[Show abstract][Hide abstract] ABSTRACT: Soil microorganisms are critical to ecosystem functioning and the maintenance of soil fertility. However, despite global increases in the inputs of nitrogen (N) and phosphorus (P) to ecosystems due to human activities, we lack a predictive understanding of how microbial communities respond to elevated nutrient inputs across environmental gradients. Here we used high-throughput sequencing of marker genes to elucidate the responses of soil fungal, archaeal, and bacterial communities using an N and P addition experiment replicated at 25 globally distributed grassland sites. We also sequenced metagenomes from a subset of the sites to determine how the functional attributes of bacterial communities change in response to elevated nutrients. Despite strong compositional differences across sites, microbial communities shifted in a consistent manner with N or P additions, and the magnitude of these shifts was related to the magnitude of plant community responses to nutrient inputs. Mycorrhizal fungi and methanogenic archaea decreased in relative abundance with nutrient additions, as did the relative abundances of oligotrophic bacterial taxa. The metagenomic data provided additional evidence for this shift in bacterial life history strategies because nutrient additions decreased the average genome sizes of the bacterial community members and elicited changes in the relative abundances of representative functional genes. Our results suggest that elevated N and P inputs lead to predictable shifts in the taxonomic and functional traits of soil microbial communities, including increases in the relative abundances of faster-growing, copiotrophic bacterial taxa, with these shifts likely to impact belowground ecosystems worldwide.
Proceedings of the National Academy of Sciences 08/2015; 112(35). DOI:10.1073/pnas.1508382112 · 9.67 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Exotic species dominate many communities; however the functional significance of species’ biogeographic origin remains highly contentious. This debate is fuelled in part by the lack of globally replicated, systematic data assessing the relationship between species provenance, function and response to perturbations. We examined the abundance of native and exotic plant species at 64 grasslands in 13 countries, and at a subset of the sites we experimentally tested native and exotic species responses to two fundamental drivers of invasion, mineral nutrient supplies and vertebrate herbivory. Exotic species are six times more likely to dominate communities than native species. Furthermore, while experimental nutrient addition increases the cover and richness of exotic species, nutrients decrease native diversity and cover. Native and exotic species also differ in their response to vertebrate consumer exclusion. These results suggest that species origin has functional significance, and that eutrophication will lead to increased exotic dominance in grasslands.
[Show abstract][Hide abstract] ABSTRACT: Humans dominate many important Earth system processes including the nitrogen (N) cycle. Atmospheric N deposition affects fundamental processes such as carbon cycling, climate regulation, and biodiversity, and could result in changes to fundamental Earth system processes such as primary production. Both modelling and experimentation have suggested a role for anthropogenically altered N deposition in increasing productivity, nevertheless, current understanding of the relative strength of N deposition with respect to other controls on production such as edaphic conditions and climate is limited. Here we use an international multiscale data set to show that atmospheric N deposition is positively correlated to aboveground net primary production (ANPP) observed at the 1-m2 level across a wide range of herbaceous ecosystems. N deposition was a better predictor than climatic drivers and local soil conditions, explaining 16% of observed variation in ANPP globally with an increase of 1 kg N·ha−1·yr−1 increasing ANP...
[Show abstract][Hide abstract] ABSTRACT: Tracing organic matter (OM) in soil is challenging, because runoff and leaching processes are interrelated and have multiple sources. Therefore, multiple tracers with low background concentrations such as rare earth element oxides (REOs) are necessary to delineate the origin of sources of the organic materials in groundwater, rivers or in catchments. The main objective of this study was to examine the potential use of REOs as a tracer in various forms of OM (1) whole slurry, (2) solid, and (3) liquid phase of cattle slurry after mechanical separation. A laboratory experiment was carried out using five REOs (La, Gd, Sm, Pr, and Nd oxides) mixed directly into soil or mixed with various fractions of cattle slurry and then applied to the soil surface. In the additional grassland experiment, Gd oxide was spiked with soil and cattle slurry and then applied to the soil surface. The mineral N in the liquid phase (urine) of the slurry in the grassland experiment was labelled with 15N urea (16 atom%). In the laboratory experiment, results showed that the five REOs concentration of soil in 0–1 cm soil section after the rainfall simulation was still up to 20 times more than the background values. In 1–2 cm soil section, the concentration of only Gd (two fold higher) and La oxides (50% higher) were significantly higher than the soil background values. Therefore, we hypothesized that Gd and La oxides were associated also with relatively finer organic particles in slurry, thus 1–2 cm soil section were enriched with these oxides. The five REOs concentration below 2 cm soil depth were similar to the background values in all treatments. In line with the laboratory experiment, Gd concentrations in the deeper soil layers (2–4 and 4–8 cm) in the grassland experiment were not significantly affected by any treatment. Both in grassland and laboratory experiment, solid phase of the slurry (dung) was collected from the soil surface after rainfall simulation. Here, about 56% of REOs were measured on the solid phase of the slurry which indicates the strong binding potential of REOs on slurry OM. The present novel study, where REO tagged slurry was uniquely tested to study geochemical cycle of organic fertilizers, clearly highlighted the potential for their use as multiple-tracers of (animal derived-) OM in agricultural soils.
