02769nas a2200253 4500008004100000245011800041210006900159300001300228490000700241520200700248653001902255653001902274653001402293653001502307653001402322653001902336653002202355653002002377653001002397100001802407700002002425700002102445856004902466 2000 eng d00aPatterns and determinants of potential carbon gain in the C3 evergreen Yucca glauca (Liliaceae) in a C4 grassland0 aPatterns and determinants of potential carbon gain in the C3 eve a230 -2360 v873 aYucca glauca is a C3 evergreen rosette species locally common in the C4-dominated grasslands of the central Great Plains. Most congeners of Y. glauca are found in deserts, and Y. glauca’s morphological similarities to desert species (steeply angled leaves, evergreen habit) may be critical to its success in grasslands. We hypothesized that the evergreen habit of Y. glauca, coupled with its ability to remain physiologically active at cool temperatures, would allow this species to gain a substantial portion of its annual carbon budget when the C4 grasses are dormant. Leaf-level gas exchange was measured over an 18-mo period at Konza Prairie in northeast Kansas to assess the annual pattern of potential C gain. Two short-term experiments also were conducted in which nighttime temperatures were manipulated to assess the cold tolerance of this species. The annual pattern of C gain in Y. glauca was bimodal, with a spring productive period (maximum monthly photosynthetic rate = 21.1 ± 1.97 μmol·m−2·s−1) in March through June, a period of midseason photosynthetic depression, and a fall productive period in October (15.6 ± 1.25 μmol·m−2·s−1). The steeply angled leaves resulted in interception of photon flux density at levels above photosynthetic saturation throughout the year. Reduced photosynthetic rates in the summer may have been caused by low soil moisture, but temperature was strongly related (r2 = 0.37) to annual variations in photosynthesis, with nocturnal air temperatures below −5°C in the late fall and early spring, and high air temperatures (>32°C) in the summer, limiting gas exchange. Overall, 31% of the potential annual carbon gain in Y. glauca occurred outside the “frost-free” period (April–October) at Konza Prairie and 43% occurred when the dominant C4 grasses were dormant. Future climates that include warmer minimum temperatures in the spring and fall may enhance the success of Y. glauca relative to the C4 dominants in these grasslands.10aClimate change10acold tolerance10aevergreen10aGrasslands10aLiliaceae10aphotosynthesis10atallgrass prairie10aWater relations10aYucca1 aMaragni, L.A.1 aKnapp, Alan, K.1 aMcAllister, C.A. uhttp://www.amjbot.org/content/87/2/230.short02439nas a2200265 4500008004100000245008500041210006900126300001500195490000800210520160100218653001801819653002801837653001401865653001801879653002201897653002001919100002001939700001601959700001801975700002101993700001502014700001402029700001802043856011202061 1999 eng d00aElevated CO2 and leaf longevity in the C4 grassland dominant Andropogon gerardii0 aElevated CO2 and leaf longevity in the C4 grassland dominant And a1057 -10610 v1603 aIn 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 (×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 CO2.10aEcophysiology10aelevated carbon dioxide10agrassland10aleaf lifespan10atallgrass prairie10aWater relations1 aKnapp, Alan, K.1 aBargman, N.1 aMaragni, L.A.1 aMcAllister, C.A.1 aBremer, D.1 aHam, J.M.1 aOwensby, C.E. uhttp://lter.konza.ksu.edu/content/elevated-co2-and-leaf-longevity-c4-grassland-dominant-andropogon-gerardii01868nas a2200181 4500008004100000245014500041210006900186300001300255490000800268520125600276653002001532100002101552700002101573700002001594700001401614700001801628856004001646 1997 eng d00aPhotosynthetic gas exchange and water relations responses of three tallgrass prairie species to elevated carbon dioxide and moderate drought0 aPhotosynthetic gas exchange and water relations responses of thr a608 -6160 v1583 aUndisturbed 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—a C4 grass, Andropogon gerardii; a broad-leaved woody C3 shrub, Symphiocarpos orbiculatus; and a C3 perennial forb, Salvia pitcheri—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.10aWater relations1 aHamerlynck, E.P.1 aMcAllister, C.A.1 aKnapp, Alan, K.1 aHam, J.M.1 aOwensby, C.E. uhttp://www.jstor.org/stable/247492102906nas a2200217 4500008004100000245010500041210006900146300001100215490000800226520215900234653001702393653001602410653002502426653002202451653002002473100002002493700002102513700001402534700001802548856012202566 1996 eng d00aResponses in stomatal conductance to elevated CO2 in 12 grassland species that differ in growth form0 aResponses in stomatal conductance to elevated CO2 in 12 grasslan a31 -410 v1253 aResponses 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 6–12% 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 CO2.10aelevated CO210aGrowth form10aStomatal Conductance10atallgrass prairie10aWater relations1 aKnapp, Alan, K.1 aHamerlynck, E.P.1 aHam, J.M.1 aOwensby, C.E. uhttp://lter.konza.ksu.edu/content/responses-stomatal-conductance-elevated-co2-12-grassland-species-differ-growth-form00691nas a2200193 4500008004100000245010700041210006900148300001300217653002000230100002000250700002000270700002100290700001900311700001800330700001600348700001800364700001400382856010100396 1994 eng d00aWater relations and biomass responses to irrigation across a topographic gradient in tallgrass prairie0 aWater relations and biomass responses to irrigation across a top a215 -22010aWater relations1 aKnapp, Alan, K.1 aKoelliker, J.K.1 aFahnestock, J.T.1 aBriggs, J., M.1 aWickett, R.G.1 aLewis, P.D.1 aWoodliffe, A.1 aPratt, P. uhttp://images.library.wisc.edu/EcoNatRes/EFacs/NAPC/NAPC13/reference/econatres.napc13.aknapp.pdf02615nas a2200157 4500008004100000245012300041210006900164300001100233490000700244520200800251653002002259100001602279700002002295700001902315856012302334 1993 eng d00aComparative water relations of seedling and adult Quercus species during gallery forest expansion in tallgrass prairie0 aComparative water relations of seedling and adult Quercus specie a29 -410 v563 aSeasonal patterns in xylem pressure potential (ψ) and stomatal conductance to water vapor (g) were compared between seedlings (1–5 years old) invading tallgrass prairie and adult trees of Quercus macrocarpa (Bur oak) and Quercus muehlenbergii (Chinquapin