@article {KNZ001211, title = {Assessing the multi-resolution information content of remotely sensed variables and elevation for evapotranspiration in a tall-grass prairie environment}, journal = {Remote Sensing of Environment}, volume = {112}, year = {2008}, pages = {2977 -2987}, abstract = {

Understanding the spatial scaling behavior of evapotranspiration and its relation to controlling factors on the land surface is necessary to accurately estimate regional water cycling. We propose a method for ascertaining this scaling behavior via a combination of wavelet multi-resolution analysis and information theory metrics. Using a physically-based modeling framework, we are able to compute spatially distributed latent heat fluxes over the tall-grass prairie in North-central Kansas for August 8, 2005. Comparison with three eddy-covariance stations and a large aperture scintillometer demonstrates good agreement, and thus give confidence in the modeled fluxes. Results indicate that the spatial variability in radiometric temperature (a proxy for soil moisture) most closely controls the spatial variability in evapotranspiration. Small scale variability in the water flux can be ascribed to the small scale spatial variance in the fractional vegetation. In addition, correlation analysis indicates general scale invariance and that low spatial resolution data may be adequate for accurately determining water cycling in prairie ecosystems.

}, keywords = {LTER-KNZ, Entropy, information theory, Konza Prairie, Latent heat, MODIS, Spatial heterogeneity, SVAT model, wavelets}, doi = {10.1016/j.rse.2008.02.002}, url = {https://www.sciencedirect.com/science/article/abs/pii/S0034425708000655?via\%3Dihub}, author = {N. Brunsell and J.M. Ham and Owensby, C.E.} } @article {KNZ001066, title = {Natural 15N abundances in a tallgrass prairie exposed to 8 years of elevated atmospheric CO2}, journal = {Soil Biology \& Biochemistry}, volume = {37}, year = {2006}, pages = {409 -412}, abstract = {

After 8-y of elevated CO2, we previously detected greater amounts of total soil nitrogen, suggesting that rates of ecosystem N flux into or out of tallgrass prairie had been altered. Denitrification and associative N fixation rates are the two primary biological processes that are known to control N loss and accumulation in tallgrass prairie soil. Therefore, our objective was to assess the natural abundance of plant and soil 15N isotopes as a cumulative index of potential change in efflux or influx of N into and out of the tallgrass prairie after 8-y of exposure to elevated CO2. Aboveground plant delta 15N values of Andropogon gerardii were close to zero and more positive as a result of elevated CO2, but whole-soil values at the 5\–30 cm depth were significantly reduced (6.8 vs 7.3; P\<0.05) under elevated CO2-chamber (EC) relative to ambient CO2- chamber (AC). Total, aboveground plant biomass, root-in-growth, extractable N, microbial biomass N, and soil pools collectively exhibited a range of delta 15N values from \−2.8 to 7.3. Measurements of surface soil 15N indicate that a change in N inputs and outputs has occurred as a result of elevated atmospheric CO2. In addition to possible changes in denitrification and N2 fixation, other sources of N such as the re-translocation of N to the surface from deeper soil layers are needed to explain how soil N accrues in surface soils as a consequence of elevated CO2. Our results support the notion that C accrual may promote N accrual, possibly driven by high plant and microbial N demand amplified by soil N limitation.

}, keywords = {LTER-KNZ}, doi = {10.1016/j.soilbio.2005.06.009}, author = {Williams, M.A. and C. W. Rice and Owensby, C.E.} } @article {KNZ00879, title = {Grazing management effects on plant species diversity in tallgrass prairie}, journal = {Journal of Range Management}, volume = {57}, year = {2004}, pages = {58 -65}, abstract = {A 6-year study was conducted in tallgrass prairie to assess the effects of grazing management (cattle stocking densities and grazing systems) on plant community composition and diversity. Treatments included sites grazed season-long (May to October) at 3 stocking densities (3.8, 2.8, and 1.8 hectares per animal unit), ungrazed control sites, and sites under a late-season rest rotation grazing system at this same range of stocking densities. Plant communities were sampled twice each season using a nearest-point procedure. Native plant species diversity, species richness, and growth form diversity were significantly higher in grazed compared to ungrazed prairie, and diversity was greatest at the highest stocking density. This enhancement of plant species diversity under grazing was not a result of increased frequency of weedy/exotic species. There were no significant effects of grazing system on plant diversity, nor any significant stocking density {\texttimes} grazing system interactions, indicating that animal density is a key management variable influencing plant species diversity and composition in tallgrass prairie and that effects of animal density override effects of grazing systems. Increasing cattle stocking densities decreased the abundance of the dominant perennial tall grasses, and increased abundance of the C4 perennial mid-grasses. The frequency of perennial forbs was relatively stable across grazing treatments. Abundance of annual forbs varied among years and grazing treatments. In half of the years sampled, annual forbs showed the highest frequency under intermediate stocking density. Patterns of responses among plant groups suggest that some species may respond principally to direct effects of grazers and others may respond to indirect effects of grazers on competitive relationships or on the spatial patterns of fuel loads and fires. Thus, this study suggests that large grazer densities, fire, and annual climatic variability interact to influence patterns of plant community composition and diversity in tallgrass prairie. Effects of varying management such as stocking densities and grazing systems on plant species diversity and the relative abundances of different plant growth forms or functional groups may have important consequences for grassland community stability and ecosystem function.