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Long-term nitrogen (N) fertilization imposes strong selection on nitrifying communities in agricultural soil, but how a progressively changing niche affects potentially active nitrifiers in the field remains poorly understood. Using a 44-year grassland fertilization experiment, we investigated community shifts of active nitrifiers by DNA-based stable isotope probing (SIP) of field soils that received no fertilization (CK), high levels of organic cattle manure (HC), and chemical N fertilization (CF). Incubation of DNA-SIP microcosms showed significant nitrification activities in CF and HC soils, whereas no activity occurred in CK soils. The 44 years of inorganic N fertilization selected only 13C-ammonia-oxidizing bacteria (AOB), whereas cattle slurry applications created a niche in which both ammonia-oxidizing archaea (AOA) and AOB could be actively 13C-labeled. Phylogenetic analysis indicated that Nitrosospira sp. 62-like AOB dominated inorganically fertilized CF soils, while Nitrosospira sp. 41-like AOB were abundant in organically fertilized HC soils. The 13C-AOA in HC soils were affiliated with the 29i4 lineage. The 13C-nitrite-oxidizing bacteria (NOB) were dominated by both Nitrospira- and Nitrobacter-like communities in CF soils, and the latter was overwhelmingly abundant in HC soils. The 13C-labeled nitrifying communities in SIP microcosms of CF and HC soils were largely similar to those predominant under field conditions. These results provide direct evidence for a strong selection of distinctly active nitrifiers after 44 years of different fertilization regimes in the field. Our findings imply that niche differentiation of nitrifying communities could be assessed as a net result of microbial adaption over 44 years to inorganic and organic N fertilization in the field, where distinct nitrifiers have been shaped by intensified anthropogenic N input.

In this study, we show that composition shifts of ammonia oxidizer communities imposed by a 22-year field fertilization regime could be well retained in both fresh and air-dried soils. The abundance and composition of ammonia-oxidizing bacteria (AOB) and archaea (AOA) were measured in fresh soils, which received no fertilization (CK), chemical fertilization (NPK), and chemical plus organic matter fertilization (NPK/OM) for 22 years. The air-drying treatment of fresh soil was also conducted for pairwise analysis. We found that in fresh soils DGGE fingerprints of AOB showed significant changes under both NPK and NPK/OM treatments when compared with control (CK) and that microbial shift was almost identical in air-dried soils. Long-term nutrient fertilization did not affect AOA communities in either air-dried or fresh soils. Compared to CK treatment, real-time PCR indicated that AOB amoA genes increased significantly in fresh soils of NPK (59-fold) and NPK/OM (48-fold) plots and in air-dried NPK and NPK/OM soils by 22-fold and 19-fold respectively. Our results demonstrate that community shifts of AOB in fresh soils under chronic N fertilization could be well preserved in air-dried soils, despite the apparent decline in absolute abundance of ammonia oxidizers. These results suggest that air-dried soil could be a useful resource for deciphering the adaptive strategy of ammonia oxidizers under N enrichment when the significant changes of community composition occurred in fresh soils.

Plant roots can significantly alter soil pH and the chemical concentration and distribution of different elements in the rhizosphere environment. Here we ask whether cadmium (Cd) bioavailability in the rhizosphere of Cd-hyperaccumulator Sedum plumbizincicola can be influenced by root-induced effects on soil pH. The Cd-hyperaccumulator S. plumbizincicola and the Cd non-hyperaccumulator ecotype Sedum alfredii were both grown in four different Cd-contaminated soils. We used the planar optode imaging technique to produce two-dimensional and high-resolution measurements of soil pH. Shoot excess cation concentration, root architecture and Cd concentrations ([Cd]) in soil pore water were also measured. Spatial analyses based on kernel density estimate of roots (KDE) and a Moran’s I correlogram were performed to assess spatial patterns and potential relationships among root distribution, soil pH and [Cd]. Both Sedum species showed root-induced increases in soil acidification (i.e. soil pH decreases of 0.1 to 0.62 units), which were clearly associated with greater root density of these plants. Remarkable excess cation uptakes by both Sedum species were detected and likely a driving factor for the root-induced acidification. The presence of the roots of S. plumbizincicola were then related to higher [Cd] in the rhizosphere than in bulk soil in Orthic Acrisol (+342%) and in Hydragric Antrosol soils (+296%). The hyperaccumulator S. plumbizincicola had larger root systems, higher acidification ability, and was associated with greater soil [Cd] than S. alfredii. Spatial patterns of root distribution and soil pH were similar between Sedum plants, however, spatial patterns of [Cd] differed across polluted soils. Rhizosphere acidification induced by S. plumbizincicola plants can play an important role on soil Cd mobilization, but overall effects on soil Cd bioavailability will depend on intrinsic soil biogeochemical properties.

