02547nas a2200169   4500008004100000245012700041210006900168300001500237490000800252520195400260100001702214700001802231700002002249700001802269700001302287856007702300       2009                        eng d00aCross-site comparison of herbivore impact on nitrogen availability in grasslands: the role of plant nitrogen concentration0 aCrosssite comparison of herbivore impact on nitrogen availabilit  a1613 -16220 v1183 a<p>Herbivores may influence the nitrogen (N) recycling rates and consequently increase or decrease the productivity of grasslands. Plant N concentration emerged as a critical parameter to explain herbivore effects from several conceptual models, which predict that herbivores decrease soil N availability when plant N concentration is low whereas they increase it when plant N concentration is high (Hobbs 1996, Ritchie et al. 1998, Pastor et al. 2006). However, a broader cross-site comparison among published studies to test these predictions is hampered by the different methodologies used to measure soil N availability or a proxy thereof, and a lack of measurements of plant N concentration. Therefore it remains unclear whether these model predictions are generally valid across a range of grasslands. We tested whether there is a relationship between plant N concentration and herbivore impact on soil N availability (measured with resin bags) with a study of replicate 6&ndash;8 year old exclosures (with an unfenced control) of vertebrate herbivores (&gt;1 kg) established at each of seven grassland sites in North America and Europe. Contrary to model predictions, we found a negative relationship between the effect of herbivores on resin bag soil N availability and plant N concentration. Our study confirms the importance of plant N concentration as a predictor of herbivore effect on soil N availability across grasslands, but contradicts the models. A possible explanation may be that the results represent a transient situation as the exclosures were relatively young whereas the models may refer to an equilibrium state. Simultaneous measurements of both plant N concentration and herbivore effect on soil N availability from more grassland sites, preferably with contrasting plant N concentrations and including exclosures of different ages, should resolve the contrast between model predictions and our field measurements.</p>1 aBakker, E.S.1 aKnops, J.M.H.1 aMilchunas, D.G.1 aRitchie, M.E.1 aOlff, H.  uhttps://onlinelibrary.wiley.com/doi/abs/10.1111/j.1600-0706.2009.17199.x01684nas a2200169   4500008004100000245010100041210006900142300001300211490000600224520106900230100001701299700001801316700001301334700002001347700001801367856012901385       2006                        eng d00aHerbivore impact on grassland plant diversity depends on habitat productivity and herbivore size0 aHerbivore impact on grassland plant diversity depends on habitat  a780 -7880 v93 aMammalian herbivores can have pronounced effects on plant diversity but are currently declining in many productive ecosystems through direct extirpation, habitat loss and fragmentation, while being simultaneously introduced as livestock in other, often unproductive, ecosystems that lacked such species during recent evolutionary times. The biodiversity consequences of these changes are still poorly understood. We experimentally separated the effects of primary productivity and herbivores of different body size on plant species richness across a 10-fold productivity gradient using a 7-year field experiment at seven grassland sites in North America and Europe. We show that assemblages including large herbivores increased plant diversity at higher productivity but decreased diversity at low productivity, while small herbivores did not have consistent effects along the productivity gradient. The recognition of these large-scale, cross-site patterns in herbivore effects is important for the development of appropriate biodiversity conservation strategies.1 aBakker, E.S.1 aRitchie, M.E.1 aOlff, H.1 aMilchunas, D.G.1 aKnops, J.M.H.  uhttp://lter.konza.ksu.edu/content/herbivore-impact-grassland-plant-diversity-depends-habitat-productivity-and-herbivore-size02707nas a2200205   4500008004100000245010700041210006900148300001300217490000800230520200200238100001902240700001602259700001802275700002402293700001402317700001602331700002002347700001702367856011702384       2005                        eng d00aDo individual plant speciesshow predictable responses to nitrogen addition across multipleexperiments?0 aDo individual plant speciesshow predictable responses to nitroge  a547 -5550 v1103 aA number of experiments have addressed how increases in nitrogen availability increase the productivity and decrease the diversity of plant communities. We lack, however, a rigorous mechanistic understanding of how changes in abundance of particular species combine to produce changes in community productivity and diversity. Single experiments cannot provide insight into this issue because each species occurs only once per experiment, and each experiment is conducted in only one location; thus, it is impossible from single experiments to determine whether responses of particular species are consistent across environments or dependent on the particular environmental context in which the experiment was conducted. To address this issue, we assembled a dataset of 20 herbaceous species that were each represented in at least 6 different fertilization experiments and tested whether responses were general across experiments. Of the 20 species, one consistently increased in relative abundance and five consistently decreased across replicate experiments. A partially-overlapping group of 8 species displayed responses to nitrogen that varied predictably among experiments as a function of geographic location, neighboring species, or a handful of other community characteristics (ANPP, precipitation, species richness, relative abundance of focal species in control plots, and community composition). Thus, despite modest replication and a limited number of predictor variables, we were able to identify consistent patterns in response of 10 out of 20 species across multiple experiments. We conclude that the responses of individual species to nitrogen addition are often predictable, but that in most cases these responses are functions of the abiotic or biotic environment. Thus, a rigorous understanding of how plant species respond to nitrogen addition will have to consider not only the traits of individual plant species, but also aspects of the communities in which those plants live.1 aPennings, S.C.1 aClark, C.M.1 aCleland, E.E.1 aCollins, Scott., L.1 aGough, L.1 aGross, K.L.1 aMilchunas, D.G.1 aSuding, K.N.  uhttp://lter.konza.ksu.edu/content/do-individual-plant-speciesshow-predictable-responses-nitrogen-addition-across01973nas a2200205   4500008004100000245009900041210006900140300001500209490000800224520126300232100001701495700002401512700001401536700001601550700001801566700001601584700002001600700001701620856013001637       2005                        eng d00aFunctional and abundance based mechanisms explain diversity loss due to nitrogen fertilization0 aFunctional and abundance based mechanisms explain diversity loss  a4387 -43920 v1023 aHuman activities have increased N availability dramatically in terrestrial and aquatic ecosystems. Extensive research demonstrates that local plant species diversity generally declines in response to nutrient enrichment, yet the mechanisms for this decline remain unclear. Based on an analysis of >900 species responses from 34 N-fertilization experiments across nine terrestrial ecosystems in North America, we show that both trait-neutral and trait-based mechanisms operate simultaneously to influence diversity loss as production increases. Rare species were often lost because of soil fertilization, randomly with respect to traits. The risk of species loss due to fertilization ranged from >60% for the rarest species to 10% for the most abundant species. Perennials, species with N-fixing symbionts, and those of native origin also experienced increased risk of local extinction after fertilization, regardless of their initial abundance. Whereas abundance was consistently important across all systems, functional mechanisms were often system-dependent. As N availability continues to increase globally, management that focuses on locally susceptible functional groups and generally susceptible rare species will be essential to maintain biodiversity.1 aSuding, K.N.1 aCollins, Scott., L.1 aGough, L.1 aClark, C.M.1 aCleland, E.E.1 aGross, K.L.1 aMilchunas, D.G.1 aPennings, S.  uhttp://lter.konza.ksu.edu/content/functional-and-abundance-based-mechanisms-explain-diversity-loss-due-nitrogen-fertilization