03564nas a2200601 4500008004100000245012300041210006900164300001600233490000700249520175600256653002402012653001802036653001302054653002102067653002302088653002102111100002202132700001902154700002602173700002502199700002802224700001402252700002502266700002302291700002202314700001602336700001902352700002002371700002302391700002002414700002102434700001802455700002202473700002702495700001902522700002002541700002602561700002802587700002302615700002602638700002502664700002202689700002402711700002102735700002102756700002002777700001902797700002102816700001902837700001602856700002302872856006702895 2019 eng d00aBelowground biomass response to nutrient enrichment depends on light limitation across globally distributed grasslands0 aBelowground biomass response to nutrient enrichment depends on l a1466–14770 v223 a

Anthropogenic activities are increasing nutrient inputs to ecosystems worldwide, with consequences for global carbon and nutrient cycles. Recent meta-analyses show that aboveground primary production is often co-limited by multiple nutrients; however, little is known about how root production responds to changes in nutrient availability. At twenty-nine grassland sites on four continents, we quantified shallow root biomass responses to nitrogen (N), phosphorus (P) and potassium plus micronutrient enrichment and compared below- and aboveground responses. We hypothesized that optimal allocation theory would predict context dependence in root biomass responses to nutrient enrichment, given variation among sites in the resources limiting to plant growth (specifically light versus nutrients). Consistent with the predictions of optimal allocation theory, the proportion of total biomass belowground declined with N or P addition, due to increased biomass aboveground (for N and P) and decreased biomass belowground (N, particularly in sites with low canopy light penetration). Absolute root biomass increased with N addition where light was abundant at the soil surface, but declined in sites where the grassland canopy intercepted a large proportion of incoming light. These results demonstrate that belowground responses to changes in resource supply can differ strongly from aboveground responses, which could significantly modify predictions of future rates of nutrient cycling and carbon sequestration. Our results also highlight how optimal allocation theory developed for individual plants may help predict belowground biomass responses to nutrient enrichment at the ecosystem scale across wide climatic and environmental gradients.

10abelowground biomass10aFertilization10anitrogen10aNutrient Network10aoptimal allocation10aphosphorus roots1 aCleland, Elsa, E.1 aLind, Eric, M.1 aDeCrappeo, Nicole, M.1 aDeLorenze, Elizabeth1 aWilkins, Rachel, Abbott1 aAdler, P.1 aBakker, Jonathan, D.1 aBrown, Cynthia, S.1 aDavies, Kendi, F.1 aEsch, Ellen1 aFirn, Jennifer1 aGressard, Scott1 aGruner, Daniel, S.1 aHagenah, Nicole1 aHarpole, Stanley1 aHautier, Yann1 aHobbie, Sarah, E.1 aHofmockel, Kirsten, S.1 aKirkman, Kevin1 aKnops, Johannes1 aKopp, Christopher, W.1 aLa Pierre, Kimberly, J.1 aMacDougall, Andrew1 aMcCulley, Rebecca, L.1 aMelbourne, Brett, A.1 aMoore, Joslin, L.1 aProber, Suzanne, M.1 aRiggs, Charlotte1 aRisch, Anita, C.1 aSchuetz, Martin1 aStevens, Carly1 aWragg, Peter, D.1 aWright, Justin1 aBorer, E.T.1 aSeabloom, Eric, W. uhttps://link.springer.com/article/10.1007%2Fs10021-019-00350-402039nas a2200193 4500008004100000245011200041210006900153300001200222490000700234520138600241653001101627653001801638653002201656653002601678653002101704100001601725700001701741856008701758 2016 eng d00aMechanisms driving the soil organic matter decomposition response to nitrogen enrichment in grassland soils0 aMechanisms driving the soil organic matter decomposition respons a54 - 650 v993 a

Empirical studies show that nitrogen (N) addition often reduces microbial decomposition of soil organic matter (SOM) and carbon dioxide (CO2) production via microbial respiration. Although predictions from theoretical models support these findings, the mechanisms that drive this response remain unclear. To address this uncertainty, we sampled soils of three grassland sites in the U.S. Central Great Plains that each have received seven years of continuous experimental nutrient addition in the field. Nitrogen addition significantly decreased the decomposition rate of slowly cycling SOM and the cumulative carbon (C) respired per mass soil C. We evaluated whether this effect of N addition on microbial respiration resulted from: 1) increased microbial carbon use efficiency (CUE), 2) decreased microbial oxidative enzyme activity, or 3) decreased microbial biomass due to plant and/or soil mediated responses to N enrichment. In contrast to our hypotheses – as well as results from N addition studies in forest ecosystems and theoretical predictions – N did not increase microbial CUE or decrease microbial oxidative enzyme activity. Instead, reduced microbial biomass likely caused the decreased respiration in response to N enrichment. Identifying what factors drive this decreased microbial biomass response to N should be a priority for further inquiry.

10acarbon10aFertilization10aMicrobial biomass10aMicrobial respiration10aNutrient Network1 aRiggs, C.E.1 aHobbie, S.E. uhttps://www.sciencedirect.com/science/article/abs/pii/S0038071716300608?via%3Dihub02851nas a2200385 4500008004100000245011400041210006900155300001800224490000800242520175500250653001802005653002502023653001802048653001702066653001502083100001502098700001602113700001702129700001802146700001602164700001502180700001802195700001702213700002002230700001802250700001902268700002802287700001402315700001902329700002002348700001802368700001802386700001502404856004602419 2015 eng d00aConsistent responses of soil microbial communities to elevated nutrient inputs in grasslands across the globe0 aConsistent responses of soil microbial communities to elevated n a10967 - 109720 v1123 a

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.