}, keywords = {LTER-KNZ, Biodiversity, cattle grazing, Flint Hills, grazing systems, plant ecology, range management, stocking rates}, doi = {10.2111/1551-5028(2004)057[0058:GMEOPS]2.0.CO;2}, author = {Hickman, K.R. and D.C. Hartnett and Cochran, R.C. and Owensby, C.E.} } @article {KNZ00796, title = {Nitrogen competition in a tallgrass prairie ecosystem exposed to elevated carbon dioxide}, journal = {Soil Science Society of America Journal}, volume = {65}, year = {2001}, pages = {340 -346}, abstract = {Because N is a limiting nutrient in tallgrass prairie and most ecosystems, changes in N availability or N cycling could control the long-term response of ecosystems to elevated atmospheric CO2 If more C is sequestered into the soil, then greater microbial demand for N could decrease plant-available soil N. Alterations in N dynamics such as plant uptake, N fixation, nutrient cycling, microbial utilization, and partitioning of N into plant and soil fractions ultimately could affect the capability of ecosystems to sequester C. Our objective was to determine if competition for N between plants and microorganisms changes after 8 yr of elevated CO2 relative to ambient conditions. Treatments (three replications, randomized complete block design) were ambient CO2{\textendash}no chamber (NC), ambient CO2{\textendash}chamber (AC), and 2 {\texttimes} ambient CO2{\textendash}chamber (EC). Several short laboratory incubations assessed whether turnover rates of N in soil would be altered under elevated CO2 Gross transformations of N were not altered significantly under elevated CO2 compared with ambient conditions. To examine plant{\textendash}microbial competition and altered allocation patterns of N under elevated CO2, 15NH4{\textendash}N was added to 25-cm-diam. polyvinyl chloride (PVC) cores (15-cm depth) in the field, which were destructively sampled after ≈5 mo. Microbial biomass contained ≈75\% of the total 15N that occurred in the soil organic matter (SOM) and, thus, appeared to be a significant regulator of plant-available N. The SOM under elevated CO2 contained significantly more (>27\%) 15N compared with ambient CO2 conditions. Though a chamber effect was apparent, greater 15N in the SOM pool and greater percentage 15N SOM/percentage 15N plant suggest greater microbial demand for N under elevated CO2}, keywords = {LTER-KNZ, tallgrass prairie}, doi = {10.2136/sssaj2001.652340x}, author = {Williams, M.A. and C. W. Rice and Owensby, C.E.} } @article {KNZ00752, title = {Carbon dynamics and microbial activity in tallgrass prairie exposed to elevated CO2 for 8 years}, journal = {Plant and Soil}, volume = {227}, year = {2000}, pages = {127 -137}, abstract = {Alterations in microbial mineralization and nutrient cycling may control the long-term response of ecosystems to elevated CO2. Because micro-organisms constitute a labile fraction of potentially available N and are regulators of decomposition, an understanding of microbial activity and microbial biomass is crucial. Tallgrass prairie was exposed to twice ambient CO2 for 8 years beginning in 1989. Starting in 1991 and ending in 1996, soil samples from 0 to 5 and 5 to 15 cm depths were taken for measurement of microbial biomass C and N, total C and N, microbial activity, inorganic N and soil water content. Because of increased water-use-efficiency by plants, soil water content was consistently and significantly greater in elevated CO2 compared to ambient treatments. Soil microbial biomass C and N tended to be greater under elevated CO2 than ambient CO2 in the 5{\textendash}15 cm depth during most years, and in the month of October, when analyzed over the entire study period. Microbial activity was significantly greater at both depths in elevated CO2 than ambient conditions for most years. During dry periods, the greater water content of the surface 5 cm soil in the elevated CO2 treatments increased microbial activity relative to the ambient CO2 conditions. The increase in microbial activity under elevated CO2 in the 5{\textendash}15 cm layer was not correlated with differences in soil water contents, but may have been related to increases in soil C inputs from enhanced root growth and possibly greater root exudation. Total soil C and N in the surface 15 cm were, after 8 years, significantly greater under elevated CO2 than ambient CO2. Our results suggest that decomposition is enhanced under elevated CO2 compared with ambient CO2, but that inputs of C are greater than the decomposition rates. Soil C sequestration in tallgrass prairie and other drought-prone grassland systems is, therefore, considered plausible as atmospheric CO2 increases.}, keywords = {LTER-KNZ, elevated CO2, microbial activity, Microbial biomass, Soil C and N, soil water}, doi = {10.1023/A:1026590001307}, author = {Williams, M.A. and C. W. Rice and Owensby, C.E.