02906nas a2200205   4500008004100000245016700041210006900208300001300277490000800290520214500298653001202443653001302455653001902468653002002487653001702507100002102524700001802545700002002563856011702583       1997                        eng d00aThe contribution of drought-related decreases in foliar nitrogen concentration to decreases in photosynthetic capacity during and after drought in prairie grasses0 acontribution of droughtrelated decreases in foliar nitrogen conc  a173 -1820 v1013 aWhile stomatal closure usually limits photosynthesis during drought, our previous results suggest that drought-related decreases in foliar nitrogen concentration (NL) limit photosynthesis during recovery from drought in prairie grasses. Here we estimate the importance of decreases in NL to decreased photosynthetic capacity (PScap) during drought and a subsequent recovery period in three perennial C4 prairie grasses. PScap (O2 evolution at light and CO2 saturation) decreased 69 to 78% during drought in these grasses, and full recovery of PScap required 8 to 12 days, until younger leaves were expanded or older leaves were repaired, depending on species. Decreases in NL explained 38 to 51% of the loss of PScap during drought and accounted for 51 to 69% of the total loss of PScap integrated over the post-drought recovery period. N-related loss of PScap appeared to result more from decreases in ribulose-1,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39), phosphoenolpyruvate carboxylase (4.1.1.31), and other soluble photosynthetic enzymes, than from decreases in thylakoid N-containing compounds. Decreases in quantum yield of O2 evolution and Fv/Fm (variable-to-maximum fluorescence of dark-adapted leaves) during drought were small, so we assumed that little damage to photsystem II (PSII) and thylakoid membrane function occurred. Further, F0 (minimum F) decreased or remained unchanged, dark F0 was greater than light F0, and decreases in photochemical quenching (the fraction of oxidized PSII) were reversed within 1–3 days after drought. Therefore, prolonged increases in non-photochemical quenching (qn; thermal dissipation of excess light energy) during and after drought were indicative of protective downregulation and were likely associated with disproportionate loss of soluble photosynthetic proteins during drought. In support of this, post-drought recovery of qn paralleled recovery of NL and PScap. Thus, in C4 prairie grasses, loss of PScap during drought is largely the result of decreases in shoot NL and of associated protective downregulation, decreasing carbon assimilation for 1–2 weeks after drought.10aDrought10anitrogen10aphotosynthesis10aprairie grasses10awater stress1 aHeckathorn, S.A.1 aDeLucia, E.H.1 aZielinski, R.E.  uhttp://lter.konza.ksu.edu/content/contribution-drought-related-decreases-foliar-nitrogen-concentration-decreases02440nas a2200145   4500008004100000245013400041210006900175300001300244490000700257520185300264653000902117100002102126700001802147856012902165       1996                        eng d00aRetranslocation of shoot nitrogen to rhizomes and roots in prairie grasses may limit loss of N to grazing and fire during drought0 aRetranslocation of shoot nitrogen to rhizomes and roots in prair  a396 -4000 v103 a1. It has previously been shown that perennial C4 grasses of tallgrass prairie retranslocate up to 30% of shoot nitrogen (N) to rhizomes and roots in response to water stress and that retranslocation contributes to drought-related decreases in shoot N concentration and photosynthetic capacity, resulting in decreased post-drought carbon gain for 1-2 weeks. 2. In this paper the following hypothesis is tested: under N-limited conditions, the benefits of retranslocation may include limiting loss of shoot N to grazing (or fire) during drought, resulting in increased end-of-season whole-plant biomass, N content, and reproduction. All shoot tissue was removed from young N-limited plants either before or after drought, thereby preventing or allowing the opportunity for retranslocation, and the effects of each clipping treatment on biomass and N content after flowering and senescence were determined. 3. In Spartina pectinata, a mesic species that remobilizes 20-30% of shoot N during drought, plants clipped before drought (no retranslocation) had decreased biomass, N content, and tiller (but not seed) production relative to plants clipped after drought. In contrast, Schizachyrium scoparium, a xeric species that retranslocates little shoot N, exhibited decreased biomass, N content, and tiller and seed production in plants clipped after drought: the result of growth-related increases in total shoot N during drought, and thus greater N loss in plants clipped after drought. Time of clipping had no effect on Andropogon gerardii, a species of intermediate drought tolerance that retranslocates ca. 10% of shoot N during drought. 4. These results support the hypothesis that drought-induced shoot N retranslocation to below-ground tissues represents a trade-off between N protection and post-drought carbon assimilation in prairie grasses.10afire1 aHeckathorn, S.A.1 aDeLucia, E.H.  uhttp://lter.konza.ksu.edu/content/retranslocation-shoot-nitrogen-rhizomes-and-roots-prairie-grasses-may-limit-loss-n-grazing02189nas a2200181   4500008004100000245008700041210006900128300001300197490000800210520154700218653002701765653001201792653002901804653002001833100002101853700001801874856011501892       1995                        eng d00aAmmonia volatilization during drought in perennial C4 grasses of tallgrass prairie0 aAmmonia volatilization during drought in perennial C4 grasses of  a361 -3650 v1013 aWe measured foliar NH3 volatilization as part of our study of the decrease (up to 40%) in shoot N concentration during drought in three perennial C4 grasses of tallgrass prairie. Volatilization of recently expanded leaves was quantified using cuvettes and acid traps for Spartina pectinata, Andropogon gerardii, and Schizachyrium scoparium, a mesic, intermediate, and xeric species, respectively. In general, volatilization decreased during drought, approaching zero as stomates closed, and increased with plant N status and drought