Plant Functional Group Richness Research Articles

Plot-Measured Variables Indicate Landscape-Scale Patterns of Annual Grass Invasion in Northwestern US Rangelands

Introduced annual grasses (IAGs) have invaded tens of millions of hectares of western US rangelands, displacing native vegetation and altering ecosystem functions and services. Our main goal was to assess the influence of introduced annual grasses by 1) exploring the relationships among IAG cover, species richness, diversity, and cover of other plant functional groups; and 2) identifying biotic and abiotic indicators of IAG cover. Using data from 64 sites and 420 plots from rangelands of the northwestern United States, we explored linear correlations between IAG cover and species richness, Shannon index, and plant functional group cover. We also used Least Absolute Shrinkage and Selection Operator (LASSO) regression and nonmetric multidimensional scaling to select environmental variables and plant functional groups that were associated with IAG cover. Our findings revealed a negative correlation among IAG cover and species richness, Shannon index, native perennial grass cover, and other perennial species cover and a positive correlation with other annual species cover. Our results identified several indicators: cover of native perennial grass; other perennial species (forbs and shrubs); litter; bare ground/rock; soil attributes (pH, bulk density, clay, and nitrogen); and mean annual temperatures. Our results showed that perennial vegetation, especially native perennial grasses, have a negative correlation with IAG. Warmer mean annual temperatures, but not higher daily extreme temperatures, and higher bulk density were important indicators for IAG preferred sites, while lower soil nitrogen may denote soil changes due to invasion. Given the fundamental role of disturbance in determining the magnitude and scale of IAG invasion, our results provide important insights for scientists and managers.

Contrasting responses of two typical plant communities to precipitation variability in horqin sandy land, northeast China

The ongoing modification of precipitation regime highlights the necessity to further investigate underlying vegetation processes. To figure out the key precipitation characteristics that largely affected the biomass and species richness of different plant functional groups in the semiarid sandy land, we compared the 15-year (from 2005 to 2019) variation in the aboveground biomass (AGB), precipitation use efficiency (PUE) and species richness of two typical biotopes (fixed dune and sandy grassland) in Horqin Sandy Land, a semiarid sandy land in northeast China. Results showed that the sandy grassland had higher AGB and PUE, lower species richness than the fixed dune; the annuals contributed 60.16% of the AGB and 60.32% of the species richness in sandy grassland, while contributed 53.40% and 75.77% in fixed dune, respectively; the AGB and species richness in the fixed dune had medium positive correlation with annual precipitation, while that in the sandy grassland had medium positive correlation with the total amount of specific rainfall events in the growing season (e.g. cumulative precipitation of 10–40 mm rain events and number of ≥ 10 mm rain event). There was no significant correlations were detected between PUE and annual precipitation, and weakly positive correlations were detected between PUE and amount and number of medium rainfall events in growing season. Our results suggested that the biomes dominated by annual plants were more responsive to the variability of growing season rainfall pattern rather than annual precipitation. In semiarid sandy grassland communities, the frequent medium rainfall events (5–50 mm) have significant role on the biomass, and the high species richness is likely to depend on the number of larger ones (≥ 10 mm). The AGB and species richness of grassland communities in semi-arid sandy land was the result of the combined effect of amount size, number and interval of rain event.

Effects of recurrent summer droughts on arbuscular mycorrhizal and total fungal communities in experimental grasslands differing in plant diversity and community composition

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.