} } @inbook {KNZ00746, title = {Effects of fire and grazing on soil carbon in rangelands}, booktitle = {The Potential of U.S. Grazing Lands to Sequester Carbon and Mitigate the Greenhouse Effect}, year = {2000}, pages = {323 -342}, publisher = {Lewis Publishers}, organization = {Lewis Publishers}, address = {Boca Raton, FL}, keywords = {LTER-KNZ, fire}, author = {C. W. Rice and Owensby, C.E.}, editor = {Follet, R. and Kimble, J.M. and Lal, R.} } @article {KNZ00722, title = {Predictive models for grazing distribution: a GIS approach}, journal = {Journal of Range Management}, volume = {53}, year = {2000}, pages = {39 -46}, abstract = {Grazing distribution and forage use patterns are important influences on rangeland ecosystems. Spatial patterns of grazing by domestic cattle (Bos taurus) were observed over 2 consecutive years under 2 grazing systems, intensive-early stocking and season-long stocking. The purposes were to determine factors influencing observed patterns and develop predictive models for grazing distribution and forage removal. Field-collected data on grazing distribution were linked with associated geophysical properties of pastures utilizing a GIS. Separate models were developed to predict grazing distribution and forage utilization using a backward stepwise regression procedure. The forage utilization model was linked with grazing distribution by utilizing Tobit analysis. Nineteen independent variables were used to interpret the observed variation in grazing distribution. Comparison of predicted probability of grazing values from the model with the observed grazing distribution in a hold-out data set yielded a close fit (R=.99). Eighteen independent variables were included in the forage removal model. Comparison of predicted forage removal with observed values in a hold-out data set yielded a poor fit (R=.28). Lack of forage quality variables probably accounts for the poor performance of the forage removal model. Differences in the success of the 2 models support the hypothesis that grazing distribution and forage utilization operate at different spatial scales and parameters. The use of GIS holds promise as a technique for developing useful predictive models for range management.}, keywords = {LTER-KNZ}, doi = {10.2307/4003390}, author = {B. Brock and Owensby, C.E.} } @article {KNZ00705, title = {Biomass production and species composition change in a tallgrass prairie ecosystem after long-term exposure to elevated atmospheric CO2}, journal = {Global Change Biology}, volume = {5}, year = {1999}, pages = {497 -506}, abstract = {To determine the long-term impact of elevated CO2 on primary production of native tallgrass prairie, we compared the responses of tallgrass prairie at ambient and twice-ambient atmospheric CO2 levels over an 8-year period. Plots in open-top chambers (4.5 m diameter) were exposed continuously (24 h) to ambient and elevated CO2 from early April to late October each year. Unchambered plots were monitored also. Above-ground peak biomass was determined by clipping each year in early August, and root growth was estimated by harvesting roots from root ingrowth bags. Plant community composition was censused each year in early June. In the last 2 years of the study, subplots were clipped on 1 June or 1 July, and regrowth was harvested on 1 October. Volumetric soil water content of the 0{\textendash}100 cm soil layer was determined using neutron scattering, and was generally higher in elevated CO2 plots than ambient. Peak above-ground biomass was greater on elevated CO2 plots than ambient CO2 plots with or without chambers during years with significant plant water stress. Above-ground regrowth biomass was greater under elevated CO2 than under ambient CO2 in a year with late-season water stress, but did not differ in a wetter year. Root ingrowth biomass was also greater in elevated CO2 plots than ambient CO2 plots when water stress occurred during the growing season. The basal cover and relative amount of warm-season perennial grasses (C4) in the stand changed little during the 8-year period, but basal cover and relative amount of cool-season perennial grasses (C3) in the stand declined in the elevated CO2 plots and in ambient CO2 plots with chambers. Forbs (C3) and members of the Cyperaceae (C3) increased in basal cover and relative amount in the stand at elevated compared to ambient CO2. Greater biomass production under elevated CO2 in C4-dominated grasslands may lead to a greater carbon sequestration by those ecosystems and reduce peak atmospheric CO2 concentrations in the future.}, keywords = {LTER-KNZ, tallgrass prairie}, doi = {10.1046/j.1365-2486.1999.00245.x}, author = {Owensby, C.E. and J.M. Ham and Alan K. Knapp and Auen, L.M.} } @article {KNZ00696, title = {Elevated CO2 and leaf longevity in the C4 grassland dominant Andropogon gerardii}, journal = {International Journal of Plant Sciences}, volume = {160}, year = {1999}, pages = {1057 -1061}, abstract = {In central U.S. grasslands, plant and ecosystem responses to elevated CO2 are most pronounced when water availability is limited. In a northeast Kansas grassland, responses to elevated CO2 in leaf area, number, development, and longevity were quantified for the tallgrass prairie dominant, Andropogon gerardii. Plants were grown in open-top chambers (OTCs) modified to limit water availability and to maximize responses to elevated CO2. In OTCs with elevated ({\texttimes}2 ambient) levels of CO2, aboveground biomass production and leaf water potentials were increased significantly compared with those of plants in OTCs with ambient CO2. There were no differences in leaf area or leaf number per tiller in A. gerardii in elevated compared with ambient OTCs. However, leaf area in adjacent unchambered plots with greater water availability was significantly higher than in the OTCs. The time required for developing leaves to achieve maximum leaf area was reduced by 29\%, and the period of time until leaves senesced was increased by 20\% for plants exposed to elevated compared with ambient CO2. Thus, leaves of this C4 grass species expanded more rapidly (6 d) and remained green longer (9 d) when exposed to elevated CO2. Such CO2-mediated increases in leaf longevity in the dominant species may allow this grassland to respond more opportunistically to temporally variable rainfall patterns in high-CO2 environments. These responses should be included in leaf-based simulation models that attempt to mechanistically link physiological alterations to predicted canopy responses to increased CO2.