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Aboveground-belowground interactions exert critical controls on the composition and function of terrestrial ecosystems, yet the fundamental relationships between plant diversity and soil microbial diversity remain elusive. Theory predicts predominantly positive associations but tests within single sites have shown variable relationships, and associations between plant and microbial diversity across broad spatial scales remain largely unexplored. We compared the diversity of plant, bacterial, archaeal and fungal communities in one hundred and forty-five 1m(2) plots across 25 temperate grassland sites from four continents. Across sites, the plant alpha diversity patterns were poorly related to those observed for any soil microbial group. However, plant beta diversity (compositional dissimilarity between sites) was significantly correlated with the beta diversity of bacterial and fungal communities, even after controlling for environmental factors. Thus, across a global range of temperate grasslands, plant diversity can predict patterns in the composition of soil microbial communities, but not patterns in alpha diversity.

Tall fescue pastures cover extensive acreage in the eastern half of the United States and contribute to important ecosystem services, including the provisioning of forage for grazing livestock. Yet little is known concerning how these pastures will respond to climate change. Tall fescue’s ability to persist and provide forage under a warmer and wetter environment, as is predicted for much of this region as a result of climate change, will likely depend on a symbiotic relationship the plant can form with the fungal endophyte, Epichloe coenophiala. While this symbiosis can confer environmental stress tolerance to the plant, the endophyte also produces alkaloids toxic to insects (e.g., lolines) and mammals (ergots; which can cause ‘fescue toxicosis’ in grazing animals). The negative animal health and economic consequences of fescue toxicosis make understanding the response of the tall fescue symbiosis to climate change critical for the region. We experimentally increased temperature (+3oC) and growing season precipitation (+30% of the long-term mean) from 2009 – 2013 in a mixed species pasture, that included a tall fescue population that was 40% endophyte-infected. Warming reduced the relative abundance of tall fescue within the plant community, and additional precipitation did not ameliorate this effect. Warming did not alter the incidence of endophyte infection within the tall fescue population; however, warming significantly increased concentrations of ergot alkaloids (by 30-40%) in fall-harvested endophyte-infected individuals. Warming alone did not affect loline alkaloid concentrations, but when combined with additional precipitation, levels increased in fall-harvested material. Although future warming may reduce the dominance of tall fescue in eastern U.S. pastures and have limited effect on the incidence of endophyte infection, persisting endophyte-infected tall fescue will have higher concentrations of toxic alkaloids which may exacerbate fescue toxicosis.

Decomposition of leaf litter is a key component of biogeochemical cycles but the mechanisms driving it in arid and semiarid ecosystems (drylands) remain unresolved. Here, we review recent findings that demonstrate dual roles of solar radiation (ultraviolet and photosynthetically active radiation) and soil–litter mixing as drivers of decomposition in drylands. We focus on the known and potential mechanisms by which these factors influence leaf litter decomposition, explore how the importance of these two drivers may shift over time, and propose possible avenues by which these factors may interact. Special attention is given to UV in sunlight, as this radiation is known to have multiple roles in influencing decomposition and has received considerable recent research attention. We also identify important uncertainties and challenges and offer a generalized conceptual model to guide future research aimed at enhancing our mechanistic understanding and quantitative modeling of the processes by which soil deposition and solar radiation together influence leaf litter decomposition rates in globally extensive dryland ecosystems.

Innovative plant breeding and technology transfer fostered the Green Revolution (GR), which transformed agriculture worldwide by increasing grain yields in developing countries. The GR temporarily alleviated world hunger, but also reduced biodiversity, nutrient cycling, and carbon (C) sequestration that agricultural lands can provide. Meanwhile, economic disparity and food insecurity within and among countries continues. Subsequent agricultural advances, focused on objectives such as increasing crop yields or reducing the risk of a specific pest, have failed to meet food demands at the local scale or to restore lost ecosystem services. An increasing human population, climate change, growing per capita food and energy demands, and reduced ecosystem potential to provide agriculturally relevant services have created an unrelenting need for improved crop production practices. Meeting this need in a sustainable fashion will require interdisciplinary approaches that integrate plant and microbial ecology with efforts to advance crop production while mitigating effects of a changing climate. Metagenomic advances are revealing microbial dynamics that can simultaneously improve crop production and soil restoration while enhancing crop resistance to

