bluuebunny/crossref_metadata_2025 huggingface dataset:
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

Previous 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

The 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

The 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

Summary

We 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

Increased 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

We 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

Understanding 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

The 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

In 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.
Human modification of the landscape and surface climate in the next fifty years
Authors: Defries R. S. , Bounoua L , Collatz G. J.
Published: March 2003

Human modification of the landscape potentially affects exchanges of energy and water between the terrestrial biosphere and the atmosphere. This study develops a possible scenario for land cover in the year 2050 based on results from the IMAGE 2 (Integrated Model to Assess the Greenhouse Effect) model, which projects land‐cover changes in response to demographic and economic activity. We use the land‐cover scenario as a surface boundary condition in a biophysically‐based land‐surface model coupled to a general circulation model for a 15‐years simulation with prescribed sea surface temperature and compare with a control run using current land cover. To assess the sensitivity of climate to anthropogenic land‐cover change relative to the sensitivity to decadal‐scale interannual variations in vegetation density, we also carry out two additional simulations using observed normalized difference vegetation index (NDVI) from relatively low (1982–83) and high (1989–90) years to describe the seasonal phenology of the vegetation.

In the past several centuries, large‐scale land‐cover change occurred primarily in temperate latitudes through conversion of forests and grassland to highly productive cropland and pasture. Several studies in the literature indicate that past changes in surface climate resulting from this conversion had a cooling effect owing to changes in vegetation morphology (increased albedo). In contrast, this study indicates that future land‐cover change, likely to occur predominantly in the tropics and subtropics, has a warming effect governed by physiological rather than morphological mechanisms. The physiological mechanism is to reduce carbon assimilation and consequently latent relative to sensible heat flux resulting in surface temperature increases up to 2 °C and drier hydrologic conditions in locations where land cover was altered in the experiment. In addition, in contrast to an observed decrease in diurnal temperature range (DTR) over land expected with greenhouse warming, results here suggest that future land‐cover conversion in tropics could increase the DTR resulting from decreased evaporative cooling during the daytime. For grid cells with altered land cover, the sensitivity of surface temperature to future anthropogenic land‐cover change is generally within the range induced by decadal‐scale interannual variability in vegetation density in temperate latitudes but up to 1.5 °C warmer in the tropics.
Climate change and breeding parameters of great and blue tits throughout the western Palaearctic
Authors: Sanz Juan José
Published: March 2003

Increasing evidence suggests that climate change has consequences on avian breeding phenology. Here, variations in laying date and clutch size of great tit Parus major and blue tit Parus caeruleus within and between breeding populations through the western Palaearctic are examined in relation to climatic fluctuations, measured by the winter North Atlantic Oscillation (NAO) index. Within and across breeding sites, laying date was related to winter‐NAO index such that great and blue tit females lay earlier after warmer, moister winters (positive values of winter NAO‐index). The present study shows that for most populations there is an advancement of laying date, but the rate of change with respect to NAO significantly differed geographically across the western Palaearctic and did not differ between species. However, clutch size of great and blue tits was not affected by climatic fluctuations, presumably because the whole season is being shifted, but not in relation to food supplies. These combined analyses for the two species controlled for potentially confounding variables such as latitude, longitude, elevation and habitat of each study site.
Annual variation in soil respiration and its components in a coppice oak forest in Central Italy
Authors: Rey Ana , Pegoraro Emiliano , Tedeschi Vanessa , De Parri Ilaria , Jarvis Paul G. , Valentini Riccardo
Published: March 2003

In order to investigate the annual variation of soil respiration and its components in relation to seasonal changes in soil temperature and soil moisture in a Mediterranean mixed oak forest ecosystem, we set up a series of experimental treatments in May 1999 where litter (no litter), roots (no roots, by trenching) or both were excluded from plots of 4 m2. Subsequently, we measured soil respiration, soil temperature and soil moisture in each plot over a year after the forest was coppiced. The treatments did not significantly affect soil temperature or soil moisture measured over 0–10 cm depth.