Tree Diversity, Site Index, and Carbon Storage Decrease With Aridity in Douglas-Fir Forests in Western Canada

Forests are important for biodiversity, timber production and carbon accumulation, but these ecosystem services may be impacted by climate change. Field data collected from individual forest types occurring across a climatic gradient can contribute to forecasting these consequences. We examined how changes in temperature, precipitation and aridity affect ecosystem services in 23 mature Douglas-fir (Pseudotsuga menziesii) forests in nine climatic regions across a 900 km gradient in British Columbia, Canada. Using Canadian National Forest Inventory methodology, we assessed richness and diversity of plant functional groups, site index, and above- and below-ground carbon stocks. As aridity increased, ecosystem-level tree species richness declined on average from four to one species, Douglas-fir site index declined from 30 to 15 m, and ecosystem carbon storage decreased from 565 to 222 Mg ha–1. Tree species richness was positively and herb species richness negatively correlated with carbon storage. Carbon storage by ecosystem compartment was largest in aboveground live tree biomass, declining in the following order: mineral soils > coarse woody debris and dead standing trees > forest floor > small and fine woody debris > understory plants. Mineral soil carbon at depths of 0-15 cm, 15-35 cm, and 35-55 cm increased with increasing mean annual precipitation and decreasing aridity. Our results indicate that as aridity increases and precipitation decreases, tree species richness, site index and carbon storage in existing Douglas-fir forests declines. However, assisted or natural migration of Douglas-fir into more humid regions could be associated with more diverse, productive, carbon-rich forests. This study informs carbon stock vulnerability and provides empirical data essential for carbon stock forecasts.

Fire and functional traits: Using functional groups of birds and plants to guide management in a fire‐prone, heathy woodland ecosystem

AbstractAimMany dry forests and woodlands worldwide are fire‐prone and support bird and plant communities shaped by fire. Changes in fire regimes, including the time between fires, have important implications for population trajectories. We studied the responses of bird and plant communities of heathy woodlands to time since the last fire, a key measure underpinning fire management, to evaluate whether current management strategies will enhance conservation of multiple taxa.LocationOtway Ranges, south‐eastern Australia.MethodsWe surveyed birds and plants at 38 sites, stratified by an 80‐year post‐fire chronosequence, and modelled the responses of individual species, functional groups and community composition to fire history. Model outputs were used to evaluate the impacts of fire management as guided by (a) domains of tolerable fire intervals, a concept based on plant life history traits, and (b) the spatial arrangement of post‐fire age classes, a surrogate for animal habitats.ResultsBird and plant communities both responded to time since fire. Notable relationships included the following: a high reporting rate of ground‐foraging birds and high cover and species richness of shrubs immediately after fire; and a gradual increase up to ~50 years and ~20 years post‐fire of birds that forage in the mid‐storey and facultative‐resprouting plants, respectively. Post‐fire age classes had distinct bird and plant assemblages. Tolerable fire intervals currently used by land managers (min 12–max 45 years between fires) encompassed the peak in richness of most plant functional groups but not the preferred habitat of lower‐mid‐storey foraging birds.Main conclusionsFire management based solely on birds or plants risks population declines in other biota. Use of functional groups can help guide strategic planning, such as spatial representation of post‐fire age classes across the landscape. Maintaining late‐successional vegetation will provide habitat for several groups of birds, while fire is needed at sufficient frequency to prevent loss of plants and ground‐foraging birds.

Incorporation of mineral nitrogen into the soil food web as affected by plant community composition.

Although nitrogen (N) deposition is increasing globally, N availability still limits many organisms, such as microorganisms and mesofauna. However, little is known to which extent soil organisms rely on mineral‐derived N and whether plant community composition modifies its incorporation into soil food webs. More diverse plant communities more effectively compete with microorganisms for mineral N likely reducing the incorporation of mineral‐derived N into soil food webs. We set up a field experiment in experimental grasslands with different levels of plant species and functional group richness. We labeled soil with 15NH4 15NO3 and analyzed the incorporation of mineral‐derived 15N into soil microorganisms and mesofauna over 3 months. Mineral‐derived N incorporation decreased over time in all investigated organisms. Plant species richness and presence of legumes reduced the uptake of mineral‐derived N into microorganisms. In parallel, the incorporation of mineral‐derived 15N into mesofauna species declined with time and decreased with increasing plant species richness in the secondary decomposer springtail Ceratophysella sp. Effects of both plant species richness and functional group richness on other mesofauna species varied with time. The presence of grasses increased the 15N incorporation into Ceratophysella sp., but decreased it in the primary decomposer oribatid mite Tectocepheus velatus sarekensis. The results highlight that mineral N is quickly channeled into soil animal food webs via microorganisms irrespective of plant diversity. The amount of mineral‐derived N incorporated into soil animals, and the plant community properties affecting this incorporation, differed markedly between soil animal taxa, reflecting species‐specific use of food resources. Our results highlight that plant diversity and community composition alter the competition for N in soil and change the transfer of N across trophic levels in soil food webs, potentially leading to changes in soil animal population dynamics and community composition. Sustaining high plant diversity may buffer detrimental effects of elevated N deposition on soil biota.