tolerance. Prior to drought, NH3 volatilization was greater in xeric than mesic species (179 and 131 vs. 115 ng m-2 s-1 for individual leaves of S. scoparium and A. gerardii vs. Sp. pectinata). During a 2–3 week drought, whole-shoot volatile N losses can exceed 5% of total plant N in these species, accounting for 2–10% of the decrease in shoot percent N (again, xeric > mesic). Drought-induced N retranslocation of shoot N to roots and rhizomes is responsible for c. 63% of the decrease in percent N in Sp. pectinata, 28% in A. gerardii, and 8% in S. scoparium. The remainder of the decrease in percent N is attributable to growth dilution of existing shoot N, accounting for 34, 65, and 87% of the decrease in shoot percent N during drought in Sp. pectinata, A. gerardii, and S. scoparium, respectively. Thus, the relative importance of volatilization, retranslocation, and dilution in decreasing foliar percent N during drought in prairie grasses is species dependent and related to drought tolerance.10aAmmonia volatilization10aDrought10aNitrogen Prairie grasses10aRetranslocation1 aHeckathorn, S.A.1 aDeLucia, E.H.  uhttp://lter.konza.ksu.edu/content/ammonia-volatilization-during-drought-perennial-c4-grasses-tallgrass-prairie02781nas a2200145   4500008004100000245009000041210006900131300001500200490000700215520223400222653002202456100002102478700001802499856011802517       1994                        eng d00aDrought-induced nitrogen retranslocation in perennial C4 grasses of tallgrass prairie0 aDroughtinduced nitrogen retranslocation in perennial C4 grasses   a1877 -18860 v753 aWe determined if drought—induced nitrogen retranslocation occurs in perrenial grasses of tallgrass prairie, as suggested from studies of annual changes in plant N content. To test this, we analyzed six C4 grasses representing a wide range of drought tolerance for shoot, rhizome, and root N before and after controlled drought. Shoot N concentration decreased in all species during drought (31—41%), including in recently expanded leaves (23—38%). No consistent pattern with respect to drought tolerance was apparent in these decreases or in observed changes in distribution of whole—plant N, although there was some suggestion of a mesic—to—xeric gradient in the magnitude of retranslocation. For example, the proportion of total plant N allocated to shoots decreased during drought 20—29% in the most mesic species over three experiments, 2—12% in the three intermediate species, and 4—6% in the two most xeric species, for pre— vs. post—drought comparisons. However, when drought—stressed plants were compared to well—watered age controls, the respective values were 20—21%, 12—20%, and 0.19%, the apparent result of size—related changes in N allocation in control plants in one experiment. In most cases, shoot N was moved primarily into rhizomes, though in one species with intermediate drought tolerance, evidence suggested that much of the retranslocated shoot N was apparently lost through fine—root turnover. Retranslocation of shoot N to rhizomes and roots, confirmed by monitoring movement of 35S—methionine, was in response to drought stress rather than phenology and involved the entire shoot (e.g., blades, culms, recently expanded leaves). Post—drought photosynthesis and leaf N concentration remained well below predrought levels 6 d following rewatering. Thus decreases in leaf N status during drought as a consequence of retranslocation likely result in lower photosynthetic capacity and decreased whole—plant carbon gain following relief of water stress after rain. Drought—induced retranslocation may serve to protect plant N from loss of herbivory, fire, and volatilization during periods when soil N uptake and carbon assimilation are limited by water availability.10atallgrass prairie1 aHeckathorn, S.A.1 aDeLucia, E.H.  uhttp://lter.konza.ksu.edu/content/drought-induced-nitrogen-retranslocation-perennial-c4-grasses-tallgrass-prairie00593nas a2200145   4500008004100000245011700041210006900158300001300227490000800240653002100248100001800269700002100287700001400308856012500322       1992                        eng d00aEffects of soil temperature on growth, biomass allocation and resource acquisition of Andropogon gerardii Vitman0 aEffects of soil temperature on growth biomass allocation and res  a543 -5490 v12010asoil temperature1 aDeLucia, E.H.1 aHeckathorn, S.A.1 aDay, T.A.  uhttp://lter.konza.ksu.edu/content/effects-soil-temperature-growth-biomass-allocation-and-resource-acquisition-andropogon01717nas a2200145   4500008004100000245011000041210006900151300001300220490000800233520114500241653002101386100002101407700001801428856012501446       1991                        eng d00aEffect of leaf rolling on gas exchange and leaf temperature of Andropogon gerardii and Spartina pectinata0 aEffect of leaf rolling on gas exchange and leaf temperature of A  a263 -2680 v1523 a<p>We examined the effect of leaf rolling on CO2 and water vapor exchange of two C4 prairie grasses with contrasting patterns of leaf rolling. Andropogon gerardii (big bluestem) is a drought-resistant species with predominantly hypostomatal leaves that fold (adaxial surface inward) in response to low leaf water potential, while leaves of Spartina pectinata (prairie cordgrass), a mesic species, are epistomatal and roll into spirals (also adaxial surface inward). Adaxial stomata of both species are closed in completely rolled or folded leaves; thus these leaf movements have a minor effect on total leaf conductance. Energy budget calculations indicate that leaf rolling reduces transpiration by 7%-13% in water-stressed plants by lowering leaf temperature and, therefore, leaf-to- air vapor pressure deficit. This reduction is small relative to the direct effect of stomatal closure on transpiration. However, small decreases in transpiration, leaf temperature, and incident irradiance associated with leaf rolling may decrease the potential for photoinhibition, prolong physiological activity, and increase survival during drought</p>10aLeaf temperature1 aHeckathorn, S.A.1 aDeLucia, E.H.  uhttp://lter.konza.ksu.edu/content/effect-leaf-rolling-gas-exchange-and-leaf-temperature-andropogon-gerardii-and-spartina