bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of elevated atmospheric CO2 on soil microbiota in calcareous grassland
Authors: Niklaus Pascal A. 
Published: March 2003

AbstractMicrobial responses to three years of CO2 enrichment (600 μL L–1) in the field were investigated in calcareous grassland. Microbial biomass carbon (C) and soil organic C and nitrogen (N) were not significantly influenced by elevated CO2. Microbial C:N ratios significantly decreased under elevated CO2 (– 15%, P = 0.01) and microbial N increased by + 18% (P = 0.04). Soil basal respiration was significantly increased on one out of 7 sampling dates (+ 14%, P = 0.03; December of the third year of treatment), whereas the metabolic quotient for CO2 (qCO2 = basal respiration/microbial C) did not exhibit any significant differences between CO2 treatments. Also no responses of microbial activity and biomass were found in a complementary greenhouse study where intact grassland turfs taken from the field site were factorially treated with elevated CO2 and phosphorus (P) fertilizer (1 g P m–2 y–1). Previously reported C balance calculations showed that in the ecosystem investigated growing season soil C inputs were strongly enhanced under elevated CO2. It is hypothesized that the absence of microbial responses to these enhanced soil C fluxes originated from mineral nutrient limitations of microbial processes. Laboratory incubations showed that short‐term microbial growth (one week) was strongly limited by N availability, whereas P was not limiting in this soil. The absence of large effects of elevated CO2 on microbial activity or biomass in such nutrient‐poor natural ecosystems is in marked contrast to previously published large and short‐term microbial responses to CO2 enrichment which were found in fertilized or disturbed systems. It is speculated that the absence of such responses in undisturbed natural ecosystems in which mineral nutrient cycles have equilibrated over longer periods of time is caused by mineral nutrient limitations which are ineffective in disturbed or fertilized systems and that therefore microbial responses to elevated CO2 must be studied in natural, undisturbed systems.
N‐poor ecosystems may respond more to elevated [CO2] than N‐rich ones in the long term. A model analysis of grassland.
Authors: Cannell M. G. R. , Thornley J. H. M. 
Published: March 2003

AbstractThe Hurley Pasture Model was used to examine the short and long‐term responses of grazed grasslands in the British uplands to a step increase from 350 to 700 μmol mol–1 CO2 concentration ([CO2]) with inputs of 5 or 100 kg N ha–1 y–1. In N‐rich grassland, [CO2] doubling quickly increased net primary productivity (NPP), total carbon (Csys) and plant biomass by about 30%. By contrast, the N‐poor grassland underwent a prolonged ‘transient’, when there was little response, but eventually NPP, Csys and plant biomass more than doubled. The ‘transient’ was due to N immobilization and severe depletion of the soil mineral N pool. The large long‐term response was due to slow N accumulation, as a result of decreased leaching, decreased gaseous N losses and increased N2‐fixation, which amplified the CO2 response much more in the N‐poor than in the N‐rich grassland. It was concluded that (i) ecosystems use extra carbon fixed at high [CO2] to acquire and retain nutrients, supporting the contention of Gifford et al. (1996), (ii) in the long term, and perhaps on the real timescale of increasing [CO2], the response (in NPP, Csys and plant biomass) of nutrient‐poor ecosystems may be proportionately greater than that of nutrient‐rich ones, (iii) short‐term experiments on nutrient‐poor ecosystems may observe only the transient responses, (iv) the speed of ecosystem responses may be limited by the rate of nutrient accumulation rather than by internal rate constants, and (v) ecosystem models must represent processes affecting nutrient acquisition and retention to be able to simulate likely real‐world CO2 responses.
Do slow‐growing species and nutrient‐stressed plants respond relatively strongly to elevated CO2?
Authors: POORTER HENDRIK 
Published: March 2003

AbstractMainly based on a simulation model,Lloyd & Farquhar (1996;Functional Ecology, 10, 4–32) predict that inherently slow‐growing species and nutrient‐stressed plants show a relatively strong growth response to an increased atmospheric CO2concentration. Compiling published experiments, I conclude that these predictions are not supported by the available data. On average, inherently fast‐growing species are stimulated proportionately more in biomass than slow‐growing species and plants grown at a high nutrient supply respond more strongly than nutrient‐stressed plants.
Solar UV‐B and visible radiation in tropical forest gaps: measurements partitioning direct and diffuse radiation
Authors: FLINT STEPHAN D. , CALDWELL MARTYN M. 
Published: March 2003

