@article {KNZ001898, title = {Ambient changes exceed treatment effects on plant species abundance in long-term global change experiments}, journal = {Glob Chang Biol}, volume = {24}, year = {2018}, pages = {5668 - 5679}, abstract = {

The responses of species to environmental changes will determine future community composition and ecosystem function. Many syntheses of global change experiments examine the magnitude of treatment effect sizes, but we lack an understanding of how plant responses to treatments compare to ongoing changes in the unmanipulated (ambient or background) system. We used a database of long-term global change studies manipulating CO2 , nutrients, water, and temperature to answer three questions: (a) How do changes in plant species abundance in ambient plots relate to those in treated plots? (b) How does the magnitude of ambient change in species-level abundance over time relate to responsiveness to global change treatments? (c) Does the direction of species-level responses to global change treatments differ from the direction of ambient change? We estimated temporal trends in plant abundance for 791 plant species in ambient and treated plots across 16 long-term global change experiments yielding 2,116 experiment-species-treatment combinations. Surprisingly, for most species (57\%) the magnitude of ambient change was greater than the magnitude of treatment effects. However, the direction of ambient change, whether a species was increasing or decreasing in abundance under ambient conditions, had no bearing on the direction of treatment effects. Although ambient communities are inherently dynamic, there is now widespread evidence that anthropogenic drivers are directionally altering plant communities in many ecosystems. Thus, global change treatment effects must be interpreted in the context of plant species trajectories that are likely driven by ongoing environmental changes.

}, keywords = {LTER-KNZ, elevated CO2, nitrogen, Phosphorus, plant community, Warming, water}, doi = {10.1111/gcb.14442}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.14442}, author = {Langley, A. and Chapman, S.K. and Kimberly J. La Pierre and M.L. Avolio and W.D. Bowman and Johnson, D. and Isbell, F. and K.R. Wilcox and Foster, B. and Hovenden, M. and Alan K. Knapp and Koerner, S.E. and Lortie, C. and Megonigal, J. and Newton, P. and Reich, B. and M.D. Smith and Suttle, B.K. and Tilman, D.} } @article {KNZ001766, title = {Nitrogen, phosphorus, and eutrophication in streams}, journal = {Inland Waters}, volume = {6}, year = {2016}, pages = {155 - 164}, abstract = {

Flowing waters receive substantial nutrient inputs, including both nitrogen (N) and phosphorus (P), in many parts of the world. Eutrophication science for rivers and streams has unfortunately lagged behind that for lakes, and results from lakes might inform those interested in stream eutrophication. A key controversy in lake eutrophication science is the relative importance of controlling P and N in water quality management, and we are interested how the science of this controversy transfers to flowing waters. A literature review indicates (1) stream benthic chlorophyll is significantly correlated to both total N and total P in the water column, with both nutrients explaining more variance than either considered alone; (2) nutrients have increased substantially in many rivers and streams of the United States over reference conditions, and strong shifts in N and P stoichiometry have occurred as well; (3) bioassays often indicate N responses alone or in concert with P responses for autotrophic (primary production and chlorophyll) and heterotrophic (respiration) responses; (4) both heterotrophic and autotrophic processes are influenced by the availability of N and P; and (5) N-fixing cyanobacteria usually do not seem to be able to fully satisfy N limitations in rivers and streams when P is present in excess of N. These data suggest both N and P control should be considered in the eutrophication management of streams.

}, keywords = {LTER-KNZ, eutrophication, nitrogen, Phosphorus, streams}, doi = {10.5268/IW-6.2.909}, url = {https://www.tandfonline.com/doi/abs/10.5268/IW-6.2.909}, author = {W. K. Dodds and Smith, V.H.} } @article {KNZ001719, title = {Soil nutrient additions increase invertebrate herbivore abundances, but not herbivory, across three grassland systems}, journal = {Oecologia}, volume = {180}, year = {2016}, pages = {485 -497}, abstract = {