Soil respiration varied markedly during the year with high rates in spring and autumn and low rates in summer, coinciding with summer drought, and in winter, with the lowest temperatures. Very high respiration rates, however, were observed during the summer immediately after rainfall events. The mean annual rate of soil respiration was 2.9 µmol m−2 s−1, ranging from 1.35 to 7.03 µmol m−2 s−1.

Soil respiration was highly correlated with temperature during winter and during spring and autumn whenever volumetric soil water content was above 20%. Below this threshold value, there was no correlation between soil respiration and soil temperature, but soil moisture was a good predictor of soil respiration. A simple empirical model that predicted soil respiration during the year, using both soil temperature and soil moisture accounted for more than 91% of the observed annual variation in soil respiration.

All the components of soil respiration followed a similar seasonal trend and were affected by summer drought. The Q10 value for soil respiration was 2.32, which is in agreement with other studies in forest ecosystems. However, we found a Q10 value for root respiration of 2.20, which is lower than recent values reported for forest sites. The fact that the seasonal variation in root growth with temperature in Mediterranean ecosystems differs from that in temperate regions may explain this difference. In temperate regions, increases in size of root populations during the growing season, coinciding with high temperatures, may yield higher apparent Q10 values than in Mediterranean regions where root growth is suppressed by summer drought.

The decomposition of organic matter and belowground litter were the major components of soil respiration, accounting for almost 55% of the total soil respiration flux. This proportion is higher than has been reported for mature boreal and temperate forest and is probably the result of a short‐term C loss following recent logging at the site.

The relationship proposed for soil respiration with soil temperature and soil moisture is useful for understanding and predicting potential changes in Mediterranean forest ecosystems in response to forest management and climate change.
Linking sequestration of 13C and 15N in aggregates in a pasture soil following 8 years of elevated atmospheric CO2
Authors: VAN GROENIGEN KEES‐JAN , HARRIS DAVID , HORWATH WILLIAM R. , HARTWIG UELI A. , VAN KESSEL CHRIS
Published: March 2003

The influence of N availability on C sequestration under prolonged elevated CO2 in terrestrial ecosystems remains unclear. We studied the relationships between C and N dynamics in a pasture seeded to Lolium perenne after 8 years of elevated atmospheric CO2 concentration (FACE) conditions. Fertilizer‐15N was applied at a rate of 140 and 560 kg N ha2−1 y2−1 and depleted 13C‐CO2 was used to increase the CO2 concentration to 60 Pa pCO2. The 13C–15N dual isotopic tracer enabled us to study the dynamics of newly sequestered C and N in the soil by aggregate size and fractions of particulate organic matter (POM), made up by intra‐aggregate POM (iPOM) and free light fraction (LF). Eight years of elevated CO2 did not increase total C content in any of the aggregate classes or POM fractions at both rates of N application. The fraction of new C in the POM fractions also remained largely unaffected by N fertilization. Changes in the fractions of new C and new N (fertilizer‐N) under elevated CO2 were more pronounced between POM classes than between aggregate size classes. Hence, changes in the dynamics of soil C and N cycling are easier to detect in the POM fractions than in the whole aggregates. Within N treatments, fractions of new C and N in POM classes were highly correlated with more new C and N in large POM fractions and less in the smaller POM fractions. Isotopic data show that the microaggregates were derived from the macro‐aggregates and that the C and N associated with the microaggregates turned over slower than the C and N associated with the macroaggregates. There was also isotopic evidence that N immobilized by soil microorganisms was an important source of N in the iPOM fractions. Under low N availability, 3.04 units of new C per unit of fertilizer N were sequestered in the POM fractions. Under high N availability, the ratio of new C sequestered per unit of fertilizer N was reduced to 1.47. Elevated and ambient CO2 concentrations lead to similar 15N enrichments in the iPOM fractions under both low and high N additions, clearly showing that the SOM‐N dynamics were unaffected by prolonged elevated CO2 concentrations.
Response of tundra ecosystem in southwestern Alaska to Younger‐Dryas climatic oscillation
Authors: HU F. S. , LEE B. Y. , KAUFMAN D. S. , YONEJI S. , NELSON D. M. , HENNE P. D.
Published: March 2003

