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1. The success of grassland biodiversity restoration schemes is determined by many factors; as such their outcomes can be unpredictable. There is a need for improved understanding of the relative importance of belowground factors to restoration success, such as contrasting soil type and management intensities, as well as plant community composition and order of assembly.2. We carried out an eight-year mesocosm experiment across three locations in the UK to explore the relative and interactive roles of various aboveground and belowground factors in the establishment of target species, to determine general constraints on grassland restoration. Each location had a series of mesocosms with contrasting soil types and management status, which were initially sown with six grasses typical of species-poor grasslands targeted for restoration. 3. Over five years, sets of plant species were added, to test how different vegetation treatments, including early-coloniser species and the hemiparasite Rhinanthus minor, and soil type and management, influenced the establishment of target plant species and community diversity.4. The addition of early-coloniser species to model grasslands suppressed the establishment of target species, indicating a strong priority effect. Soil type was also an important factor, but effects varied considerably across locations. In the absence of early-coloniser species, low soil nutrient availability improved establishment of target species across locations, although R. minor had no beneficial effect. 5. Synthesis and applications. Our long-term, multi-site study indicates that successful restoration of species rich grassland is dependent primarily on priority effects, especially in the form of early-coloniser species that suppress establishment of slow-growing target species. We also show that priority effects vary with soil conditions, being stronger in clay than sandy soils, and on soils of high nutrient availability. As such, our work emphasises the importance of considering priority effects and local soil conditions in developing management strategies for restoring plant species diversity in grassland.

The importance of managing land to optimize carbon sequestration for climate change mitigation is widely recognized, with grasslands being identified as having the potential to sequester additional carbon. However, most soil carbon inventories only consider surface soils, and most large-scale surveys group ecosystems into broad habitats without considering management intensity. Consequently, little is known about the quantity of deep soil carbon and its sensitivity to management. From a nationwide survey of grassland soils to 1 m depth, we show that carbon in grassland soils is vulnerable to management and that these management effects can be detected to considerable depth down the soil profile, albeit at decreasing significance with depth. Carbon concentrations in soil decreased as management intensity increased, but greatest soil carbon stocks (accounting for bulk density differences), were at intermediate levels of management. Our study also highlights the considerable amounts of carbon in subsurface soil below 30 cm, which is missed by standard carbon inventories. We estimate grassland soil carbon in Great Britain to be 2097 Tg C to a depth of 1 m, with ~60% of this carbon being below 30 cm. Total stocks of soil carbon (t ha(-1) ) to 1 m depth were 10.7% greater at intermediate relative to intensive management, which equates to 10.1 t ha(-1) in surface soils (0-30 cm), and 13.7 t ha(-1) in soils from 30 to 100 cm depth. Our findings highlight the existence of substantial carbon stocks at depth in grassland soils that are sensitive to management. This is of high relevance globally, given the extent of land cover and large stocks of carbon held in temperate managed grasslands. Our findings have implications for the future management of grasslands for carbon storage and climate mitigation, and for global carbon models which do not currently account for changes in soil carbon to depth with management.

Northern peatlands are recognized as globally important stores of terrestrial carbon (C), yet we have limited understanding of how global changes, including land use, affect C cycling processes in these ecosystems. Making use of a long-term (>50 year old) peatland land management experiment in the UK, we investigated, using a 13CO2 pulse chase approach, how managed burning and grazing influenced the short-term uptake and cycling of C through the plant–soil system. We found that burning affected the composition and growth stage of the plant community, by substantially reducing the abundance of mature ericoid dwarf-shrubs. Burning also affected the structure of the soil microbial community, measured using phospholipid fatty acid analysis, by reducing fungal biomass. There was no difference in net ecosystem exchange of CO2, but burning was associated with an increase in photosynthetic uptake of 13CO2 and increased transfer of 13C to the soil microbial community relative to unburned areas. In contrast, grazing had no detectable effects on any measured C cycling process. Our study provides new insight into how changes in vegetation and soil microbial communities arising from managed burning affect peatland C cycling processes, by enhancing the uptake of photosynthetic C and the transfer of C belowground, whilst maintaining net ecosystem exchange of CO2 at pre-burn levels.

The controls on aboveground community composition and diversity have been extensively studied, but our understanding of the drivers of belowground microbial communities is relatively lacking, despite their importance for ecosystem functioning. In this study, we fitted statistical models to explain landscape-scale variation in soil microbial community composition using data from 180 sites covering a broad range of grassland types, soil and climatic conditions in England. We found that variation in soil microbial communities was explained by abiotic factors like climate, pH and soil properties. Biotic factors, namely community-weighted means (CWM) of plant functional traits, also explained variation in soil microbial communities. In particular, more bacterial-dominated microbial communities were associated with exploitative plant traits versus fungal-dominated communities with resource-conservative traits, showing that plant functional traits and soil microbial communities are closely related at the landscape scale. © 2012 Blackwell Publishing Ltd/CNRS.

