bluuebunny/crossref_metadata_2025_split huggingface dataset:
Toward an allocation scheme for global terrestrial carbon models
Authors: Friedlingstein P. , Joel G. , Field C. B. , Fung I. Y. 
Published: March 2003

SummaryThe distribution of assimilated carbon among the plant parts has a profound effect on plant growth, and at a larger scale, on terrestrial biogeochemistry. Although important progress has been made in modelling photosynthesis, less effort has been spent on understanding the carbon allocation, especially at large spatial scales. Whereas several individual‐level models of plant growth include an allocation scheme, most global terrestrial models still assume constant allocation of net primary production (NPP) among plant parts, without any environmental coupling. Here, we use the CASA biosphere model as a platform for exploring a new global allocation scheme that estimates allocation of photosynthesis products among leaves, stems, and roots depending on resource availability. The philosophy underlying the model is that allocation patterns result from evolved responses that adjust carbon investments to facilitate capture of the most limiting resources, i.e. light, water, and mineral nitrogen. In addition, we allow allocation of NPP to vary in response to changes in atmospheric CO2. The relative magnitudes of changes in NPP and resource‐use efficiency control the response of root:shoot allocation. For ambient CO2, the model produces realistic changes in above‐ground allocation along productivity gradients. In comparison to the CASA standard estimate using fixed allocation ratios, the new allocation scheme tends to favour root allocation, leading to a 10% lower global biomass. Elevated CO2, which alters the balance between growth and available resources, generally leads to reduced water stress and consequently, decreased root:shoot ratio. The major exception is forest ecosystems, where increased nitrogen stress induces a larger root allocation.
A moderate increase in the annual CH4 efflux by raised CO2 or NH4NO3 supply in a boreal oligotrophic mire
Authors: Saarnio Sanna , Saarinen T.I.M.O. , Vasander Harri , Silvola Jouko 
Published: March 2003

SummaryNatural wetlands release about 20% of global emissions of CH4, an effective greenhouse gas contributing to the total radiative forcing. Thus, changes in the carbon cycle in wetlands could have significant impacts on climate. The effect of raised supply of CO2 or NH4NO3 on the annual CH4 efflux from the lawn of a boreal oligotrophic mire was investigated over two years. Ten study plots were enclosed with mini‐FACE rings, five vented with CO2‐enriched air and the other five with ambient air. In addition, five plots were sprayed with NH4NO3 so that the cumulative addition of N was 3 g m−2 y−1; and five plots were controls. The CO2 enrichment (target concentration 560 ppmv) increased CH4 efflux about 30–40%, but half of this increase seemed to be caused by the air‐blowing system. The increasing atmospheric concentration of CO2 would promote CH4 release in boreal mires, but the increase in CH4 efflux would be clearly smaller than that reported in studies made in temperate or subtropical temperature conditions. Addition of N enhanced the annual release of CH4 only slightly. At least over the short‐term, the increase in N deposition would have little effect on CH4 effluxes. The increase in CH4 release would probably increase radiative forcing and thus accelerate climate change. However, CH4 effluxes are only a small part in the whole matter balance in mires and thus further studies are needed to define the net effects of raised supply of CO2 or N for carbon accumulation, trace gas fluxes and radiative forcing.
Links between large‐scale anomalies, rainfall and wine quality in the Iberian Peninsula during the last three decades
Authors: Rodó Xavier , Comín F. A. 
Published: March 2003