Climatic warming during the last glacial–interglacial transition (LGIT) was punctuated by reversals to glacial‐like conditions. Palaeorecords of ecosystem change can help document the geographical extent of these events and improve our understanding of biotic sensitivity to climatic forcing. To reconstruct ecosystem and climatic variations during the LGIT, we analyzed lake sediments from southwestern Alaska for fossil pollen assemblages, biogenic‐silica content (BSiO2%), and organic‐carbon content (OC%). Betula shrub tundra replaced herb tundra as the dominant vegetation of the region around 13 600 cal BP (cal BP: 14C calibrated calendar years before present), as inferred from an increase of Betula pollen percentages from << 5% to >> 20% with associated decreases in Cyperaceae, Poaceae, and Artemisia. At c. 13 000 cal BP, a decrease of Betula pollen from 28 to << 5% suggests that shrub tundra reverted to herb tundra. Shrub tundra replaced herb tundra to resume as the dominant vegetation at 11 600 cal BP. Higher OC% and BSiO2% values suggest more stable soils and higher aquatic productivity during shrub‐tundra periods than during herb‐tundra periods, although pollen changes lagged behind changes in the biogeochemical indicators before c. 13 000 cal BP. Comparison of our palaeoecological data with the ice‐core dδ18O record from Greenland reveals strikingly similar patterns from the onset through the termination of the Younger Dryas (YD). This similarity supports the hypothesis that, as in the North Atlantic region, pronounced YD climatic oscillations occurred in the North Pacific region. The rapidity and magnitude of ecological changes at the termination of the YD are consistent with greenhouse experiments and historic photographs demonstrating tundra sensitivity to climatic forcing.
Northern hemisphere photosynthetic trends 1982–99
Authors: Slayback Daniel A. , Pinzon Jorge E. , Los Sietse O. , Tucker Compton J.
Published: March 2003

We examined trends in the averaged May–September AVHRR normalized difference vegetation index (NDVI) from 1982 to 1999 for the northern hemisphere. NDVI is closely related to the amount of absorbed photosynthetically active radiation; hence, trends in NDVI reflect trends in photosynthetic activity of land‐surface vegetation. Linear and nonlinear trend analysis techniques were applied to four differently processed and corrected Advanced Very High Resolution Radiometer (AVHRR) NDVI data sets. The results were compared in order to evaluate the effects of trends in NDVI unrelated to vegetation activity. We consistently found significant positive trends in averaged NDVI for latitude bands above 35°N in all but one data set; this one data set lacked corrections for sensor drift and instrument calibration. An impressive improvement in data quality was achieved by applying calibration and corrections for atmospheric effects.

Conservative estimates of the trends over the 1982–99 period range from 0.0015 to 0.0045 NDVI units year−1 for global latitude bands from 35 to 75°N, with trends generally higher in the 1990s than in the 1980s; trends in NDVI were larger than trends explained by artefacts. In the 1980s, North American and Eurasian trends were roughly comparable, whereas in the 1990s the North American trends were generally higher. A pixel‐level analysis shows the trends to be widespread, with large areas of Canada, Europe and northern Asia experiencing significant positive increases across all vegetated landcovers.
Nitrous oxide emission factors for agricultural soils in Great Britain: the impact of soil water‐filled pore space and other controlling variables
Authors: Dobbie Karen E. , Smith Keith A.
Published: March 2003