The abundance of microbes in soil is thought to be strongly influenced by plant productivity rather than by plant species richness per se . However, whether this holds true for different microbial groups and under different soil conditions is unresolved. We tested how plant species richness, identity and biomass influence the abundances of arbuscular mycorrhizal fungi (AMF), saprophytic bacteria and fungi, and actinomycetes, in model plant communities in soil of low and high fertility using phospholipid fatty acid analysis. Abundances of saprophytic fungi and bacteria were driven by larger plant biomass in high diversity treatments. In contrast, increased AMF abundance with larger plant species richness was not explained by plant biomass, but responded to plant species identity and was stimulated by Anthoxantum odoratum . Our results indicate that the abundance of saprophytic soil microbes is influenced more by resource quantity, as driven by plant production, while AMF respond more strongly to resource composition, driven by variation in plant species richness and identity. This suggests that AMF abundance in soil is more sensitive to changes in plant species diversity per se and plant species composition than are abundances of saprophytic microbes.

1. In Europe, grassland agriculture is one of the dominant land uses. A major aim of European agri-environment policy is the management of grassland for botanical diversity conservation and restoration, together with the delivery of ecosystem services including soil carbon (C) sequestration. 2. To test whether management for biodiversity restoration has additional benefits for soil C sequestration, we investigated C and nitrogen (N) accumulation rates in soil and C and N pools in vegetation in a long-term field experiment (16 years) in which fertilizer application and plant seeding were manipulated. In addition, the abundance of the legume Trifolium pratense was manipulated for the last 2 years. To unravel the mechanisms underlying changes in soil C and N pools, we also tested for effects of diversity restoration management on soil structure, ecosystem respiration and soil enzyme activities. 3. We show that the long-term biodiversity restoration practices increased soil C and N storage especially when these treatments were combined with the recent promotion of the legume Trifolium pratense, sequestering 317 g C and 35 g N m−2 year−1 in the most successful management treatment. These high rates of C and N accumulation were associated with reduced ecosystem respiration, increased soil organic matter content and improved soil structure. Cessation of fertilizer use, however, reduced the amount of C and N contained in vegetation. 4. Synthesis and applications. Our findings show that long-term diversity restoration practices can yield significant benefits for soil C storage when they are combined with increased abundance of a single, sub-ordinate legume species. Moreover, we show that these management practices deliver additional ecosystem benefits such as N storage in soil and improved soil structure.

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

This study determined temporal variability in N pools, both aboveground and belowground, across two contrasting plant communities in high-Arctic Spitsbergen, Svalbard (78°N). We measured N pools in plant material, soil microbial biomass and soil organic matter in moist (Alopecurus borealis dominated) and dry (Dryas octopetala dominated) meadow communities at four times during the growing season. We found that plant, microbial and dissolved inorganic and organic N pools were subject to significant, but surprisingly low, temporal variation that was controlled primarily by changes in temperature and moisture availability over the short growing season. This temporal variability is much less than that experienced in other seasonally cold ecosystems such as alpine tundra where strong seasonal partitioning of N occurs between plant and soil microbial pools. While only a small proportion of the total ecosystem N, the microbial biomass represented the single largest of the dynamic N pools in both moist and dry meadow communities (3.4% and 4.6% of the total ecosystem N pool, respectively). This points to the importance of soil microbial community dynamics for N cycling in high-Arctic ecosystems. Microbial N was strongly and positively related to soil temperature in the dry meadow, but this relationship did not hold true in the wet meadow where other factors such as wetter soil conditions might constrain biological activity. Vascular live belowground plant parts represented the single largest plant N pool in both dry and moist meadow, constituting an average of 1.6% of the total N pool in both systems; this value did not vary across the growing season or between plant communities. Overall, our data illustrate a surprisingly low growing season variability in labile N pools in high-Arctic ecosystems, which we propose is controlled primarily by temperature and moisture.