Soil organic carbon (SOC) sequestration across agroecosystems worldwide can contribute to mitigate the effects of climate change by reducing levels of atmospheric CO2. Stabilisation of organic carbon (OC) in the fine soil fraction (< 20 µm) is considered an important long-term store of SOC, and the saturation deficit (difference between measured OC and estimated maximum OC in the fine fraction) is frequently used to assess SOC sequestration potential following the linear regression equation developed by Hassink (1997). However, this approach is often taken without any assessment of the fit of the equation to the soils being studied. The statistical limitations of linear regression have previously been noted, giving rise to the proposed use of boundary line (BL) analysis and quantile regression (QR) to provide more robust estimates of maximum SOC stabilisation. The objectives of this work were to assess the suitability of the Hassink (1997) equation to estimate maximum fine-fraction OC in UK grassland soils of varying sward ages and to evaluate the linear regression, boundary line and quantile regression methods to estimate maximum fine-fraction OC. A chronosequence of 10 grasslands was sampled, in order to assess the relationship between sward age (time since the last reseeding event) and the measured and predicted maximum fine-fraction OC. Significantly different regression equations show that the Hassink (1997) equation does not accurately reflect maximum fine-fraction OC in UK grasslands when determined using the proportion of the fine soil fraction (< 20 µm, %) and measured fine-fraction OC (g C per kg soil). The QR estimate of maximum SOC stabilisation was almost double that of the linear regression and BL analysis (0.89 ± 0.074, 0.43 ± 0.017 and 0.57 ± 0.052 g C per kg soil, respectively). Sward age had an inconsistent effect on the measured variables and potential maximum fine-fraction OC. Fine-fraction OC across the grasslands made up 4.5 % to 55.9 % of total SOC, implying that there may be either high potential for additional C sequestration in the fine fraction of these soils or that protection in aggregates is predominant in these grassland soils. This work highlights the need to ensure that methods used to predict maximum fine-fraction OC reflect the soil in situ, resulting in more accurate assessments of carbon sequestration potential.

The role of soils in the global carbon cycle and in reducing GHG emissions from agriculture has been increasingly acknowledged. The '4 per 1000' (4p1000) initiative has become a prominent action plan for climate change mitigation and achieve food security through an annual increase in soil organic carbon (SOC) stocks by 0.4%, (i.e. 4 parts per thousand per year). However, the feasibility of the 4p1000 scenario and, more generally, the capacity of individual countries to implement soil carbon sequestration (SCS) measures remain highly uncertain. Here, we evaluated country-specific SCS potentials of agricultural land for 24 countries in Europe. Based on a detailed survey of available literature, we estimate that between 0.1% and 27% of the agricultural greenhouse gas (GHG) emissions can potentially be compensated by SCS annually within the next decades. Measures varied widely across countries, indicating differences in country-specific environmental conditions and agricultural practices. None of the countries' SCS potential reached the aspirational goal of the 4p1000 initiative, suggesting that in order to achieve this goal, a wider range of measures and implementation pathways need to be explored. Yet, SCS potentials exceeded those from previous pan-European modelling scenarios, underpinning the general need to include national/regional knowledge and expertise to improve estimates of SCS potentials. The complexity of the chosen SCS measurement approaches between countries ranked from tier 1 to tier 3 and included the effect of different controlling factors, suggesting that methodological improvements and standardization of SCS accounting are urgently required. Standardization should include the assessment of key controlling factors such as realistic areas, technical and practical feasibility, trade-offs with other GHG and climate change. Our analysis suggests that country-specific knowledge and SCS estimates together with improved data sharing and harmonization are crucial to better quantify the role of soils in offsetting anthropogenic GHG emissions at global level.

