b` dBdB @@@ @@@@\#qdBdC EN DB dC     & . 67 V CR Bd(L Davis2002 Ehleringer1991 Ehleringer1999 Ehleringer2000  Ehleringer2000 Ehleringer2001 Ehleringer2002 Ehleringer2002 Ehleringer2003 Fay2003 Gebauer1999 Gebauer2000 Gebauer2002 Haddad20030 Harte2003 Huxman20030 Knapp2003 Lin2003 Loik20030Phillips19919 Pockman2003 Richardson2002 Sandquist1991Schuster19919 Schwinning1999 Schwinning2001 Schwinning2002 Schwinning2002 Schwinning2003 Schwinning2003 Shaw20030 Small2003 Smith2003 Smith2003 Starr2003 Tissue20033 Weltzin2003 Williams2000Williams20030 Zak2003  zhSuodlc mo eabkct ohtsip parel tare .hTre'e s aol tfor veeiiwgno htrew ro knilcduni ght eaJapenes sna dmeipiraceWnire ,.JT oham,sS C.. 9168>7iSezv raaiibilyta dnc moepititnoi nlpna tomonuctlruse. iOoks7412-1222 IOOKS eWnire<6erivwe ,samyemrtcic moepititno ,isezs rtcuuter ,omedsl,%aMek sht eraugemtnt ah tlpnastc moepeta ysmmteiracll yna dofmrs zi eihrerahcei shtorgu hocpmtetioi.n1 4uo tfo1 6tsduei suspproet dhttac moepititnoi ssamy AuthorsJournals Keywords :                                 Barker, M.G. Davis, K.Ehleringer, J REhleringer, J. R.Ehleringer, J.R. Fay, P. A. Gebauer, R.Gebauer, R. L. E. Haddad, B. M. Harte, J. Huxman, T. E. Knapp, A. K. Lin, G. H. Loik, M. E. Phillips, S LPockman, W. T. Press, M.C.Richardson, L.Sandquist, D R Scholes, J.D.Schuster, W S FSchwinning, S. Shaw, M. R. Small, E. E. Smith, M. D. Smith, S. D. Starr, B. I. Tissue, D. T.Weltzin, J. F.Williams, D. G. Zak, J. C.  d BioscienceEcological Monographs EcologyJournal of EcologyOecologia Oecologia  : annualsarid ecosystempjarid ecosystems, plant functional types, precipitation pulse use, stable isotope label, water partitioningAtriplex confertifolia, Chrysothamnus nauseosus, Colorado plateau, desert, Gutierrezia sarothrae, neighbor removal, plant competition, resource pulses, stable isotopes, water uptake availabilitybiosphere model carbon carbon-isotope discriminationchihuahuan desertclimate-changecold desert communitycolorado plateauColorado Plateau (USA), desert perennials, nitrogen uptake patterns, pulse utilization, resource partitioning, stable isotopes, water uptake patterns communityD/H ratios, Juniperus osteosperma, Pinus edulis, pinyon-juniper ecosystem, plant water sources, precipitation use, Quercus gambelii, roots desert shrubsPJdesert, genetic algorithm, plant functional types, whole-plant carbon gain\Ydeuterium-labeled irrigation, niche separation, precipitation change, rain use efficiency ecosystem ecosystems elevated co2DAglobal change, community, ecosystem, precipitation, soil moisture grasses great-basinheavy precipitation4/hydrogen isotope, water sources, spring, summerisotopic compositionn-15 natural-abundance nitrogen patternsphotosynthetic capacityplant competition plantsprimary productivityrainfall events responses root systemsshortgrass steppe shrubssoil soil-moisturesoil-water dynamicssonoran desertspecies-diversitystomatal conductance succulentssummer precipitation systems temperaturetemporal dynamicstrees united-states vegetationvegetation distributionwater water-uptake water-usexylem embolism   nB://000086795100019*#Gebauer, R. L. E. Ehleringer, J. R.^WWater and nitrogen uptake patterns following moisture pulses in a cold desert communityEcology("Colorado Plateau (USA), desert perennials, nitrogen uptake patterns, pulse utilization, resource partitioning, stable isotopes, water uptake patterns n-15 natural-abundance; isotopic composition; plant competition; colorado plateau; great-basin; soil; responses; carbon; ecosystems; systems~wVariation in the ability to utilize pulses of both water and nitrogen (N) is one possible mechanism allowing the coexistence of species in the cold desert community on the Colorado Plateau. We simulated 25-mm precipitation events and used stable isotope tracers (H-2 and N-15) to follow water and N uptake patterns in six dominant perennials (Artemisia filifolia, Coleogyne ramosissima, Cryptantha flava, Ephedra viridis, Quercus havardii, and Vanclevea stylosa) at different times of the growing season. Water pulse utilization varied on a seasonal basis and was to some extent different among species during the summer. Carbon isotope discrimination was negatively related to both plant use of moisture in upper soil layers and foliar N concentration. Species that were similar in water pulse utilization patterns differed in the natural abundances of N-15, suggesting partitioning in N sources. All species were able to utilize N pulses after rain events, but there were temporal differences in the responses among species. We