bluuebunny/crossref_metadata_2025_split huggingface dataset:
Non‐climatic variations in the oxygen isotopic compositions of plants
Authors: WANG XUE‐FENG. , YAKIR DAN. , AVISHAI MICHAEL 
Published: March 2003

AbstractThe 18O content of leaf water strongly influences the 18O contents of atmospheric CO2 and O2. The 18O signatures of these atmospheric gases, in turn, emerge as important indicators of large‐scale gas exchange processes. Better understanding of the factors that influence the isotopic composition of leaf water is still required, however, for the quantitative utilization of these tracers. The 18O enrichment of leaf water relative to local meteoric water, is known to reflect climatic conditions. Less is known about the extent variations in the 18O content of leaf water are influenced by nonclimatic, species‐specific characteristics. In a collection of 90 plant species from all continents grown under the same climatic conditions in the Jerusalem Botanical Garden we observed variations of about 9‰ in the δ18O values of stem water, δs, and of about 14‰ in the mid‐day δ18O enrichment of bulk leaf water, δLW–δs. Differences between δ18O values predicted by a conventional evaporation model, δM, and δLW ranged between – 3.3‰ and + 11.8‰. The δ18O values of water in the chloroplasts (δch) in leaves of 10 selected plants were estimated from on‐line CO2 discrimination measurements. Although much uncertainty is still involved in these estimates, the results indicated that δch can significantly deviate from δM in species with high leaf peclet number. The δ18O values of bulk leaf water significantly correlated with δ18O values of leaf cellulose (directly) and with instantaneous water use efficiency (A/E, inversely). Differences in isotopic characteristics among conventionally defined vegetation types were not significant, except for conifers that significantly differed from shrubs in δ18O and δ13C values of cellulose and in their peclet numbers, and from deciduous woodland species in their δ18O and δ13C values of cellulose. The results indicated that predictions of the δ18O values of leaf water (δLW, δM and δch) could be improved by considering plant species‐specific characteristics.
The δ13C of tree rings in full‐bark and strip‐bark bristlecone pine trees in the White Mountains of California
Authors: Tang Kuilian , Feng Xiahong , Funkhouser GarY. 
Published: March 2003

AbstractDendrochronological work at Sheep Mountain in the White Mountains, CA has demonstrated that bristlecone pine trees in two forms, full‐bark and strip‐bark, have experienced different cambial growth rates over the past century or longer. The strip‐bark trees showed a greater growth increase than the full‐bark ones. A calculation of the plant water‐use efficiency (W) in response to anthropogenic CO2released into the atmosphere shows that W of trees in both forms has increased for the past 200 years. However, there is no significant difference between the two tree forms in the rate of increase in W. This implies at least two possibilities with respect to the CO2fertilization effect. First, the biomass in both tree forms might have increased, but carbon distribution among different parts of a tree was different. Second, the biomass may increase without causing any corresponding change in the plant water‐use efficiency.
Trophic relationships in the soil microfood‐web: predicting the responses to a changing global environment
Authors: WARDLE DAVID A. , VERHOEF HERMAN A. , CLARHOLM MARIANNE 
Published: March 2003

AbstractIn this article, we evaluate how global environmental change may affect microfood‐webs and trophic interactions in the soil, and the implications of this at the ecosystem level. First we outline how bottom‐up (resource control) and top‐down (predation‐control) forces regulate food‐web components. Food‐web components can respond either positively or negatively to shifts in NPP resulting from global change, thus creating difficulties in developing general principles about the response of soil biota to global change phenomena. We also demonstrate that top‐down effects can be important in soil food‐webs, creating negative feed‐backs which may partially counter bottom‐up effects. Secondly, we determine how soil food‐webs and the processes they regulate respond to various global change phenomena. Enhanced atmospheric CO2levels can have two main effects on plants which are relevant for the soil food‐web, i.e. enhanced NPP (often positive) and diminished organic matter quality (with negative effects, at least in the short term). Climate change effects resulting from elevated CO2levels may be mainly secondary through alteration of vegetation, as shown by examples. Intensification of land management is usually associated with greater disturbance, which alters soil food‐web composition and key processes; this is particularly apparent in comparisons of conventionally tilled and nontilled agroecosystems. Global change involves shifts in plant species composition and diversity, possibly affecting soil food‐webs; we interpret this in terms of theories relating biodiversity to ecosystem function. We conclude that a more detailed understanding of interactions between NPP, soil organic matter and components of the soil food‐web, as well as their regulation of biogeochemical processes and ultimately ecosystem‐level properties, is essential in better understanding long‐term aspects of global change phenomena.
Long‐term responses of boreal vegetation to global change: an experimental and modelling investigation
Authors: Beerling D. J. 
Published: March 2003