Human alterations to nutrient cycles and herbivore communities are affecting global biodiversity dramatically. 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 systems. 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. © 2014 Macmillan Publishers Limited. Fil: Borer, Elizabeth. University of Minnesota; Estados Unidos Fil: Seabloom, Eric. University of Minnesota; Estados Unidos Fil: Gruner, Daniel. University of Maryland; Estados Unidos Fil: Harpole, Stanley. Iowa State University; Estados Unidos Fil: Hillebrand, Helmut. Carl-von- Ossietzky University; Alemania Fil: Lind, Eric M.. University of Minnesota; Estados Unidos Fil: Adler, Peter B.. Utah State University; Estados Unidos Fil: Alberti, Juan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Anderson, Michael. Wake Forest University; Estados Unidos Fil: Bakker, Jonathan D.. University of Washington; Estados Unidos Fil: Biederman, Lori. Iowa State University; Estados Unidos Fil: Blumenthal, Dana. United States Department of Agriculture. Agricultural Research Service; Estados Unidos Fil: Brown, Cynthia S.. State University of Colorado - Fort Collins; Estados Unidos Fil: Brudvig, Lars A.. University of Minnesota; Estados Unidos Fil: Buckley, Yvonne M.. The University Of Queensland; Australia Fil: Cadotte, Marc. University of Toronto Scarborough; Canadá Fil: Chu, Chengjin. Lanzhou University; China Fil: Cleland, Elsa. University of California; Estados Unidos Fil: Crawley, Michael. Imperial College at Silwood Park; Reino Unido Fil: Daleo, Pedro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Damschen, Ellen. University of Wisconsin; Estados Unidos Fil: Davies, Kendi. State University of Colorado - Fort Collins; Estados Unidos Fil: DeCrappeo, Nicole. Forest and Rangeland Ecosystem Science Center; Estados Unidos Fil: Du, Guozhen. Lanzhou University; Estados Unidos Fil: Firn, Jennifer. Queensland University of Technology; Australia Fil: Hautier, Yann. University of Minnesota; Estados Unidos Fil: Heckman, Robert. University of North Carolina at Chapel Hill; Estados Unidos Fil: Hector, Andy. University of Oxford; Reino Unido Fil: Hillerislambers, Janneke. University of Washington; Estados Unidos Fil: Iribarne, Oscar Osvaldo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Klein, Julia. State University of Colorado - Fort Collins; Estados Unidos Fil: Knops, Johannes M. H.. University of Nebraska; Estados Unidos Fil: La Pierre, Kimberly. University of California; Estados Unidos Fil: Leakey, Andrew D. B.. University of Illinois at Urbana-Champaign; Estados Unidos Fil: Li, Wei. Iowa State University; Estados Unidos Fil: MacDougall, Andrew S.. University of Guelph; Canadá Fil: McCulley, Rebecca. University Of Kentucky; Estados Unidos Fil: Melbourne, Brett. State University of Colorado - Fort Collins; Estados Unidos Fil: Mitchell, Charles. University of North Carolina at Chapel Hill; Estados Unidos Fil: Moore, Joslin. University of Melbourne; Australia Fil: Mortensen, Brent. Iowa State University; Estados Unidos Fil: O'Halloran, Lydia. Oregon State University; Estados Unidos Fil: Orrock, John. University of Wisconsin; Estados Unidos Fil: Pascual, Jesus Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Prober, Suzanne. CSIRO Ecosystem Sciences; Australia Fil: Pyke, David. Forest and Rangeland Ecosystem Science Center; Canadá Fil: Risch, Anita. Swiss Federal Institute For Forest, Snow And Landscape Research; Suiza Fil: Schuetz, Martin. Swiss Federal Institute For Forest, Snow And Landscape Research; Suiza Fil: Smith, Melinda D.. State University of Colorado - Fort Collins; Estados Unidos Fil: Stevens, Carly. Lancaster University; Reino Unido Fil: Sullivan, Lauren. Iowa State University; Estados Unidos Fil: Williams, Ryan. Iowa State University; Estados Unidos Fil: Wragg, Peter. University of Minnesota; Estados Unidos Fil: Yang, Louie. University of California; Estados Unidos