Resource availability may influence invertebrate communities, with important consequences for ecosystem function, such as biomass production. We assessed: (1) the effects of experimental soil nutrient additions on invertebrate abundances and feeding rates and (2) the resultant changes in the effects of invertebrates on aboveground plant biomass at three grassland sites spanning the North American Central Plains, across which plant tissue chemistry and biomass vary. Invertebrate communities and rates of herbivory were sampled within a long-term nutrient-addition experiment established at each site along the broad Central Plains precipitation gradient. Additionally, the effects of invertebrates on aboveground plant biomass were determined under ambient and elevated nutrient conditions. At the more mesic sites, invertebrate herbivore abundances increased and their per capita rate of herbivory decreased with nutrient additions. In contrast, at the semi-arid site where plant biomass is low and plant nutrient concentrations are high, invertebrate herbivore abundances did not vary and per capita rates of herbivory increased with nutrient additions. No change in the effect of invertebrate herbivores on aboveground plant biomass was observed at any of the sites. In sum, nutrient additions induced shifts in both plant biomass and leaf nutrient content, which altered invertebrate abundances and feeding rate. However, due to the inverse relationship between changes in herbivore abundance and per capita rates of herbivory, nutrient additions did not alter the effect of invertebrates on aboveground biomass. Overall, we suggest that this inverse response of herbivore abundance and per capita feeding rate may buffer ecosystems against changes in invertebrate damage in response to fluctuations in nutrient levels.

}, keywords = {LTER-KNZ, Central Plains, nitrogen, Per capita herbivory rate, Phosphorus, Plant tissue chemistry}, doi = {https://doi.org/10.1007/s00442-015-3471-7}, url = {https://link.springer.com/article/10.1007\%2Fs00442-015-3471-7}, author = {Kimberly J. La Pierre and M.D. Smith} } @article {KNZ001274, title = {Plant nitrogen and phosphorus limitation in 98 North American grassland soils}, journal = {Plant and Soil}, volume = {334}, year = {2010}, pages = {73 -84}, abstract = {

The availability of nutrients is a critical determinant of ecological dynamics in grasslands, but the relationships between soil resource availability and nutrient limitation across ecosystems are not clear. To better understand how soil nutrient availability determines nutrient limitation in vegetation, we grew the same species of grass (Schizachyrium scoparium) in 98 North American grassland soils and fertilized them factorially with nitrogen (N) and phosphorus (P). On average adding N, P, and the two nutrients together increased biomass relative to unfertilized plants by 81\%, 22\%, and 131\%, respectively. Plants grown on low-P soils were not primarily limited by P. Instead, these plants were colimited by N and P, while plants grown on high-P soils were primarily limited by N and only secondarily limited by P. Limitation was not predicted by total soil N. The preponderance of colimitation between N and P on low-P soils suggests that low P availability alters the N cycle to constrain supplies to plants such that N and P are made available in proportion to their demand by plants.