AbstractThe response of boreal ecosystems to future global change is an uncertain but potentially critical component of the feedback between the terrestrial biosphere and the atmosphere. To reduce some of the uncertainties in predicting the responses of this key ecosystem, the climate change experiment (CLIMEX) exposed an entire undisturbed catchment of boreal vegetation to CO2 enrichment (560 ppmv) and climate change (+ 5 °C in winter, + 3 °C in summer) for three years (1994–96). This paper describes the leaf metabolic responses of the vegetation to the experimental treatment and model simulations of possible future changes in the hydrological and carbon balance of the site. Randomized intervention analysis of the leaf gas exchange measurements for the dominant species indicated Pinus sylvestris had significantly (P < 0.01) higher photosynthetic rates and Betula pubescens and Vaccinium myrtillus had significantly (P < 0.01) lower stomatal conductances after three years treatment compared to the controls. These responses led to sustained increases in leaf water‐use efficiency of all species of trees and ground shrubs, as determined from carbon isotope analyses. Photosynthesis (A) vs. intercellular CO2 (ci) response curves (A/ci responses), RuBisCo analysis and leaf nitrogen data together suggested none of the species investigated exhibited down‐regulation in photosynthetic capacity. At the whole ecosystem level, the improved water economy of the plants did not translate into increased catchment runoff. Modelling simulations for the site indicate this was most likely brought about by a compensatory increase in evapotranspiration. In terms of the carbon budget of the site, the ecosystem model indicates that increased CO2 and temperature would lead to boreal ecosystems of the type used in CLIMEX, and typical of much of southern Norway, acting as moderate net sinks for CO2.
Monoterpene emission from coniferous trees in response to elevated CO2 concentration and climate warming
Authors: Constable JohN. V. H. , Litvak Marcy E. , Greenberg James P. , Monson Russell K. 
Published: March 2003

AbstractIt was hypothesized that high CO2 availability would increase monoterpene emission to the atmosphere. This hypothesis was based on resource allocation theory which predicts increased production of plant secondary compounds when carbon is in excess of that required for growth. Monoterpene emission rates were measured from needles of (a) Ponderosa pine grown at different CO2 concentrations and soil nitrogen levels, and (b) Douglas fir grown at different CO2 concentrations. Ponderosa pine grown at 700 μmol mol–1 CO2 exhibited increased photosynthetic rates and needle starch to nitrogen (N) ratios when compared to trees grown at 350 μmol mol–1 CO2. Nitrogen availability had no consistent effect on photosynthesis. Douglas fir grown at 550 μmol mol–1 CO2 exhibited increased photosynthetic rates as compared to growth at 350 μmol mol–1 CO2 in old, but not young needles, and there was no influence on the starch/N ratio. In neither species was there a significant effect of elevated growth CO2 on needle monoterpene concentration or emission rate. The influence of climate warming and leaf area index (LAI) on monoterpene emission were also investigated. Douglas fir grown at elevated CO2 plus a 4 °C increase in growth temperature exhibited no change in needle monoterpene concentration, despite a predicted 50% increase in emission rate. At elevated CO2 concentration the LAI increased in Ponderosa pine, but not Douglas fir. The combination of increased LAI and climate warming are predicted to cause an 80% increase in monoterpene emissions from Ponderosa pine forests and a 50% increase in emissions from Douglas fir forests. This study demonstrates that although growth at elevated CO2 may not affect the rate of monoterpene emission per unit biomass, the effect of elevated CO2 on LAI, and the effect of climate warming on monoterpene biosynthesis and volatilization, could increase canopy monoterpene emission rate.
A search for predictive understanding of plant responses to elevated [CO2]
Authors: Luo YiqI. , Reynolds James , Wang Yingping , Wolfe David 
Published: March 2003