Journal of Plant Nutrition and Soil Science 02/2015; 178(2). DOI:10.1002/jpln.201400465 · 1.46 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Nitrogen (N) deposition is predicted to impact on the structure and functioning of Mediterranean ecosystems. In this study, we measured plant species composition, production and root phosphatase activity in a field experiment in which N (0, 10, 20 and 50 kg N ha−1 year−1) was added since October 2007 to a semiarid shrubland in central Spain. The characteristically dominant annual forb element responded negatively to N after ~2.5 and ~3.5 years. In contrast, the nitrophilous element (mainly crucifers) increased with N after ~2.5 and ~5.5 years, a response controlled by between-year variations in rainfall and the heterogeneous distribution of P availability. We also described a hierarchy of factors driving the structure and composition of the plant community: soil fertility was the most important driver, whereas calcareousness/acidity of soils and shrub cover played a secondary role; finally, N deposition contributed to explain a smaller fraction of the total variance, and its effects were predominantly negative, which was attributed to ammonium toxicity. Root phosphatase activity of three species was not responsive to N after ~2.5 years but there was a negative relationship with soil P in two of them. We conclude that increased N deposition in semiarid Mediterranean ecosystems of Europe can contribute to cause a shift in plant communities associated with an increase in the nitrophilous element and with a decline in abundance of various forb species adapted to the local conditions.
Water Air and Soil Pollution 02/2015; 226:5(2). DOI:10.1007/s11270-014-2278-1 · 1.55 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Anthropogenic eutrophication impacts ecosystems worldwide. Here, we use a vegetation dataset from semi-natural grasslands on acidic soils sampled along a gradient in north-western Europe to examine the response of species frequency to nitrogen (N) deposition, controlling for the effects of other environmental variables. A second dataset of acidic grasslands from Germany and the Netherlands containing plots from different time periods was analysed to examine whether the results of the spatial gradient approach coincided with temporal changes in the abundance of species. Out of 44 studied species, 16 were affected by N deposition, 12 of them negatively. Soil pH and phosphorus (P) influenced 24 and 14 species, respectively, predominantly positively. Fewer species were related to the soil contents of NO3
− or NH4
+, with no significant differences between the number of positive and negative effects. Whereas the temporal change of species was unrelated to their responses to pH, species responding negatively to N deposition, soil P and NO3
− showed a significant decline over time in both countries. Species that were negatively affected by high N deposition and/or high soil P also showed a negative temporal trend and could be characterised by short stature and slow growth. The results confirm the negative role of N deposition for many plant species in semi-natural acidic grasslands. The negative temporal trends of species sensitive to high N deposition and soil P values clearly show a need for maintaining low soil nutrient status and for restoring the formerly infertile conditions in nutrient-enriched grasslands.
[Show abstract][Hide abstract] ABSTRACT: Aim Evidence linking the accumulation of exotic species to the suppression of native diversity is equivocal, often relying on data from studies that have used different methods. Plot-level studies often attribute inverse relationships between native and exotic diversity to competition, but regional abiotic filters, including anthropogenic influences, can produce similar patterns. We seek to test these alternatives using identical scale-dependent sampling protocols in multiple grasslands on two continents. Location Thirty-two grassland sites in North America and Australia. Methods We use multiscale observational data, collected identically in grain and extent at each site, to test the association of local and regional factors with the plot-level richness and abundance of native and exotic plants. Sites captured environmental and anthropogenic gradients including land-use intensity, human population density, light and soil resources, climate and elevation. Site selection occurred independently of exotic diversity, meaning that the numbers of exotic species varied randomly thereby reducing potential biases if only highly invaded sites were chosen. Results Regional factors associated directly or indirectly with human activity had the strongest associations with plot-level diversity. These regional drivers had divergent effects: urban-based economic activity was associated with high exotic : native diversity ratios; climate- and landscape-based indicators of lower human population density were associated with low exotic : native ratios. Negative correlations between plot-level native and exotic diversity, a potential signature of competitive interactions, were not prevalent; this result did not change along gradients of productivity or heterogeneity. Main conclusion We show that plot-level diversity of native and exotic plants are more consistently associated with regional-scale factors relating to urbanization and climate suitability than measures indicative of competition. These findings clarify the long-standing difficulty in resolving drivers of exotic diversity using single-factor mechanisms, suggesting that multiple interacting anthropogenic-based processes best explain the accumulation of exotic diversity in modern landscapes.