}, keywords = {LTER-KNZ, Ecophysiology, elevated carbon dioxide, grassland, leaf lifespan, tallgrass prairie, Water relations}, doi = {10.1086/314202}, author = {Alan K. Knapp and Bargman, N. and Maragni, L.A. and McAllister, C.A. and D. Bremer and J.M. Ham and Owensby, C.E.} } @inbook {KNZ00665, title = {Climate change, elevated CO2 and predictive modeling: Past and future climate change scenarios for the tallgrass prairie}, booktitle = {Grassland Dynamics: Long-Term Ecological Research in Tallgrass Prairie}, year = {1998}, pages = {283 -300}, publisher = {Oxford University Press}, organization = {Oxford University Press}, address = {New York}, keywords = {LTER-KNZ, tallgrass prairie}, url = {http://www.colostate.edu/Depts/GDPE/Distinguished_Ecologists/2005/Hayden/grassland\%20dynamics\%20ch16.pdf}, author = {Seastedt, T.R. and Hayden, B.P. and Owensby, C.E. and Alan K. Knapp}, editor = {Alan K. Knapp and J. M. Briggs and D.C. Hartnett and Scott. L. Collins} } @article {KNZ00621, title = {Responses of soil respiration to clipping and grazing in a tallgrass prairie}, journal = {Journal of Environmental Quality}, volume = {27}, year = {1998}, pages = {1539 -1548}, abstract = {Soil-surface CO2 flux (Fs) is an important component in prairie C budgets. Although grazing is common in grasslands, its effects on Fs have not been well documented. Three clipping treatments: (i) early-season clipping (EC); (ii) full-season clipping (FC); and (iii) no clipping (NC); which represented two grazing strategies and a control, were applied to plots in a tallgrass prairie in northeastern Kansas, USA. Measurements of Fs were made with a portable gas-exchange system at weekly to monthly intervals for 1 yr. Concurrent measurements of soil temperature and volumetric soil water content at 0.1 m were obtained with dual-probe heat-capacity sensors. Measurements of Fs also were obtained in grazed pastures. Fs ranged annually from 8.8 {\texttimes} 10-3 mg m-2 S-1 during the winter to 0.51 mg m-2 s-1 during the summer, following the patterns of soil temperature and canopy growth and phenology. Clipping typically reduced Fs 21 to 49\% by the second day after clipping despite higher soil temperatures in clipped plots. Cumulative annual Fs were 4.94, 4.04, and 4.11 kg m-2 yr-1 in NC, EC, and FC treatments, respectively; thus, dipping reduced annual Fs by 17.5\%. Differences in Fs between EC and FC were minimal, suggesting that different grazing strategies had little additional impact on annual Fs. Daily Fs in grazed pastures was 20 to 37\% less than Fs in ungrazed pastures. Results suggest that grazing moderates Fs during the growing season by reducing canopy photosynthesis and slowing translocation of carbon to the rhizosphere.}, keywords = {LTER-KNZ, tallgrass prairie}, doi = {10.2134/jeq1998.00472425002700060034x}, author = {D. Bremer and J.M. Ham and Owensby, C.E. and Alan K. Knapp} } @article {KNZ00590, title = {Photosynthetic gas exchange and water relations responses of three tallgrass prairie species to elevated carbon dioxide and moderate drought}, journal = {International Journal of Plant Science}, volume = {158}, year = {1997}, pages = {608 -616}, abstract = {Undisturbed tallgrass prairie was exposed to ambient and elevated (twice-ambient) levels of atmospheric CO2 and experimental dry periods. Seasonal and diurnal midday leaf water potential (Ψ leaf), net photosynthesis $(A_{\text{net}})$, and stomatal conductance (g s) responses of three tallgrass prairie growth forms{\textemdash}a C4 grass, Andropogon gerardii; a broad-leaved woody C3 shrub, Symphiocarpos orbiculatus; and a C3 perennial forb, Salvia pitcheri{\textemdash}were assessed. $\Psi _{\text{leaf}}$ in A. gerardii and S. orbiculatus was higher under elevated CO2, regardless of soil moisture, while $\Psi _{\text{leaf}}$ in S. pitcheri responded only to drought. Elevated CO2 always stimulated $A_{\text{net}}$ in the C3 species, while A. gerardii $A_{\text{net}}$ increased only under dry conditions. However, $A_{\text{net}}$ under elevated CO2 in the C3 species declined with drought but not in the C4 grass. Under wet conditions, g s reduced in elevated CO2 for all species. During dry periods, gs at elevated CO2 was sometimes higher than in ambient CO2. Our results support claims that elevated CO2 will stimulate tallgrass prairie productivity during dry periods and possibly reduce temporal and spatial variability in productivity in these grasslands.}, keywords = {LTER-KNZ, Water relations}, url = {http://www.jstor.org/stable/2474921}, author = {Hamerlynck, E.P. and McAllister, C.A. and Alan K. Knapp and J.M. Ham and Owensby, C.E.