AbstractThis paper reviews two decades of effort by the scientific community in a search for predictive understanding of plant responses to elevated [CO2]. To evaluate the progress of research in leaf photosynthesis, plant respiration, root nutrient uptake, and carbon partitioning, we divided scientific activities into four phases: (I) initial assessments derived from our existing knowledge base to provide frameworks for experimental studies; (II) experimental tests of the initial assessments; (III) in cases where assessments were invalidated, synthesis of experimental results to stimulate alternative hypotheses and further experimentation; and (IV) formation of new knowledge. This paper suggests that photosynthetic research may have gone through all four phases, considering that (a) variable responses of photosynthesis to [CO2] are generally explainable, (b) extrapolation of leaf‐level studies to the global scale has been examined, and (c) molecular studies are under way. Investigation of plant respiratory responses to [CO2] has reached the third phase: experimental results have been accumulated, and mechanistic approaches are being developed to examine alternative hypotheses in search for new concepts and/or new quantitative frameworks to understand respiratory responses to elevated [CO2]. The study of nutrient uptake kinetics is still in the second phase: experimental evidence has contradicted some of the initial assessments, and more experimental studies need to be designed before generalizations can be made. It is quite unfortunate that we have not made much progress in understanding mechanisms of carbon partitioning during the past two decades. This is due in part to the fact that some of the holistic theories, such as functional balance and optimality, have not evolved into testable hypotheses to guide experimental studies. This paper urges modelers to play an increasing role in plant–CO2research by disassembling these existing theories into hypotheses and urges experimentalists to design experiments to examine these holistic concepts.
Solar ultraviolet‐B radiation influence on Sphagnum bog and Carex fen ecosystems: first field season findings in Tierra del Fuego, Argentina
Authors: Searles Peter S. , Flint Stephan D. , Díaz Susana B. , Rousseaux M. Cecilia , Ballaré Carlos L. , Caldwell Martyn M. 
Published: March 2003

AbstractStratospheric ozone depletion occurs over Tierra del Fuego, southern Argentina and Chile, in the austral spring and summer due to the precession of the Antarctic ‘ozone hole’ and the general erosion of the ozone layer. Plots receiving either near‐ambient or reduced UV‐B radiation were established using different louvered plastic film filters over Sphagnum bog and Carex fen ecosystems in October 1996. In the Sphagnum bog system, growth measurements during the late spring and summer showed no significant differences in the moss Sphagnum magellanicum, or the vascular plants (Empetrum rubrum, Nothofagus antarctica, and Tetroncium magellanicum) between near‐ambient and attenuated UV‐B radiation treatments. In the Carex fen system, leaf length and spike height did not differ in the two dominant species, Carex decidua and C. curta, between UV‐B radiation treatments. The length of individual spikelets of C. curta under near‐ambient UV‐B radiation was less than under the reduced UV‐B radiation treatment, but this was not evident in C. decidua. No differences in seed number, seed mass, or viability were seen in either Carex species between the UV‐B treatments. Two important constituents of the microfauna that inhabit the Sphagnum bog are testate amoebae and rotifers. These both appeared to be more numerous under near‐ambient UV‐B radiation than under reduced UV‐B radiation. The subtle responses of the Sphagnum and Carex ecosystems may become more apparent in subsequent years as the treatments are continued. Trophic‐level changes, such as the differences in number of amoebae and rotifers, may be more sensitive to solar UV‐B radiation than growth and productivity of the vegetation.
Biomass production and species composition change in a tallgrass prairie ecosystem after long‐term exposure to elevated atmospheric CO2
Authors: Owensby Clenton E. , Ham Jay. M. , Knapp Alan. K. , Auen Lisa. M. 
Published: March 2003