Plant functional group drives the community structure of saprophytic fungi in a grassland biodiversity experiment

AimsSaprophytic fungi are important agents of soil mineralization and carbon cycling. Their community structure is known to be affected by soil conditions such as organic matter and pH. However, the effect of plant species, whose roots provide the litter input into the soil, on the saprophytic fungal community is largely unknown.MethodsWe examined the saprophytic fungi in a grassland biodiversity experiment with eight plant species belonging to two functional groups (grasses and forbs), combining DNA extraction from plant roots, next-generation sequencing and literature research.ResultsWe found that saprophyte richness increased with plant species richness, but plant functional group richness was the best predictor. Plant functional group was also the main factor driving fungal saprophytic community structure. This effect was correlated with differences in root lignin content and C:N ratio between grasses and forbs. In monocultures, root traits and plant functional group type explained 16% of the variation in community structure. The saprophyte taxa detected in mixed plant communities were to a large extent subsets of those found in monocultures.ConclusionsOur work shows that the richness and community structure of the root-associated saprophytic fungi can largely be predicted by plant functional groups and their associated root traits. This means that the effects of plant diversity on ecosystem functions such as litter decomposition may also be predictable using information on plant functional groups in grasslands.

When history matters: The overlooked role of priority effects in grassland overyielding

Abstract 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.

Key Species Superpose the Effect of Species Richness and Species Interaction on Carbon Fluxes in a Restored Minerotrophic Peatland

In a controlled field experiment, we tested the effect of plant biodiversity on carbon accumulation in a formerly-extracted peatland that was rewetted and re-vegetated. We monitored carbon fluxes in experimental units re-vegetated with different numbers and types of characteristic minerotrophic peatland species, planted in monoculture and mixed treatments. Using measured environmental variables, we modelled the different components of carbon flux (photosynthesis, respiration and methane flux) and simulated the Net Seasonal Carbon Flux for three standard wetness scenarios of each planting treatment. We tested the effect of species and functional group richness, species and functional group identity and species interactions on Net Seasonal Carbon Flux. Our findings did not indicate any significant effect of the richness of species or plant functional groups on carbon accumulation. However, the presence of key species was important; Carex aquatilis, particularly when planted alone, significantly increased carbon accumulation; other graminoid species were not associated with the same effect. Mixed-species treatments did not accumulate more carbon than was expected of the same species when planted in monoculture, providing no evidence for an overall species interaction effect. Our results suggest that in the context of restored minerotrophic peatlands, species identity is more important than species/functional group richness or species-interaction for driving carbon accumulation.