Invasive species may owe some of their success in competing and co-existing with native species to microbial symbioses they are capable of forming. Tall fescue is a cool-season, non-native, invasive grass capable of co-existing with native warm-season grasses in North American grasslands that frequently experience fire, drought, and cold winters, conditions to which the native species should be better-adapted than tall fescue. We hypothesized that tall fescue’s ability to form a symbiosis with Neotyphodium coenophialum, an aboveground fungal endophyte, may enhance its environmental stress tolerance and persistence in these environments. We used a greenhouse experiment to examine the effects of endophyte infection (E+ vs. E−), prescribed fire (1 burn vs. 2 burn vs. unburned control), and watering regime (dry vs. wet) on tall fescue growth. We assessed treatment effects for growth rates and the following response variables: total tiller length, number of tillers recruited during the experiment, number of reproductive tillers, tiller biomass, root biomass, and total biomass. Water regime significantly affected all response variables, with less growth and lower growth rates observed under the dry water regime compared to the wet. The burn treatments significantly affected total tiller length, number of reproductive tillers, total tiller biomass, and total biomass, but treatment differences were not consistent across parameters. Overall, fire seemed to enhance growth. Endophyte status significantly affected total tiller length and tiller biomass, but the effect was opposite what we predicted (E−>E+). The results from our experiment indicated that tall fescue was relatively tolerant of fire, even when combined with dry conditions, and that the fungal endophyte symbiosis was not important in governing this ecological ability. The persistence of tall fescue in native grassland ecosystems may be linked to other endophyte-conferred abilities not measured here (e.g., herbivory release) or may not be related to this plant-microbial symbiosis.