Measurements were made of nitrous oxide (N2O) emissions from N‐fertilised ungrazed grassland and arable land at sites widely distributed across Great Britain during 1999–2001. The closed static chamber method was used throughout. Emissions varied widely throughout the year at each site, and between sites. Daily fluxes up to 1200 g N2O–N ha−1 d−1 were recorded. The highest annual flux was 27.6 kg N2O–N ha−1 at a grassland site in Wales, whereas the lowest, 1.7 kg N2O–N ha−1, occurred on a soil overlying chalk in southern England. The key factors affecting N2O emissions from agricultural soil were soil WFPS, temperature and soil NO3––N content. On grassland, rainfall (particularly around the time of N application), with its consequent effect on water‐filled pore space (WFPS), was the main driving factor during the growing season. Annual emission factors (EFs), uncorrected for background emission, varied from 0.4 to 6.5% of the nitrogen (N) applied, covering a similar range for grassland to that found previously for sites restricted to Scotland. Continued monitoring at a grassland reference site near Edinburgh showed that annual EFs vary greatly from year to year, even with similar management, and that several years' data are required to produce a robust mean EF. The overall distribution of EFs in this and previous studies was log‐normal. The EFs for small‐grain cereals (and oilseed rape) peaked at a much lower value than those for grassland, whereas the values for leafy vegetables and potato crops fitted well into the grassland distribution. These differences in EF between various types of crop should be taken into account when compiling regional or national N2O emission inventories.
Development of region‐specific emission factors and estimation of methane emission from rice fields in the East, Southeast and South Asian countries
Authors: Yan Xiaoyuan , Ohara Toshimasa , Akimoto Hajime
Published: March 2003

Rice cultivation areas in East, Southeast and South Asia account for 89% of the world total, and field measurements of methane (CH4) emission from rice cultivation have been widely performed in this area. In this paper, we assembled most of the measurements and developed region‐specific CH4 emission factors. Efforts were made in order to regionalize rice fields by climate and soil properties, and to incorporate the effect of organic input and water regime on emission. Data on rice cultivation areas of 1995 were collected at subdivision level (province, state, prefecture, etc.). Total emission from these areas was estimated at 25.1 Tg CH4 year−1, of which 7.67 Tg was emitted from China and 5.88 Tg from India. Irrigated and rainfed rice fields contributed 70.4 and 27.5% to the total emission, respectively. Deepwater rice fields had a very small share. A high‐resolution and quality emission distribution map was constructed as the emission was directly estimated at province level and below that, a 30‐second land‐use dataset was used in order to translate the emission to grid format. As the rice cultivation area in the study region accounts for 89% of the world total, extrapolating the estimate to the global scale indicates a global emission of 28.2 Tg CH4 year−1.

The estimate was compared with country reports made by local scientists. For some countries – such as Indonesia, Myanmar, Thailand, Vietnam, Japan, South Korea, Pakistan and the Philippines – the results of this estimate agree reasonably well with their country reports (CV < 15%). For some other countries – such as China, India and Bangladesh – there is relatively large disagreement between our estimate and their country reports. The reasons for the discrepancies were discussed.
Evaluation of ecosystem dynamics, plant geography and terrestrial carbon cycling in the LPJ dynamic global vegetation model
Authors: Sitch S. , Smith B. , Prentice I. C. , Arneth A. , Bondeau A. , Cramer W. , Kaplan J. O. , Levis S. , Lucht W. , Sykes M. T. , Thonicke K. , Venevsky S.
Published: March 2003

The Lund–Potsdam–Jena Dynamic Global Vegetation Model (LPJ) combines process‐based, large‐scale representations of terrestrial vegetation dynamics and land‐atmosphere carbon and water exchanges in a modular framework. Features include feedback through canopy conductance between photosynthesis and transpiration and interactive coupling between these ‘fast’ processes and other ecosystem processes including resource competition, tissue turnover, population dynamics, soil organic matter and litter dynamics and fire disturbance. Ten plants functional types (PFTs) are differentiated by physiological, morphological, phenological, bioclimatic and fire‐response attributes. Resource competition and differential responses to fire between PFTs influence their relative fractional cover from year to year. Photosynthesis, evapotranspiration and soil water dynamics are modelled on a daily time step, while vegetation structure and PFT population densities are updated annually.