[Show abstract][Hide abstract] ABSTRACT: Nutrient pollution presents a serious threat to biodiversity conservation. In terrestrial ecosystems, the deleterious effects of nitrogen pollution are increasingly understood and several mitigating environmental policies have been developed. Compared to nitrogen, the effects of increased phosphorus have received far less attention, although some studies have indicated that phosphorus pollution may be detrimental for biodiversity as well. Based on a dataset covering 501 grassland plots throughout Europe, we demonstrate that, independent of the level of atmospheric nitrogen deposition and soil acidity, plant species richness was consistently negatively related to soil phosphorus. We also identified thresholds in soil phosphorus above which biodiversity appears to remain at a constant low level. Our results indicate that nutrient management policies biased towards reducing nitrogen pollution will fail to preserve biodiversity. As soil phosphorus is known to be extremely persistent and we found no evidence for a critical threshold below which no environmental harm is expected, we suggest that agro-environmental schemes should include grasslands that are permanently free from phosphorus fertilization. This article is protected by copyright. All rights reserved.
Global Change Biology 06/2014; DOI:10.1111/gcb.12650 · 8.04 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Human alterations to nutrient cycles1, 2 and herbivore communities3, 4, 5, 6, 7 are affecting global biodiversity dramatically2. Ecological theory predicts these changes should be strongly counteractive: nutrient addition drives plant species loss through intensified competition for light, whereas herbivores prevent competitive exclusion by increasing ground-level light, particularly in productive systems8, 9. Here we use experimental data spanning a globally relevant range of conditions to test the hypothesis that herbaceous plant species losses caused by eutrophication may be offset by increased light availability due to herbivory. This experiment, replicated in 40 grasslands on 6 continents, demonstrates that nutrients and herbivores can serve as counteracting forces to control local plant diversity through light limitation, independent of site productivity, soil nitrogen, herbivore type and climate. Nutrient addition consistently reduced local diversity through light limitation, and herbivory rescued diversity at sites where it alleviated light limitation. Thus, species loss from anthropogenic eutrophication can be ameliorated in grasslands where herbivory increases ground-level light.
[Show abstract][Hide abstract] ABSTRACT: We aimed to answer the question of whether the species richness and composition of calcareous grasslands in North-western Germany had changed over the last 70 years as a result of atmospheric nitrogen (N) deposition. In total, 1186 plots of Festuco-Brometea (alliance Bromion erecti) grasslands from the sub-oceanic regions of the country were compiled (1061 plots from literature sources spanning a time period from 1936 to 1996, 125 new plots from 2008). Environmental descriptors recorded for each plot included geographic coordinates, altitude, heat index (combining slope and aspect), mean Ellenberg indicator values for light, soil moisture, soil pH and soil N, and cumulative N deposition (the latter being highly positively correlated with the year of sampling).
In a Detrended Correspondence Analysis, the sample plot scores along axis one were highly correlated with the mean Ellenberg N-values, those along axis two were significantly affected by the year of sampling. In a general linear model, species richness of vascular plants showed a markedly hump-shaped relationship with mean Ellenberg N-value, whereas it was weakly affected by year (cumulative N load). Species with a significant negative trend over time were more often (than expected by chance) habitat specialists of dry grasslands, small, light-demanding and winter-green or evergreen with smaller seeds and scleromorphic leaves. In contrast to what has been found for acidic grasslands, N deposition in calcareous grasslands did not result in a decline in species richness, most likely because calcareous grasslands are water- and phosphorus-limited, and are well-buffered in terms of soil pH. To prevent a further change in species composition towards more mesophytic communities, grassland management by the site managers needs to be intensified.
[Show abstract][Hide abstract] ABSTRACT: This chapter reports the findings of a Working Group on how atmospheric nitrogen (N) deposition affects both terrestrial and freshwater biodiversity. Regional and global scale impacts on biodiversity are addressed, together with potential indicators. Key conclusions are that: the rates of loss in biodiversity are greatest at the lowest and initial stages of N deposition increase; changes in species compositions are related to the relative amounts of N, carbon (C) and phosphorus (P) in the plant soil system; enhanced N inputs have implications for C cycling; N deposition is known to be having adverse effects on European and North American vegetation composition; very little is known about tropical ecosystem responses, while tropical ecosystems are major biodiversity hotspots and are increasingly recipients of very high N deposition rates; N deposition alters forest fungi and mycorrhyzal relations with plants; the rapid response of forest fungi and arthropods makes them good indicators of change; predictive tools (models) that address ecosystem scale processes are necessary to address complex drivers and responses, including the integration of N deposition, climate change and land use effects; criteria can be identified for projecting sensitivity of terrestrial and aquatic ecosystems to N deposition. Future research and policy-relevant recommendations are identified.