} } @article {KNZ00608, title = {Water vapor fluxes and their impact under elevated CO2 in a C4 tallgrass prairie}, journal = {Global Change Biology}, volume = {3}, year = {1997}, pages = {189 -195}, abstract = {We measured leaf-level stomatal conductance, xylem pressure potential, and stomate number and size as well as whole plant sap flow and canopy-level water vapour fluxes in a C4-tallgrass prairie in Kansas exposed to ambient and elevated CO2. Stomatal conductance was reduced by as much as 50\% under elevated CO2 compared to ambient. In addition, there was a reduction in stomate number of the C4 grass, Andropogon gerardii Vitman, and the C3 dicot herb, Salvia pitcheri Torr., under elevated CO2 compared to ambient. The result was an improved water status for plants exposed to elevated CO2 which was reflected by a less negative xylem pressure potential compared to plants exposed to ambient CO2. Sap flow rates were 20 to 30\% lower for plants exposed to elevated CO2 than for those exposed to ambient CO2. At the canopy level, evapotranspiration was reduced by 22\% under elevated CO2. The reduced water use by the plant canopy under elevated CO2 extended the photosynthetically-active period when water became limiting in the ecosystem. The result was an increased above- and belowground biomass production in years when water stress was frequent.}, keywords = {LTER-KNZ, tallgrass prairie}, doi = {10.1046/j.1365-2486.1997.00084.x}, author = {Owensby, C.E. and J.M. Ham and Alan K. Knapp and D. Bremer and Auen, L.M.} } @inbook {KNZ00564, title = {Ecosystem level responses of tallgrass prairie to elevated CO2}, booktitle = {Carbon Dioxide and Terrestrial Ecosystems}, year = {1996}, pages = {147 -162}, publisher = {Academic Press}, organization = {Academic Press}, address = {London}, keywords = {LTER-KNZ, tallgrass prairie}, author = {Owensby, C.E. and J.M. Ham and Alan K. Knapp and C. W. Rice and Coyne, P.I. and Auen, L.M.}, editor = {Koch, G.W and Mooney, H.A.} } @article {KNZ00556, title = {Responses in stomatal conductance to elevated CO2 in 12 grassland species that differ in growth form}, journal = {Vegetatio}, volume = {125}, year = {1996}, pages = {31 -41}, abstract = {Responses in stomatal conductance (g st ) and leaf xylem pressure potential (ψ leaf ) to elevated CO2 (2x ambient) were compared among 12 tallgrass prairie species that differed in growth form and growth rate. Open-top chambers (OTCs, 4.5 m diameter, 4.0 m in height) were used to expose plants to ambient and elevated CO2 concentrations from April through November in undisturbed tallgrass prairie in NE Kansas (USA). In June and August, ψ leaf was usually higher in all species at elevated CO2 and was lowest in adjacent field plots (without OTCs). During June, when water availability was high, elevated CO2 resulted in decreased g st in 10 of the 12 species measured. Greatest decreases in g st (ca. 50\%) occurred in growth forms with the highest potential growth rates (C3 and C4 grasses, and C3 ruderals). In contrast, no significant decrease in g st was measured in the two C3 shrubs. During a dry period in September, reductions in g st at elevated CO2 were measured in only two species (a C3 ruderal and a C4 grass) whereas increased g st at elevated CO2 was measured in the shrubs and a C3 forb. These increases in g st were attributed to enhanced ψ leaf in the elevated CO2 plants resulting from increased soil water availability and/or greater root biomass. During a wet period in September, only reductions in g st were measured in response to elevated CO2. Thus, there was significant interspecific variability in stomatal responses to CO2 that may be related to growth form or growth rate and plant water relations. The effect of growth in the OTCs, relative to field plants, was usually positive for g st and was greatest (>30\%) when water availability was low, but only 6{\textendash}12\% when ψ leaf was high. The results of this study confirm the importance of considering interactions between indirect effects of high CO2 of plant water relations and direct effects of elevated CO2 on g st , particularly in ecosystems such as grasslands where water availability often limits productivity. A product of this interaction is that the potential exists for either positive or negative responses in g st to be measured at elevated levels of CO2.}, keywords = {LTER-KNZ, elevated CO2, Growth form, Stomatal Conductance, tallgrass prairie, Water relations}, doi = {10.1007/BF00045202}, author = {Alan K. Knapp and Hamerlynck, E.P. and J.M. Ham and Owensby, C.E.} } @article {KNZ00455, title = {Effect of elevated C02 on stomatal density and distribution in a C4 grass and a C3 forb under field conditions}, journal = {Annals of Botany}, volume = {74}, year = {1994}, pages = {595 -599}, abstract = {Two common tallgrass prairie species, Andropogon gerardii, the dominant C4 grass in this North American grassland, and Salvia pitcheri, a C3 forb, were exposed to ambient and elevated (twice ambient) CO2 within open-top chambers throughout the 1993 growing season. After full canopy development, stomatal density on abaxial and adaxial surfaces, guard cell length and specific leaf mass (SLM; mg cm-2) were determined for plants in the chambers as well as in adjacent unchambered plots. Record high rainfall amounts during the 1993 growing season minimized water stress in these plants (leaf xylem pressure potential was usually > -1{\textperiodcentered}5 MPa in A. gerardii) and also minimized differences in water status among treatments. In A. gerardii, stomatal density was significantly higher (190 {\textpm} 7 mm-2; mean {\textpm} s.e.) in plants grown outside of the chambers compared to plants that developed inside the ambient CO2 chambers (161 {\textpm} 5 mm-2). Thus, there was a significant {\textquoteright}chamber