oak) in adjacent gallery forest. Water is often limiting to productivity in the Flint Hills of NE Kansas, thus, we hypothesized that seedlings invading a grassland would have lower ψ and g compared with adult trees, reflecting competitive interactions for water between seedlings and the dominant grasses. We found that ψ was usually lower in adult trees than in older seedlings, but in the very smallest seedlings ψ was significantly reduced compared with mature (greater than 50 years) individuals. Adult and 1- to 2-year-old seedlings had similar g during the season with highest g occurring in older (4- to 5-year-old) seedlings. In general, Q. muehlenbergii had higher ψ and lower g than Q. macrocarpa consistent with reports that Q. muehlenbergii is more drought tolerant. Rapid and extensive root growth characteristic of Quercus seedlings reduced the period of time when seedlings invading prairie must compete with the grasses for water, although water stress may still be an important factor affecting first-year seedlings in this ecosystem. In contrast, strong intraspecific competition for water within mature gallery forests may have reduced ψ and g in forest trees. Thus, the potential for water stress to impact Quercus survival and growth in this drought-prone ecosystem is greatest during establishment and then after forest development is complete. Older seedlings (greater than 4–5 years old), saplings and isolated trees within the prairie may experience the least water stress due to a reduction in both inter- and intraspecific competition for water. These data suggest that in the absence of severe fire or drought occurring during the growing season, gallery forests will continye to expand into tallgrass prairie.10aWater relations1 aBragg, W.K.1 aKnapp, Alan, K.1 aBriggs, J., M. uhttp://lter.konza.ksu.edu/content/comparative-water-relations-seedling-and-adult-quercus-species-during-gallery-forest02518nas a2200145 4500008004100000245010200041210006900143300001300212490000800225520203800233653002002271100002102291700002002312856004002332 1993 eng d00aWater relations and growth of tallgrass prairie forbs in response to selective herbivory by bison0 aWater relations and growth of tallgrass prairie forbs in respons a432 -4400 v1543 aThe indirect effects of selective grass herbivory by bison (Bison bison) on the xylem pressure potentials (ψ) and primary production of ungrazed tallgrass prairie forbs were assessed during the 1990 growing season on the Konza Prairie Research Natural Area (KPRNA) in northeast Kansas. Responses in three forb species, Vernonia baldwinii, Ambrosia psilostachya, and Aster ericoides, were measured in grazed and adjacent ungrazed patches. Seasonal predawn and midday ψ responses in these forbs were also compared with responses in Andropogon gerardii, the dominant grass in tallgrass prairie. Reductions in grass leaf area by herbivory may result in greater availability of soil water to the remaining forbs, if the forbs and grasses utilize similar soil water resources. Overall, selective herbivory of the grasses had an inconsistent effect on leaf ψ in the remaining forbs. When ψ were relatively high during the growing season, no significant differences in water status were detected between A. gerardii and the forbs. However, when ψ were low, predawn and midday ψ were higher in V. baldwinii (as much as 1.0 MPa), and midday ψ were higher in A. psilostachya (0.5 MPa) compared with A. gerardii. In contrast, ψ were not significantly different between A. ericoides and A. gerardii. Grazing by bison substantially increased light availability to ungrazed forbs (> 40%) in grazed relative to ungrazed areas. Compared with ungrazed areas, end-of-season aboveground biomass in grazed patches was 40% greater for individuals of A. psilostachya and 33% and 26% greater for reproductive biomass and floret numbers, respectively, in V. baldwinii. We conclude that the potential benefits of selective grass herbivory on forb water relations may be reduced or offset by other factors such as significant alterations in the microclimate of grazed patches. Nonetheless, increased productivity in grazed patches in two of the three forbs studied indicates that selective consumption of grasses by bison may benefit some forb species.10aWater relations1 aFahnestock, J.T.1 aKnapp, Alan, K. uhttp://www.jstor.org/stable/299566201771nas a2200145 4500008004100000245011100041210006900152300001300221490000700234520120100241653002001442100001701462700002001479856012601499 1993 eng d00aWater relations of Juniperus virginiana and Andropogon gerardii in an unburned tallgrass prairie watershed0 aWater relations of Juniperus virginiana and Andropogon gerardii  a325 -3300 v383 aWe assessed several factors influencing the success of Juniperus virginiana in unburned tallgrass prairie by mapping the distribution of individuals in a 21-ha watershed on the Konza Prairie Research Natural Area in NE Kansas. We also compared the water relations of this tree with those of the dominant grass Andropogon gerardii. No general relationships were detected between the distribution of J. virginiana and plant water status, plant size, soil type, slope, aspect or elevation. Leaf xylem pressure potential (ψ) in upland trees was significantly lower (0.44 MPa) than in lowland trees, but only during the driest portion of the growing season. In contrast, topographic position influenced ψ more strongly in A. gerardii with ψ in upland plants as much as 1.0 MPa lower than in lowland plants. During wetter periods, photosynthetic rates in A. gerardii were higher than in J. virginiana in uplands, but the reverse occurred during the driest period of the growing season. The ability of J. virginiana to maintain higher ψ and higher photosynthetic rates relative to A. gerardii during periods of water limitation may contribute to its success in tallgrass prairie protected from fire.10aWater relations1 aAxmann, B.D.1 aKnapp, Alan, K. uhttp://lter.konza.ksu.edu/content/water-relations-juniperus-virginiana-and-andropogon-gerardii-unburned-tallgrass-prairie02664nas a2200145 4500008004100000245009200041210006900133300001300202490000600215520212300221653002002344100002002364700002102384856011302405 1990 eng d00aInfluence of plant size on the carbon and water relations of Cucurbita foetidissima HBK0 aInfluence of plant size on the carbon and water relations of Cuc a789 -7970 v43 a