Grassland management intensification can significantly affect the structure and composition of important soil microbial groups such as bacteria and fungi. Changes to these microbial communities can greatly influence carbon (C) and nitrogen (N) cycling in grassland soils. Here we specifically address how microbial abundances might shift under the effect of multiple management practices and how this in turn might relate to changes in soil C and N storage. Soil samples were collected from a 23-year-old grassland experiment and real-time quantitative Polymerase Chain Reaction (PCR) was performed to address whether and how (1) chronic nutrient additions, (2) liming (i.e., the addition of CaCO3 to soils), and (3) grazing by rabbits might affect archaeal, bacterial and fungal microbial groups. We found that liming additions significantly increased archaeal and bacterial abundance whilst strongly reducing fungal abundance. The addition of N-only (as NH4NO3) significantly reduced bacterial abundance while chronic grazing by rabbits resulted in positive effects on archaeal abundance. Despite long-term grassland management significantly affecting soil microbial abundances (and Fungal-to-Bacterial ratios), microbial changes were not related to either changes in soil C or N pools. Overall, our results suggest that (1) important microbial-‘soil functioning’ relationships may only be detected at lower taxonomic levels, and (2) liming-induced increases in soil pH determined significant shifts in soil microbial abundance, which could have important consequences for the delivery of multiple soil ecosystem services (i.e., nutrient regulation, C and N sequestration) from permanent grassland.

The addition of organic amendments to soils can significantly increase soil organic matter (SOM) content as well as the mass of large (e.g. 2000–250 μm) particulate organic matter (POM) fractions. Here we address whether the addition of organic amendments might affect both POM pools and the phytoextraction efficiency of Sedum plumbizincicola (S. plumbizincicola) in cadmium (Cd) polluted soils. We carried out a 442-days long pot experiment and measured Cd uptake by S. plumbizincicola for four successive plant crops in two polluted paddy soils subjected to rice straw (RS) amendment. We also measured soil pH, nutrient availability, pore water dissolved organic carbon (DOC) and Cd concentrations across different soil particle-size fractions. We found that RS amendments had no significant effects on soil pH, DOC or Cd concentrations in bulk soils during repeated phytoextraction. However, RS amendments were associated with significant (1) increases (i.e. 14.3 to 20.7%) in Cd uptake by S. plumbizincicola plants from the first crop harvest, (2) increases in available soil nutrients content, (3) increases in the percentage of oxidizable Cd fractions and the mass of soil POM fractions, and (4) decreases in POM Cd concentrations after repeated phytoextraction. These findings suggest that POM fractions may represent important accessible pools of Cd for uptake by S. plumbizincicola plants. RS amendments enhance both Cd bioavailability within soil POM pools and Cd uptake by the hyperaccumulator S. plumbizincicola thus providing an effective management practice to improve Cd removal from polluted soils through phytoextraction.

Human-managed grasslands receive significant inputs of fertilizing materials, which can greatly influence soil biological processes associated with the cycling of nitrogen (N), including microbial nitrification. Here we specifically address how soil ammonia oxidizing archaea (AOA) and ammonia oxidizing bacteria (AOB) respond to 23 years of different management practices in a permanent grassland experiment. We found that AOB amoA gene copy numbers were significantly higher in limed soils (associated with greater pH values) whereas AOA amoA gene copy numbers were higher in grazed grasslands. The chronic addition of inorganic N fertilizer in the form of ammonium nitrate (either applied alone or in combination with other macro-nutrients) greatly contributed to increase AOB abundance. Our study brings evidence of how soil-nitrifying communities can differently respond to the long-term effect of animal (i.e. rabbit) grazing and to repeated applications of nutrient (e.g. NH4NO3) and non-nutrient (i.e. CaCO3) fertilizing materials.