also found that water and N uptake in shallow roots do not necessarily occur simultaneously. Artemisia, Cryptantha, and Quercus showed significant uptake of both water and N from the upper soil layers. In contrast, Coleogyne and Ephedra showed the capacity to utilize the water pulse, but not the N pulse. Vanclevea only took up N. The results indicate that different parts of the root system may be responsible for the acquisition of water and N. Our results also suggest that N and water partitioning could contribute to the coexistence of species in highly variable environments such as the Colorado Plateau desert system.u 2000 Mayv815sISI:000086795100019h 2602-2616$://00017815390002382Gebauer, R. L. E. Schwinning, S. Ehleringer, J. R.ZSInterspecific competition and resource pulse utilization in a cold desert communityEcologypjAtriplex confertifolia, Chrysothamnus nauseosus, Colorado plateau, desert, Gutierrezia sarothrae, neighbor removal, plant competition, resource pulses, stable isotopes, water uptake carbon-isotope discrimination; n-15 natural-abundance; shortgrass steppe; summer precipitation; chihuahuan desert; arid ecosystem; soil-moisture; root systems; water-uptake; plantsIn desert ecosystems a large proportion of water and nitrogen is supplied in rain-induced pulses. It has been suggested that competitive interactions among desert plants would be most intense during these pulse periods of high resource availability. We tested this hypothesis with three cold desert shrub species of the Colorado Plateau (Gutierrezia sarothrae, Atriplex confertifolia. and Chrysothamnus nauseosus), which differ in their distribution of functional roots. In a three-year field study we conducted a neighbor removal experiment in conjunction with simulated 25-mm precipitation events and the addition of a nitrogen pulse. in either spring or summer. We measured predawn water potential (Psi), gas exchange, leaf delta(15)N, carbon isotope discrimination (Delta), and growth of target plants for the duration of the study. We found that G. sarothrae used resource pulses to a larger extent than A. confertifolia, which has more functional roots at depth. In all species, the addition of a water or nitrogen pulse did not significantly affect maximal rates of photosynthesis or branch growth. Contrary to our initial hypothesis, we did not find that pulse use was reduced by the presence of neighboring plants. Nevertheless, there was strong evidence for competitive interactions, which were more likely mediated by water at depth than by nitrogen. in the more deep-rooted species A. confertifolia, neighbor removal affected T, gas exchange, Delta, percentage of carbon, and growth. G. sarothrae, which has a much smaller proportion of roots at depth, was less affected by the removal of neighboring shrubs, and not at all when only predominantly shallow-rooted herbaceous species were removed.These results suggest that shrubs in this cold desert community may primarily compete for water in deeper soil layers, where water depletion is slow and dominated by plant water uptake. There appeared to be little competition for water in shallow soil layers, where depletion is fast and dominated by evaporation. 2002 Sep839ISI:000178153900023 " 2 464-480$://000169689900013& Schwinning, S. Ehleringer, J. R.RLWater use trade-offs and optimal adaptations to pulse-driven arid ecosystemsJournal of Ecologydesert, genetic algorithm, plant functional types, whole-plant carbon gain desert shrubs; summer precipitation; shortgrass steppe; plants; soil; community; annuals; availability; temperature; succulents$1 We introduce a hydraulic soil-plant model with water uptake from two soil layers; one a pulse-dominated shallow soil layer, the other a deeper soil layer with continuous, but generally less than saturated soil moisture. Water uptake is linked to photosynthetic carbon assimilation through a photosynthesis model for C-3 plants.2 A genetic algorithm is used to identify character suites that maximize photosynthetic carbon gain for plants that experience a particular soil moisture pattern. The character suites include allocation fraction to stem, leaves and shallow root, stem capacitance and stem water storage capacity, maximal leaf conductance and sensitivity of leaf conductance to plant water potential, and a critical soil water potential at which shallow roots cease to transfer water.3 We find that if pulse water is a more important water source than deeper soil water in the environment, optimal phenotypes lean towards adaptations that maximize pulse