SummaryRecent strong El Niño‐Southern Oscillation (ENSO) signals have been identified in precipitation records from the Iberian Peninsula. Interannual association with ENSO accounts for more than half the total annual variance in selected stations of the south‐east, with ENSO leading rainfall by one year. In contrast, association with the North Atlantic Oscillation (NAO) at the Westernmost stations is much lower (25%). The potential of simple linear models is tested in the ENSO‐sensitive area, suggesting high capability of the Southern Oscillation Index (SOI) for predicting interannual rainfall fluctuations (mainly droughts and floods). Wine quality is associated with several factors, e.g. grape variety, soil type and processing, which can be considered invariable, mainly due to the strict regulations imposed by the quality regulating councils. Climate, however, has a great influence on resulting wine quality, and represents the most important source of variability at both short (day‐to‐day) and long (interannual) time scales.Over the last 30 years, high‐quality harvests in the five main wine regions in Spain, show a high probability (P < 0.0002) of being associated with an El Niño event occurring the same year or the year before. NAO influence is not significant during the same period. Thus, apart from considering the role of local climatic conditions in certain regions, which favour the production of excellent wines, larger‐scale climatic phenomena appear responsible for the year‐to‐year variations in quality.
Elevated atmospheric CO2 and increased nitrogen deposition: effects on C and N metabolism and growth of the peat moss Sphagnum recurvum P. Beauv. var. mucronatum (Russ.) Warnst
Authors: Van Der Heijden Edwin , Verbeek Steven K. , Kuiper Pieter J. C. 
Published: March 2003

Summary Sphagnum bogs play an important role when considering the impacts of global change on global carbon and nitrogen cycles. Sphagnum recurvum P. Beauv. var. mucronatum (Russ.) was grown at 360 (ambient) and 700 μL L−1 (elevated) atmospheric [CO2] in combination with different nitrogen deposition rates (6, 15, 23 g N m−2 y−1), in a short‐ and long‐term growth chamber experiment.After 6 months, elevated atmospheric [CO2] in combination with the lowest nitrogen deposition rate, increased plant dry mass by 17%. In combination with a high nitrogen deposition rate, biomass production was not significantly stimulated.At the start of the experiment, photosynthesis was stimulated by elevated atmospheric [CO2], but it was downregulated to control levels after three days of exposure. Elevated [CO2] substantially reduced dark respiration, which resulted in a continuous increase in soluble sugar content in capitula. Differences in growth response among different nitrogen and CO2 treatments could not be related to measured carbon exchange rates, which was mainly due to interference of microbial respiration.Doubling atmospheric [CO2] reduced total nitrogen content in capitula but not in stems at all nitrogen deposition rates. Reduction in total nitrogen content coincided with a decrease in amino acids, but soluble protein levels remained unaffected. Thus, elevated [CO2] induced a substantial shift in the partitioning of nitrogen compounds in capitula. Soluble sugar concentration was negatively correlated with total nitrogen content, which implies that the reduction in amino acid content in capitula, exposed to elevated [CO2], might be caused by the accumulation of soluble sugars.Growth was not stimulated by increased nitrogen deposition. High nitrogen deposition, resulting in a capitulum nitrogen content in excess of 15 mg g−1 dw, was detrimental to photosynthesis, reduced water content and induced necrosis. We propose a capitulum nitrogen content of 15 mg g−1 dw as a possible bioindicator for the detection of nitrogen pollution stress in oligo‐mesotrophic peat bog ecosystems.At the lowest nitrogen deposition level, nitrogen recovery was higher than 100%, which indicates substantial dry deposition and/or gaseous nitrogen fixation by bacteria, associated with Sphagnum. Increasing nitrogen deposition rates decreased nitrogen recovery percentages, which indicates reduced efficiency of nitrogen fixation.
Mechanisms and kinetics of nitric and nitrous oxide production during nitrification in agricultural soil
Authors: Venterea Rodney T. , Rolston Dennis E. 
Published: March 2003

SummaryLaboratory experiments were conducted with three California agricultural soils to examine substrate and process controls over temporal variability of NO and N2O production during nitrification, and to quantify the kinetics of HNO2‐mediated chemical reactions. Gross NO production rates were highly correlated (r2 = 0.93–0.97) with calculated concentrations of HNO2, which were shown to originate from autotrophic microbial oxidation of