Common grassland management practices include animal grazing and the repeated addition of lime and nutrient fertilizers to soils. These practices can greatly influence the size and distribution of different soil aggregate fractions, thus altering the cycling and storage of carbon (C) and nitrogen (N) in grassland soils. So far, very few studies have simultaneously addressed the potential long-term effect that multiple management practices might have on soil physical aggregation. Here we specifically ask whether and how grazing, liming and nutrient fertilization might influence C and N content (%) as well as C and N pools of different soil aggregate fractions in a long-term grassland experiment established in 1991 at Silwood Park, Berkshire, UK. We found that repeated liming applications over 23years significantly decreased the C pool (i.e. gCKg-1 soil) of Large Macro Aggregate (LMA>2mm) fractions and increased C pools within three smaller soil aggregate fractions: Small Macro Aggregate (SMA, 250μm-2mm), Micro Aggregate (MiA, 53-250μm), and Silt Clay Aggregate (SCA

Multi-functional silvopastoral systems provide a wide range of services to human society including the regulation of nutrients and water in soils and the sequestration of atmospheric carbon dioxide (CO2). Although silvopastoral systems significantly contribute to enhance aboveground carbon (C) sequestration (e.g. C accumulation in woody plant biomass), their long-term effects on soil C pools are less clear. In this study we performed soil physical fractionation analyses to quantify the C pool of different aggregate fractions across three land use types including (1) silvopastoral system with ash trees (Fraxinus excelsior L.), (2) planted woodland with ash trees, and (3) permanent grassland, which were established in 1989 at Loughgall, Northern Ireland, UK. Our results show that 26 years after the conversion of permanent grassland to either silvopastoral or woodland systems, soil C (and N) stocks (0–20 cm depth) did not significantly change between the three land use types. We found, however, that permanent grassland soils were associated with significantly higher C pools (g C kg−1 soil; P 2 mm) whereas soil C pools of the micro-aggregate (53–250 μm) and silt and clay (

Summary Recent studies have revealed many potential benefits of increasing plant diversity in natural ecosystems, as well as in agroecosystems and production forests. Plant diversity potentially provides a partial to complete substitute for many costly agricultural inputs, such as fertilizers, pesticides, imported pollinators and irrigation. Diversification strategies include enhancing crop genetic diversity, mixed plantings, rotating crops, agroforestry and diversifying landscapes surrounding croplands. Here we briefly review studies considering how increasing plant diversity influences the production of crops, forage, and wood, yield stability, and several regulating and supporting agroecosystem services. We also discuss challenges and recommendations for diversifying agroecosystems. There is consistently strong evidence that strategically increasing plant diversity increases crop and forage yield, wood production, yield stability, pollinators, weed suppression and pest suppression, whereas effects of diversification on soil nutrients and carbon remain poorly understood. Synthesis. The benefits of diversifying agroecosystems are expected to be greatest where the aims are to sustainably intensify production while reducing conventional inputs or to optimize both yields and ecosystem services. Over the next few decades, as monoculture yields continue to decelerate or decline for many crops, and as demand for ecosystem services continues to rise, diversification could become an essential tool for sustaining production and ecosystem services in croplands, rangelands and production forests.