Plant size varies by two orders of maginitude within populations of Cucurbita foetidissima HBK. a perennial, prostrate vine of deserts and grasslands in the western USA. Differences in plant size in in this species growing in Kansas (USA) brome grassland were most evident in leaf size (10 times greater in larger vs 13 g in small plants). and taproot mass (c 7000g in large vs 13g in small plants). This study examined the influence of plant size on net photosynthetic CO2 uptake (A), stomatal conductance to water vapour (g), transpiration rate (E), xylem pressure potential and leaf temperature (Tleaf). During a period of drought in which co-occurring grasses and forbs experienced significant water stress (xylem pressure potential< -2*5 MPa), xylem pressure potential in large- and intermediate-sized plants of C. foetidissima was always> -0*6 MPa. In small plants, minimum xylem pressur potential was c-1*3 MPa. No substantial diurnal reductions in A or g were measured in the two groups of larger plants, but CO2 uptake was reduced to zero after midday in small plants, presumably due to water stress. Increased mass of succulent taproots and greater rooting depth may have contributed to greater xylem pressure potential in larger vs small individuals of C. foetidissima. Water use efficiency (WUE) was greater in larger vs small individuals of C. foetidissima. Water use efficiency (WUE) was greater in leaves from large- and intermediate-sized plants relative to small plants under all environmental conditions. During brief periods of low irradiance due to clouds or artificial shading, 5-10oC reduction in Tleaf in plants with large leaves resulted in low E, enhancing WUE. Much smaller reductions in Tleaf and E occurred during shade in the small leaves of small individuals. These results indicate the greater size in C. foetidissima, while not increasing interception of irradiance in this grassland, resulted in greater independence from resource limitations as well as water conservation during periods of variable sunlight. Key words: Cucurbita, photosynthesis, plant size, water stress