water use (small root : shoot ratio, predominantly shallow root system, high leaf conductance with high stomatal sensitivity to plant water status). if deeper soil water is more important, phenotypes lean towards adaptations that maximize deeper soil water use (large root : shoot ratio, predominantly deep root system, lower leaf conductance with low stomatal sensitivity). Stem succulence is adaptive only when deeper soil water is unavailable.4 From among the continuum of derived phenotypes, four phenotypes are selected that resemble the character suites of winter annuals, drought-deciduous perennials, evergreen perennials and stem succulents. Under common conditions, these phenotypes reproduce many of the responses to drought and water pulse observed in their respective life-form counterparts. The comparison also highlights the differences in plant life-form sensitivity to summer and winter drought conditions.5 Based on these results, we discuss the possible role of annual precipitation patterns in shaping plant adaptations and determining the plant composition of arid and semi-arid environments. 2001 Jun893ISI:000169689900013345-355$://000174215200004@9Schwinning, S. Davis, K. Richardson, L. Ehleringer, J. R.gxrDeuterium enriched irrigation indicates different forms of rain use in shrub/grass species of the Colorado Plateau Oecologiaarid ecosystems, plant functional types, precipitation pulse use, stable isotope label, water partitioning cold desert community; soil-water dynamics; summer precipitation; shortgrass steppe; shrubs; trees; vegetation; ecosystem; patterns; grassescWe contrasted the seasonal use of simulated large rain events (24 mm) by three native species of the and Colorado Plateau: the perennial grass Hilaria jamesii and two shrubs Artemesia filifolia and Coleogyne ramosissima. Deuterium-enriched water was used to distinguish shallow "pulse" water from water in deeper soil layers that were unaffected by the water input. We also measured the leaf gas exchange rates of watered and unwatered control plants for 5 days after the rain event. H. jamesii had twice the pulse water proportion in its xylem than the two shrubs in spring (approx. 70% vs 35%). In summer, the pulse water proportions of all species were around 70%. The increase in the relative pulse water uptake of the two shrubs was caused primarily by a reduction in the rate of water uptake from deeper sources, consistent with the decrease in the availability of stored winter water. Rain increased the rates of gas exchange in C. ramosissima in both seasons, in H. jamesii only in summer and had no significant effect on A. filifolia. In H. jamesii, summer rain also increased water use efficiency. This suggests three principle mechanisms for rainwater use: (1) immediate increase in gas exchange via stomatal opening (C. ramisissima), (2) immediate increase in water use efficiency through restoration of the photosynthetic apparatus (H. jamesii) and (3) conservation of deeper soil water, potentially extending photosynthetic activity into later drought periods (A. filifolia). On a ground-area basis, A. filifolia was by far the largest consumer of spring and summer rain, due to its greater ground cover, while rain use by H. jamesii was negligible. We hypothesize that a population's fraction of the total community Leaf Area Index, more than species identity, determines which species takes up most of the spring and summer precipitation and we discuss this idea in the context of Walter and Stadelmann's (1974, In: Brown JW Jr (ed) Desert biology. Academic-Press, New York, pp 213-310) water partitioning hypothesis. 2002 Feb 1303ISI:000174215200004252-260$://0001840925000104-Schwinning, S. Starr, B. I. Ehleringer, J. R.mZTDominant cold desert plants do not partition warm season precipitation by event size Oecologiadeuterium-labeled irrigation, niche separation, precipitation change, rain use efficiency rainfall events; photosynthetic capacity; stomatal conductance; heavy precipitation; shortgrass steppe; colorado plateau; water; community; nitrogen; shrubsWe conducted experiments to examine the quantitative relationships between rainfall event size and rainwater uptake and use by four common native plant species of the Colorado Plateau, including two perennial grasses, Hilaria jamesii (C-4) and Oryzopsis hymenoides (C-3), and two shrubs, Ceratoides lanata (C-3), and Gutierrezia sarothrae (C-3). Specifically, we tested the hypothesis that grasses use small rainfall events more efficiently than shrubs and lose this advantage when events