Important biochemical reactions in soils are catalyzed by extracellular enzymes, which are synthesized by microbes and plant roots. Although enzyme activities can significantly affect the decomposition of soil organic matter and thus influence the storage and cycling of carbon (C) and nitrogen (N), it is not clear how enzyme activities relate to changes in the C and N content of different grassland soils. Here we address whether the activity of C-acquiring (b-1,4-glucosidase, BG) and N-acquiring (L-leucine amino-peptidase (LAP) and b-1,4-N-acetyl-glucosaminidase (NAG)) enzymes is linked to changes in the C and N content of a variety of human-managed grassland soils. We selected soils which have a well-documented management history going back at least 19 years in relation to changes in land use (grazing, mowing, ploughing), nutrient fertilization and lime (CaCO 3) applications. Overall we found a positive relationship between BG activity and soil C content as well as between LAP þ NAG activity and soil N. These positive relationships occurred across grasslands with very different soil pH and management history but not in intensively managed grasslands where increases in soil bulk density (i.e. high soil compaction) negatively affected enzyme activity. We also found evidence that chronic nutrient fertilization contributed to increases in soil C content and this was associated with a significant increase in BG activity when compared to unfertilized soils. Our study suggests that while the activities of C-and N-acquiring soil enzymes are positively related to soil C and N content, these activities respond significantly to changes in management (i.e. soil compaction and nutrient fertilization). In particular, the link between BG activity and the C content of long-term fertilized soils deserves further investigation if we wish to improve our understanding of the C sequestration potential of human-managed grassland soils.

Agricultural grasslands comprise over 50% of the total land area of the UK and provide important ecosystem services that include livestock and forage production. These services are rarely measured against the effects that key management practices might have on the long-term ability of grassland soils to cycle and store carbon (C). The common management practice of re-seeding (i.e. the ploughing and seeding of grasslands with more productive grass cultivars) can cause significant soil disturbance; yet the net long-term effects of re-seeding on soil C gains and losses in permanent grasslands are poorly understood. Here, we selected a chronosequence of 45 permanent grasslands across Northern Ireland with a well-documented history of single re-seeding events over the last 50 years. Second, we asked whether and how soil C cycling and storage might differ between recently re-seeded ‘young’ grasslands and increasingly ‘older’ (or never re-seeded) grasslands. We measured (1) soil CO2 fluxes, (2) soil C stocks, (3) the C content of different soil aggregate fractions, and (4) root C stocks. We found that soil CO2 fluxes were significantly higher in recently re-seeded, ‘young’, grasslands. However, total soil C stocks (0–20 cm depth) did not increase in ‘older’ grasslands despite these grasslands showing greater root C stocks. Instead, soil C stocks significantly decreased with increases in soil bulk density. Higher soil bulk density was also associated with lower C content in smaller organo-mineral aggregate sizes (i.e. more recalcitrant C pools) regardless of grassland age (time since re-seeding). Overall, our results suggest that management-induced effects on key soil physical properties, i.e. bulk density, may have significantly greater implications for C sequestration in permanent grassland soils than high disturbance, but infrequent, re-seeding events.

Grasslands cover more than a third of the European agricultural area and are often intensively managed to support the livestock-farming sector. Despite grassland intensification can greatly influence soil carbon (C) cycling, changes in soil C stocks both across years and at increasing soil depths remain difficult to quantify simultaneously. Here we measured spatial and temporal changes in soil C stocks to assess C stocks’ response to intensive grassland management. We measured soil C stocks (a) in a long-term nutrient fertilization experiment on permanent grassland (established in 1970), and (b) in 126 grassland fields distributed across 11 lowland farms in Northern Ireland (UK), which are associated with different frequencies of soil tillage. Using 45 years of data from the plot-scale grassland experiment we found evidence that significant changes in soil C stocks mainly occurred in the soil top 20 cm (not in deeper soils) and only between ‘extreme’ nutrient treatments (i.e. unfertilized vs. highly fertilized soils). Soil physical fractionation, radiocarbon and stable nitrogen isotope analyses all suggest that new C has accumulated in these soils but perhaps not fast enough to affect C stocks in deeper soil layers. Results at the field-scale from intensively managed grasslands show how the frequency of soil tillage neither affected soil C stocks between 0–20, 20–40 or 40–60 cm depth layers nor the C pool of different soil physical fractions at increasing soil depths. Our findings demonstrate how the response of soil C stocks to grassland intensification (i.e. C stocks response to different rates of nutrient fertilization or frequency of soil tillage) can be very slow both in time and space under cool and humid climate conditions. We suggest how the persistence of these soil C stocks under intensive grassland management offers the unique opportunity to improve nutrient use efficiency and cycling thus promoting the delivery of multiple ecosystem processes.