effect{\textquoteright} on stomatal density. At elevated levels of CO2, stomatal density was even lower (P < 0{\textperiodcentered}05; 121 {\textpm} 5 mm-2). Most stomata were on abaxial leaf surfaces in this grass, but the ratio of adaxial to abaxial stomatal density was greater at elevated levels of CO2. In S. pitcheri, stomatal density was also significantly lower when plants were grown in the open-top chambers (235 {\textpm} 10 mm-2 outside vs. 140 {\textpm} 6 mm-2 in the ambient CO2 chamber). However, stomatal density was greater at elevated CO2 (218 {\textpm} 12 mm-2) compared to plants from the ambient CO2 chamber. The ratio of stomata on adaxial vs. abaxial surfaces did not vary significantly in this herb. Guard cell lengths were not significantly affected by growth in the chambers or by elevated CO2 for either species. Growth within the chambers resulted in lower SLM in S. pitcheri, but CO2 concentration had no effect. In A. gerardii, SLM was lower at elevated CO2. These results indicate that stomatal and leaf responses to elevated CO2 are species specific, and reinforce the need to assess chamber effects along with treatment effects (CO2) when using open-top chambers.}, keywords = {LTER-KNZ, Andropogon gerardii, elevated CO2, Salvia pitcheri, stomatal density, tallgrass prairie}, doi = {10.1006/anbo.1994.1159}, author = {Alan K. Knapp and Cocke, M. and Hamerlynck, E.P. and Owensby, C.E.} } @article {KNZ00454, title = {Elevated CO2 alters dynamic stomatal responses to sunlight in a C4 grass}, journal = {Plant Cell and Environment}, volume = {17}, year = {1994}, pages = {189 -195}, abstract = {Native tallgrass prairie in NE Kansas was exposed to elevated (twice ambient) or ambient atmospheric CO2 levels in open-top chambers. Within chambers or in adjacent unchambered plots, the dominant C4 grass, Andropogon gerardii, was subjected to fluctuations in sunlight similar to that produced by clouds or within canopy shading (full sun > 1500 μmol m-2 s-1 versus 350 μmol m-2 s-1 shade) and responses in gas exchange were measured. These field experiments demonstrated that stomatal conductance in A. gerardii achieved new steady state levels more rapidly after abrupt changes in sunlight at elevated CO2 when compared to plants at ambient CO2. This was due primarily to the 50\% reduction in stomatal conductance at elevated CO2, but was also a result of more rapid stomatal responses. Time constants describing stomatal responses were significantly reduced (29{\textendash}33\%) at elevated CO2. As a result, water loss was decreased by as much as 57\% (6.5\% due to more rapid stomatal responses). Concurrent increases in leaf xylem pressure potential during periods of sunlight variability provided additional evidence that more rapid stomatal responses at elevated CO2 enhanced plant water status. CO2-induced alterations in the kinetics of stomatal responses to variable sunlight will likely enhance direct effects of elevated CO2 on plant water relations in all ecosystems.}, keywords = {LTER-KNZ}, doi = {10.1111/j.1365-3040.1994.tb00282.x}, author = {Alan K. Knapp and Fahnestock, J.T. and Owensby, C.E.} } @article {KNZ00464, title = {Long and short-term effects of fire on nitrogen cycling in tallgrass prairie}, journal = {Biogeochemistry}, volume = {24}, year = {1994}, pages = {67 -84}, abstract = {Fires in the tallgrass prairie are frequent and significantly alter nutrient cycling processes. We evaluated the short-term changes in plant production and microbial activity due to fire and the long-term consequences of annual burning on soil organic matter (SOM), plant production, and nutrient cycling using a combination of field, laboratory, and modeling studies. In the short-term, fire in the tallgrass prairie enhances microbial activity, increases both above-and belowground plant production, and increases nitrogen use efficiency (NUE). However, repeated annual burning results in greater inputs of lower quality plant residues causing a significant reduction in soil organic N, lower microbial biomass, lower N availability, and higher C:N ratios in SOM. Changes in amount and quality of below-ground inputs increased N immobilization and resulted in no net increases in N availability with burning. This response occurred rapidly (e.g., within two years) and persisted during 50 years of annual burning. Plant production at a long-term burned site was not adversely affected due to shifts in plant NUE and carbon allocation. Modeling results indicate that the tallgrass ecosystem responds to the combined changes in plant resource allocation and NUE. No single factor dominates the impact of fire on tallgrass plant production.}, keywords = {LTER-KNZ, carbon, fire, immobilization, Mineralization, Nitrogen use efficiency, soil organic matter, tallgrass prairie}, doi = {10.1007/BF02390180}, author = {Ojima, D.S. and Schimel, D.S. and Parton, W.J. and Owensby, C.E.