Invasions have increased the size of regional species pools, but are typically assumed to reduce native diversity. Invasions have increased the size of regional species pools, but are typically assumed to reduce native diversity. However, global-scale tests of this assumption have been elusive because of the focus on exotic species richness, rather than relative abundance. This is problematic because low invader richness can indicate invasion resistance by the native community or, alternatively, dominance by a single exotic species. Here, we used a globally replicated study to quantify relationships between exotic richness and abundance in grass-dominated ecosystems in 13 countries on six continents, ranging from salt marshes to alpine tundra. We tested effects of human land use, native community diversity, herbivore pressure, and nutrient limitation on exotic plant dominance. Despite its widespread use, exotic richness was a poor proxy for exotic dominance at low exotic richness, because sites that contained few exotic species ranged from relatively pristine (low exotic richness and cover) to almost completely exotic-dominated ones (low exotic richness but high exotic cover). Both exotic cover and richness were predicted by native plant diversity (native grass richness) and land use (distance to cultivation). Although climate was important for predicting both exotic cover and richness, climatic factors predicting cover (precipitation variability) differed from those predicting richness (maximum temperature and mean temperature in the wettest quarter). Herbivory and nutrient limitation did not predict exotic richness or cover. Exotic dominance was greatest in areas with low native grass richness at the site- or regional-scale. Although this could reflect native grass displacement, a lack of biotic resistance is a more likely explanation, given that grasses comprise the most aggressive invaders. These findings underscore the need to move beyond richness as a surrogate for the extent of invasion, because this metric confounds monodominance with invasion resistance. Monitoring species' relative abundance will more rapidly advance our understanding of invasions. Fil: Seabloom, Eric W.. University of Minnesota; Estados Unidos Fil: Borer, Elizabeth T.. University of Minnesota; Estados Unidos Fil: Buckley, Yvonne. The University Of Queensland; Australia Fil: Cleland, Elsa E.. University of California, San Diego; Estados Unidos Fil: Kendi, Davies. State University of Colorado Boulder; Estados Unidos Fil: Firn, Jennifer. Queensland University of Technology. Brisbane; Australia Fil: Hartpole, Stanley W.. Iowa State University; Estados Unidos Fil: Hautier, Yann. University of Zurich; Suiza Fil: Lind, Eric. Universidad de Minnesota; Estados Unidos Fil: MacDougall, Andrew. University of Guelph; Canadá Fil: Orrock, John L.. University of Wisconsin; Estados Unidos Fil: Prober, Suzanne M.. CSIRO Ecosystem Sciences; Australia Fil: Adler, Peter. Utah State University; Estados Unidos Fil: Alberti, Juan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Anderson, T. Michael. Wake Forest University; Estados Unidos Fil: Bakker, Jonathan D.. University of Washington; Estados Unidos Fil: Biederman, Lori A.. Iowa State University; Estados Unidos Fil: Blumenthal, Dana. Rangeland Resources Research Unit; Estados Unidos Fil: Browns, Cynthia S.. State University of Colorado - Fort Collins; Estados Unidos Fil: Brudvig, Lars A.. Michigan State University; Estados Unidos Fil: Caldeira, Maria. Technical University of Lisbon; Portugal Fil: Chu, Chengjin. Lanzhou University; China Fil: Crawley, Michel. Imperial College London; Reino Unido Fil: Daleo, Pedro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Damschen, Ellen I.. University of Wisconsin; Estados Unidos Fil: D'antonio, Carla. University of California; Estados Unidos Fil: Decrappeo, Nicole. Geological Survey Forest and Rangeland Ecosystem Science Center; Estados Unidos Fil: Dickman, Chris. University of Sydney; Australia Fil: Du, Guozhen. Lanzhou University; China Fil: Fay, Philip. Grassland Soil and Water Research Lab; Estados Unidos Fil: Frater, Paul. Iowa State University; Estados Unidos Fil: Gruner, Daniel S.. University of Queensland; Australia Fil: Hagenah, Nicole. University of KwaZulu-Natal; Sudáfrica Fil: Hector, Andrew. University of Zurich; Suiza Fil: Helm, Avellina. University Of Tartu.; Estonia Fil: Hillebrand, Helmut. Carl-von-Ossietzky University; Alemania Fil: Hofmockel, Kirsten. Iowa State University; Estados Unidos Fil: Humphries, Hope. State University of Colorado - Fort Collins; Estados Unidos Fil: Iribarne, Oscar Osvaldo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Jin, Virginia L.. Agroecosystem Management Research Unit; Estados Unidos Fil: Kay, Adam. University of St. Thomas; Estados Unidos Fil: Kirkman, Kevin. University of KwaZulu-Natal; Estonia Fil: Klein, Julia. State University of Colorado - Fort Collins; Estados Unidos Fil: Knops, Johannes M. H.. University Of Nebraska; Estados Unidos Fil: La Pierre, Kimberly. Yale University; Estados Unidos Fil: Ladwig, Laura M.. University Of New Mexico; Estados Unidos Fil: Lambrinos, John G.. Oregon State University; Estados Unidos Fil: Leakey, Andrew. University of Illinois at Urbana-Champaign; Estados Unidos Fil: Li, Qi. Northwest Institute of Plateau Biology, Chinese Academy of Sciences; China Fil: Li, Wei. Southwest Forestry University; China Fil: McCulley, Rebecca. University Of Kentucky; Estados Unidos Fil: Melbourne, Brett. State University of Colorado Boulder; Estados Unidos Fil: Mitchell, Charles. University of North Carolina; Estados Unidos Fil: Moore, Joslin. Australian Research Centre for Urban Ecology; Australia Fil: Morgan, John. La Trobe University; Australia Fil: Mortensen, Brent. Iowa State University; Estados Unidos Fil: O'Halloran, Lydia. Oregon State University; Estados Unidos Fil: Pärtel, Meelis. University Of Tartu.; Estonia Fil: Pascual, Jesus Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Pyke, David A.. University of California; Estados Unidos Fil: Risch, Anita. Swiss Federal Institute For Forest, Snow And Landscape Research; Suiza Fil: Salguero Goméz, Roberto. The University Of Queensland; Australia Fil: Sankaran, Mahesh. National Centre for Biological Sciences; India Fil: Schuetz, Martin. Swiss Federal Institute For Forest, Snow And Landscape Research; Suiza Fil: Simonsen, Anna. University of Toronto; Canadá Fil: Smith, Melinda. State University of Colorado - Fort Collins; Estados Unidos Fil: Stevens, Carly. Lancaster Environment Center; Canadá Fil: Sullivan, Lauren. Iowa State University; Estados Unidos Fil: Wardle, Glenda M.. University of Sydney; Australia Fil: Wolkovich, Elizabeth M.. University of British Columbia; Canadá Fil: Wragg, Peter D.. The University Of Queensland; Australia Fil: Wright, Justin. University of Duke; Estados Unidos Fil: Yang, Louie. University of California; Estados Unidos

