@article {KNZ001910, title = {Restoring grassland in the context of climate change}, journal = {Grasslands and Climate Change}, year = {2019}, pages = {310 -322}, keywords = {LTER-KNZ}, doi = {10.1017/9781108163941.020}, url = {https://doi.org/10.1017/9781108163941.020}, author = {S.G. Baer and D.J. Gibson and Johnson, L.C.}, editor = {D.J. Gibson and Newman, J.A.} } @article {KNZ001854, title = {Phenotypic distribution models corroborate species distribution models: A shift in the role and prevalence of a dominant prairie grass in response to climate change}, journal = {Global Change Biology}, volume = {23}, year = {2017}, pages = {4365{\textendash}4375}, abstract = {

Phenotypic distribution within species can vary widely across environmental gradients but forecasts of species\’ responses to environmental change often assume species respond homogenously across their ranges. We compared predictions from species and phenotype distribution models under future climate scenarios for Andropogon gerardii, a widely distributed, dominant grass found throughout the central United States. Phenotype data on aboveground biomass, height, leaf width, and chlorophyll content were obtained from 33 populations spanning a ~1000 km gradient that encompassed the majority of the species\’ environmental range. Species and phenotype distribution models were trained using current climate conditions and projected to future climate scenarios. We used permutation procedures to infer the most important variable for each model. The species-level response to climate was most sensitive to maximum temperature of the hottest month, but phenotypic variables were most sensitive to mean annual precipitation. The phenotype distribution models predict that A. gerardii could be largely functionally eliminated from where this species currently dominates, with biomass and height declining by up to ~60\% and leaf width by ~20\%. By the 2070s, the core area of highest suitability for A. gerardii is projected to shift up to ~700 km northeastward. Further, short-statured phenotypes found in the present-day short grass prairies on the western periphery of the species\’ range will become favored in the current core ~800 km eastward of their current location. Combined, species and phenotype models predict this currently dominant prairie grass will decline in prevalence and stature. Thus, sourcing plant material for grassland restoration and forage should consider changes in the phenotype that will be favored under future climate conditions. Phenotype distribution models account for the role of intraspecific variation in determining responses to anticipated climate change and thereby complement predictions from species distributions models in guiding climate adaptation strategies.

}, keywords = {LTER-KNZ}, doi = {10.1111/gcb.13666}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.13666}, author = {Smith, A.B. and Alsdurf, J. and Knapp, M. and S.G. Baer and Johnson, L.C.} } @article {KNZ001638, title = {Comparing nondestructive and destructive methods of measuring leaf chlorophyll content: tracking changes in foliar chlorophyll of five Andropogon gerardii ecotypes (Poaceae)}, journal = {Photosynthetica}, volume = {52}, year = {2014}, pages = {511-518}, keywords = {LTER-KNZ}, author = {Caudle, K.L. and Johnson, L.C. and S.G. Baer and Maricle, B.R.} } @article {KNZ001563, title = {Environmental and genetic variation in leaf anatomy among populations of Andropogon gerardii (Poaceae) along a precipitation gradient}, journal = {American Journal of Botany}, volume = {100}, year = {2013}, pages = {1957 -1968}, abstract = {

\• Premise of the study: Phenotypes of two Andropogon gerardii subspecies, big bluestem and sand bluestem, vary throughout the prairie ecosystem of North America. This study sought to determine the role of genetics and environment in driving adaptive variation of leaf structure in big bluestem and sand bluestem. \• Methods: Four populations of big bluestem and one population of sand bluestem were planted in common gardens at four sites across a precipitation gradient from western Kansas to southern Illinois. Internal leaf structure and trichome density of A. gerardii were examined by light microscopy to separate genetic and environmentally controlled traits. Leaf thickness, midrib thickness, bulliform cells, interveinal distance, vein size, and trichome density were quantified. \• Key results: At all planting sites, sand bluestem and the xeric population of A. gerardii had thicker leaves and fewer bulliform cells compared with mesic populations. Environment and genetic source population were both influential for leaf anatomy. Leaves from plants grown in mesic sites (Carbondale, Illinois and Manhattan, Kansas) had thicker midribs, larger veins, fewer trichomes, and a greater proportion of bulliform cells compared to plants grown in drier sites (Colby and Hays, Kansas). \• Conclusions: Water availability has driven adaptive variation in leaf structure in populations of A. gerardii, particularly between sand bluestem and big bluestem. Genetically based differences in leaves of A. gerardii indicate adaptive variation and evolutionary forces differentiating sand bluestem from big bluestem. Environmental responses of A. gerardii leaves suggest an ability to adjust to drought, even in populations adapted to mesic home environments.