Drivers of plant functional group richness and beta diversity in fire‐dependent pine savannas

AbstractAimTo assess the drivers of plant functional group richness and beta diversity in fire‐maintained North American Coastal Plain (NACP) savannas.LocationThe southern portion of the NACP, a global biodiversity hotspot. This region is characterized by fire‐dependent pine savanna fragments that are isolated within a matrix of agriculture, urban development, non‐pyrogenic plant communities and plantation forestry.MethodsWe used nested quadrats to sample plant species on 30 fire‐maintained savanna preserves in Florida and Georgia, USA. We analysed between‐site Sørenson dissimilarity, a measure of beta diversity, using NMDS and PerMANOVA. We measured nestedness using NODF, and we used Betapart to partition Sørenson dissimilarity into nestedness and turnover components. We used linear and generalized linear mixed models to explore drivers of functional group richness and composition, including fire regime (return interval, number of fires, time since fire and seasonality), vegetation structure (herbaceous cover, woody cover and tree density) and spatial factors (surrounding landscape and geographic distance).ResultsWe found turnover‐dominated beta‐diversity patterns in all functional groups. Turnover was explained partly by spatial and environmental gradients, but roughly half of the turnover between sites was unexplained. Species richness was higher on sites where fire and fire surrogates had been used longer and more consistently, and these effects were partly independent of current vegetation structure. Fire regimes containing more growing season fire and more diversity of burn seasons promoted higher species richness. Relationships between small‐scale and large‐scale species richness varied by soil type and functional group.Main conclusionsFire‐maintained savannas in the southeastern NACP vary greatly in their plant functional group richness, but high beta diversity resulting primarily from species turnover suggests that even species‐poor sites can harbour less‐common members of the regional plant metacommunity. Prescribed fire regimes that include growing season fire as well as a diversity of burn seasons may best promote species and functional group richness.

Diversity‐dependent plant–soil feedbacks underlie long‐term plant diversity effects on primary productivity

AbstractAlthough diversity‐dependent plant–soil feedbacks (PSFs) may contribute significantly to plant diversity effects on ecosystem functioning, the influences of underlying abiotic and biotic mechanistic pathways have been little explored to date. Here, we assessed such pathways with a PSF experiment using soil conditioned for ≥12 yr from two grassland biodiversity experiments. Model plant communities differing in plant species and functional group richness (current plant diversity treatment) were grown in soils conditioned by plant communities with either low‐ or high‐diversity (soil history treatment). Our results indicate that plant diversity can modify plant productivity through both diversity‐mediated plant–plant and plant–soil interactions, with the main driver (current plant diversity or soil history) differing with experimental context. Structural equation modeling suggests that the underlying mechanisms of PSFs were explained to a significant extent by both abiotic and biotic pathways (specifically, soil nitrogen availability and soil nematode richness). Thus, effects of plant diversity loss on plant productivity may persist or even increase over time because of biotic and abiotic soil legacy effects.

Phosphorus Release from Mineral Soil by Acid Hydrolysis: Method Development, Kinetics, and Plant Community Composition Effects

Core Ideas A modified pHstat approach captures P release kinetics in soil relevant for plant nutrition. The fast‐reacting P pool comprises P from charged surfaces and easily soluble Ca‐phosphates. The slow‐reacting P pool is a mixture of Ca‐phosphates and P released by dissolution of pedogenic oxides. Legumes increase the exploitation of more stable P pools. The release kinetics of phosphate (inorganic P [Pi]) at constant proton pressure in a pHstat experiment may be used as a proxy for P mobilization by rhizosphere acidification. pHstat experiments are challenging for calcareous soils because of the strong carbonate buffering. Our objectives were (i) to modify an existing pHstat method for calcareous soils and (ii) to determine plant species richness, plant functional group richness, and identity effects on pool sizes and rate constants (i.e., the fast‐ and slow‐reacting Pools A and B, respectively, and the associated release constants ka and kb). The study was conducted in “The Jena Experiment” comprising grassland mixtures with different functional group composition and species richness. In 27 samples with inorganic C concentrations <10 g kg–1, a constant pH value of 3 after 2 h was reached by removing all released cations with ion‐exchange membranes until all carbonates were destroyed. Thereafter, P release kinetics followed a biphasic course: the fast‐reacting Pool A contained 86% of the bioavailable Pi extractable with NaHCO3 plus NaOH. The slow‐reacting P pool additionally comprised P from dissolution of pedogenic oxides and more stable Ca‐phosphates containing 17 to 40% of HCl‐extractable Pi. Legumes decreased both pools (Pool A: 40.61 ± 3.83 with legumes vs. 65.24 ± 5.88 mg kg–1 Pi without legumes; Pool B: 36.88 ± 1.89 vs. 48.85 ± 1.81 mg kg–1 Pi) because of their increased P demand and associated ability to access hardly available P fractions. In conclusion, pHstat experiments are suitable for studying P dynamics in soil and reveal an aboveground plant composition feedback on soil P dynamics.