Studies of experimental grassland communities1,2,3,4,5,6,7 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 others1,2. However, it remains unknown whether these findings are relevant to natural ecosystems, especially those for which species diversity is threatened by anthropogenic global change8,9,10,11. 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 globally8. 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. Fil: Hautier, Yann. University of Minnesota; Estados Unidos. Universitat Zurich; Suiza Fil: Seabloom, Eric. University of Minnesota; Estados Unidos Fil: Borer, Elizabeth T. University of Minnesota; Estados Unidos Fil: Adler, Peter. State University of Utah; Estados Unidos Fil: Harpole, E. Stanley. University of Iowa; Estados Unidos Fil: Hillebrand, Helmut. University Oldenburg; Alemania Fil: Lind, Eric M.. University of Minnesota; Estados Unidos Fil: McDougall, Andrew S.. University of Guelph; Canadá Fil: Stevens, Carly J.. Lancaster University; Reino Unido Fil: Bakker, Jonathan D. University of Washington; Estados Unidos Fil: Buckley, Yvonne M.. University of Queensland; Australia. Trinity College Dublin; Irlanda Fil: Chu, Chengjin. Lanzhou University; China Fil: Collins, Scott L.. University Of New Mexico; Estados Unidos Fil: Daleo, Pedro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Damschen, Ellen I.. University of Wisconsin; Estados Unidos Fil: Davies, Kendi F.. State University of Colorado Boulder; Estados Unidos Fil: Fay, Philip A.. United States Department of Agriculture Agricultural Research Service; Estados Unidos Fil: Frin, Jennifer. Queensland University of Technology; Australia Fil: Gruner, Daniel S.. University of Maryland; Estados Unidos Fil: Jin, Virginia L.. United States Department of Agriculture Agricultural Research Service; Estados Unidos Fil: Klein, Julia A.. State University of Colorado - Fort Collins; Estados Unidos Fil: Knops, Johannes M. H.. University Of Nebraska; Estados Unidos Fil: La Pierre, Kimberly J.. University of California at Berkeley; Estados Unidos Fil: Li, Wei. Southwest Forestry University; China Fil: McCulley, Rebecca L.. University Of Kentucky; Estados Unidos Fil: Melbourne, Brett A.. State University of Colorado - Fort Collins; Estados Unidos Fil: Moore, Joslin L.. University of Melbourne; Australia. Monash University; Australia Fil: O'Halloran, Lydia R.. Oregon State University; Estados Unidos Fil: Prober, Suzanne M.. CSIRO Ecosystem Sciences; Australia Fil: Risch, Anita C.. Swiss Federal Institute for Forest; Suiza Fil: Sankaran, Mahesh. University of Leeds; Reino Unido. National Centre for Biological Sciences; India Fil: Schuetz, Martin. Swiss Federal Institute for Forest; Suiza Fil: Hector, Andy. University of Oxford; Reino Unido