NH4 + to
NO2 − Production of NO was not correlated with
NH4 + or NO3–, or with the overall nitrification rate. Distinct periods of high NO2– accumulation occurred below critical pH values in each soil, apparently due to inhibition of microbial NO2– oxidation. Data suggest that even during periods of relatively low NO2– accumulation and rapid overall nitrification, HNO2‐mediated reactions may have been the primary source of NO. Rate coefficients (kPNO) relating NO production to HNO2 concentrations were determined for sterile (λ‐irradiated) soils, and were similar to kPNO values in 2 of 3 nonsterile soils undergoing nitrification. Production of N2O was correlated with HNO2 (r2 = 0.88–0.99) in sterile soils, and with NO2– and NO3– (R2 = 0.72–0.91) in nonsterile soils. Experiments using 15N confirmed that dissimilatory NO3– reduction contributed to N2O production even under primarily aerobic conditions. Sterile kPNO and kPN2O values were correlated (r2 = 0.90 and 0.82) with soil organic matter content. Overall, the results demonstrate that both steps of the nitrification sequence, together with abiotic reactions involving NO2–/HNO2 need to be considered in developing improved models of NO and N2O emissions from soils.
Infection with the parasitic angiosperm Striga hermonthica influences the response of the C3 cereal Oryza sativa to elevated CO2
Authors: Watling Jennifer R. , Press Malcolm C. 
Published: March 2003

SummaryUpland rice (Oryza sativa L.) was grown at both ambient (350 μmol mol−1) and elevated (700 μmol mol−1) CO2 in either the presence or absence of the root hemi‐parasitic angiosperm Striga hermonthica (Del) Benth. Elevated CO2 alleviated the impact of the parasite on host growth: biomass of infected rice grown at ambient CO2 was 35% that of uninfected, control plants, while at elevated CO2, biomass of infected plants was 73% that of controls. This amelioration occurred despite the fact that O. sativa grown at elevated CO2 supported both greater numbers and a higher biomass of parasites per host than plants grown at ambient CO2. The impact of infection on host leaf area, leaf mass, root mass and reproductive tissue mass was significantly lower in plants grown at elevated as compared with ambient CO2. There were significant CO2 and Striga effects on photosynthetic metabolism and instantaneous water‐use efficiency of O. sativa. The response of photosynthesis to internal [CO2] (A/Ci curves) indicated that, at 45 days after sowing (DAS), prior to emergence of the parasites, uninfected plants grown at elevated CO2 had significantly lower CO2 saturated rates of photosynthesis, carboxylation efficiencies and ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco; EC 4.1.1.39) contents than uninfected, ambient CO2‐grown O. sativa. In contrast, infection with S. hermonthica prevented down‐regulation of photosynthesis in O. sativa grown at elevated CO2, but had no impact on photosynthesis of hosts grown at ambient CO2. At 76 DAS (after parasites had emerged), however, infected plants grown at both elevated and ambient CO2 had lower carboxylation efficiencies and Rubisco contents than uninfected O. sativa grown at ambient CO2. The reductions in carboxylation efficiency (and Rubisco content) were accompanied by similar reductions in nitrogen concentration of O. sativa leaves, both before and after parasite emergence. There were no significant CO2 or infection effects on the concentrations of soluble sugars in leaves of O. sativa, but starch concentration was significantly lower in infected plants at both CO2 concentrations. These results demonstrate that elevated CO2 concentrations can alleviate the impact of infection with Striga on the growth of C3 hosts such as rice and also that infection can delay the onset of photosynthetic down‐regulation in rice grown at elevated CO2.
A mechanistic evaluation of photosynthetic acclimation at elevated CO2
Authors: Rogers Alistair , Humphries Steven W. 
Published: March 2003

SummaryPlants grown at elevated pCO2 often fail to sustain the initial stimulation of net CO2 uptake rate (A). This reduced, acclimated, stimulation of A often occurs concomitantly with a reduction in the maximum carboxylation velocity (Vc,max) of Rubisco. To investigate this relationship we used the Farquhar model of C3 photosynthesis to predict the minimum Vc,max capable of supporting the acclimated stimulation in A observed at elevated pCO2. For a wide range of species grown at elevated pCO2 under contrasting conditions we found a strong correlation between observed and predicted values of Vc,max. This exercise mechanistically and quantitatively demonstrated that the observed acclimated stimulation of A and the simultaneous decrease in Vc,max observed at elevated pCO2 is mechanistically consistent. With the exception of plants grown at a high elevated pCO2 (> 90 Pa), which show evidence of an excess investment in Rubisco, the failure to maintain the initial stimulation of A is almost entirely attributable to the decrease in Vc,max and investment in Rubisco is coupled to requirements.
Terrestrial organic carbon storage in a British moorland
Authors: Garnett MarK. H. , Ineson Philip , Stevenson Anthony C. , Howard David C. 
Published: March 2003