} } @article {KNZ00438, title = {Mathematical simulation of C4 grass photosynthesis in ambient and elevated C02}, journal = {Ecological Modelling}, volume = {73}, year = {1994}, pages = {63 -80}, abstract = {A mechanistic leaf photosynthesis model was developed for C4 grasses based on a general simplified scheme of C4 plant carbon metabolism. In the model, the PEPcase-dependent C4-cycle was described in terms of CO2 concentration in the mesophyll space using Michaelis-Menten kinetics, and the activity of PEPcase was related to the incident PAR to take account of the influence of light on the activity of C4-cycle processes. The CO2 refixation by Rubisco in the bundle sheath was described using a widely accepted C3 photosynthesis model. The model assumes a steady state balance among CO2 diffusion from surrounding atmosphere into the mesophyll space, CO2 transport into the bundle sheath by the C4-cycle, CO2 refixation by the C3-cycle in the bundle sheath, and CO2 leakage from the bundle sheath. The response to temperature of photosynthesis was incorporated via the temperature dependence of model parameters. The photosynthesis model was coupled with a stomatal conductance model in order to predict leaf photosynthesis rates at different atmospheric conditions. The empirical model of Ball et al. (1987) was adopted and slightly modified to describe responses in stomatal conductance. The coupled model was parameterized for the C4 grass Andropogon gerardii grown in both ambient (350 ppm) and elevated (700 ppm) CO2 atmospheres. The key parameters of the model were estimated by fitting the model to the measured data using non-linear regression. The model was validated by comparison the predicted photosynthetic response to PAR in both CO2-pretreatments with the measured data from an independent gas exchange experiment. The predicted photosynthesis and stomatal conductance matched the measured data quite well for both atmospheric CO2-pretreatments. At 25{\textdegree}C, the estimated maximum carboxylation rate of Rubisco Vcm,25, potential electron transport rate Jm,25 and quantum efficiency α were increased by CO2 enrichment. The maximum PEPcase activity Vpm,25 was lower in elevated CO2. The model predicted that the light-saturated leaf photosynthesis will increase by about 10\% with the rising of atmospheric CO2 from 350 to 700 ppm at 30{\textdegree}C, and that the optimal temperature of photosynthesis will shift from 37 to 38.5{\textdegree}C. The estimated slope of the stomatal conductance model was increased by atmospheric CO2 enrichment. Stomatal conductance was significantly reduced by increasing atmospheric CO2 concentration.}, keywords = {LTER-KNZ, Andropogon gerardii, C4 grass, CO2 enrichment, photosynthesis, Stomatal Conductance}, doi = {10.1016/0304-3800(94)90098-1}, author = {Chen, D.X. and Coughenour, M.B. and Alan K. Knapp and Owensby, C.E.} } @article {KNZ00417, title = {Biomass production in a tallgrass prairie ecosystem exposed to ambient and elevated CO2}, journal = {Ecological Applications}, volume = {3}, year = {1993}, pages = {644 -653}, keywords = {LTER-KNZ, Aboveground biomass, Andropogon gerardii, Carbon dioxide, elevated CO2, kansas, Poa pratensis, Root biomass, tallgrass prairie, water-use efficiency, xylem pressure potential}, doi = {10.2307/1942097}, author = {Owensby, C.E. and Coyne, P.I. and Ham, J.M. and Auen, L.M. and Alan K. Knapp} } @article {KNZ00282, title = {The influence of mycorrhizae on big bluestem rhizome regrowth and clipping tolerance}, journal = {Journal of Range Management}, volume = {43}, year = {1990}, pages = {286 -290}, abstract = {

Mycorrhizal symbiosis is critical to growth of many warm-season prairie grass seedlings, but its effect on regrowth of rhizomes has not been determined. As forage species, the effect of grazing on the symbiosis is also important. When the impact of mycorrhizae on regrowth of Andropogon gerardii Vit. rhizomes was assessed, A. gerardii rhizomes collected from the field and grown with mycorrhizal inoculum produced larger plants than rhizomes grown in the absence of the symbiont. The effect of the symbiosis on clipping (simulated grazing) tolerance was quantified by growing A. gerardii in steamed or nonsterile prairie soil, with or without mycorrhizal fungus inoculation. Plants were cliped and a portion of the plants harvested at 6, 12, 18, 24, and 30 weeks after planting. As an additional control, Benomyl fungicide was applied to plants to inhibit the symbiosis. Mycorrhizal clipped plants were larger than nonmycorrhizal clipped plants, but the difference diminished with successive clippings. Mycorrhizal root colonization also decreased in response to repeated clipping. Maximum shoot and root biomass of mycorrhizal plants was produced at 12 and 18 weeks, respectively. Fungicide-treated plants did not grow appreciably after the first clipping. Thus, mycorrhizae improved clipping tolerance, but with repeated intensive clipping, significant changes in root/shoot ratio occurred and eventually mycorrhizal root colonization and growth benefit were lost. Key words: grazing, vesicular-arbuscular mycorrhizae, big bluestem, herbage yield

}, keywords = {LTER-KNZ}, doi = {10.2307/3898918}, author = {Hetrick, B.A.D. and G.T. Wilson and Owensby, C.E.} } @article {KNZ00276, title = {Net carbon dioxide exchange in canopies of burned and unburned tallgrass prairie}, journal = {Theoretical and Applied Climatology}, volume = {42}, year = {1990}, pages = {237 -244}, abstract = {