Sustainable grassland intensification aims to increase plant yields while maintaining the ability of soil to act as a sink rather than sources of atmospheric CO2. High biomass yields from managed grasslands, however, can be only maintained through long-term nutrient fertilization, which can significantly affect soil carbon (C) storage and cycling. Key questions remain about (1) how long-term inorganic vs. organic fertilization influences soil C stocks, and (2) how soil C gains (or losses) contribute to the long-term C balance of managed grasslands. Using 43 years of data from a permanent grassland experiment, we show that soils not only act as significant C sinks but have not yet reached C saturation. Even unfertilized control soils showed C sequestration rates of 0.35 Mg C ha−1 yr−1 (i.e. 35 g C m−2 yr−1; 0–15 cm depth) between 1970 and 2013. High application rates of liquid manure (i.e. cattle slurry) further increased soil C sequestration to 0.86 Mg C ha−1 yr−1 (i.e. 86 g C m−2 yr−1) and a key cause of this C accrual was greater C inputs from cattle slurry. However, average coefficients of slurry-C retention in soils suggest that 85 % of C added yearly through liquid manure is lost possibly via CO2 fluxes and organic C leaching. Inorganically fertilized soils (i.e. NPK) had the lowest C-gain efficiency (i.e. unit of C gained per unit of N added) and lowest C sequestration (similar to control soils). Soils receiving cattle slurry showed higher C-gain and N-retention efficiencies compared to soils receiving NPK or pig slurry. We estimate that net rates of CO2-sequestration in the top 15 cm of the soil can offset 9–25 % of GHG (greenhouse gas) emissions from intensive management. However, because of multiple GHG sources associated with livestock farming, the net C balance of these grasslands remains positive (9–12 Mg CO2-equivalent ha−1 yr−1), thus contributing to climate change. Further C-gain efficiencies (e.g. reduced enteric fermentation and use of feed concentrates, better nutrient management) are required to make grassland intensification more sustainable.

International audience; AbstractThe delivery of multiple ecosystem services from intensively managed cropping systems remains challenging mainly because increases in crop yields are rarely associated with greater soil carbon (C) sequestration or efficient ecosystem nitrogen (N) cycling. The sustainability of intensive cropping systems depends on trade-offs between multiple ecosystem services but experimental evidence from long-term field studies remains limited. The common expectation is that highly productive agroecosystems will be associated with lower soil C and reduced nutrient use efficiency. Here we use data spanning 30 years of a long-term field experiment established in 1985 near Lodi in Northern Italy where four arable systems (i.e., three crop rotations and a grain maize monoculture) and a no-till permanent meadow were all compared across two levels of agronomic inputs. We asked how (i) soil C stocks, (ii) fertilizer N-use efficiency, (iii) productivity, (iv) crude protein, and (v) feed units for lactation might differ across the five traditional cropping systems. We found that soil C sequestration, N-use efficiency, and crude protein production were all significantly higher in the no-till permanent meadow, which was however associated with lower dry matter yields and reduced feed units for lactation when compared with the arable systems. These findings suggest that converting arable soil into no-till permanent meadow is a win-lose solution. The most productive annual rotation (silage maize + Italian ryegrass) offers a complementary win-lose solution whereby high yields and feed units for lactation can be obtained from a smaller cropland area. The other cropping systems are less productive and provide little (or none) soil C storage benefits. Our study is one of the first to show clear trade-offs between multiple ecosystem services and to demonstrate that high fertilization rates might be only justified when the management goal is to spare land for less intensive uses such as permanent meadow.