Plant diversity has contrasting effects on herbivore and parasitoid abundance in Centaurea jacea flower heads.

High biodiversity is known to increase many ecosystem functions, but studies investigating biodiversity effects have more rarely looked at multi‐trophic interactions. We studied a tri‐trophic system composed of Centaurea jacea (brown knapweed), its flower head‐infesting tephritid fruit flies and their hymenopteran parasitoids, in a grassland biodiversity experiment. We aimed to disentangle the importance of direct effects of plant diversity (through changes in apparency and resource availability) from indirect effects (mediated by host plant quality and performance). To do this, we compared insect communities in C. jacea transplants, whose growth was influenced by the surrounding plant communities (and where direct and indirect effects can occur), with potted C. jacea plants, which do not compete with the surrounding plant community (and where only direct effects are possible). Tephritid infestation rate and insect load, mainly of the dominant species Chaetorellia jaceae, decreased with increasing plant species and functional group richness. These effects were not seen in the potted plants and are therefore likely to be mediated by changes in host plant performance and quality. Parasitism rates, mainly of the abundant chalcid wasps Eurytoma compressa and Pteromalus albipennis, increased with plant species or functional group richness in both transplants and potted plants, suggesting that direct effects of plant diversity are most important. The differential effects in transplants and potted plants emphasize the importance of plant‐mediated direct and indirect effects for trophic interactions at the community level. The findings also show how plant–plant interactions critically affect results obtained using transplants. More generally, our results indicate that plant biodiversity affects the abundance of higher trophic levels through a variety of different mechanisms.

Differential responses of soil bacteria, fungi, archaea and protists to plant species richness and plant functional group identity.

Plants are known to influence belowground microbial community structure along their roots, but the impacts of plant species richness and plant functional group (FG) identity on microbial communities in the bulk soil are still not well understood. Here, we used 454-pyrosequencing to analyse the soil microbial community composition in a long-term biodiversity experiment at Jena, Germany. We examined responses of bacteria, fungi, archaea, and protists to plant species richness (communities varying from 1 to 60 sown species) and plant FG identity (grasses, legumes, small herbs, tall herbs) in bulk soil. We hypothesized that plant species richness and FG identity would alter microbial community composition and have a positive impact on microbial species richness. Plant species richness had a marginal positive effect on the richness of fungi, but we observed no such effect on bacteria, archaea and protists. Plant species richness also did not have a large impact on microbial community composition. Rather, abiotic soil properties partially explained the community composition of bacteria, fungi, arbuscular mycorrhizal fungi (AMF), archaea and protists. Plant FG richness did not impact microbial community composition; however, plant FG identity was more effective. Bacterial richness was highest in legume plots and lowest in small herb plots, and AMF and archaeal community composition in legume plant communities was distinct from that in communities composed of other plant FGs. We conclude that soil microbial community composition in bulk soil is influenced more by changes in plant FG composition and abiotic soil properties, than by changes in plant species richness per se.