}, keywords = {LTER-KNZ, adaptive variatio, big bluestem, bulliform cells, drought adaptation, ecotypes, Kranz anatomy, leaf structure, n Andropogon gerardii, population, sand bluestem}, doi = {10.3732/ajb.1200628}, url = {https://bsapubs.onlinelibrary.wiley.com/doi/full/10.3732/ajb.1200628}, author = {Olsen, J.T. and Caudle, K.L. and Johnson, L.C. and S.G. Baer and Maricle, B.} } @inbook {KNZ001113, title = {Biogeochemical changes associated with Juniperus virginia encroachment into grasslands}, booktitle = {Ecological Studies Vol. 196, Western North American Juniperus communities: A dynamic vegetation type}, year = {2008}, pages = {170 -187}, publisher = {Springer-Verlag, NY}, organization = {Springer-Verlag, NY}, keywords = {LTER-KNZ}, author = {McKinley, D.C. and Norris, M.D. and Johnson, L.C. and John M. Blair}, editor = {Van Auken, O.W.} } @article {KNZ001095, title = {Altered ecosystem nitrogen dynamics as a consequence of land cover change in tallgrass prairie}, journal = {American Midland Naturalist}, volume = {158}, year = {2007}, pages = {432 -445}, abstract = {In recent decades, substantial areas of North American tallgrass prairie have been lost to the establishment and expansion of woodlands and forests, including those dominated by eastern redcedar (Juniperus virginiana). This shift in dominant plant life form, from C4 grasses to coniferous trees, may be accompanied by changes in productivity, standing stocks of biomass and nutrients and biogeochemical cycles. The goal of this study was to quantify and compare major pools and fluxes of nitrogen in recently established (<= 80 y) redcedar forests and adjacent native grasslands. Three former grassland sites in the Flint Hills region of Kansas that developed closed-canopy redcedar forests in the recent past were paired with adjacent grassland sites on similar soil type and topographic position (n  =  3 sites/land cover type), and selected soil and plant nitrogen pools and fluxes were measured in replicate plots (n  =  6/site) along transects in each forest or grassland site over a 20-mo period. We found few significant differences in median soil inorganic N pools or net N mineralization rates between the forest and grassland sites, though there was a trend for greater concentrations of inorganic N in grassland sites on most sample dates, and cumulative growing season net N mineralization averaged 15\% less in forest sites (14.3 kg N{\textperiodcentered}ha-1{\textperiodcentered}yr-1) than in grassland sites (16.9 kg N{\textperiodcentered}ha-1{\textperiodcentered}yr-1). Mean aboveground plant productivity of forest sites (9162 kg ha-1 yr-1) was about 2.5{\texttimes} greater than that of comparable grasslands (similar soils and topographic position), in spite of similar levels of soil N availability. This resulted in an ecosystem-level nitrogen use efficiency (ANPP:litterfall N) in forests that was more than double that of the grasslands they replaced. Additional changes in N cycling associated with redcedar forest development included large accumulations of N in aboveground biomass and transfer to the forest floor via litterfall; redcedar aboveground biomass contained 617 kg N/ha, forest floor litter N was 253 kg N/ha, and litterfall N flux was 41 kg ha-1{\textperiodcentered}yr-1. These are substantial increases in aboveground biomass N accumulation, surface litter N inputs, and surface litter N accumulation compared to the native grasslands characteristic of this region. These fundamental shifts in ecosystem patterns and processes have the potential to alter regional biogeochemistry and both nitrogen and carbon storage throughout areas of the eastern Central Plains where coverage of redcedars is increasing.}, keywords = {LTER-KNZ}, doi = {10.1674/0003-0031(2007)158[432:AENDAA]2.0.CO;2}, author = {Norris, M.D. and John M. Blair and Johnson, L.C.} } @article {KNZ001049, title = {Can rDNA analyses of diverse fungal communities in soil and rootsdetect effects of environmental manipulations--a case study from tallgrass prairie}, journal = {Mycologia}, volume = {97}, year = {2005}, pages = {1177 -1194}, abstract = {