}, keywords = {LTER-KNZ, Colimitation, Grasslands, nitrogen, Phosphorus, stoichiometry}, doi = {10.1007/s11104-009-0237-1}, url = {https://link.springer.com/article/10.1007\%2Fs11104-009-0237-1}, author = {Craine, J.M. and Jackson, R.D.} } @article {KNZ001058, title = {Controls on nutrients across a prairie stream watershed: Land use and riparian cover effects}, journal = {Environmental Management}, volume = {37}, year = {2006}, pages = {636 -646}, abstract = {Nutrient inputs generally are increased by human-induced land use changes and can lead to eutrophication and impairment of surface waters. Understanding the scale at which land use influences nutrient loading is necessary for the development of management practices and policies that improve water quality. The authors assessed the relationships between land use and stream nutrients in a prairie watershed dominated by intermittent stream flow in the first-order higher elevation reaches. Total nitrogen, nitrate, and phosphorus concentrations were greater in tributaries occupying the lower portions of the watershed, closely mirroring the increased density of row crop agriculture from headwaters to lower-elevation alluvial areas. Land cover classified at three spatial scales in each sub-basin above sampling sites (riparian in the entire catchment, catchment land cover, and riparian across the 2 km upstream) was highly correlated with variation in both total nitrogen (r2 = 53\%, 52\%, and 49\%, respectively) and nitrate (r2 = 69\%, 65\%, and 56\%, respectively) concentrations among sites. However, phosphorus concentrations were not significantly associated with riparian or catchment land cover classes at any spatial scale. Separating land use from riparian cover in the entire watershed was difficult, but riparian cover was most closely correlated with in-stream nutrient concentrations. By controlling for land cover, a significant correlation of riparian cover for the 2 km above the sampling site with in-stream nutrient concentrations could be established. Surprisingly, land use in the entire watershed, including small intermittent streams, had a large influence on average downstream water quality although the headwater streams were not flowing for a substantial portion of the year. This suggests that nutrient criteria may not be met only by managing permanently flowing streams.}, keywords = {LTER-KNZ, nitrogen, Phosphorus, Prairie watershed, Riparian, water quality}, doi = {10.1007/s00267-004-0072-3}, author = {W. K. Dodds and Oakes, R.M.} } @article {KNZ001032, title = {Determining ecoregional reference conditions for nutrients, secchi depth, and chlorophyll a in Kansas lakes and reservoirs}, journal = {Lake and Reservoir Management}, volume = {22}, year = {2006}, pages = {151 -159}, abstract = {Baseline environmental conditions are a critical consideration in the development of scientifically defensible aquatic nutrient criteria. We applied three methods to ecoregionally stratified data to determine reference conditions in Kansas lakes and reservoirs with respect to total phosphorus, total nitrogen, Secchi depth, and planktonic chlorophyll a (chl a). First, minimally developed lake/watershed units were identified based on existing geographical databases and visual basin surveys. Lakes and reservoirs in these watersheds were considered minimally-to-least impacted {\textquotedblleft}reference{\textquotedblright} waters. Second, median nutrient, Secchi depth, and chl a values were determined for the best one-third of lakes and reservoirs and applied as indicators of reference condition (trisection). Third, a regression-based extrapolation method was applied to estimate water quality conditions in the absence of anthropogenic influences. The first method suggested no ecoregional effect on the trophic status of minimally impacted reference water bodies, whereas the other two methods indicated some significant ecoregional differences. Lack of ecoregional effect in reference bodies could indicate that differences were driven by anthropogenic influences rather than natural regional characteristics. Reference conditions, as determined by these three methods, broadly agreed for all parameters and were generally at or less than literature values for the mesotrophic-eutrophic threshold for lakes and reservoirs worldwide. Reference values for total phosphorus were primarily less than levels commonly associated with cyanobacterial blooms. Overall, the data suggest that multiple methods can be used to determine reference condition, and that in Kansas lakes and reservoirs reference condition corresponds to mesotrophic state.}, keywords = {LTER-KNZ, ecoregion, eutrophication, nitrogen, nutrient criteria, Phosphorus}, doi = {10.1080/07438140609353892}, author = {W. K. Dodds and Carney, E. and Angelo, R.T.} } @article {KNZ00861, title = {Effects of fire, mowing and fertilization effects on density and biomass of macroinvertebrates in North American tallgrass prairie soils}, journal = {Soil Biology \& Biochemistry}, volume = {35}, year = {2003}, pages = {1079 -1093}, abstract = {The 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.}, keywords = {LTER-KNZ, biomass, Cicadidae, Curculionidae, disturbance, earthworms, Elateridae, Fertilization, Fertilizer, fire, grassland, insect herbivores, nitrogen, Phosphorus, Scarabaeidae}, doi = {10.1016/S0038-0717(03)00153-6}, author = {Callaham, M.A. Jr. and John M. Blair and T.C. Todd and Kitchen, D.J. and M.R. Whiles} } @article {KNZ00888, title = {The role of periphyton in phosphorus retention in shallow freshwater aquatic systems}, journal = {Journal of Phycology}, volume = {39}, year = {2003}, pages = {830 -849}, abstract = {

Eutrophication caused by phosphorus (P) leads to water quality problems in aquatic systems, particularly freshwaters, worldwide. Processing of nutrients in shallow habitats removes P from water naturally and periphyton influences P removal from the water column in flowing waters and wetlands. Periphyton plays several roles in removing P from the water column, including P uptake and deposition, filtering particulate P from the water, and attenuating flow, which decreases advective transport of particulate and dissolved P from sediments. Furthermore, periphyton photosynthesis locally increases pH by up to 1 unit, which can lead to increased precipitation of calcium phosphate, concurrent deposition of carbonate-phosphate complexes, and long-term burial of P. Actively photosynthesizing periphyton can cause super-saturated O2 concentrations near the sediment surface encouraging deposition of metal phosphates. However, anoxia associated with periphyton respiration at night may offset this effect. Linking the small-scale functional role of periphyton to ecosystem-level P retention will require more detailed studies in a variety of ecosystems or large mesocosms. A case study from the Everglades illustrates the importance of considering the role of periphyton in P removal from wetlands. In general, periphyton tends to increase P retention and deposition. In pilot-scale constructed periphyton-dominated wetlands in South Florida, about half of the inflowing total P was removed.

