@article {KNZ002041, title = {Increasing effects of chronic nutrient enrichment on plant diversity loss and ecosystem productivity over time}, journal = {Ecology}, volume = {102}, year = {2021}, pages = {e03218}, abstract = {

Human activities are enriching many of Earth\’s ecosystems with biologically limiting mineral nutrients such as nitrogen (N) and phosphorus (P). In grasslands, this enrichment generally reduces plant diversity and increases productivity. The widely demonstrated positive effect of diversity on productivity suggests a potential negative feedback, whereby nutrient-induced declines in diversity reduce the initial gains in productivity arising from nutrient enrichment. In addition, plant productivity and diversity can be inhibited by accumulations of dead biomass, which may be altered by nutrient enrichment. Over longer timeframes, nutrient addition may increase soil fertility by increasing soil organic matter and nutrient pools. We examined the effects of 5-11 years of nutrient addition at 47 grasslands in twelve countries. Nutrient enrichment increased aboveground live biomass and reduced plant diversity at nearly all sites, and these effects became stronger over time. We did not find evidence that nutrient-induced losses of diversity reduced the positive effects of nutrients on biomass, however nutrient effects on live biomass increased more slowly at sites where litter was also increasing, regardless of plant diversity. This work suggests that short-term experiments may underestimate the long-term nutrient enrichment effects on global, grassland ecosystems.

}, keywords = {LTER-KNZ}, doi = {10.1002/ecy.3218}, url = {https://onlinelibrary.wiley.com/doi/10.1002/ecy.3218}, author = {Seabloom, E.W. and Adler, P.B. and Alberti, J. and Biederman, L. and Buckley, Y.M. and Cadotte, M.W. and S.L Collins and Dee, L. and Fay, P.A. and Firn, J. and Hagenah, N. and Harpole, W. S. and Hautier, Y. and Hector, A. and Hobbie, S.E. and Isbell, F. and Knops, J.M.H. and Kimberly J. Komatsu and Laungani, R. and MacDougall, A. and McCulley, R.L. and Moore, J.L. and Morgan, J.W. and Ohlert, T. and Prober, S.M. and Risch, A.C. and Schuetz, M. and Stevens, C.J. and Borer, E.T.} } @article {KNZ002037, title = {SoDaH: the SOils DAta Harmonization database, an open-source synthesis of soil data from research networks, version 1.0}, journal = {Earth System Science Data Discussion}, year = {2020}, keywords = {LTER-KNZ}, doi = {10.5194/essd-2020-195}, url = {https://essd.copernicus.org/preprints/essd-2020-195/}, author = {Wieder, W.R. and Pierson, D. and Earl, S.R. and Lajtha, K. and Baer, S. and Ballantyne, F. and Berhe, A.A. and Billings, S. and Brigham, L.M. and Chacon, S.S. and Fraterrigo, J. and Frey, S.D. and Georgiou, K. and de Graaff, M. and Grandy, A.S. and Hartman, M.D. and Hobbie, S.E. and Johnson, C. and Kaye, J. and Snowman, E. and Litvak, M.E. and Mack, M.C. and Malhotra, A. and Moore, J.A.M. and Nadelhoffer, K. and Rasmussen, C. and Silver, W.L. and Sulman, B.N. and Walker, X. and Weintraub. S.} } @article {KNZ001786, title = {Mechanisms driving the soil organic matter decomposition response to nitrogen enrichment in grassland soils}, journal = {Soil Biology and Biochemistry}, volume = {99}, year = {2016}, pages = {54 - 65}, abstract = {

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.

}, keywords = {LTER-KNZ, carbon, Fertilization, Microbial biomass, Microbial respiration, Nutrient Network}, doi = {10.1016/j.soilbio.2016.04.023}, url = {https://www.sciencedirect.com/science/article/abs/pii/S0038071716300608?via\%3Dihub}, author = {Riggs, C.E. and Hobbie, S.E.} } @article {KNZ001789, title = {Consistent responses of soil microbial communities to elevated nutrient inputs in grasslands across the globe}, journal = {Proceedings of the National Academy of Sciences}, volume = {112}, year = {2015}, pages = {10967 - 10972}, 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.