We tested whether fungal communities are impacted by nitrogen deposition or increased precipitation by PCR-amplifying partial fungal rRNA genes from 24 soil and 24 root samples from a nitrogen enrichment and irrigation experiment in a tallgrass prairie at Konza Prairie Biological Station in northeastern Kansas, U.S.A. Obtained fungal sequences represented great fungal diversity that was distributed mainly in ascomycetes and basiodiomycetes; only a few zygomycetes and glomeromycetes were detected. Conservative extrapolated estimates of the fungal species richness suggest that the true richness may be at least twice as high as observed. The effects of nitrogen enrichment or irrigation on fungal community composition, diversity or clone richness could not be unambiguously assessed because of the overwhelming diversity. However, soil communities differed from root communities in diversity, richness and composition. The compositional differences were largely attributable to an abundant, soil-inhabiting group placed as a well-supported sister group to other ascomycetes. This group likely represents a novel group of fungi. We conclude that the great fungal richness in this ecosystem precluded a reliable assessment of anthropogenic impacts on soil or rhizosphere communities using the applied sampling scheme, and that detection of novel fungi in soil may be more a rule than an exception.

}, keywords = {LTER-KNZ, Biodiversity, environmental change, fungi, nitrogen, Precipitation, soil DNA}, doi = {10.3852/mycologia.97.6.1177}, author = {A. Jumpponen and Johnson, L.C.} } @article {KNZ00985, title = {Environmental constraints on a global relationship among leaf and root traits of grasses}, journal = {Ecology}, volume = {86}, year = {2005}, pages = {12 -19}, abstract = {Uncertainties regarding the relationships between leaf and root traits have impeded an integrated understanding of plant evolution and the efficient parameterization of ecosystem models. We measured key root and leaf traits of grasses from 77 sites in four grassland regions of the world (New Zealand, Australia, South Africa, North America). Within each region, the relationships among leaf traits paralleled those among root traits. Plants with low root or leaf N concentrations had roots or leaves with high tissue density, high lignin concentrations, low amount of mass that was soluble in a neutral detergent solution, large diameter/thickness, and were less enriched in 15N. Yet, whether comparing plants within a region or among all four regions, there was little relationship between root traits and leaf traits, except for a positive relationship between root and leaf N concentration and between root and leaf δ15N. At the global scale, factors such as soil freezing and the type of nutrient limitation appear to determine relationships among leaves and roots. C4 grasses not only had lower leaf N concentrations than C3 grasses but also lower root N concentrations. When compared at the same root N concentration, C4 grasses had greater leaf N concentrations than C3 grasses.}, keywords = {LTER-KNZ}, doi = {10.1890/04-1075}, author = {Craine, J.M. and Lee, W.G. and Bond, W.J. and Willians, R.J. and Johnson, L.C.} } @article {KNZ00983, title = {Nitrogen enrichment causes minimal changes in arbuscular mycorrhizal colonization but shifts community composition - evidence from rDNA data}, journal = {Biology and Fertility of Soils}, volume = {41}, year = {2005}, pages = {217 -224}, abstract = {Intracellular arbuscular mycorrhizal (AM) colonization was compared between nitrogen (NH4NO3) fertilized (10 g N m-2) and nonfertilized tallgrass prairie plots. In the microscopic analyses of host roots, only intracellular coils showed an increasing trend as a result of N fertilization, whereas intracellular colonization by arbuscules, hyphae, or vesicles did not differ between the N treatments. Clone libraries established from pooled PCR products of AM fungi contained exclusively species of Glomus; no other genera were detected indicating that Glomus spp. dominated the host roots. Comparisons between observed and random topologies indicated that cloned sequence placement covaried with N treatment: unique clades within Glomus originated exclusively from N-fertilized or nonfertilized treatments. We conclude that the communities of dominant and most commonly occurring AM fungi changed in response to N amendment, although the root colonization showed minimal or no response.