AbstractSolar ultraviolet‐B (UV‐B) radiation penetrates plant canopies to a different degree than photosynthetically active radiation (PAR) because UV‐B is diffused to a greater degree by the atmosphere. We measured both global (total) and diffuse solar radiation in canopy gaps of a semideciduous tropical forest in Panama. Measurements were simultaneously made in the UV‐B and PAR wavebands. Compared to unobstructed measurements taken outside the forest, the sunlit portions of gaps were depleted in the proportion of UV‐B relative to PAR, especially at midday. Shaded areas, in contrast, were always richer in UV‐B relative to PAR, but the magnitude of the change varied greatly. Presumably this variation was due to the differences in the directional nature of diffuse solar UV‐B radiation as compared to diffuse PAR. Measurements in the gaps showed substantial reductions in the proportion of radiation in the diffuse components of both the UV‐B and PAR wavebands. However, because of the greater proportion of UV‐B which is diffuse, it tended to predominate in shaded areas. Similar patterns were seen in measurements taken at temperate latitudes. Response of shade‐ and gap‐dwelling plants to these high UV‐B:PAR ratios has received little attention.
CO2 partial pressure controls the calcification rate of a coral community
Authors: Leclercq N.I.colas , Gattuso J.E.A.N.‐Pierre , Jaubert J.E.A.N. 
Published: March 2003

SummaryPrevious studies have demonstrated that coral and algal calcification is tightly regulated by the calcium carbonate saturation state of seawater. This parameter is likely to decrease in response to the increase of dissolved CO2 resulting from the global increase of the partial pressure of atmospheric CO2. We have investigated the response of a coral reef community dominated by scleractinian corals, but also including other calcifying organisms such as calcareous algae, crustaceans, gastropods and echinoderms, and kept in an open‐top mesocosm. Seawater pCO2 was modified by manipulating the pCO2 of air used to bubble the mesocosm. The aragonite saturation state (Ωarag) of the seawater in the mesocosm varied between 1.3 and 5.4. Community calcification decreased as a function of increasing pCO2 and decreasing Ωarag. This result is in agreement with previous data collected on scleractinian corals, coralline algae and in a reef mesocosm, even though some of these studies did not manipulate CO2 directly. Our data suggest that the rate of calcification during the last glacial maximum might have been 114% of the preindustrial rate. Moreover, using the average emission scenario (IS92a) of the Intergovernmental Panel on Climate Change, we predict that the calcification rate of scleractinian‐dominated communities may decrease by 21% between the pre‐industrial period (year 1880) and the time at which pCO2 will double (year 2065).
Effects of lengthened growing season and soil warming on the phenology and physiology of Polygonum bistorta
Authors: Starr G.R.egory , Oberbauer Steven F. , Pop E.R.I.C. W. 
Published: March 2003

SummaryThe phenological and physiological responses of arctic tundra plant species are key to predicting their survival in a warmer climate. One of the consequences of a warmer climate in the Arctic will be a longer growing season. We examined the effects of lengthened growing season and soil warming on the widely distributed forb, Polygonum bistorta L. Three treatments were established near Toolik Lake, Alaska in 1995 and 1996: extended season, extended season with soil warming, and an unmanipulated control. The season was extended by removing the snow load in the spring and keeping the treatments free of snow in the autumn. The spring snow removal extended the snow‐free period over that of controls by 8 d in 1995 and 24 d in 1996. As a result, the number of accumulated soil thaw days and consequently the depth of soil thaw increased on the treatment plots. Polygonum bistorta responded to the treatments by becoming active earlier and senescing earlier, resulting in a growth period of similar duration to that of the controls. Leaf size and leaf number were unaffected by the treatments, as were leaf photosynthetic assimilation rates and nutrient concentrations. The results indicate that internal constraints limit the response of this species to lengthened growing season, suggesting that it is a determinant or periodic species. With climate warming, this periodic growth will put P. bistorta at a competitive disadvantage relative to plants that can respond to lengthened growing season.
The effect of elevated atmospheric carbon dioxide levels on soil bacterial communities
Authors: Bruce K. D. , Jones T. H. , Bezemer T. M. , Thompson L. J. , Ritchie D. A. 
Published: March 2003