Flood-Induced Changes in Soil Microbial Functions as Modified by Plant Diversity

Flooding frequency is predicted to increase during the next decades, calling for a better understanding of impacts on terrestrial ecosystems and for developing strategies to mitigate potential damage. Plant diversity is expected to buffer flooding effects by providing a broad range of species’ responses. Here we report on the response of soil processes to a severe summer flood in 2013, which affected major parts of central Europe. We compared soil microbial respiration, biomass, nutrient limitation and enzyme activity in a grassland biodiversity experiment in Germany before flooding, one week and three months after the flood. Microbial biomass was reduced in the severely flooded plots at high, but not at low plant functional group richness. Flooding alleviated microbial nitrogen limitation, presumably due the input of nutrient-rich sediments. Further, the activity of soil enzymes including 1,4-β-N-acetylglucosaminidase, phenol oxidase and peroxidase increased with flooding severity, suggesting increased chitin and lignin degradation as a consequence of the input of detritus in sediments. Flooding effects were enhanced at higher plant diversity, indicating that plant diversity temporarily reduces stability of soil processes during flooding. The long-term impacts, however, remain unknown and deserve further investigation.

Cover crops to increase soil microbial diversity and mitigate decline in perennial agriculture. A review

Commercial perennial agriculture is prone to declining productivity due to negative plant-soil feedback. An alternative to costly and environmentally harmful conventional treatment such as soil fumigation could be to manipulate soil microbial diversity through careful selection and management of cover crop mixtures. Although cover crops are already used in these systems for other reasons, their capacity to influence soil biota is unexploited. Here, we examine the role of plant diversity and identity on plant-soil feedbacks in the context of perennial agriculture. We identify key microorganisms involved in these feedbacks and explore plant-based strategies for mitigating decline of perennial crop plants. We conclude that (1) increasing plant diversity increases soil microbial diversity, minimizing the proliferation of soil-borne pathogens; (2) populations of beneficial microbes can be increased by increasing plant functional group richness, e.g., legumes, C4 grasses, C3 grasses, and non-leguminous forbs; (3) brassicas suppress fungal pathogens and promote disease-suppressive bacteria; (4) native plants may further promote beneficial soil microbiota; and (5) frequent tillage, herbicide use, and copper fungicides can harm populations of beneficial microbes and, in some cases, contribute to greater crop decline. Non-crop vegetation management is a viable and cost-effective means of minimizing crop decline in perennial monocultures but is in need of more direct experimental investigation in perennial agroecosystems.

Utilisation of plant functional diversity in wildflower strips for the delivery of multiple agroecosystem services

AbstractIncreased plant diversity in cropping systems can play an important role in agriculture by enhancing arthropod‐mediated ecosystem services, including biological control and pollination. However, there is limited research investigating the concurrent influence of plant functional diversity within cultivated systems on different arthropod functional groups, the provision of multiple ecosystem services, and crop yield. During a field experiment, repeated over 2 years, we measured the effect of increasing plant functional diversity on community structure of arthropod visitors, the abundance of multiple pests and induced crop damage, and fruit production in two varieties of tomato. Plant resources (floral and extra‐floral nectar and pollen) were included within experimental plots in four levels, with each level increasing the plant functional group richness, based on floral morphology and availability of resources, in a replacement series. The presence of sown flower mixtures in experimental plots was associated with increased abundance and diversity of natural enemy functional groups and an enhanced abundance of bees (Hymenoptera:Apiformes). However, we only detected relatively small variability in arthropod visitors among types of mixtures, and increased abundance of natural enemies did not translate into stronger pest suppression or reduced crop damage. Lepidoptera pest damage was significantly higher in plots adjacent to wildflower strips, an ecosystem disservice, but a significantly higher crop productivity was recorded from these plots. Our results provide evidence that inclusion of non‐crop plant resources in agroecosystems can improve the conservation of beneficial arthropods and may lead to increased crop productivity.