10aWater relations1 aKnapp, Alan, K.1 aFahnestock, J.T. uhttp://lter.konza.ksu.edu/content/influence-plant-size-carbon-and-water-relations-cucurbita-foetidissima-hbk02178nas a2200133 4500008004100000245011800041210006900159300001300228490000700241520162800248653002001876100001701896856013101913 1988 eng d00aGenetic variation in leaf morphology and plant and tissue water relations during drought in Cercis canadensis . L0 aGenetic variation in leaf morphology and plant and tissue water  a200 -2070 v343 a

Genetic variation in plant and tissue water relations in response to drought, and in leaf morphology, were examined in greenhouse-grown Cercis canadensis L. (eastern redbud) seedlings originating from seed obtained in three contrasting habitats: a relatively xeric Kansas prairie, a Kansas gallery forest understory, and a relatively mesic Indiana understory. Kansas prairie redbud maintained significantly greater leaf conductance (gwv) during a 13-day drought than did Kansas and Indiana understory redbud, despite similar decreases in leaf water potential in all three sources. Moreover, Kansas paririe redbud had significantly lower osmotic potentials at full and zero turgor compared to Indiana redbud at both the early and later stages of drought. Kansas understory redbud was the only source to undergo a signigicant decrease in relative water content at zero turgor and the bulk modulus of elasticity during drought. Kansas prairie redbud leaver were smaller and thicker and had higher specific leaf mass (i.e., more xerophytic) than understory redbud leaves. Kansas understory redbud had intermediate characteristics in terms of gwv at the early to middle stages of drought, osmotic potentials at high and low leaf water potential, and leaf area and thickness compared to Kansas prairie and Indiana understory redbud. These results suggest that genetically controlled physiological and morphological adaptation has occurred in redbud that should facilitate its survival in greatly contrasting habitats. ADDITIONAL KEY WORDS: Ecophysiology, Kansas prairie, gallery forest, Indiana understory, leaf morphology

10aWater relations1 aAbrams, M.D. uhttp://lter.konza.ksu.edu/content/genetic-variation-leaf-morphology-and-plant-and-tissue-water-relations-during-drought-cercis02075nas a2200133 4500008004100000245014000041210006900181300001500250490000700265520150500272653002001777100001701797856012701814 1986 eng d00aPhysiological plasticity in water relations and leaf structure of understory versus open-grown Cercis canadensis in northeastern Kansas0 aPhysiological plasticity in water relations and leaf structure o a1170 -11740 v163 a