Based on regional-scale studies, aboveground production and litter decomposition are thought to positively covary, because they are driven by shared biotic and climatic factors. Until now we have been unable to test whether production and decomposition are generally coupled across climatically dissimilar regions, because we lacked replicated data collected within a single vegetation type across multiple regions, obfuscating the drivers and generality of the association between production and decomposition. Furthermore, our understanding of the relationships between production and decomposition rests heavily on separate meta-analyses of each response, because no studies have simultaneously measured production and the accumulation or decomposition of litter using consistent methods at globally relevant scales. Here, we use a multi-country grassland dataset collected using a standardized protocol to show that live plant biomass (an estimate of aboveground net primary production) and litter disappearance (represented by mass loss of aboveground litter) do not strongly covary. Live biomass and litter disappearance varied at different spatial scales. There was substantial variation in live biomass among continents, sites and plots whereas among continent differences accounted for most of the variation in litter disappearance rates. Although there were strong associations among aboveground biomass, litter disappearance and climatic factors in some regions (e.g. U.S. Great Plains), these relationships were inconsistent within and among the regions represented by this study. These results highlight the importance of replication among regions and continents when characterizing the correlations between ecosystem processes and interpreting their global-scale implications for carbon flux. We must exercise caution in parameterizing litter decomposition and aboveground production in future regional and global carbon models as their relationship is complex.

Human assisted plant invasions from Europe to North America have been more common than the reverse. We tested endophyte-mediated performance of tall fescue in parallel three year experiments in Europe and the USA using endophyte infected and uninfected wild and cultivated plants. Experimental plants were subjected to nutrient and water treatments. Whereas endophyte infection increased tall fescue performance in general, the effects of endophytes on plant growth and reproduction varied among plant origins under different environmental conditions. Naturally endophyte-free Finnish cultivar 'Retu' performed equally well as 'Kentucky-31' in both geographic locations. All Eurasian origin plants performed well in the US. In Finland, plants established well and both cultivars survived over the first winter. However, winter mortality of 'Kentucky-31' plants was higher, particularly in fertilized soils in the subsequent winters. Our results suggest that tall fescue ecotype 'Kentucky-31' that flourishes in North America is poorly adapted to Northern European conditions.

For more than 30 years, the relationship between net primary productivity and species richness has generated intense debate in ecology about the processes regulating local diversity. The original view, which is still widely accepted, holds that the relationship is hump-shaped, with richness first rising and then declining with increasing productivity. Although recent meta-analyses questioned the generality of hump-shaped patterns, these syntheses have been criticized for failing to account for methodological differences among studies. We addressed such concerns by conducting standardized sampling in 48 herbaceous-dominated plant communities on five continents. We found no clear relationship between productivity and fine-scale (meters(-2)) richness within sites, within regions, or across the globe. Ecologists should focus on fresh, mechanistic approaches to understanding the multivariate links between productivity and richness.

• Climate change (altered CO(2) , warming, and precipitation) may affect plant-microbial interactions, such as the Lolium arundinaceum-Neotyphodium coenophialum symbiosis, to alter future ecosystem structure and function. • To assess this possibility, tall fescue tillers were collected from an existing climate manipulation experiment in a constructed old-field community in Tennessee (USA). Endophyte infection frequency (EIF) was determined, and infected (E+) and uninfected (E-) tillers were analysed for tissue chemistry. • The EIF of tall fescue was higher under elevated CO(2) (91% infected) than with ambient CO(2) (81%) but was not affected by warming or precipitation treatments. Within E+ tillers, elevated CO(2) decreased alkaloid concentrations of both ergovaline and loline, by c. 30%; whereas warming increased loline concentrations 28% but had no effect on ergovaline. Independent of endophyte infection, elevated CO(2) reduced concentrations of nitrogen, cellulose, hemicellulose, and lignin. • These results suggest that elevated CO(2) , more than changes in temperature or precipitation, may promote this grass-fungal symbiosis, leading to higher EIF in tall fescue in old-field communities. However, as all three climate factors are likely to change in the future, predicting the symbiotic response and resulting ecological consequences may be difficult and dependent on the specific atmospheric and climatic conditions encountered.

[1] The dynamics of biologic Si cycling in grassland ecosystems are largely unknown and likely to impact mineral weathering rates regionally and diatom productivity globally; key regulatory processes in the global Si cycle are closely tied to the global carbon cycle. Across a bioclimatic sequence spanning major grassland ecosystems in the Great Plains, soil biogenic silica depth distributions are similar to that of soil organic carbon; however, unlike soil organic carbon, quantities of soil biogenic silica decrease with increasing precipitation, despite an increase in annual biogenic inputs through litterfall across the same gradient. Though comprising only 1–3% of the total Si pool, faster turnover of biogenic Si and annual cycling by grasses should positively impact mineral dissolution. Our results suggest that the largest reservoir of biogenic Si in terrestrial ecosystems resides in soils, and emphasize the potential significance of grasslands in the global biogeochemical cycle of Si.