Fertile soil is fundamental to our ability to achieve food security, but problems with soil degradation (such as acidification) are exacerbated by poor management. Consequently, there is a need to better understand management approaches that deliver multiple ecosystem services from agricultural land. There is global interest in sustainable soil management including the re-evaluation of existing management practices. Liming is a long established practice to ameliorate acidic soils and many liming-induced changes are well understood. For instance, short-term liming impacts are detected on soil biota and in soil biological processes (such as in N cycling where liming can increase N availability for plant uptake). The impacts of liming on soil carbon storage are variable and strongly relate to soil type, land use, climate and multiple management factors. Liming influences all elements in soils and as such there are numerous simultaneous changes to soil processes which in turn affect the plant nutrient uptake; two examples of positive impact for crops are increased P availability and decreased uptake of toxic heavy metals. Soil physical conditions are at least maintained or improved by liming, but the time taken to detect change varies significantly. Arable crops differ in their sensitivity to soil pH and for most crops there is a positive yield response. Liming also introduces implications for the development of different crop diseases and liming management is adjusted according to crop type within a given rotation. Repeated lime applications tend to improve grassland biomass production, although grassland response is variable and indirect as it relates to changes in nutrient availability. Other indicators of liming response in grassland are detected in mineral content and herbage quality which have implications for livestock-based production systems. Ecological studies have shown positive impacts of liming on biodiversity; such as increased earthworm abundance that provides habitat for wading birds in upland grasslands. Finally, understanding of liming impacts on soil and crop processes are explored together with functional aspects (in terms of ecosystems services) in a new qualitative framework that includes consideration of how liming impacts change with time. This holistic approach provides insights into the far-reaching impacts that liming has on ecosystems and the potential for liming to enhance the multiple benefits from agriculturally managed land. Recommendations are given for future research on the impact of liming and the implications for ecosystem services.

The functioning of human-managed grassland ecosystems strongly depends on how common management practices will affect grassland ‘belowground compartment’ including soil biogeochemistry and plant roots. Key questions remain about how animal grazing, liming (e.g. the addition of CaCO3 to soils), and nutrient fertilization might affect, in the long-term, soil nutrient cycling and multiple root traits. Here we focus on a mesotrophic grassland located in Berkshire, UK, where contrasting levels of rabbit grazing, liming and different inorganic fertilizers have been applied since 1991. We ask how (1) soil nitrogen (N) availability and cycling, (2) total root mass, (3) root mass decomposition, and (4) arbuscular mycorrhizal fungal (AMF) root colonisation might respond to 22 years of very different management. We found that liming strongly affected total root mass, root decomposition, root AMF colonisation as well as soil N availability and cycling and that these effects were mainly driven by liming-induced increases in soil pH. Increases in soil pH were associated with significant (1) decreases in root mass, (2) increases in root mass decomposability and in the mineralization of N in decomposing root detritus, and (3) increases in AMF infection. Soil pH was also significantly related to greater N availability (i.e. soil NO3 levels) and to lower δ15N natural abundance, which suggests more efficient N uptake by plants in limed soils as we found in our study. The application of multiple nutrients (NPKMg) also reduced total root mass, while N-only fertilization was associated with greater AMF infection. Surprisingly the long-term impact of grazing was generally weak and not significant on most plant and soil parameters. Despite soil pH affecting most belowground variables, changes in soil pH were not associated with any change in soil C and N stocks. Because liming can improve nutrient cycling (and benefits soil pH and grass yields) without negatively affecting soil C sequestration, we suggest that regular liming applications may provide management solutions for increasing the long-term sustainability of permanent grassland. This article is protected by copyright. All rights reserved.