SummaryThe effect of elevated carbon dioxide levels on total bacterial communities was studied in a series of controlled and replicated model terrestrial ecosystems over a period of 38 weeks. The bacterial community was profiled using Denaturing Gradient Gel Electrophoresis (DGGE) analysis of bacterial 16S rRNA gene fragments amplified by the Polymerase Chain Reaction from DNA extracted directly from soil. Bacterial community DGGE profiles provided three major findings: (i) there was a high degree of profile similarity after ≈ 12 weeks (one plant generation); (ii) whilst overall DGGE profile was maintained over the 38 weeks (three plant generations), the banding patterns became more diverse with time; (iii) DGGE data provided no evidence for a shift in bacterial community structure resulting from exposure of the ecosystem to an increased atmospheric CO2 level.
Measuring and modelling seasonal variation of carbon dioxide and water vapour exchange of a Pinus ponderosa forest subject to soil water deficit
Authors: Law B. E. , Williams M. , Anthoni P. M. , Baldocchi D. D. , Unsworth M. H. 
Published: March 2003

SummaryWe conducted ecosystem carbon and water vapour exchange studies in an old‐growth Pinus ponderosa forest in the Pacific North‐west region of the United States. The canopy is heterogeneous, with tall multiaged trees and an open, clumped canopy with low leaf area. Carbon assimilation can occur throughout relatively mild winters, although night frosts can temporarily halt the process and physiological factors limit its efficiency. In contrast, carbon assimilation is often limited in the ‘growing season’ by stomatal closure associated with high evaporative demand (D) and soil water deficits. All of these factors present a challenge to effectively modelling ecosystem processes. Our objective was to generate an understanding of the controls on ecosystem processes across seasonal and annual cycles from a combination of fine‐scale process modelling, ecophysiological measurements, and carbon and water vapour fluxes measured by the eddy covariance method. Flux measurements showed that 50% and 70% of the annual carbon uptake occurred outside the ‘growing season’ (defined as bud break to senescence, ∼ days 125–275) in 1996 and 1997. On a daily basis in summer, net ecosystem productivity (NEP) was low when D and soil water deficits were large. Whole ecosystem water vapour fluxes (LE) increased from spring to summer (1.0–1.9 mm d−1) as conducting leaf area increased by 30% and as evaporative demand increased, while evaporation from the soil surface became a smaller portion of total LE as soil water deficits increased. The models underestimated soil evaporation, particularly following rain. In the SPA model, varying the temperature optimum for photosynthesis seasonally resulted in overestimation of carbon uptake in winter and spring, showing that in coniferous forests, assumptions about temperature optima are clearly important. Daily estimates of soil surface CO2 flux from measurements and site meteorological data demonstrated that modelling of soil CO2 flux based on an Arrhenius‐type equation in CANPOND overestimated CO2 respired from the soil during drought and when temperatures were low.
Biomass allocation in old‐field annual species grown in elevated CO2environments: no evidence for optimal partitioning
Authors: Bernacchi C. J. , Coleman J. S. , Bazzaz F. A. , McConnaughay K. D. M. 
Published: March 2003