10aFertilization10ashotgun metagenomics10aSoil bacteria10aSoil ecology10aSoil fungi1 aLeff, J.W.1 aJones, S.E.1 aProber, S.M.1 aBarberán, A.1 aBorer, E.T.1 aFirn, J.L.1 aHarpole, W.S.1 aHobbie, S.E.1 aHofmockel, K.S.1 aKnops, J.M.H.1 aMcCulley, R.L.1 aLa Pierre, Kimberly, J.1 aRisch, A.1 aSeabloom, E.W.1 aSchütz, Martin1 aSteenbock, C.1 aStevens, C.J.1 aFierer, N. uhttps://www.pnas.org/content/112/35/1096702817nas a2200337 4500008004100000245014100041210006900182300001500251490000700266520177500273653001202048653001402060653001802074653001602092653001502108653001502123653001802138653001502156653000902171653001402180653002202194653001302216653001502229653001702244100001902261700002002280700001502300700001802315700001702333856012902350 2003 eng d00aEffects of fire, mowing and fertilization effects on density and biomass of macroinvertebrates in North American tallgrass prairie soils0 aEffects of fire mowing and fertilization effects on density and  a1079 -10930 v353 aThe responses of tallgrass prairie plant communities and ecosystem processes to fire and grazing are well characterized. However, responses of invertebrate consumer groups, and particularly soil-dwelling organisms, to these disturbances are not well known. At Konza Prairie Biological Station, we sampled soil macroinvertebrates in 1994 and 1999 as part of a long-term experiment designed to examine the effects and interactions of annual fire, mowing, and fertilization (N and P) on prairie soil communities and processes. For nearly all taxa, in both years, responses were characterized by significant treatment interactions, but some general patterns were evident. Introduced European earthworms (Aporrectodea spp. and Octolasion spp.) were most abundant in plots where fire was excluded, and the proportion of the total earthworm community consisting of introduced earthworms was greater in unburned, unmowed, and fertilized plots. Nymphs of two Cicada genera were collected (Cicadetta spp. and Tibicen spp.). Cicadetta nymphs were more abundant in burned plots, but mowing reduced their abundance. Tibicen nymphs were collected almost exclusively from unburned plots. Treatment effects on herbivorous beetle larvae (Scarabaeidae, Elateridae, and Curculionidae) were variable, but nutrient additions (N or P) usually resulted in greater densities, whereas mowing usually resulted in lower densities. Our results suggest that departures from historical disturbance regimes (i.e. frequent fire and grazing) may render soils more susceptible to increased numbers of European earthworms, and that interactions between fire, aboveground biomass removal, and vegetation responses affect the structure and composition of invertebrate communities in tallgrass prairie soils.10abiomass10aCicadidae10aCurculionidae10adisturbance10aearthworms10aElateridae10aFertilization10aFertilizer10afire10agrassland10ainsect herbivores10anitrogen10aPhosphorus10aScarabaeidae1 aCallaham, M.A.1 aBlair, John, M.1 aTodd, T.C.1 aKitchen, D.J.1 aWhiles, M.R. uhttp://lter.konza.ksu.edu/content/effects-fire-mowing-and-fertilization-effects-density-and-biomass-macroinvertebrates-north02968nas a2200205 4500008004100000245011300041210006900154300001300223490000700236520224400243653000902487653001802496653002902514653002402543653001402567653002302581100001702604700001802621856012302639 1999 eng d00aNitrogen limitation in dryland ecosystems: responses to temporal and geographical variation in precipitation0 aNitrogen limitation in dryland ecosystems responses to temporal  a247 -2930 v463 aWe investigated the relationship between plant nitrogen limitation and water availability in dryland ecosystems. We tested the hypothesis that at lower levels of annual precipitation, aboveground net primary productivity (ANPP) is limited primarily by water whereas at higher levels of precipitation, it is limited primarily by nitrogen. Using a literature survey of fertilization experiments in arid, semi-arid, and subhumid ecosystems, we investigated the response of ANPP to nitrogen addition as a function of variation in precipitation across geographic gradients, as well as across year-to-year variation in precipitation within sites. We used four different indices to assess the degree of N limitation: (1) Absolute Increase of plant production in response to fertilization (the slope of ANPP vs. amount of added N at different levels of annual precipitation); (2) Relative Response (the percent increase in fertilized over control ANPP at different levels of N addition); (3) Fertilizer Use Efficiency (FUE, the absolute gain in productivity per amount of fertilizer N), and (4) Maximum Response (the greatest absolute increase in ANPP at saturating levels of N addition). Relative Response to fertilization did not significantly increase with increasing precipitation either across the geographic gradient or across year-to-year variation within sites. Nor did the Maximum Response to fertilization increase with increasing precipitation across the geographic gradient. On the other hand, there was a significant increase in the Absolute Increase and FUE indices with both geographical and temporal variation in precipitation. Together, these results indicate that there is not necessarily a shift of primary limitation from water to N across the geographic water availability gradient. Instead, our results support the hypothesis of co-limitation. The apparently contradictory results from the four indices of N limitation can best be explained by an integration of plant ecophysiological, community, and ecosystem mechanisms whereby plants are co-limited by multiple resources, species shifts occur in response to changing resource levels, and nitrogen and water availability are tightly linked through biogeochemical feedbacks.10aarid10aFertilization10aNet primary productivity10anitrogen limitation10asemi-arid10aWater availability1 aHooper, D.U.1 aJohnson, L.C. uhttp://lter.konza.ksu.edu/content/nitrogen-limitation-dryland-ecosystems-responses-temporal-and-geographical-variation