Net carbon dioxide exchange (NCE) rates were measured in a tallgrass prairie, a grassland with high productivity, to determine photosynthetic rates of the canopy. Canopy measurements were made in large, plexiglass chambers (1.21 m long; 0.91 m wide; 1.40 m tall) placed on burned and unburned areas of the prairie. The NCE rates of the canopy were compared with those of individual leaves of Andropogon gerardii Vitman (big bluestem). In addition, CO2 flux from the soil was quantified and compared with net photosynthetic flux. The canopy NCE rates were generally lower than those made on individual leaves. In mid-summer (11 July 1987), the maximum canopy NCE rates were 55\% and 64\% of those measured on individual leaves in burned and unburned treatments, respectively. Canopy NCE rates were lower than individual-leaf NCE rates for two reasons. First, the individual-leaf measurements were made on young, unshaded, healthy leaves, while the canopy measurements were made on all types of leaves including senescing, shaded, and damaged leaves. Second, soil CO2 flux into the chambers lowered NCE values. The CO2 flux from the soil ranged from 7.2\% to 28.4\% of the total NCE. One needs to add soil CO2 flux rates to the measured canopy NCE rates to obtain canopy NCE rates closer to individual-leaf NCE rates. Soil CO2 flux decreased when conditions became dry, reaching a low of 0.06mg CO2m-2s-1, but increased after rain to 0.16mg CO2m-2s-1. Also, after rain, when plants were well watered, they were not light saturated at 1900{\ae}Em-2s-1. The NCE rates on the burned treatment were either higher or similar to those on the unburned treatment. For example, on 11 July 1987, NCE rates were higher on the burned treatment (0.66 mg CO2m-2s-1) compared to the unburned treatment (0.47 mg CO2m-2s-1). During the rest of July and August, the rates of the two treatments were not significantly different. but in September and October, the NCE rates were again higher on the burned treatment compared to the unburned treatment. The results indicated that canopy NCE rates may be more indicative of the productivity of the prairie than individual-leaf measurements made only on young, highly productive leaves

}, keywords = {LTER-KNZ, tallgrass prairie}, doi = {10.1007/BF00865984}, author = {Gale, W.J. and Kirkham, M.B. and Kanemasu, E.T. and Owensby, C.E.} } @article {KNZ00234, title = {Influence of mycorrhizal fungi and fertilization on big bluestem seedling biomass}, journal = {Journal of Range Management}, volume = {42}, year = {1989}, pages = {213 -216}, abstract = {

The relationship between fertilization of prairie soils and mycorrhizal symbiosis in big bluestem (Andropogon gerardii Vit.) was explored. In 10 steamed prairie soils of varied P level, inoculation with a mycorrhizal fungus resulted in a 7- to 70-fold increase in big bluestem seedling biomass, compared to noninoculated controls. Fertilization with N and K (25-0-25) significantly increased biomass of mycorrhizal seedlings but did not alter growth of nonmycorrhizal seedlings. In a second experiment which assessed the impact of N and P on seedling growth, in both steamed and nonsterile soil, P fertilization did not significantly increase plant biomass, while N fertilization did substantially increase biomass of mycorrhizal, but not nonmycorrhizal plants. Fertilization with N and P together produced the greatest biomass in both mycorrhizal and nonmycorrhizal plants. Apparently, in the range soils tested N is the most limiting nutrient, despite the low P availability exhibited by these soils. In the absence of mycorrhizae, however, P is most limiting and no response to N is observed unless sufficient P is also applied. These studies confirm an extremely important role for mycorrhizal fungi on big bluestem seedling growth. Key words: phosphorous, nitrogen, Glomus etunicatum, mycorrhizae, Andropogon gerardii

}, keywords = {LTER-KNZ}, doi = {10.2307/3899475}, author = {Hetrick, B.A.D. and G.T. Wilson and Owensby, C.E.} } @article {KNZ00169, title = {Effects of dormant-season herbage removal on Flint Hills rangeland}, journal = {Journal of Range Management}, volume = {41}, year = {1988}, pages = {481 -482}, abstract = {

Intensive-early stocking in the Kansas Flint Hills has greatly increased livestock production efficiency. The potential grazing of regrowth on intensive-early stocked Flint Hills pastures was studied by monthly mowing to 5-cm height form October to April, 1983-1985. Those treatments had no effect on total nonstructural carbohydrates (TNC) in Andropogon gerardii Vitman rhizomes or on herbage production the following seasons. Since there was no reduction in herbage yield for any mowing date, cattle producers can apparently restock IES pastures after 1 October. Key Words: total nonstructural carbohydrates, Andropogon gerardii , winter removal, near-infrared reflectance spectroscopy

}, keywords = {LTER-KNZ}, author = {Auen, L.M. and Owensby, C.E.} } @proceedings {KNZ00153, title = {Simulating the long-term impact of burning on C, N, and P cycling in a tallgrass prairie}, year = {1988}, pages = {353 -370}, publisher = {Via Nizza}, address = {Roma, Italy}, abstract = {

A model has been developed to simulate the long-term dynamics of soil organic matter and plant production in response to different management practices. The model simulates the flow of C, N, and P in soil-plant systems and deals primarily with the cycling of nutrients in various soil organic matter pools. The model was used to simulate the long- term effects of different fire frequency and timing of the burning on soil organic matter levels, nutrient cycling and plant production. The model results are compared to nutrient cycling data, soil organic matter data and plant production data from a site in Kansas which was established in 1928 to study the impact of annual burning on a tallgrass prairie. The model results compare very favorably with the observed data and show that maximum production is achieved by annual burning in the late spring (April 20). The annual burning also causes the soil organic matter levels and N mineralization potential to decrease. Burning tends to increase the inorganic P levels at the soil surface, which results in increased N fixation

}, keywords = {LTER-KNZ, tallgrass prairie}, author = {Ojima, D.S. and Parton, W.J. and Schimell, D.S. and Owensby, C.E.}, editor = {Giovannozzi-Sermanni, G. and Nannipieri, P.} }