Intercropping is commonly practiced worldwide because of its benefits to plant productivity and resource-use efficiency. Belowground interactions in these species-diverse agro-ecosystems can greatly contribute to enhancing crop yields; however, our understanding remains quite limited of how plant roots might interact to influence crop biomass, photosynthetic rates, and the regulation of different proteins involved in CO2 fixation and photosynthesis. We address this research gap by using a pot experiment that included three root-barrier treatments with full, partial and no root interactions between foxtail millet (Setaria italica (L.) P.Beauv.) and peanut (Arachis hypogaea L.) across two growing seasons. Biomass of millet and peanut plants in the treatment with full root interaction was 3.4 and 3.0 times higher, respectively, than in the treatment with no root interaction. Net photosynthetic rates also significantly increased by 112–127% and 275–306% in millet and peanut, respectively, with full root interaction compared with no root interaction. Root interactions (without barriers) contributed to the upregulation of key proteins in millet plants (i.e. ribulose 1,5-biphosphate carboxylase; chloroplast β-carbonic anhydrase; phosphoglucomutase, cytoplasmic 2; and phosphoenolpyruvate carboxylase) and in peanut plants (i.e. ribulose 1,5-biphosphate carboxylase; glyceraldehyde-3-phosphate dehydrogenase; and phosphoglycerate kinase). Our results provide experimental evidence of a molecular basis that interspecific facilitation driven by positive root interactions can contribute to enhancing plant productivity and photosynthesis.

The application of calcium- and magnesium-rich materials to soil, known as liming, has long been a foundation of many agro-ecosystems worldwide because of its role in counteracting soil acidity. Although liming contributes to increased rates of respiration from soil thereby potentially reducing soils ability to act as a CO2 sink, the long-term effects of liming on soil organic carbon (Corg) sequestration are largely unknown. Here, using data spanning 129 years of the Park Grass Experiment at Rothamsted (UK), we show net Corg sequestration measured in the 0–23cm layer at different time intervals since 1876 was 2–20 times greater in limed than in unlimed soils. The main cause of this large Corg accrual was greater biological activity in limed soils, which despite increasing soil respiration rates, led to plant C inputs being processed and incorporated into resistant soil organo-mineral pools. Limed organo-mineral soils showed: (1) greater Corg content for similar plant productivity levels (i.e. hay yields); (2) higher 14C incorporation after 1950s atomic bomb testing and (3) lower C:N ratios than unlimed organo-mineral soils, which also indicate higher microbial processing of plant C. Our results show that greater Corg sequestration in limed soils strongly reduced the global warming potential of long-term liming to permanent grassland suggesting the net contribution of agricultural liming to global warming could be lower than previously estimated. Our study demonstrates that liming might prove to be an effective mitigation strategy, especially because liming applications can be associated with a reduced use of nitrogen fertilizer which is a key cause for increased greenhouse gas emissions from agro-ecosystems.

The functioning of human-managed grassland ecosystems strongly depends on how common management practices (e.g., animal grazing and the chronic addition of fertilizing materials to soils) interact to influence plant and soil element stoichiometry. Here we use data from a 22-yr-long grassland experiment to address whether and how plant element stoichiometry (i.e., carbon [C], nitrogen [N], phosphorus [P] ratios) might respond to (1) animal grazing, (2) agricultural liming (i.e., CaCO3) applications, and (3) nutrient fertilization. We also ask whether plant C:N:P stoichiometry could predict changes in soil N and P availability and in soil C, N, and P stocks. We found that grassland management significantly affected plant C:N:P ratios as predicted by ecological stoichiometry theory. For example, plant aboveground and belowground C:N and C:P ratios decreased under chronic N and P fertilization, respectively. Plant C:N and C:P ratios were significantly greater in unfertilized (control) soils. Also plant C:N ratios were highest under P-only additions, whereas plant C:P ratios were highest under N-only additions. However, unpredictable changes in C:N:P ratios also occurred, suggesting that plant tissue chemistry may not be a simple reflection of soil nutrient availability. Changes in plant C:nutrient ratios well predicted variation in soil nutrient availability, but not in soil C, N, and P stocks. Contrary to expectations, soil C stocks significantly increased with decreasing plant C:N ratios in the nutrient-fertilized grasslands and not with increasing plant C:N ratios in the unfertilized grasslands. We suggest that a better mechanistic understanding of the negative relationship between plant C:N stoichiometry and soil C accrual will greatly help in improving the sustainability of human-managed grasslands.