Explanations for the occurrence of deep-rooted plants in arid and semi-arid ecosystems have traditionally emphasized the uptake of relatively deep soil water. However, recent hydrologic data from arid systems show that soil water potentials at depth fluctuate little over long time periods, suggesting this water may be rarely utilized or replenished. In this study, we examine the distributions of root biomass, soil moisture and nutrient contents to 10-m depths at five semi-arid and arid sites across southwestern USA. We couple these depth distributions with strontium (Sr) isotope data that show deep (>1 m) nutrient uptake is prevalent at four of the five sites. At all of the sites, the highest abundance of one or more of the measured nutrients occurred deep within the soil profile, particularly for P, Ca2+ and Mg2+. Phosphate contents were greater at depth than in the top meter of soil at three of five sites. At Jornada, for example, the 2-3 m depth increment had twice the extractable P as the top meter of soil, despite the highest concentrations of P occurring at the surface. The prevalence of such deep resource pools, and our evidence for cation uptake from them, suggest nutrient uptake as a complementary explanation for the occurrence of deep-rooted plants in arid and semi-arid systems. We propose that hydraulic redistribution of shallow surface water to deep soil layers by roots may be the mechanism through which deep soil nutrients are mobilized and taken up by plants.

Plant ecologists have long been interested in aspect-related contrasts of montane forests. Few studies have assessed correlation (linkage) among vegetation strata; fewer have included soil microbial communities. This study assessed contrasts in overstory, spring herbaceous, and soil microbial communities between northeast (NE) - and southwest (SW) -facing slopes in a second-growth West Virginia hardwood forest. We addressed three questions: (1) how do soil microbial, herbaceous layer, and overstory communities vary with slope aspect? (2) do forest vegetation strata and soil microbial communities exhibit linkage? (3) do biotic relationships and linkage vary with slope aspect? Moisture, organic matter, pH, soil NO3−, and net nitrification were significantly higher in NE soils; soil NH4+ was significantly higher in SW soils, and net N mineralization was virtually identical between aspects. Vegetation communities markedly differed between the slopes. Overall, 29 tree and 118 herbaceous species were encountere...

Walvoord et al . ([ 1 ][1]) reported a large nitrate pool located deep (>1 m) beneath desert soils. Two aspects of this work were particularly surprising: the large pool size, estimated to be up to ∼104 kilograms of nitrogen per hectare, as nitrate (kg N ha-1); and the shape of the nitrate

Many grass species are symbiotic with systemic, vertically-transmitted, asymptomatic Epichloe endophytic fungi. These fungi often produce alkaloids that defend the host against herbivores. We studied how environmental variables affect alkaloids in endophyte-infected tall fescue (Schedonorus phoenix) from three Northern European wild origins and the widely planted US cultivar ‘Kentucky-31’ (KY31). The plants were grown in identical common garden experiments in Finland and Kentucky for two growing seasons. Plants were left as controls (C) or given water (W), nutrient (N) or water and nutrient (WN) treatments. For 8–10 replications of each plant origin and treatment combination in both experiments, we analyzed ergot alkaloids, lysergic acid, and lolines. In Finland, tall fescue plants produced 50 % more ergot alkaloids compared to plants of the same origin and treatments in Kentucky. Origin of the plants affected the ergot alkaloid concentration at both study sites: the wild origin plants produced 2–4 times more ergot alkaloids than KY31, but the ergot alkaloid concentration of KY31 plants was the same at both locations. Overall lysergic acid content was 60 % higher in plants grown in Kentucky than in those grown in Finland. Nutrient treatments (N, WN) significantly increased ergot alkaloid concentrations in plants from Finland but not in plants from Kentucky. These results suggest that the success of KY31 in US is not due to selection for high ergot alkaloid production but rather other traits associated with the endophyte. In addition, the environmental effects causing variation in alkaloid production of grass-endophyte combinations should be taken into account when using endophyte-infected grasses agriculturally.