SummaryAccurate estimates for the size of terrestrial organic carbon (C) stores are needed to determine their importance in regulating atmospheric CO2 concentrations. The C stored in vegetation and soil components of a British moorland was evaluated in order to: (i) investigate the importance of these ecosystems for C storage and (ii) test the accuracy of the United Kingdom's terrestrial C inventory. The area of vegetation and soil types was determined using existing digitized maps and a Geographical Information System (GIS). The importance of evaluating C storage using 2D area projections, as opposed to true surface areas, was investigated and found to be largely insignificant. Vegetation C storage was estimated from published results of productivity studies at the site supplemented by field sampling to evaluate soil C storage. Vegetation was found to be much less important for C storage than soil, with peat soils, particularly Blanket bog, containing the greatest amounts of C. Whilst the total amount of C in vegetation was similar to the UK national C inventory's estimate for the same area, the national inventory estimate for soil C was over three times higher than the value derived in the current study. Because the UK's C inventory can be considered relatively accurate compared to many others, the results imply that current estimates for soil C storage, at national and global scales, should be treated with caution.
Interspecies variation in nitrogen uptake kinetic responses of temperate forest species to elevated CO2: potential causes and consequences
Authors: Zerihun Ayalsew , Bassirirad Hormoz 
Published: March 2003

SummaryDespite the recognition that the capacity to acquire N is critical in plant response to CO2 enrichment, there is little information on how elevated CO2 affects root N uptake kinetics. The few available data indicate a highly variable pattern of response to elevated CO2, but it is presently unclear if the observed inconsistencies are caused by differences in experimental protocols or by true species differences. Furthermore, if there are interspecific variations in N uptake responses to elevated CO2, it is not clear whether these are associated with different functional groups. Accordingly, we examined intact root‐system NH4+ and NO3– uptake kinetic responses to elevated CO2 in seedlings of six temperate forest tree species, representing (i) fast‐ vs. slow‐growers and (ii) broad‐leaves vs. conifers, that were cultured and assayed in otherwise similar conditions. In general, the species tested had a higher uptake capacity (Vmax) for NH4+ than for NO3–. Species substantially differed in their NO3– and NH4+ uptake capacities, but the interspecific differences were markedly greater for NO3– than NH4+ uptake. Elevated CO2 had a species‐dependent effect on root uptake capacity for NH4+ ranging from an increase of 215% in Acer negundo L. to a decrease of about 40% in Quercus macrocarpa Michx. In contrast, NO3– uptake capacity responded little to CO2 in all the species except A. negundo in which it was significantly down‐regulated at elevated CO2. Across species, the capacity for NH4+ uptake was positively correlated with the relative growth rate (RGR) of species; however, the CO2 effect on NH4+ uptake capacity could not be explained by changes in RGR. The observed variation in NH4+ uptake response to elevated CO2 was also inconsistent with life‐form differences. Other possible mechanisms that may explain why elevated CO2 elicits a species‐specific response in root N uptake kinetics are discussed. Despite the fact that the exact mechanism(s) for such interspecific variation remains unresolved, these differences may have a significant implication for competitive interactions and community responses to elevated CO2 environment. We suggest that differential species responses in nutrient uptake capacity could be one potential mechanism for the CO2‐induced shifts in net primary productivity and species composition that have been observed in experimental communities exposed to elevated levels of CO2.
Assessing forest growth across southwestern Oregon under a range of current and future global change scenarios using a process model, 3‐PG
Authors: Coops N. C. , Waring R. H. 
Published: March 2003