are large. Rainfall events between 2 and 20 mm were simulated in spring and summer by applying pulses of deuterium-labeled irrigation water. Afterwards, pulse water fractions in stems and the rates of leaf gas exchange were monitored for 9 days. Cumulative pulse water uptake over this interval (estimated by integrating the product of pulse fraction in stem water and daytime transpiration rate over time) was approximately linearly related to the amount of pulse water added to the ground in all four species. Across species, consistently more pulse water was taken up in summer than in spring. Relative to their leaf areas, the two grass species took up more pulse water than the two shrub species, across all event sizes and in both seasons, thus refuting the initial hypothesis. In spring, pulse water uptake did not significantly increase photosynthetic rates and in summer, pulse water uptake had similar, but relatively small effects on the photosynthetic rates of the three C-3 plants, and a larger effect on the C-4 plant H. jamesii. Based on these data, we introduce an alternative hypothesis for the responses of plant functional types to rainfall events of different sizes, building on cost-benefit considerations for active physiological responses to sudden, unpredictable changes in water availability. 2003 Jul 1362ISI:000184092500010941-952$://000185816100007gWeltzin, J. F. Loik, M. E. Schwinning, S. Williams, D. G. Fay, P. A. Haddad, B. M. Harte, J. Huxman, T. E. Knapp, A. K. Lin, G. H. Pockman, W. T. Shaw, M. R. Small, E. E. Smith, M. D. Smith, S. D. Tissue, D. T. Zak, J. C.\VAssessing the response of terrestrial ecosystems to potential changes in precipitation Bioscienceglobal change, community, ecosystem, precipitation, soil moisture climate-change; biosphere model; united-states; elevated co2; vegetation distribution; primary productivity; species-diversity; temporal dynamics; sonoran desert; water-useChanges in Earth's surface temperatures caused by anthropogenic emissions of greenhouse gases are expected to affect global and regional precipitation regimes. Interactions between changing precipitation regimes and other aspects of global change are likely to affect natural and managed terrestrial ecosystems as well as human society. Although much recent research has focused on assessing the responses of terrestrial ecosystems to rising carbon dioxide or temperature, relatively little research has focused on understanding how ecosystems respond to changes in precipitation regimes. Here we review predicted changes in global and regional precipitation regimes, outline the consequences of precipitation change for natural ecosystems and human activities, and discuss approaches to improving understanding of ecosystem responses to changing precipitation. Further, we introduce the Precipitation and Ecosystem Change Research Network (PrecipNet), a new interdisciplinary research network assembled to encourage and foster communication and collaboration across research groups with common interests in the impacts of global change on precipitation regimes, ecosystem structure and function, and the human enterprise. 2003 Octa5310ISI:000185816100007 l941-952$://000185816100007gWeltzin, J. F. Loik, M. E. Schwinning, S. Williams, D. G. Fay, P. A. Haddad, B. M. Harte, J. Huxman, T. E. Knapp, A. K. Lin, G. H. Pockman, W. T. Shaw, M. R. Small, E. E. Smith, M. D. Smith, S. D. Tissue, D. T. Zak, J. C.\VAssessing the response of terrestrial ecosystems to potential changes in precipitation Bioscienceglobal change, community, ecosystem, precipitation, soil moisture climate-change; biosphere model; united-states; elevated co2; vegetation distribution; primary productivity; species-diversity; temporal dynamics; sonoran desert; water-useChanges in Earth's surface temperatures caused by anthropogenic emissions of greenhouse gases are expected to affect global and regional precipitation regimes. Interactions between changing precipitation regimes and other aspects of global change are likely to affect natural and managed terrestrial ecosystems as well as human society. Although much recent research has focused on assessing the responses of terrestrial ecosystems to rising carbon dioxide or temperature, relatively little research has focused on understanding how ecosystems respond to changes in precipitation regimes. Here we review predicted changes in global and regional precipitation regimes, outline the consequences of precipitation change for natural ecosystems and human activities, and discuss approaches to improving understanding of ecosystem responses to changing precipitation. Further, we introduce the Precipitation and Ecosystem Change Research Network (PrecipNet), a new interdisciplinary research network assembled to encourage and foster communication and collaboration across research groups with common interests in the impacts of global change on precipitation regimes, ecosystem structure and function, and the human enterprise. 