SummaryIncreased atmospheric carbon dioxide supply is predicted to alter plant growth and biomass allocation patterns. It is not clear whether changes in biomass allocation reflect optimal partitioning or whether they are a direct effect of increased growth rates. Plasticity in growth and biomass allocation patterns was investigated at two concentrations of CO2([CO2]) and at limiting and nonlimiting nutrient levels for four fast‐ growing old‐field annual species.Abutilon theophrasti,Amaranthus retroflexus,Chenopodium album, andPolygonum pensylvanicumwere grown from seed in controlled growth chamber conditions at current (350 μmol mol−1, ambient) and future‐ predicted (700 μmol mol−1, elevated) CO2levels. Frequent harvests were used to determine growth and biomass allocation responses of these plants throughout vegetative development. Under nonlimiting nutrient conditions, whole plant growth was increased greatly under elevated [CO2] for three C3 species and moderately increased for a C4 species (Amaranthus). No significant increases in whole plant growth were observed under limiting nutrient conditions. Plants grown in elevated [CO2] had lower or unchanged root:shoot ratios, contrary to what would be expected by optimal partitioning theory. These differences disappeared when allometric plots of the same data were analysed, indicating that CO2‐induced differences in root:shoot allocation were a consequence of accelerated growth and development rates. Allocation to leaf area was unaffected by atmospheric [CO2] for these species. The general lack of biomass allocation responses to [CO2] availability is in stark contrast with known responses of these species to light and nutrient gradients. We conclude that biomass allocation responses to elevated atmospheric [CO2] are not consistent with optimal partitioning predictions.
Effects of elevated atmospheric CO2 on fine root production and activity in an intact temperate forest ecosystem
Authors: Matamala Roser , Schlesinger William H. 
Published: March 2003

SummaryWe investigated the effects of elevated atmospheric CO2 concentrations (ambient + 200 ppm) on fine root production and soil carbon dynamics in a loblolly pine (Pinus taeda) forest subject to free‐air CO2 enrichment (FACE) near Durham, NC (USA). Live fine root mass (LFR) showed less seasonal variation than dead fine root mass (DFR), which was correlated with seasonal changes in soil moisture and soil temperature. LFR mass increased significantly (by 86%) in the elevated CO2 treatment, with an increment of 37 g(dry weight) m−2 above the control plots after two years of CO2 fumigation. There was no long‐term increment in DFR associated with elevated CO2, but significant seasonal accumulations of DFR mass occurred during the summer of the second year of fumigation. Overall, root net primary production (RNPP) was not significantly different, but annual carbon inputs were 21.7 gC m−2 y−1 (68%) higher in the elevated CO2 treatment compared to controls. Specific root respiration was not altered by the CO2 treatment during most of the year; however, it was significantly higher by 21% and 13% in September 1997 and May 1998, respectively, in elevated CO2. We did not find statistically significant differences in the C/N ratio of the root tissue, root decomposition or phosphatase activity in soil and roots associated with the treatment. Our data show that the early response of a loblolly pine forest ecosystem subject to CO2 enrichment is an increase in its fine root population and a trend towards higher total RNPP after two years of CO2 fumigation.
Global and regional modelling of Arctic–boreal vegetation distribution and its sensitivity to altered forcing
Authors: Kittel T. G. F. , Steffen W. L. , Chapin F. S. 
Published: March 2003

SummaryUnderstanding the distribution and function of Arctic and boreal ecosystems under current conditions and their vulnerability to altered forcing is crucial to our assessment of future global environmental change. Such efforts can be facilitated by the development and application of ecological models that simulate realistic patterns of vegetation change at high latitudes. This paper reviews three classes of ecological models that have been implemented to extrapolate vegetation information in space (e.g. across the Arctic and adjacent domains) and over historical and future periods (e.g. under altered climate and other forcings). These are: (i) equilibrium biogeographical models; (ii) frame‐based transient ecosystem models, and (iii) dynamic global vegetation models (DGVMs). The equilibrium response of high‐latitude vegetation to scenarios of increased surface air temperatures projected by equilibrium biogeographical models is for tundra to be replaced by a northward shift of boreal woodland and forests. A frame‐based model (ALFRESCO) indicates the same directional changes, but illustrates how response time depends on rate of temperature increase and concomitant changes in moisture regime and fire disturbance return period. Key disadvantages of the equilibrium models are that they do not simulate time‐dependent responses of vegetation and the role of disturbance is omitted or highly generalized. Disadvantages of the frame‐based models are that vegetation type is modelled as a set unit as opposed to an association of individually simulated plant functional types and that the role of ecosystem biogeochemistry in succession is not explicitly considered. DGVMs explicitly model disturbance (e.g. fire), operate on plant functional types, and incorporate constraints of nutrient availability on biomass production in the simulation of vegetation dynamics. Under changing climate, DGVMs detail conversion of tundra to tree‐dominated boreal landscapes along with time‐dependent responses of biomass, net primary production, and soil organic matter turnover–‐which all increase with warming. Key improvements to DGVMs that are needed to portray behaviour of arctic and boreal ecosystems adequately are the inclusion of anaerobic soil processes for inundated landscapes, permafrost dynamics, and moss‐lichen layer biogeochemistry, as well as broader explicit accounting of disturbance regimes (including insect outbreaks and land management). Transient simulation of these landscapes can be further tailored to high‐latitude processes and issues by spatially interactive, gridded application of arctic/boreal frame‐based models and development of dynamic regional vegetation models (DRVMs) utilizing plant functional type schemes that capture the variety of high‐latitude environments.
Climate and vegetation controls on boreal zone energy exchange
Authors: Baldocchi Dennis , Kelliher Francis M. , Black T. A. , Jarvis Paul 
Published: March 2003