Simulations have been made over the industrial period both for specific sites where field measurements were available for model evaluation, and globally on a 0.5°° × 0.5°° grid. Modelled vegetation patterns are consistent with observations, including remotely sensed vegetation structure and phenology. Seasonal cycles of net ecosystem exchange and soil moisture compare well with local measurements. Global carbon exchange fields used as input to an atmospheric tracer transport model (TM2) provided a good fit to observed seasonal cycles of CO2concentration at all latitudes. Simulated inter‐annual variability of the global terrestrial carbon balance is in phase with and comparable in amplitude to observed variability in the growth rate of atmospheric CO2. Global terrestrial carbon and water cycle parameters (pool sizes and fluxes) lie within their accepted ranges. The model is being used to study past, present and future terrestrial ecosystem dynamics, biochemical and biophysical interactions between ecosystems and the atmosphere, and as a component of coupled Earth system models.
Potential effects of warming and drying on peatland plant community composition
Authors: Weltzin Jake F. , Bridgham Scott D. , Pastor John , Chen Jiquan , Harth Calvin
Published: March 2003

Boreal peatlands may be particularly vulnerable to climate change, because temperature regimes that currently constrain biological activity in these regions are predicted to increase substantially within the next century. Changes in peatland plant community composition in response to climate change may alter nutrient availability, energy budgets, trace gas fluxes, and carbon storage. We investigated plant community response to warming and drying in a field mesocosm experiment in northern Minnesota, USA. Large intact soil monoliths removed from a bog and a fen received three infrared warming treatments crossed with three water‐table treatments (n = 3) for five years. Foliar cover of each species was estimated annually.

In the bog, increases in soil temperature and decreases in water‐table elevation increased cover of shrubs by 50% and decreased cover of graminoids by 50%. The response of shrubs to warming was distinctly species‐specific, and ranged from increases (for Andromeda glaucophylla) to decreases (for Kalmia polifolia). In the fens, changes in plant cover were driven primarily by changes in water‐table elevation, and responses were species‐ and lifeform‐specific: increases in water‐table elevation increased cover of graminoids – in particular Carex lasiocarpa and Carex livida– as well as mosses. In contrast, decreases in water‐table elevation increased cover of shrubs, in particular A. glaucophylla and Chamaedaphne calyculata. The differential and sometimes opposite response of species and lifeforms to the treatments suggest that the structure and function of both bog and fen plant communities will change – in different directions or at different magnitudes – in response to warming and/or changes in water‐table elevation that may accompany regional or global climate change.
Above‐ and below‐ground responses of C3–C4 species mixtures to elevated CO2 and soil water availability
Authors: DERNER JUSTIN D. , JOHNSON HYRUM B. , KIMBALL BRUCE A. , PINTER PAUL J. , POLLEY H. Wayne , TISCHLER CHARLES R. , BOUTTON THOMAS W. , LAMORTE ROBERT L. , WALL GERALD W. , ADAM NEIL R. , LEAVITT STEVEN W. , OTTMAN MICHAEL J. , MATTHIAS ALLAN D. , BROOKS TALBOT J.
Published: March 2003