}, keywords = {LTER-KNZ, eutrophication, microalgae, microphytobenthos, periphyton, phosphate, Phosphorus, tertiary treatment, water quality}, doi = {10.1046/j.1529-8817.2003.02081.x}, author = {W. K. Dodds} } @article {KNZ00636, title = {Suggested classification for stream trophic state: Distributions of temperate stream types by chlorophyll, total nitrogen and phosphorus}, journal = {Water Research}, volume = {32}, year = {1998}, pages = {1455 -1462}, abstract = {Aquatic scientists and managers have no conventional mechanism with which to characterize and compare nutrients and algal biomass in streams within a broader context analogous to trophic state categorization in lakes by chlorophyll (chl) and nutrients. We analyzed published data for a large number of distinct, temperate, stream sites for mean benthic chl (n=286), maximum benthic chl (n=176), sestonic chl (n=292), total nitrogen (n=1070), and total phosphorus (n=1366) as a first effort to establish criteria for trophic boundaries. Two classification systems are proposed. In the first system, the boundary between oligotrophic and mesotrophic categories is defined by the lower third of the cumulative distribution of the values. The mesotrophic{\textendash}eutrophic boundary is defined by the upper third of the distribution. In the second system, individual streams are placed more precisely in a broad geographic context by assessing the proportion of streams that have greater or lesser nutrient and chl values. The proposed relationships for streams were compared to trophic criteria published for lakes. The proposed trophic boundaries for streams generally include a broader range of values in the mesotrophic range than conventional criteria for lakes. The ratio of maximum to mean benthic chl for streams was significantly higher than that found for planktonic chl in lakes, reflecting the greater variance in streams. This high variance in streams suggests that the proposed stream trophic criteria should be viewed only as a general first approach to categorizing stream ecosystems.}, keywords = {LTER-KNZ, Chlorophyll, eutrophic, mesotrophic, nitrogen, nutrients, oligotrophic, periphyton, Phosphorus, rivers, streams}, doi = {10.1016/S0043-1354(97)00370-9}, author = {W. K. Dodds and Jones, J.R. and Welch, E.B.} } @article {KNZ00541, title = {Interspecific nutrient transfer in a tallgrass prairie plant community}, journal = {American Journal of Botany}, volume = {83}, year = {1996}, pages = {180 -184}, abstract = {Interplant nutrient transfer may be an important ecological process in grasslands, and may significantly influence plant neighborhood interactions. We investigated the potential for phosphorus transfer between the dominant grass Andropogon gerardii and several neighboring plant species in tallgrass prairie via a field 32PO4 labelling experiment. The mean amount of 32P received from donor shoots differed significantly among neighboring species and decreased with increasing distance from the donor. In general, forbs and cool-season C3 grasses received more labelled 32P than warm-season C4 grasses. Phosphorus transfer occurred over distances up to 0.5 m. The effects of species and distance on movement of phosphorus changed with increasing time after labelling. The relative mass of receiver and donor shoots did not affect amounts of 32P transfer. A benomyl fungicide treatment, applied to suppress mycorrhizal activity, likely did not affect existing vegetative hyphae and did not affect the amount of 32P transferred. These studies demonstrate that: (1) phosphorus is transferred among neighboring species in tallgrass prairie plant communities, (2) phosphorus may be transferred over significantly greater distances than reported in other grasslands, and (3) there is differential transfer among co-occurring species. Hypothesized mechanisms accounting for these patterns in tallgrass prairie include mycorrhizal hyphal interconnections and/or extensive and differential root and rhizosphere overlap among neighboring species.}, keywords = {LTER-KNZ, mycorrhizae, Phosphorus, tallgrass prairie}, url = {http://www.jstor.org/stable/2445936}, author = {Walter, L.E.F. and D.C. Hartnett and Hetrick, B.A.D. and Schwab, A.P.} }