SummaryThe boreal forest, one of the world's larger biomes, is distinct from other biomes because it experiences a short growing season and extremely cold winter temperatures. Despite its size and impact on the earth's climate system, measurements of mass and energy exchange have been rare until the past five years. This paper overviews results of recent and comprehensive field studies conducted in Canada, Siberia and Scandinavia on energy exchanges between boreal forests and the atmosphere.How the boreal biosphere and atmosphere interact to affect the interception of solar energy and how solar energy is used to evaporate water and heat the air and soil is examined in detail. Specifically, we analyse the magnitudes, temporal and spatial patterns and controls of solar energy, moisture and sensible heat fluxes across the land–atmosphere interface. We interpret and synthesize field data with the aid of a soil–vegetation–atmosphere transfer model, which considers the coupling of the energy and carbon fluxes and nutrient status.Low precipitation and low temperatures limit growth of many boreal forests. These factors restrict photosynthetic capacity and lower root hydraulic conductivity and stomatal conductance of the inhabitant forests. In such circumstances, these factors interact to form a canopy that has a low leaf area index and exerts a significant resistance to evaporation. Conifer forests, growing on upland soils, for example, evaporate at rates between 25 and 75% of equilibrium evaporation and lose less than 2.5 mm day−1 of water. The open nature of many boreal conifer forest stands causes a disproportionate amount of energy exchange to occur at the soil surface. The climatic and physiological factors that yield relatively low rates of evaporation over conifer stands also cause high rates of sensible heat exchange and the diurnal development of deep planetary boundary layers. In contrast, evaporation from broad‐leaved aspen stands and fen/wetlands approach equilibrium evaporation rates and lose up to 6 mm day−1.
Direct and acclimatory responses of stomatal conductance to elevated carbon dioxide in four herbaceous crop species in the field
Authors: Bunce James A. 
Published: March 2003

SummaryIn order to separate the net effect of growth at elevated [CO2] on stomatal conductance (gs) into direct and acclimatory responses, mid‐day values of gs were measured for plants grown in field plots in open‐topped chambers at the current ambient [CO2], which averaged 350 μmol mol−1 in the daytime, and at ambient + 350 μmol mol−1[CO2] for winter wheat, winter barley, potato and sorghum. The acclimatory response was determined by comparing gs measured at 700 μmol mol−1[CO2] for plants grown at the two [CO2]. The direct effect of increasing [CO2] from 350 to 700 μmol mol−1 was determined for plants grown at the lower concentration. Photosynthetic rates were measured concurrently with gs. For all species, growth at the higher [CO2] significantly reduced gs measured at 700 μmol mol−1[CO2]. The reduction in gs caused by growth at the higher [CO2] was larger for all species on days with low leaf to air water vapour pressure difference for a given temperature, which coincided with highest conductances and also the smallest direct effects of increased [CO2] on conductance. For barley, there was no other evidence for stomatal acclimation, despite consistent down‐regulation of photosynthetic rate in plants grown at the higher [CO2]. In wheat and potato, in addition to the vapour pressure difference interaction, the magnitude of stomatal acclimation varied directly in proportion to the magnitude of down‐regulation of photosynthetic rate through the season. In sorghum, gs consistently exhibited acclimation, but there was no down‐regulation of photosynthetic rate. In none of the species except barley was the direct effect the larger component of the net reduction in gs when averaged over measurement dates. The net effect of growth at elevated [CO2] on mid‐day gs resulted from unique combinations of direct and acclimatory responses in the various species.