2003 Octa5310ISI:000185816100007517-537$://000165521600002(!Williams, D. G. Ehleringer, J. R.ib[Intra- and interspecific variation for summer precipitation use in pinyon-juniper woodlands Ecological Monographsa0*D/H ratios, Juniperus osteosperma, Pinus edulis, pinyon-juniper ecosystem, plant water sources, precipitation use, Quercus gambelii, roots carbon-isotope discrimination; water-uptake; vegetation distribution; colorado plateau; xylem embolism; united-states; root systems; great-basin; plants; trees$In the arid southwest of North America, winter precipitation penetrates to deep soil layers, whereas summer "monsoon" precipitation generally wets only surface layers. Use of these spatially separated water sources was determined for three dominant tree species of the pinyon-juniper ecosystem at six sites along a gradient of increasing summer precipitation in Utah and Arizona. Mean summer precipitation ranged from 79 to 286 mm, or from 18% to 60% of the annual total across the gradient. We predicted that, along this summer rainfall gradient, populations of dominant tree species would exhibit a clinal off-on response for use of water from upper soil layers, responding at particular threshold levels of summer precipitation input. This prediction was largely supported by our observations of tree water source use over a two-year period and from irrigation experiments.Hydrogen and oxygen stable isotope ratios (deltaD and delta O-18) of tree xylem water were compared to that of precipitation, groundwater, and deep and shallow soil water to distinguish among possible tree water sources. deltaD-delta O-18 relationships and seasonal xylem water potential changes revealed that trees of this ecosystem used a mixture of soil water and recent precipitation, but not groundwater. During the monsoon period, a large proportion of xylem water in Pinus edulis and Juniperus osteosperma was from monsoon precipitation, but use of this precipitation declined sharply with decreasing summer rain input at sites near the regional monsoon boundary in Utah. Quercus gambelii at most sites along the gradient used only deep soil water even following substantial inputs of summer rain. Populations of Quercus at sites with the highest average summer precipitation input, however, predominantly used water in upper soil layers from recent summer rain events. Soil temperature correlated with patterns of summer precipitation use across the gradient; high soil temperatures north of the monsoon boundary may have inhibited surface root activity for some or all of the three tree species.Irrigation experiments with deuterium-labeled water revealed that Quercus gambelii in northern Arizona and southern Utah did not use water from surface layers. In contrast, Juniperus osteosperma at these sites responded significantly to the irrigations: between 37% and 41% of xylem water originated from irrigations that wetted only the top 30 cm of soil. Responses by Pinus edulis to these irrigations were variable; uptake of labeled water by this species was greater in September at the end of the summer than during the hot midsummer period. Inactivity of Pinus roots in midsummer supports the hypothesis that root activity in this species is sensitive to soil temperature.Seasonal patterns of leaf gas exchange and plant water potential corresponded to the seasonality of rainfall at different sites. However, no correlation between a species' ability to use summer rainfall and its tolerance to water deficits at the leaf level was found. Midday stomatal conductance (g(s)) for Pinus needles approached zero at predawn water potentials near -2 MPa, whereas g(s) in Quercus and Juniperus declined to zero at -2.8 and -3.7 MPa, respectively. The relationship between photosynthesis (A) and g(s) was similar among the three species, although Quercus maintained higher overall rates of gas exchange and tended to operate higher on the A/g(s) curve than the two conifers. At sites in eastern Arizona where Quercus fully used moisture from summer rains, leaf gas exchange characteristics were similar to those of Pinus and Juniperus. 2000 Nov704ISI:000165521600002