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.

Summary 1.  Agricultural policy in the Pennine Dales Environmentally Sensitive Area in northern England aims to enhance plant species diversity in agriculturally improved meadows and return them to a ‘traditional’ species composition. The interacting effects of management on vegetation and productivity were tested in a split‐split‐split plot experiment. Three grazing treatments (autumn grazing with cattle and sheep, spring grazing with sheep, both regimes) were applied between 1990 and 98. Two fertilizer treatments (25 kg ha−1 N plus 12·5 kg ha−1 P2O5 and K2O, no fertilizer); three hay cut date treatments (14 June, 21 July, 1 September) and two seed addition treatments (no seed, seed of many species) were used within the grazing treatments. 2.  By 1998, all the main treatments had produced small but significant changes to plant species diversity. A particularly large increase in diversity occurred with the combination of autumn and spring grazing, 21 July hay cut date and seed addition treatments. This change was achieved by an episodic rather than a regular increase in species over time. 3.   Rhinanthus minor spread to most plots after its introduction as a constituent of the seed treatment. By 1996 it was particularly abundant in all treatment combinations that included autumn grazing, no mineral fertilizer and a July haycut. Populations of > 40 plants m−2 were associated with the lowest yields of hay. 4.   ‘Unimproved‐traditional’ plant communities, mainly Festuca ovina–Agrostis capillaris–Galium saxatile grassland, occupied more than 66% of the trial area. Anthoxanthum odoratum–Geranium sylvaticum grasslands were most abundant in 1996, being primarily associated with the combination of autumn and spring grazing, 21 July and 1 September hay cut dates and seed addition treatments, over both fertilizer treatments. 5.  Yields of herbage biomass initially declined over time in all treatment combinations. Lowest yields in most years were associated with the autumn and spring grazing, 14 June cutting date and no fertilizer treatments. 6.  Management to increase the number of plant species in agriculturally improved mesotrophic grassland requires the joint implementation of appropriate cut date and grazing regimes, probably to provide regeneration niches, and the application of seed to provide species to fill these niches. The small amount of mineral fertilizer used in this experiment had a measurable effect, but was of lesser importance.

Summary The enhancement of biodiversity in meadow grassland, an environmental aim of European agricultural policy, requires definition of appropriate management regimes and the rate at which they enhance biodiversity and change ecosystem properties. We describe vegetation changes in a 10‐year trial on mesotrophic grassland that was previously agriculturally improved, plus change in the soil microbial community and fertility, important factors that influence biodiversity. Management treatments were three hay‐cut dates, plus two mineral fertilizer, two seed addition and two farmyard manure (FYM) applications. Treatment combinations included the traditional management regime (21 July hay‐cut date, no mineral fertilizer, autumn grazing with cattle, spring grazing with sheep), modern variants of this (14 June hay‐cut date, mineral fertilizer) and exceptional historic variants (1 September hay‐cut date). Sowing seed increased species richness and, in the absence of fertilizer and FYM, produced a plant community similar to Geranium sylvaticum–Anthoxanthum odouratum grassland. The greatest cover of sown species was found in seeded treatments, cut for hay on 21 July, in the absence of mineral fertilizer. The target plant community (MG3b grassland) was most rapidly achieved with a 21 July hay cut. Initial decrease in Ellenberg fertility scores only persisted in the 21 July and 1 September cut dates when mineral fertilizer was absent. Soil phosphate was lowest in the joint absence of mineral fertilizer and FYM. There were few treatment effects on the soil microflora. Bacterial biomass was reduced when FYM was applied with the 14 June cut date, but increased when FYM was applied with the 1 September cut date. Fungal biomass decreased when mineral fertilizer was applied. Increased species richness, primarily through an increase in legumes, stress‐tolerant and stress‐tolerant ruderal plant strategists, was associated with an increase in soil fungi and the abundance of fungi relative to bacteria. All these were associated with seed addition to unfertilized plots cut on 21 July, in the absence of FYM, indicating a functional role for individual species. Synthesis and applications. The enhancement of biodiversity in meadow grassland is a long‐term (> 10‐year) secondary succession, most rapidly achieved in the absence of mineral fertilizer by cutting for hay in mid‐July and autumn grazing with cattle. The sowing of key functional species, i.e. legumes and Rhinanthus minor, was important in facilitating the staged colonization of other sown species.

Summary1. 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.

The NERC and CEH trademarks and logos ('the Trademarks') are registered trademarks of NERC in the UK and other countries, and may not be used without the prior written consent of the Trademark owner. Accepted ArticleThis article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1111/gcb.13246 This article is protected by copyright. All rights reserved. Accepted ArticleThis article is protected by copyright. All rights reserved.Keywords: soil carbon, soil depth, grassland, management intensity, soil carbon stocks, legacy effect, carbon inventory Type of paper: Primary Research Article AbstractThe importance of managing land to optimise carbon sequestration for climate change mitigation is widely recognised, 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 grasslands 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 sub-surface soil below 30cm, 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 30cm. 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 30-100 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 Accepted ArticleThis article is protected by copyright. All rights reserved.mitigation, and for global carbon models which do not currently account for changes in soil carbon to depth with management.