}, keywords = {LTER-KNZ, Arbuscular mycorrhiza, Nitrogen deposition, Ribosomal DNA, tallgrass prairie}, doi = {10.1007/s00374-005-0845-8}, author = {A. Jumpponen and Trowbridge, J. and Mandyam, K.G. and Johnson, L.C.} } @article {KNZ00961, title = {Vegetation-mediated changes in microclimate reduce soil respiration as woodlands expand into grasslands}, journal = {Ecology}, volume = {85}, year = {2004}, pages = {3348 -3361}, abstract = {This study compared annual and growing-season in situ soil respiration and soil C cycling in paired juniper woodland and C4-dominated grassland sites in eastern Kansas (USA) to determine if, under similar edaphic and regional climate conditions, vegetation change alters soil CO2 dynamics. We found marked differences in soil respiration related to vegetation: Growing season mean woodland soil respiration rates (4.6 μmoles{\textperiodcentered}m-2{\textperiodcentered}s-1) averaged 38\% less than paired grassland sites. Soil moisture did not explain the difference in soil respiration between woodlands and grasslands. Soil temperatures at the 10-cm depth were 5{\textdegree}C cooler in woodlands during the growing season and significantly different between woodlands and grasslands throughout the year, explaining most of the low soil respiration in woodlands. However, there were subtle intrinsic differences in the response of soil respiration to temperature between woodlands and grasslands: Woodland and grassland respiration response was significantly different at the P = 0.05 level, also indicated by a grassland Q10 of 2.4 compared to 2.2 in woodlands. We found no significant differences between woodlands and grasslands in long-term (82-week) laboratory incubations of potentially mineralizable soil C and short-term incubations for microbial biomass C. Similarly, root biomass did not differ between woodlands and grasslands and could not explain the lower in situ woodland soil respiration. Thus, vegetation-mediated reduction in soil temperature under the canopy explained much of the lower in situ woodland soil respiration. Lower soil respiration in the woodland resulted in an annual flux of 533.6 ({\textpm}21.7) compared to 858.4 ({\textpm}14.5) g C{\textperiodcentered}m-2{\textperiodcentered}yr-1 in grasslands, nearly 38\% lower in the woodland (means {\textpm} 1 se). Assuming root respiration is 50\% of soil respiration, we estimate that the turnover of woodland soil C stocks may be slowed by 15 years relative to grassland. This suggests that, if juniper expansion (now occurring across nearly 5 million hectares in the Great Plains) proceeds to canopy closure, annual soil C flux may be potentially reduced by as much as 19 {\texttimes} 106 Mg of C below C flux rates that occurred historically from tallgrass prairie soils.}, keywords = {LTER-KNZ}, doi = {10.1890/03-0576}, author = {Smith, D.L. and Johnson, L.C.} } @article {KNZ00851, title = {Expansion of Juniperus in the Great Plains: Changes in soil organic carbon dynamics}, journal = {Global Biogeochemical Cycles}, volume = {17}, year = {2003}, pages = {1062 -}, abstract = {[1] Woody encroachment by Juniperus virginiana into Great Plains grasslands allowed us to answer: Does changing the type of plant input to soils alter soil organic carbon (SOC) distribution or soil carbon (C) storage? The answer is critical because woody encroachment may alter C cycling over millions of hectares in the Great Plains and Midwest. We predicted that (1) forest SOC would become concentrated in shallow soil layers compared to SOC distribution in grassland, (2) woody expansion would increase soil C storage, and (3) forest C would be apparent in the larger soil organic matter fractions. Using δ13C signatures of SOC, 1/5 of the C from 0 to 25 cm in juniper forest soils was derived from C3 juniper trees. Forest C3 input occurred primarily in shallow surface layers: Forest soils developed over former C4 