AbstractTo 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 0–100 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.
Nitrogen accumulation and distribution in Danthonia richardsonii swards in response to CO2 and nitrogen supply over four years of growth
Authors: Lutze Jason L. , Gifford Roger M. 
Published: March 2003

SummaryNitrogen‐stressed microcosms of the C3 grass Danthonia richardsonii gained nitrogen from the environment when grown under ambient or enriched (359, ‘amb’ or 719 μL L− 1‘enr’, respectively) atmospheric CO2 concentrations over a 4‐y period. This gain was apparent at all rates of supplied mineral N (2.2, 6.7 or 19.8 g N m− 2 y− 1– low‐N, mid‐N or high‐N), although it was small at high‐N. Small losses of N occurred from the microcosm as leachate, while gaseous losses of N were estimated to be between 10% and 25% of applied mineral N. Losses of applied mineral N were slightly lower under CO2 enrichment only at the highest rate of mineral N supply. Levels of 15N natural abundance in green leaf (δ15Ν) of − 2‰ (amb low‐N) and of below − 4‰ (enr low‐ & mid‐N) suggest that absorption of atmospheric NH3 may have been a source of some of the extra N in the low and mid‐N treatments. Biological N2 fixation, of up to 2 g m− 2 y− 1 was hypothesized to form the remainder of the environmental N source. Microcosm C:N ratio was higher under CO2 enrichment. Nitrogen productivity of microcosm carbon gain (g C accumulated g− 1 leaf N day− 1) was increased (up to 100%) by CO2 enrichment at all rates of mineral N supply. Green leaf %N was reduced by CO2 enrichment, and there was less nitrogen in the green leaf pool under CO2 enrichment. Less, or the same amount of nitrogen was present in senesced leaf, surface litter and root under CO2 enrichment while more nitrogen was present in the soil in organic forms, and as NH4 +  at the highest rate of mineral N supply.
Carbon budgeting in plant–soil mesocosms under elevated CO2: locally missing carbon?
Authors: Cheng Weixin , Sims Daniel A. , Luo Yiqi , Johnson Dale W. , Ball J. Timothy , Coleman James S. 
Published: March 2003

SummaryStudies have suggested that more carbon is fixed due to a large increase in photosynthesis in plant–soil systems exposed to elevated CO2 than could subsequently be found in plant biomass and soils –‐ the locally missing carbon phenomenon. To further understand this phenomenon, an experiment was carried out using EcoCELLs which are open‐flow, mass‐balance systems at the mesocosm scale. Naturally occurring 13C tracers were also used to separately measure plant‐derived carbon and soil‐derived carbon. The experiment included two EcoCELLs, one under ambient atmospheric CO2 and the other under elevated CO2 (ambient plus 350 μL L− 1). By matching carbon fluxes with carbon pools, the issue of locally missing carbon was investigated. Flux‐based net primary production (NPPf) was similar to pool‐based primary production (NPPp) under ambient CO2, and the discrepancy between the two carbon budgets (12 g C m− 2, or 4% of NPPf) was less than measurement errors. Therefore, virtually all carbon entering the system under ambient CO2 was accounted for at the end of the experiment. Under elevated CO2, however, the amount of NPPf was much higher than NPPp, resulting in missing carbon of approximately 80 g C m− 2 or 19% of NPPf which was much higher than measurement errors. This was additional to the 96% increase in rhizosphere respiration and the 50% increase in root growth, two important components of locally missing carbon. The mystery of locally missing carbon under elevated CO2 remains to be further investigated. Volatile organic carbon, carbon loss due to root washing, and measurement errors are discussed as some of the potential contributing factors.
Carbon‐13 input and turn‐over in a pasture soil exposed to long‐term elevated atmospheric CO2
Authors: Van Kessel Chris , Nitschelm Jennifer , Horwath William R. , Harris David , Walley Frances , Lüscher Andreas , Hartwig Ueli 
Published: March 2003