We evaluated the influences of CO2[Control, ∼ 370 µmol mol−1; 200 µmol mol−1 above ambient applied by free‐air CO2 enrichment (FACE)] and soil water (Wet, Dry) on above‐ and below‐ground responses of C3 (cotton, Gossypium hirsutum) and C4 (sorghum, Sorghum bicolor) plants in monocultures and two density mixtures. In monocultures, CO2 enrichment increased height, leaf area, above‐ground biomass and reproductive output of cotton, but not sorghum, and was independent of soil water treatment. In mixtures, cotton, but not sorghum, above‐ground biomass and height were generally reduced compared to monocultures, across both CO2 and soil water treatments. Density did not affect individual plant responses of either cotton or sorghum across the other treatments. Total (cotton + sorghum) leaf area and above‐ground biomass in low‐density mixtures were similar between CO2 treatments, but increased by 17–21% with FACE in high‐density mixtures, due to a 121% enhancement of cotton leaf area and a 276% increase in biomass under the FACE treatment. Total root biomass in the upper 1.2 m of the soil was not influenced by CO2 or by soil water in monoculture or mixtures; however, under dry conditions we observed significantly more roots at lower soil depths (> 45 cm). Sorghum roots comprised 81–85% of the total roots in the low‐density mixture and 58–73% in the high‐density mixture. CO2‐enrichment partly offset negative effects of interspecific competition on cotton in both low‐ and high‐density mixtures by increasing above‐ground biomass, with a greater relative increase in the high‐density mixture. As a consequence, CO2‐enrichment increased total above‐ground yield of the mixture at high density. Individual plant responses to CO2 enrichment in global change models that evaluate mixed plant communities should be adjusted to incorporate feedbacks for interspecific competition. Future field studies in natural ecosystems should address the role that a CO2‐mediated increase in C3 growth may have on subsequent vegetation change.
Nitrous oxide emission from agricultural drainage waters
Authors: Reay David S. , Smith Keith A. , Edwards Anthony C.
Published: March 2003

Uncertainty about the amounts of the greenhouse gas nitrous oxide (N2O), which arise from N leaching from agricultural soils, predominantly as nitrate (NO3–), is large. To date, the bulk of studies of N2O in aquatic systems have relied upon measurement of dissolved N2O concentrations at wide spatial intervals (of the order of km) down a stream, river or estuary. When we combined a fine‐scale (m) assessment of N2O concentrations in agricultural drainage water with novel measurement of net N2O emission from the same drainage system, we found that dissolved N2O in agricultural drainage water was very rapidly lost to the atmosphere, while dissolved NO3– in the same water was conserved. Consequently, the N2O emission factor (as a proportion of the nitrate‐N present, the IPCC's ‘EF5’) fell by a factor of more than 5 within only 100 m. Direct measurement of N2O emission from the drainage water confirmed the disappearance of N2O as being due to emission from water to the atmosphere, rather than in situ consumption by denitrification. Our findings indicate that making widely spaced measurements of dissolved N2O concentration and/or emissions from the water surface will not take account of this much more dynamic behaviour over short distances. Realistic assessment of the ‘indirect’ agricultural emissions of N2O from leached N will necessitate much more intensive sampling of the whole drainage system, from ditch to stream to river to estuary, accompanied by measurements of in‐stream production. The quantities of N2O actually released in the ditches gave values for EF5‐g (the IPCC's emission factor for N2O from surface drainage and groundwaters) of between 0.02 and 0.03%, compared with the IPCC value of 1.5%. For the latter to be realistic, the quantity of N2O required to be formed after the initial entry of water into the drainage system would need to exceed the initial load by the order of 50‐fold.
Nitrogen oxide gas emissions from temperate forest soils receiving long‐term nitrogen inputs
Authors: VENTEREA RODNEY T. , GROFFMAN PETER M. , VERCHOT LOUIS V. , MAGILL ALISON H. , ABER JOHN D. , STEUDLER PAUL A.
Published: March 2003