Historically, slow decomposition rates have resulted in the accumulation of large amounts of carbon in northern peatlands. Both climate warming and vegetation change can alter rates of decomposition, and hence affect rates of atmospheric CO2 exchange, with consequences for climate change feedbacks. Although warming and vegetation change are happening concurrently, little is known about their relative and interactive effects on decomposition processes. To test the effects of warming and vegetation change on decomposition rates, we placed litter of three dominant species (Calluna vulgaris, Eriophorum vaginatum, Hypnum jutlandicum) into a peatland field experiment that combined warming.with plant functional group removals, and measured mass loss over two years. To identify potential mechanisms behind effects, we also measured nutrient cycling and soil biota. We found that plant functional group removals exerted a stronger control over short-term litter decomposition than did approximately 1 degrees C warming, and that the plant removal effect depended on litter species identity. Specifically, rates of litter decomposition were faster when shrubs were removed from the plant community, and these effects were strongest for graminoid and bryophyte litter. Plant functional group removals also had strong effects on soil biota and nutrient cycling associated with decomposition, whereby shrub removal had cascading effects on soil fungal community composition, increased enchytraeid abundance, and increased rates of N mineralization. Our findings demonstrate that, in addition to litter quality, changes in vegetation composition play a significant role in regulating short-term litter decomposition and belowground communities in peatland, and that these impacts can be greater than moderate warming effects. Our findings, albeit from a relatively short-term study, highlight the need to consider both vegetation change and its impacts below ground alongside climatic effects when predicting future decomposition rates and carbon storage in peatlands.

Soil carbon (C) storage is a key ecosystem service. Soil C stocks play a vital role in soil fertility and climate regulation, but the factors that control these stocks at regional and national scales are unknown, particularly when their composition and stability are considered. As a result, their mapping relies on either unreliable proxy measures or laborious direct measurements. Using data from an extensive national survey of English grasslands, we show that surface soil (0-7cm) C stocks in size fractions of varying stability can be predicted at both regional and national scales from plant traits and simple measures of soil and climatic conditions. Soil C stocks in the largest pool, of intermediate particle size (50-250m), were best explained by mean annual temperature (MAT), soil pH and soil moisture content. The second largest C pool, highly stable physically and biochemically protected particles (045-50m), was explained by soil pH and the community abundance-weighted mean (CWM) leaf nitrogen (N) content, with the highest soil C stocks under N-rich vegetation. The C stock in the small active fraction (250-4000m) was explained by a wide range of variables: MAT, mean annual precipitation, mean growing season length, soil pH and CWM specific leaf area; stocks were higher under vegetation with thick and/or dense leaves. Testing the models describing these fractions against data from an independent English region indicated moderately strong correlation between predicted and actual values and no systematic bias, with the exception of the active fraction, for which predictions were inaccurate.Synthesis and applications. Validation indicates that readily available climate, soils and plant survey data can be effective in making local- to landscape-scale (1-100000km(2)) soil C stock predictions. Such predictions are a crucial component of effective management strategies to protect C stocks and enhance soil C sequestration. Validation indicates that readily available climate, soils and plant survey data can be effective in making local- to landscape-scale (1-100000km(2)) soil C stock predictions. Such predictions are a crucial component of effective management strategies to protect C stocks and enhance soil C sequestration.

Understanding the effects of warming on greenhouse gas feedbacks to climate change represents a major global challenge. Most research has focused on direct effects of warming, without considering how concurrent changes in plant communities may alter such effects. Here, we combined vegetation manipulations with warming to investigate their interactive effects on greenhouse gas emissions from peatland. We found that although warming consistently increased respiration, the effect on net ecosystem CO2 exchange depended on vegetation composition. The greatest increase in CO2 sink strength after warming was when shrubs were present, and the greatest decrease when graminoids were present. CH4 was more strongly controlled by vegetation composition than by warming, with largest emissions from graminoid communities. Our results show that plant community composition is a significant modulator of greenhouse gas emissions and their response to warming, and suggest that vegetation change could alter peatland carbon sink strength under future climate change.

Leaching losses of nitrogen (N) from soil and atmospheric N deposition have led to widespread changes in plant community and microbial community composition, but our knowledge of the factors that determine ecosystem N retention is limited. A common feature of extensively managed, species-rich grasslands is that they have fungal-dominated microbial communities, which might reduce soil N losses and increase ecosystem N retention, which is pivotal for pollution mitigation and sustainable food production. However, the mechanisms that underpin improved N retention in extensively managed, species-rich grasslands are unclear. We combined a landscape-scale field study and glasshouse experiment to test how grassland management affects plant and soil N retention. Specifically, we hypothesised that extensively managed, species-rich grasslands of high conservation value would have lower N loss and greater N retention than intensively managed, species-poor grasslands, and that this would be due to a greater immobilisation of N by a more fungal-dominated microbial community. In the field study, we found that extensively managed, species-rich grasslands had lower N leaching losses. Soil inorganic N availability decreased with increasing abundance of fungi relative to bacteria, although the best predictor of soil N leaching was the C/N ratio of aboveground plant biomass. In the associated glasshouse experiment we found that retention of added (15)N was greater in extensively than in intensively managed grasslands, which was attributed to a combination of greater root uptake and microbial immobilisation of (15)N in the former, and that microbial immobilisation increased with increasing biomass and abundance of fungi. These findings show that grassland management affects mechanisms of N retention in soil through changes in root and microbial uptake of N. Moreover, they support the notion that microbial communities might be the key to improved N retention through tightening linkages between plants and microbes and reducing N availability.

