongest driver of aboveground community productivity. Although we did not find an effect of PFG order of arrival on root productivity, it had a strong impact on the vertical distribution of roots. Communities where grasses were sown first rooted more shallowly than communities in which forbs or legumes were sown first.ConclusionsIn experimental dry acidic grassland communities, community composition and productivity are shaped by time since establishment and initial weather conditions, rather than PFG order of arrival (6‐week sowing interval). Importantly, our results demonstrate that manipulating PFG order of arrival is possibly an effective restoration measure to alter vertical root distribution towards more deep‐rooting communities when sowing forbs or legumes first. This in turn could benefit dry grasslands on sandy soils during periods of water deficit.

BackgroundThe priority effect of plant arrival is a key driver of community assembly and ecosystem succession during the restoration of degraded plant communities. However, the significance of the arrival order of different plant functional groups and their interactions with community assemblies remains unclear. Using a phytotron experiment with three fully crossed factors, we investigated the underlying mechanisms of priority effects and their relationships with the biomass and biodiversity effects in mixed plant communities by manipulating the order of arrival of species, isolation of roots, and removal of specific plants.ResultsThe results showed that the strength and direction of priority effects were influenced by arrival order, root interactions, asymmetric competition among species, and their interactions. The identities of early and late-sown species also determined the magnitude of priority effects. The priority effects were stronger in grass-first (24.76%) and legume-first communities (24.48%) than in forb-first communities. The pot biomass of the different priority treatments was highest in grass-first (5.85 g), followed by legume-first (3.94 g) and forb-first (2.48 g). The order of arrival in the mixture significantly affected the net biodiversity effects (P < 0.001), which were driven by dominance effects. The community had lower overall biomass when forbs were sown first, whereas the species grown later had fewer costs with an increased overall net benefit for the resulting community.ConclusionsOur results emphasize that root interactions and asymmetric competition are vital determinants of order-specific priority effects in community assemblies. In addition, the importance of the priority effect of forbs sown first is related to community assembly, which may be a key determinant in successfully establishing a highly diverse community in the early stages of restoration. Species with weak competition should be considered in the early stage of community assembly. The rational use of the priority effect is conducive to improving the quality and efficiency of ecological restoration efforts.

The vast majority of European grasslands strongly depend on the regular removal of aboveground biomass by agricultural land use, mostly grazing or mowing or a combination of both. These specific management schemes have strong influence on plant diversity and vegetation composition, depending on their particular characteristics and their intensity. For example, the presence or absence of fertilization will favour some species over others, changing plant communities accordingly. Additionally, the farmer's choice of a specific management scheme will also depend on the abiotic site conditions. This leads to a complex set of associated factors potentially affecting the structure and diversity of grasslands. In this study, we compiled a unique dataset of 169 differently managed grasslands (in total 202 plots), which were sampled in five regions across Germany. For each plot, we documented management characteristics, measured plant diversity and functional group composition, recorded endangered species according to red lists, and calculated Ellenberg indicator values. We assessed patterns in vegetation composition and diversity in relation to the particular management scheme, which was categorized as meadow, meadow with autumn or winter grazing (with mowing as predominant management), mown pasture (where mowing and grazing are used at roughly equal intensity), seasonal pasture (with grazing as predominant management) and year-round pasture. Our study showed that grasslands of different management schemes significantly differed in diversity, structure and functional composition. However, it also became obvious that vegetation composition was not strictly distinguished by management alone. Local and regional characteristics such as soil conditions, size of the grassland species pool or land-use history, often played a more prominent role than land use alone. Assumingly, the interplay of those local and regional characteristics with the pro portion of grazing and mowing at a particular site inhibit clear differences among our predefined management schemes. Nevertheless, species richness was the lowest in year-round pastures, moderate in meadows and highest in seasonal pastures. In contrast, year-round pastures harboured the highest mean numbers of endangered species. The dependency of a certain management scheme on site-specific environmental factors such as soil fertility, further complicated the clear separation of management effects from those of the environmental background. In summary, modern grassland management strongly shaped grassland vegetation, but today's combination of different management practices complicated the assessment of specific land-use effects on plant diversity. Thus, neither mowing nor grazing turned out to be ``the one and only'' management for nature conservation. Although our results challenge long-term prognoses for future vegetation development under modern grassland management, we clearly showed that low-intensity management and the absence of fertilization promoted plant diversity, with higher values in pastures compared to meadows and mown pastures.

Plant functional composition, defined by both community-weighted mean (CWM) traits and functional diversity, can provide insights into plant ecological strategies and community assembly. However, our understanding of plant functional composition during succession is largely based on aboveground traits. Here we investigated community-level traits and functional diversity for six pairs of analogous leaf and fine root traits of understory plants in a temperate forest swamp during succession with a decrease in soil pH and nutrient availability. CWMs of traits related to resource acquisition (including specific leaf area, specific root length, leaf N, leaf P, root N, and root P) decreased with succession, whereas those related to resource conservation (leaf dry matter content, root dry matter content, leaf tissue density, leaf C, and root C) increased along the forest swamp successional gradient. Multi-trait functional dispersion (FDis) of both leaf and fine root traits tended to decrease along the successional gradient, but functional richness and evenness were highest at the middle successional stage. Moreover, FDis of individual plant traits except N showed the same pattern as multi-trait FDis. Soil pH and nutrient availability were the main drivers of successional changes in both CWM traits and FDis. The changes of community-level traits along succession indicated a shift from acquisitive to conservative strategy of understory plants during forest swamp succession. Similar trends in leaf and fine root functional diversity along succession may indicate above- and belowground functional diversity are coordinated during the processes of plant community assembly. These findings of linkages between above- and belowground plant functional composition have important implications for plant community dynamics and assembly rules.