Field and laboratory studies were used to evaluate physiological plasticity in water relations and leaf structural characteristics of Cercis canadensis L. (redbud) saplings growing in a gallery forest understory and an adjacent prairie in eastern Kansas. Two study periods were defined based on high (greater than -0.2 MPa in May) and low (-1.5 MPa in July) predawn soil water potential ( soil) Leaf conductance to water vapor diffusion (gwv) was greater for prairie than understory redbud saplings during both sampling periods (maximum gwv=7.5-8.7 mm s-1) Moreover, gwv for prairie redbud remained high at both high and low soil, but was significantly lower for understory redbud during midday at low soil. Transpiration flux was also higher in the prairie than in the understory site and reach a maximum for prairie redbud (318 mg m-2s-1) in July, in conjunction with high leaf to air vapor pressure deficits (maximum 5.3 kPa). Leaf water potential declined significantly at both sites with decreased soil and the minimum values (-3.0 MPa) were recorded in understory redbud. Leaves of prairie redbud were significantly smaller, thicker, and had higher specific leaf mass and stomatal density than leaves of understory redbud, which are consistent with differences between zeric and mesic species, respectively. These differences in water relations and leaf morphology between understory and prairie redbud suggest a high degree of physiological plasticity for this species in eastern Kansas

10aWater relations1 aAbrams, M.D. uhttp://lter.konza.ksu.edu/content/physiological-plasticity-water-relations-and-leaf-structure-understory-versus-open-grown01862nas a2200133 4500008004100000245011300041210006900154300001100223490000800234520132100242653002001563100002001583856012501603 1986 eng d00aPostfire water relations, production, and biomass allocation in the shrub, Rhus glabra, in tallgrass prairie0 aPostfire water relations production and biomass allocation in th a90 -970 v1473 a

Several populations of Rhus glabra were studies to assess the effect of fire on productivity, biomass allocation, N and chlorophyll content, and seasonal water relations in a North American tallgrass prairie. Compared with shoots in unburned prairie, shoots from burned sites had reduced biomass and fewer leaves; however, a significant postfire increase in shoot density led to similar midseason leaf area indices for both populations. Productivity was greater in the unburned population principally because of the biomass of sexual reproductive structures, which were absent in the resprouting shoots. However, burned populations allocated a greater proportion of biomass to leaves and wood, utilized for vertical growth, than unburned populations. Leaves in unburned prairie had greater stomatal density, specific leaf mass, and chlorophyll and N content than leaves from the burned population. For much of the growing season, stomatal conductances were greater in unburned prairie. Despite lower soil water potentials at the burned site, differences in midday leaf water potentials were small between populations; hence, differences in N content probably contributed more to the responses. The postfire reduction in productivity and sexual reproduction in R. glabra indicates that fire reduces its fitness

10aWater relations1 aKnapp, Alan, K. uhttp://lter.konza.ksu.edu/content/postfire-water-relations-production-and-biomass-allocation-shrub-rhus-glabra-tallgrass01993nas a2200145 4500008004100000245009000041210006900131300001300200490000700213520145200220653002001672100001701692700002001709856011801729 1986 eng d00aSeasonal water relations of three gallery forest hardwood species in northeast Kansas0 aSeasonal water relations of three gallery forest hardwood specie a687 -6960 v323 a

Field and laboratory studies were used to evaluate several water relations characteristics for saplings of three species: hackberry (Celtis occidentalis), a mesic, late successional tree, and bur and chinquapin oak (Quercus macrocarpa and Q. muehlenbergii), more xeric, early successional trees growing in a northeast Kansas gallery forest understory during a dry summer. For all species, maximum stomatal conductance (gwv) (8.9-9.5 mm*s-1) was recorded early in the season when soil moisture was greatest. Seasonally, sunlit leaves generally had significantly higher gwv than shaded leaves. Both gwv and leaf water potential decreased during the season in each species, with minimum leaf water potential values ranging from - 2.13 to -2.48 MPa. Seasonally, leaf water potential remained consistently higher than the osmotic potential at zero turgor for each species (minimum values of zero turgor ranged from -2.61 to -3.02 MPa). Hackberry, the most mesic species, experienced the largest seasonal decrease in gwv in both shaded and sunlit leaves (69% and 78% reduction, respectively). Moreover, in contrast to the two oaks, a significant seasonal decline in 600 h leaf water potential was shown for hackberry. By season's end, hackberry had the lowest gwv and leaf water potential suggesting that this species was better able to utilize late season precipitation. Additional key words: Quercus, Celtis, ecophysiology, prairie, drought

10aWater relations1 aAbrams, M.D.1 aKnapp, Alan, K. uhttp://lter.konza.ksu.edu/content/seasonal-water-relations-three-gallery-forest-hardwood-species-northeast-kansas