From spring 2000 through fall 2001, we measured nitric oxide (NO) and nitrous oxide (N2O) fluxes in two temperate forest sites in Massachusetts, USA that have been treated since 1988 with different levels of nitrogen (N) to simulate elevated rates of atmospheric N deposition. Plots within a pine stand that were treated with either 50 or 150 kg N ha−1 yr−1 above background displayed consistently elevated NO fluxes (100–200 µg N m−2 h−1) compared to control plots, while only the higher N treatment plot within a mixed hardwood stand displayed similarly elevated NO fluxes. Annual NO emissions estimated from monthly sampling accounted for 3.0–3.7% of N inputs to the high‐N plots and 8.3% of inputs to the Pine low‐N plot. Nitrous oxide fluxes in the N‐treated plots were generally < 10% of NO fluxes. Net nitrification rates (NRs) and NO production rates measured in the laboratory displayed patterns that were consistent with field NO fluxes. Total N oxide gas flux was positively correlated with contemporaneous measurements of NR and concentration. Acetylene inhibited both nitrification and NO production, indicating that autotrophic nitrification was responsible for the elevated NO production. Soil pH was negatively correlated with N deposition rate. Low levels (3–11 µg N kg−1) of nitrite () were detected in mineral soils from both sites. Kinetic models describing NO production as a function of the protonated form of (nitrous acid [HNO2]) adequately described the mineral soil data. The results indicate that atmospheric deposition may generate losses of gaseous NO from forest soils by promoting nitrification, and that the response may vary significantly between forest types under similar climatic regimes. The lowering of pH resulting from nitrification and/or directly from deposition may also play a role by promoting reactions involving HNO2.
Litter dynamics of Dactylis glomerata and Vicia villosa with respect to climatic and soil characteristics
Authors: Kalburtji  , Mamolos  , Kostopoulou
Published: March 2003

The rates of litter decomposition, organic matter loss and nutrient release for Dactylis glomerata (Gramineae) and Vicia villosa (Leguminosae) were studied at two sites in north Greece, which differed in soil pH, soil particle distribution and nutrient availability.

Climate, soil characteristics and taxonomic plant differences affected the rates of litter decomposition. Litter loss was higher at site A (neutral soil) than at site B (acid soil). Organic matter loss was generally low. Dry weather affected both parameters. Nitrogen release from litter was higher for both species at site A. The rate of P and K release was higher in the neutral soil than in the acid soil for both species, while that of Ca for both species and of Mg for Vicia was higher in the acid soil. Phosphorus, Ca and Na release from the litter of the leguminous species began earlier than from the graminaceous species. P mineralization from Vicia litter seemed to start just after its incorporation into the soil.
Effluent production from grass silages treated with additives and made in large‐scale bunker silos
Authors: Haigh
Published: March 2003

Data from twenty experiments, conducted at ADAS Research Centres in England and Wales during 1986–92, were used to determine effluent production from additive‐treated grass silages made in large‐scale bunker silos. The additives compared were formic acid at 4·0  l t–1, rolled barley at 44·0 kg t–1, dried molassed sugar beet feed at 40·0 kg t–1 and liquid inoculants at 2·2 l t–1 together with a non‐additive‐treated control. The silages were made from herbage with an average dry‐matter (DM) content of 177 (s.e. 3·8) g kg–1 and water‐soluble carbohydrate content of 140 g kg–1 DM. Average silage toluene DM content was 213 (s.e. 3·8) g kg–1. The formic acid and sugar beet feed silages were both well fermented, whereas the other silages were less well fermented.

Effluent produced was determined as either effluent production (l t–1 grass ensiled) during the 52‐d period in which it was measured or peak flow (l h–1) during the first 2 d of ensilage. Compared with non‐additive‐treated silage, dried molassed sugar beet feed significantly reduced both effluent production (27%) and peak flow (36%). Formic acid significantly increased peak flow (51%), but had little effect upon effluent production, and significantly reduced effluent N and lactic acid content. Barley and inoculant treatment had no significant effect upon effluent production.

In general, poor relationships were found between DM content and effluent production. Nevertheless for silages, except those treated with absorbents or formic acid, a significant (P < 0·001) negative relationship between silage effluent production (l t–1 grass ensiled) and the DM (g kg–1) content of the ensiled grass was found.