Changes in plant life‐form, pollination syndrome and breeding system at a regional scale promoted by land use intensity

AbstractAimParallel declines in plant and insect pollinator diversity under land use intensification may occur as a result of both taxonomic groups responding similarly, but independently, to habitat change or as a consequence of interdependence as insect‐pollinated plants decline due to pollinator loss. Here, we explore the relative roles of independent and interdependent declines by comparing correlations of species richness and land use intensity for different functional groups of plants.LocationAustria.MethodsGeneralized linear and generalized linear mixed models were used to analyse trends in species richness of plant functional groups sampled along a land use intensity gradient across 100 agricultural landscapes (=625 × 625 m each). Plants were classified according to their pollination syndrome, breeding system and life span. Species numbers were related to the site‐specific proportional area of semi‐natural habitats as an indicator of land use intensity.ResultsOverall, as the level of agricultural intensification increased the proportion of outcrossing plants declined and the proportion of self‐pollinating plants increased. However, while perennial plant species richness decreased under more intensive land use independently of pollination syndrome or breeding system, the richness of annuals only declined for outcrossing species requiring specialized insect pollinators but not for those pollinated by wind‐ or unspecialized insect pollinators.Main conclusionFrom these patterns we infer that land use intensification mainly drives plant species loss by excluding perennial species which suffer from the conversion of land to annually harvested crop fields. Hence, parallel declines in plant and insect richness largely result from a common response of perennials and pollinators to habitat change. Nevertheless, for annual plants with specialized pollinator requirements our data support a cascading effect of pollinator decline on species richness.

Positive effects of plant diversity on nitrogen removal in microcosms of constructed wetlands with high ammonium loading

Wastewater with a high nitrogen (N) loading rate and high ammonium (NH4+-N)/nitrate (NO3−-N) ratio is increasingly becoming a problem in regional environment. An experimental system was established to test the effects of plant diversity on N removal in microcosms of constructed wetlands. The microcosms were treated with simulated wastewater with NH4+-N as the sole chemical form of N, and with mixed NH4+/NO3—N (1:1) as a control, both at a loading rate of 162g Nm−2yr−1. Results indicated that: (1) high plant species and functional group richness improved N removal efficiency under a high ammonium loading rate, (2) high species richness reduced the difference of N removal between sole NH4+-N and mixed NH4+/NO3−-N treatments, (3) the presence of Coix lacryma-jobi (C4 grass) increased both biomass and N removal, whereas the presence of Aeschynomene indica (legume) increased N removal but decreased biomass of the communities. Overall, the results showed that high plant diversity enhanced N removal efficiency regardless of the N-form ratios and N level in the ecosystem.

Community disassembly and invasion of remnant native grasslands under fluctuating resource supply

Summary Native vegetation fragments embedded in anthropogenic landscapes are increasingly threatened by land‐use intensification. Managing disturbance regimes and nutrient inputs may help maintain species diversity in such remnants. Yet, it is unclear the extent to which changes in resource availability due to reduced capture by resident plants and/or increased supply rates may trigger native community disassembly and exotic invasions. We examined how mowing disturbance and N fertilizer addition affected plant community recovery after a burning event in a remnant corridor of tussock pampa grassland in Argentina. The percentage cover and richness of native and exotic plant functional groups were monitored over 4 years. According to the ‘fluctuating resource theory’, we expected invasion to be the highest when both light and N availability were increased simultaneously. Mowing delayed recovery by dominant C4 tussock grasses and promoted subordinate, native C3 grasses and exotic legumes, thus enhancing both native and exotic species richness. Fertilization induced a transient increase in native forbs but decreased total plant richness. Moreover, N addition to mowed grassland led to rapid invasion by short‐lived exotic forbs, which were then replaced by exotic perennial grasses. Exotic grasses eventually spread across the grassland corridor, although at different rates depending on the treatment, and in parallel to a generalized decline in native species cover. Synthesis and applications. Community disassembly patterns reflected differential responses of native and exotic functional groups to altered resource supply rates. Synergisms between canopy disturbances and N enrichment posed the greatest threat to preserving a pampa grassland remnant prone to invasion. Establishing buffer zones may be required to enhance the viability of corridor‐like grassland remnants in agricultural landscapes.