Plant species richness and productivity often show a positive relationship, but the underlying mechanisms are not fully understood, especially at the plant species level. We examined how growing plants in species mixture influences intraspecific rates of short-term carbon (C-) translocation, and determined whether such short-term responses are reflected in biomass yields. We grew monocultures and mixtures of six common C3 grassland plant species in outdoor mesocosms, applied a (13)C-CO(2) pulse in situ to trace assimilated C through plants, into the soil, and back to the atmosphere, and quantified species-specific biomass. Pulse derived (13)C enrichment was highest in the legumes Lotus corniculatus and Trifolium repens, and relocation (i.e. transport from the leaves to other plant parts) of the recently assimilated (13)C was most rapid in T. repens grown in 6-species mixtures. The grass Anthoxanthum odoratum also showed high levels of (13)C enrichment in 6-species mixtures, while (13)C enrichment was low in Lolium perenne, Plantago lanceolata and Achillea millefolium. Rates of C loss through respiration were highest in monocultures of T. repens and relatively low in species mixtures, while the proportion of (13)C in the respired CO(2) was similar in monocultures and mixtures. The grass A. odoratum and legume T. repens were most promoted in 6-species mixtures, and together with L. corniculatus, caused the net biomass increase in 6-species mixtures. These plant species also had highest rates of (13)C-label translocation, and for A. odoratum and T. repens this effect was greatest in plant individuals grown in species mixtures. Our study reveals that short-term plant C translocation can be accelerated in plant individuals of legume and C3 grass species when grown in mixtures, and that this is strongly positively related to overyielding. These results demonstrate a mechanistic coupling between changes in intraspecific plant carbon physiology and increased community level productivity in grassland systems.

1. Restoration of high plant species diversity to sites where it has been reduced by intensive grassland management requires identification of appropriate management regimes. Understanding the combinatorial effects of management on above-ground vegetation and below-ground microbial communities will inform management prescriptions on how best to increase plant diversity, restore rare vegetation types and achieve agri-environmental objectives. 2. Changes in vegetation and soil microbial community structure are described from the second phase of a 1990-2004 field trial that investigated the interacting effects of fertilizer and farmyard manure (FYM) treatments imposed after 1998, in the context of previous hay-cut date and seed-addition treatments. 3. Hay-cut date was the main factor influencing plant species composition in phase 1, whereas FYM was the dominant factor in phase 2. 4. Poa trivialis and Lolium perenne increased in abundance with FYM application, particularly in combination with mineral fertilizer, and particularly in 2002 after the 2001 foot and mouth epidemic. The lowest Ellenberg fertility scores were associated with absence of FYM and mineral fertilizer but with addition of seed. 5. The highest plant species diversity in phase 2 was associated with seed addition and the absence of mineral fertilizer, an effect that had probably persisted from phase 1. Progressive development of the target traditional meadow vegetation occurred through phase 2. 6. Fungal:bacterial (F:B) ratios, a measure of changes in the relative abundance of fungi and bacteria in the microbial community, generally increased from 1996 to 2004, and were particularly high in the seed-addition treatments and in the absence of fertilizer. Here the high F:B ratios were associated with species (including legumes) typical of traditionally managed mesotrophic grassland in northern England. 7. Synthesis and applications. These results demonstrate that biodiversity goals for upland meadows need to plan beyond the typical 5-10-year management agreement period of agri-environment schemes. Combination treatments, in which seed addition is vital, alongside appropriate fertilizer, FYM, hay-cut date and grazing regimes, are needed for grassland restoration. However, even after 14 years the most effective treatment combinations had still not restored the target species composition and diversity. The demonstrated change in soil microbial communities, linked to the growth of legumes, might be important to facilitate future increases in plant diversity.

Parasitic plants are one of the most ubiquitous groups of generalist parasites in both natural and managed ecosystems, with over 3,000 known species worldwide. Although much is known about how parasitic plants influence host performance, their role as drivers of community- and ecosystem-level properties remains largely unexplored. Parasitic plants have the potential to influence directly the productivity and structure of plant communities because they cause harm to particular host plants, indirectly increasing the competitive status of non-host species. Such parasite-driven above-ground effects might also have important indirect consequences through altering the quantity and quality of resources that enter soil, thereby affecting the activity of decomposer organisms. Here we show in model grassland communities that the parasitic plant Rhinanthus minor, which occurs widely throughout Europe and North America, has strong direct effects on above-ground community properties, increasing plant diversity and reducing productivity. We also show that these direct effects of R. minor on the plant community have marked indirect effects on below-ground properties, ultimately increasing rates of nitrogen cycling. Our study provides evidence that parasitic plants act as a major driver of both above-ground and below-ground properties of grassland ecosystems.