prairie contained 42\% C3-SOC from 0 to 2.5 cm depth, and decreased to 6\% at 25 cm. Isotopic analysis of SOC size fractions revealed that at 0{\textendash}2.5 cm, the forest soil fraction >212 μm was -25.7{\textperthousand}. The fraction <2 μm had a 13C isotope ratio of -17.0{\textperthousand} at the same depth, reflecting the predominance of residual prairie C in the smallest fraction. In spite of fast dynamics of soil C turnover, there was no net change in SOC amounts over 40{\textendash}60 years (cumulative mineral and organic SOC in forest, 8782 g C/m2 {\textpm} 810; in grassland, 7699 {\textpm} 1004). Thus as junipers expand into mesic areas of the Great Plains, juniper forests will provide little additional soil C storage.}, keywords = {LTER-KNZ}, doi = {10.1029/2002GB001990}, author = {Smith, D.L. and Johnson, L.C.} } @article {KNZ0011, title = {Assessing the rate, mechanism and consequences of conversion of tallgrass prairie to Juniperus virginiana forest}, journal = {Ecosystems}, volume = {5}, year = {2002}, pages = {578 -586}, abstract = {We assessed the determinants and consequences of the expansion of Juniperus virginiana L. (red cedar) populations into central US grasslands using historical aerial photos and field measurements of forest extent, tree growth, fire-induced mortality, and responses in herbaceous species diversity and productivity. Photos from northeast Kansas dating back to 1956 indicate that native tallgrass prairie can be converted to closed-canopy red cedar forest in as little as 40 years (a 2.3\% increase in forest cover per year). Mean tree density in 21 forested sites ranged from 130 to 3500 trees/ha, with most sites at more than 800 trees/ha. In younger stands, maximum growth rates of individual red cedar trees exceeded 20 cm/y in height. Land management practices were critical to the establishment and growth of red cedar forest. Grazing reduced the fuel loads by more than 30\% in tallgrass prairie. Based on measurements of mortality for more than 1800 red cedar trees, fire-induced mortality in grazed areas averaged 31.6\% versus more than 90\% at ungrazed sites. When tallgrass prairie was converted to red cedar forest, herbaceous species diversity and productivity were drastically reduced, and most grassland species were virtually eliminated. Consequently, community structure shifted from dominance by herbaceous C4 species to evergreen woody C3 species; this shift is likely to be accompanied by alterations in carbon storage and other ecosystem processes in a relatively short time period. Here we present a conceptual model that integrates the ecological and socioeconomic factors that underlie the conversion of grassland to red cedar forest.}, keywords = {LTER-KNZ, fire, forest expansion, Grazing, Juniperus virginiana, land-cover change, land-use change, red cedar, tallgrass prairie}, doi = {10.1007/s10021-002-0187-4}, author = {Hoch, G.A. and J. M. Briggs and Johnson, L.C.} } @article {KNZ00781, title = {Assessing changes in biomass, productivity, and C and N stores following Juniperus virginiana forest expansion into tallgrass prairie}, journal = {Canadian Journal of Forest Research}, volume = {31}, year = {2001}, pages = {1940 -1946}, abstract = {An increase in woody plant abundance in regions historically dominated by grasses is a recent land cover change in grasslands worldwide. In tallgrass prairies of North America, this increase in woody plant cover includes the development of dense stands of eastern redcedar (Juniperus virginiana L.). To evaluate the consequences of this ongoing land cover change for ecosystem functioning, we developed allometric equations, using data from Kansas and Oklahoma, to estimate aboveground biomass and productivity in closed-canopy redcedar stands. We then applied these equations to three closed-canopy redcedar stands, 35–80 years old, which developed on sites formerly dominated by tallgrass prairie in eastern Kansas. Aboveground plant biomass for these redcedar-dominated sites ranged from 114 100 kg/ha for the youngest stand to 210 700 kg/ha for the oldest. Annual aboveground net primary productivity (ANPP) ranged from 7250 to 10 440 kg{\textperiodcentered}ha–1{\textperiodcentered}year–1 for the oldest and younger redcedar stands, respectively. Estimates of ANPP in comparable tallgrass prairie sites in this region average 3690 kg{\textperiodcentered}ha–1{\textperiodcentered}year–1 indicating a large increase in C uptake and aboveground storage as a result of the change from prairie to redcedar forests. Therefore, the widespread occurrence of redcedars across the woodland–prairie ecotone suggests that this land-cover change may have important consequences for regional net C storage.