}, keywords = {LTER-KNZ, Fertilization, shotgun metagenomics, Soil bacteria, Soil ecology, Soil fungi}, doi = {10.1073/pnas.1508382112}, url = {https://www.pnas.org/content/112/35/10967}, author = {Leff, J.W. and Jones, S.E. and Prober, S.M. and Barber{\'a}n, A. and E.T. Borer and Firn, J.L. and Harpole, W.S. and Hobbie, S.E. and Hofmockel, K.S. and Knops, J.M.H. and McCulley, R.L. and Kimberly J. La Pierre and A. Risch and Seabloom, E.W. and Sch{\"u}tz, Martin and Steenbock, C. and Stevens, C.J. and Fierer, N.} } @article {KNZ001623, title = {The effect of experimental warming and precipitation change on proteolytic enzyme activity: positive feedbacks to nitrogen availability are not universal}, journal = {Global Change Biology}, volume = {18}, year = {2012}, pages = {2617 -2625}, abstract = {

Nitrogen regulates the Earth\&$\#$39;s climate system by constraining the terrestrial sink for atmospheric CO2. Proteolytic enzymes are a principal driver of the within-system cycle of soil nitrogen, yet there is little to no understanding of their response to climate change. Here, we use a single methodology to investigate potential proteolytic enzyme activity in soils from 16 global change experiments. We show that regardless of geographical location or experimental manipulation (i.e., temperature, precipitation, or both), all sites plotted along a single line relating the response ratio of potential proteolytic activity to soil moisture deficit, the difference between precipitation and evapotranspiration. In particular, warming and reductions in precipitation stimulated potential proteolytic activity in mesic sites \– temperate and boreal forests, arctic tundra \– whereas these manipulations suppressed potential activity in dry grasslands. This study provides a foundation for a simple representation of the impacts of climate change on a central component of the nitrogen cycle.

}, keywords = {LTER-KNZ}, doi = {10.1111/j.1365-2486.2012.02685.x}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-2486.2012.02685.x}, author = {Brozostek, E.R. and John M. Blair and Dukes, J.S. and Frey, S.D. and Hobbie, S.E. and Melillo, J.M. and Mitchell, R.J. and Pendall, E.S. and P.B. Reich and Shaver, G.R. and Stefanskii, A. and Tjoelker, M.G. and Finzi, A.C.} } @article {KNZ001496, title = {Past, present, and future roles of long-term experiments in the LTER Network}, journal = {Bioscience}, volume = {62}, year = {2012}, pages = {377 -389}, abstract = {

The US National Science Foundation\–funded Long Term Ecological Research (LTER) Network supports a large (around 240) and diverse portfolio of long-term ecological experiments. Collectively, these long-term experiments have (a) provided unique insights into ecological patterns and processes, although such insight often became apparent only after many years of study; (b) influenced management and policy decisions; and (c) evolved into research platforms supporting studies and involving investigators who were not part of the original design. Furthermore, this suite of long-term experiments addresses, at the site level, all of the US National Research Council\&$\#$39;s Grand Challenges in Environmental Sciences. Despite these contributions, we argue that the scale and scope of global environmental change requires a more-coordinated multisite approach to long-term experiments. Ideally, such an approach would include a network of spatially extensive multifactor experiments, designed in collaboration with ecological modelers that would build on and extend the unique context provided by the LTER Network.

}, keywords = {LTER-KNZ, Climate change, global change, long-term research, LTER Network, multifactor experiments}, doi = {10.1525/bio.2012.62.4.9}, url = {https://academic.oup.com/bioscience/article/62/4/377/243762}, author = {Alan K. Knapp and M.D. Smith and Hobbie, S.E. and Scott. L. Collins and Fahey, T.J. and Hansen, G.J.A. and Landis, D.A. and Kimberly J. La Pierre and Melillo, J.M. and Seastedt, T.R. and Shaver, G.R. and Webster, J.R.} }