SummaryWith improvements in mapping regional distributions of vegetation using satellite‐derived information, there is an increasing interest in the assessment of current limitations on forest growth and in making projections of how productivity may be altered in response to changing climatic conditions and management policies. We utilised a simplified physiologically based process model (3‐PG) across a 54 000 km2 mountainous region of southwestern Oregon, USA, to evaluate the degree to which maximum periodic mean annual increment (PAI) of forests could be predicted at a set of 448 forest inventory plots. The survey data were pooled into six broad forest types (coastal rain forest, interior coast range forest, mixed conifer, dry‐site Douglas‐fir, subalpine forest, and pine forest) and compared to the 3‐PG predictions at a spatial resolution of 1 km2. We found good agreement (r2 = 0.84) between mean PAI values of forest productivity for the six forest types with those obtained from field surveys. With confidence at this broader level of integration, we then ran model simulations to evaluate the constraints imposed by (i) soil fertility under current climatic conditions, (ii) the effect of doubling monthly precipitation across the region, and (iii) a widely used climatic change scenario that involves modifications in monthly mean temperatures and precipitation, as well as a doubling in atmospheric CO2 concentrations. These analyses showed that optimum soil fertility would more than double growth, with the greatest response in the subalpine type and the least increase in the coastal rain forests. Doubling the precipitation increased productivity in the pine type (> 50%) with reduced responses elsewhere. The climate change scenario with doubled atmospheric CO2 increased growth by 50% on average across all forest types, primarily as a result of a projected 33% increase in photosynthetic capacity. This modelling exercise indicates that, at a regional scale, a general relationship exists between simulated maximum leaf area index and maximum aboveground growth, supporting the contention that satellite‐derived estimates of leaf area index may be good measures of the potential productivity of temperate evergreen forests.
Raised atmospheric CO2 levels and increased N deposition cause shifts in plant species composition and production in Sphagnum bogs
Authors: Berendse Frank , Van Breemen Nico , Rydin HÅkan , Buttler Alexandre , Heijmans Monique , Hoosbeek Marcel R. , Lee John A. , Mitchell Edward , Saarinen Timo , Vasander Harri , Wallén Bo 
Published: March 2003

AbstractPart of the missing sink in the global CO2 budget has been attributed to the positive effects of CO2 fertilization and N deposition on carbon sequestration in Northern Hemisphere terrestrial ecosystems. The genus Sphagnum is one of the most important groups of plant species sequestrating carbon in temperate and northern bog ecosystems, because of the low decomposability of the dead material it produces. The effects of raised CO2 and increased atmospheric N deposition on growth of Sphagnum and other plants were studied in bogs at four sites across Western Europe. Contrary to expectations, elevated CO2 did not significantly affect Sphagnum biomass growth. Increased N deposition reduced Sphagnum mass growth, because it increased the cover of vascular plants and the tall moss Polytrichum strictum. Such changes in plant species composition may decrease carbon sequestration in Sphagnum‐dominated bog ecosystems.
Evapotranspiration and soil water content in a scrub‐oak woodland under carbon dioxide enrichment
Authors: Hungate B. A. , Reichstein M. , Dijkstra P. , Johnson D. , Hymus G. , Tenhunen J. D. , Hinkle C.R. , Drake B. G. 
Published: March 2003

AbstractLeaf conductance often decreases in response to elevated atmospheric CO2 concentration (Ca) potentially leading to changes in hydrology. We describe the hydrological responses of Florida scrub oak to elevated Ca during an eight‐month period two years after Ca manipulation began. Whole‐chamber gas exchange measurements revealed a consistent reduction in evapotranspiration in response to elevated Ca, despite an increase in leaf area index (LAI). Elevated Ca also increased surface soil water content, but xylem water deuterium measurements show that the dominant oaks in this system take up most of their water from the water table (which occurs at a depth of 1.5–3 m), suggesting that the water savings in elevated Ca in this system are primarily manifested as reduced water uptake at depth. Extrapolating these results to larger areas requires considering a number of processes that operate on scales beyond these accessible in this field experiment. Nevertheless, these results demonstrate the potential for reduced evapotranspiration and associated changes in hydrology in ecosystems dominated by woody vegetation in response to elevated Ca.