}, keywords = {LTER-KNZ, tallgrass prairie}, doi = {10.1139/x01-132}, author = {Norris, M.D. and John M. Blair and Johnson, L.C. and McKane, R.B.} } @article {KNZ00770, title = {Fire and grazing regulate belowground processes in tallgrass prairie}, journal = {Ecology}, volume = {82}, year = {2001}, pages = {3377 -3389}, abstract = {In tallgrass prairie, belowground processes are even more important than in forested systems because aboveground biomass and standing dead litter are periodically removed by frequent fires or grazers. Thus, studies that address factors regulating belowground processes are especially relevant for tallgrass prairie. We predicted that effects of grazing and burning differ belowground and that changes in root productivity caused by burning or grazing provide feedback that affects ecosystem fluxes of C and N. These differences in belowground response should be driven largely by changes in N dynamics and the degree to which burning and grazing affect the pathway and magnitude of N loss and the degree of N limitation in these systems. Fire, the major pathway of N loss in ungrazed tallgrass prairie, should result in reduced net N mineralization and N availability. We expected plants to compensate for increased N limitation by increasing their allocation to roots, as manifested in increased soil respiration and C cycling belowground. In contrast, grazing conserves N in the ecosystem by redistributing the N once contained in grass to labile forms in urine and dung. Thus, we predicted that grazing should increase N cycling rates and N availability to plants. Consequently, grazed plants should be less N limited and should allocate less C to roots and more to shoots. This, in turn, should decrease belowground C cycling, manifested as reduced soil CO2 flux. We explored the roles of grazing and burning on root growth in experimental watersheds at Konza Prairie, Kansas, USA. To assess effects of fire on root productivity, we installed root ingrowth cores in two watersheds without grazers that differ in fire frequency: annually vs. infrequently burned (four years since the last fire). To assess effects of grazing, we installed root ingrowth cores in an annually burned watershed grazed by bison and in fenced controls (exclosures). Within bison {\textquotedblleft}grazing lawns,{\textquotedblright} root ingrowth cores were installed in lightly and heavily grazed patches. Concurrently, we measured in situ rates of net N mineralization and soil respiration as indices of soil N and C cycling. Annual burning resulted in a 25\% increase in root growth compared to the unburned watershed (four years since last fire), as plants compensated for N limitation by increasing allocation to roots. Grazing had the opposite effect: it decreased root growth, especially in heavily grazed patches (\~{}30\% less than in fenced controls). Grazing by ungulates increased N cycling and availability. Therefore, grazed plants, instead of being N limited, experienced C limitation as shoots regrew and plants allocated less C to roots. Interestingly, root ingrowth on the long-term unburned watershed was as low as in lightly grazed patches in the grazed watershed. Thus, seemingly disparate treatments such as infrequent burning (characterized by accumulation of detritus aboveground) and grazing (periodic biomass removal) both had higher levels of N availability than annually burned prairie in the absence of grazers. Root growth in unburned and grazed watersheds must be limited by resources other than N (e.g., C in grazing lawns or light in infrequently burned prairie). Burning and grazing