Nitrogen Deposition, Critical Loads and Biodiversity, Edited by Mark A. Sutton, Kate E. Mason, Lucy J. Sheppard, Harald Sverdrup, Richard Haeuber, W. Kevin Hicks, 04/2014: chapter 49: pages 465-480; Springer., ISBN: 978-94-007-7938-9
[Show abstract][Hide abstract] ABSTRACT: Humans are both intentionally (fertilization) and unintentionally (atmospheric nutrient deposition) adding nutrients worldwide. Increasing availability of biologically reactive nitrogen (N) is one of the major drivers of plant species loss. It remains unclear, however, whether plant diversity will be equally reduced by inputs of reactive N coming from either small and frequent N deposition events or large and infrequent N fertilization events. By independently manipulating the rate and frequency of reactive N inputs, our study teases apart these potentially contrasting effects. Plant species richness decreased more quickly at high rates and at low frequency of N addition, which suggests that previous fertilization studies have likely over-estimated the effects of N deposition on plant species loss. N-induced species loss resulted from both acidification and ammonium toxicity. Further study of small and frequent N additions will be necessary to project future rates of plant species loss under increasing aerial N deposition.This article is protected by copyright. All rights reserved.
Global Change Biology 04/2014; 20(11):3520-3529. DOI:10.1111/gcb.12611 · 8.04 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Studies of experimental grassland communities have demonstrated that plant diversity can stabilize productivity through species asynchrony, in which decreases in the biomass of some species are compensated for by increases in others. However, it remains unknown whether these findings are relevant to natural ecosystems, especially those for which species diversity is threatened by anthropogenic global change. Here we analyse diversity-stability relationships from 41 grasslands on five continents and examine how these relationships are affected by chronic fertilization, one of the strongest drivers of species loss globally. Unmanipulated communities with more species had greater species asynchrony, resulting in more stable biomass production, generalizing a result from biodiversity experiments to real-world grasslands. However, fertilization weakened the positive effect of diversity on stability. Contrary to expectations, this was not due to species loss after eutrophication but rather to an increase in the temporal variation of productivity in combination with a decrease in species asynchrony in diverse communities. Our results demonstrate separate and synergistic effects of diversity and eutrophication on stability, emphasizing the need to understand how drivers of global change interactively affect the reliable provisioning of ecosystem services in real-world systems.
[Show abstract][Hide abstract] ABSTRACT: The global nitrogen (N) cycle has been transformed by human use of reactive N as a consequence of increased demand for food and energy. Given the considerable impact of humans on the N cycle, it is essential that we raise awareness amongst the public and policy makers as this is the first step in providing individuals and governments the opportunity to reduce their impact on the N cycle and reduce the environmental and health consequences of N pollution. Here we describe an N footprint tool for the UK developed as part of the N-PRINT program. The current per capita N footprint in the UK is 27.1 kg N per capita per year with food production constituting the largest proportion of the footprint (18.0 kg N per capita per year). Calculating an N footprint for 1971 (26.0 kg N per capita per year) demonstrates that per capita N footprints have increased slightly. The average UK footprint is smaller than that found in the USA but is higher than the Netherlands and Germany. Scenario analysis demonstrates that reducing food protein consumption to the levels recommended by the FAO and World Health Organization reduces the overall N footprint by 33%. Consuming a vegetarian diet and consuming only sustainable food both decreased the N footprint by 15% but changes in energy use have a much smaller impact.
[Show abstract][Hide abstract] ABSTRACT: Anthropogenically increased input of nitrogen (N) and phosphorous (P) have led to a severe reduction of plant species richness in European semi-natural grasslands. Although it is well established that this species loss is not trait neutral, a thorough analysis of the effects of nutrient addition on trait based func-tional diversity and functional composition, inde-pendently of species loss, is lacking so far. We compiled data on the plant species abundance (re-levé 's) of 279 Nardus grasslands from nine European countries, across a gradient of soil N and P content. Functional diversity (Petchy and Gaston's FDc, weighted FDc and quadratic entropy) and mean trait composition were calculated for each relevé , based on 21 functional traits. Differences in functional diversity and functional composition were related to differences in soil N, atmospheric N deposition, soil P and pH, while controlling for geographic location and species richness. All functional diversity mea-sures decreased with increasing soil N, with wFDc also decreased by soil P, independent of species loss. This was accompanied by clear shifts in functional trait composition, associated with shifts from below-ground competition for nutrients to above-ground competition for light. This resulted in a decrease in insect-pollinated therophytes and chamaephytes and an increase in long-lived, clonal graminoids and hemicryptophytes under increasing soil N and P. These functional community changes can be ex-pected to alter both ecosystem functioning and ser-vice provisioning of the studied grasslands. Our research emphasizes the importance of a reduction of both N and P emission throughout Europe for sustainable conservation of these communities.