SummaryThe impact of elevated CO2 and N‐fertilization on soil C‐cycling in Lolium perenne and Trifolium repens pastures were investigated under Free Air Carbon dioxide Enrichment (FACE) conditions. For six years, swards were exposed to ambient or elevated CO2 (35 and 60 Pa pCO2) and received a low and high rate of N fertilizer. The CO2 added in the FACE plots was depleted in 13C compared to ambient (Δ−  40‰) thus the C inputs could be quantified.On average, 57% of the C associated with the sand fraction of the soil was ‘new’ C. Smaller proportions of the C associated with the silt (18%) and clay fractions (14%) were derived from FACE. Only a small fraction of the total C pool below 10 cm depth was sequestered during the FACE experiment.The annual net input of C in the FACE soil (0–10 cm) was estimated at 4.6 ± 2.2 and 6.3 ± 3.6 (95% confidence interval) Mg ha− 1 for T. repens and L. perenne, respectively. The maximum amount of labile C in the T. repens sward was estimated at 8.3 ± 1.6 Mg ha− 1 and 7.1 ± 1.0 Mg ha− 1 in the L. perenne sward. Mean residence time (MRT) for newly sequestered soil C was estimated at 1.8 years in the T. repens plots and 1.1 years for L. perenne. An average of 18% of total soil C in the 0–10 cm depth in the T. repens sward and 24% in the L. perenne sward was derived from FACE after 6 years exposure. The majority of the change in soil δ13C occurred in the first three years of the experiment. No treatment effects on total soil C were detected.The fraction of FACE‐derived C in the L. perenne sward was larger than in the T. repens sward. This suggests a priming effect in the L. perenne sward which led to increased losses of the old C. Although the rate of C cycling was affected by species and elevated CO2, the soil in this intensively managed grassland ecosystem did not become a sink for additional new C.
The role of low‐level ozone exposure and mycorrhizas in chemical quality and insect herbivore performance on Scots pine seedlings
Authors: Manninen Anne‐Marja , Holopainen Toini , Lyytikäinen‐Saarenmaa Päivi , Holopainen Jarmo K. 
Published: March 2003

SummaryThe effects of low‐level ozone exposure and suppression of natural mycorrhizas on the above‐ground chemical quality of Scots pine (Pinus sylvestrisL.) needles and insect herbivore performance were studied in a two‐year field experiment. Seedlings were fumigated with the ozone doses 1.5–1.7 times the ambient, and natural mycorrhizal infection level was about 35% reduced in roots with fungicide propiconazole. On ozone‐exposed seedlings the mean relative growth rate (MRGR) ofLygus rugulipennisPopp. nymphs was lower than on ambient ozone seedlings, butGilpinia pallidaKlug sawfly larvae grew better on elevated ozone seedlings than on ambient ozone seedlings. MRGR ofSchizolachnus pinetiFabr. andCinara pineaL. aphid nymphs orNeodiprion sertiferGeoffr. sawfly larvae or the oviposition ofL. rugulipennisandN. sertiferwere not affected by ozone exposure. Although ozone exposure did not affect total phenolics, total terpene, total or individual resin acid, total free amino acid, nutrient or sugar concentrations in needles, MRGR ofL. rugulipennispositively correlated with total terpenes and MRGR ofG. pallidapositively with total amino acids. In addition, ozone exposure increased serine and proline concentration and marginally also starch concentration in needles. When mycorrhizas were reduced with fungicide, only MRGR ofL. rugulipennisnymphs increased, but performance of other insect herbivores studied was not changed. However, number ofL. rugulipenniseggs correlated positively with mycorrhizal infection level and also with total sugars. Reduction of mycorrhizas did not strongly affect the concentrations of analysed compounds in needles, because only phosphorus and potassium and some individual resin acids were reduced by fungicide treatment. These results suggest that low‐level ozone exposure and moderately declined mycorrhizal infection do not drastically affect either the above‐ground chemical quality of Scots pine seedlings or performance of studied insect herbivores.