also altered root tissue chemistry in contrasting ways that further accentuated the root growth differences caused by these treatments. Frequent fires lowered substrate quality of roots (C:N = 60), thus increasing N limitation. In contrast, grazing and infrequent burning improved root tissue quality (C:N = 40), promoting faster cycling of N. These large differences in root growth and tissue chemistry can result in profound ecosystem-level changes. Grazing increased net N mineralization rates from 87\% to 617\% compared to watersheds without grazers, whereas annual burning decreased it by \~{}50\% compared to unburned prairie. Although grazing speeded up N cycling, it reduced soil respiration by 50\% compared to fenced controls, presumably because of reduced root mass. On the other hand, annual burning increased soil respiration, presumably because of increased root biomass. Ultimately, differences in the quantity and quality of roots provide feedback to affect C and N cycling and help to maintain and even promote the fundamental differences in N cycling between burning and grazing in tallgrass prairie.}, keywords = {LTER-KNZ, tallgrass prairie}, doi = {10.1890/0012-9658(2001)082[3377:FAGRBP]2.0.CO;2}, author = {Johnson, L.C. and Matchett, J.R.} } @article {KNZ00782, title = {Land cover change in eastern Kansas: litter dynamics of closed-canopy eastern redcedar forests in tallgrass prairie}, journal = {Canadian Journal of Botany}, volume = {79}, year = {2001}, pages = {214 -222}, abstract = {In the Great Plains region, eastern redcedar (Juniperus virginiana L.) abundance has increased dramatically in areas historically occupied by tallgrass prairie. This shift in dominant vegetation is likely to be accompanied by changes in ecosystem structure and function, including quantity, quality, and location (above- vs. below-ground) of litter inputs and subsequent effects on decomposition dynamics. The purpose of this study was to quantify and compare patterns of litterfall and decomposition in mature redcedar forests and adjacent prairie. Annual redcedar litterfall was 500 g{\textperiodcentered}m-2{\textperiodcentered}year-1, a large increase in foliar litter inputs compared with annually burned grassland (52 g{\textperiodcentered}m-2{\textperiodcentered}year-1). Using a reciprocal transplant decomposition study with four substrates, redcedar leaves and roots, and big bluestem (Andropogon gerardii Vitman) foliage and roots, we found marginal habitat effects, but greater differences between species, presumably owing to litter quality (including both C:N and lignin content). Decay rates were significantly higher in the prairie relative to the forest for each substrate. Additionally, within any particular habitat, grass litter had significantly faster decay rates than forest litter. These results suggest a shift in patterns of litter input and decomposition processes with afforestation of tallgrass prairie, which may result in long-term changes in C sequestration and storage.Key words: litter dynamics, eastern redcedar (Juniperus virginiana), big bluestem (Andropogon gerardii), decomposition, tallgrass prairie, nitrogen immobilization.}, keywords = {LTER-KNZ, tallgrass prairie}, doi = {10.1139/b00-159}, author = {Norris, M.D. and John M. Blair and Johnson, L.C.} } @article {KNZ00697, title = {The keystone role of bison in North American tallgrass prairie}, journal = {BioScience}, volume = {49}, year = {1999}, pages = {39 -50}, keywords = {LTER-KNZ}, url = {http://www.jstor.org/stable/10.1525/bisi.1999.49.1.39}, author = {Alan K. Knapp and John M. Blair and J. M. Briggs and Scott. L. Collins and D.C. Hartnett and Johnson, L.C. and Towne, E.G.} } @article {KNZ00694, title = {Nitrogen limitation in dryland ecosystems: responses to temporal and geographical variation in precipitation}, journal = {Biogeochemistry}, volume = {46}, year = {1999}, pages = {247 -293}, abstract = {We 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.}, keywords = {LTER-KNZ, arid, Fertilization, Net primary productivity, nitrogen limitation, semi-arid, Water availability}, doi = {10.1007/BF01007582}, author = {Hooper, D.U. and Johnson, L.C.} }