bluuebunny/crossref_metadata_2025 huggingface dataset:
Soybean leaf growth and gas exchange response to drought under carbon dioxide enrichment
Authors: Serraj Rachid , Allen L. Hartwell , Sinclair Thomas R.
Published: March 2003

This study was conducted to determine the response in leaf growth and gas exchange of soybean (Glycine max Merr.) to the combined effects of water deficits and carbon dioxide (CO2) enrichment. Plants grown in pots were allowed to develop initially in a glasshouse under ambient CO2 and well‐watered conditions. Four‐week old plants were transferred into two different glasshouses with either ambient (360 μmol mol‐1) or elevated (700 μmol mol‐1) CO2. Following a 2‐day acclimation period, the soil of the drought‐stressed pots was allowed to dry slowly over a 2‐week period. The stressed pots were watered daily so that the soil dried at an equivalent rate under the two CO2 levels. Elevated [CO2] decreased water loss rate and increased leaf area development and photosynthetic rate under both well‐watered and drought‐stressed conditions. There was, however, no significant effect of [CO2] in the response relative to soil water content of normalized leaf gas exchange and leaf area. The drought response based on soil water content for transpiration, leaf area, and photosynthesis provide an effective method for describing the responses of soybean physiological processes to the available soil water, independent of [CO2].
Seasonal variation in methane emission from a temperate Phragmites‐dominated marsh: effect of growth stage and plant‐mediated transport
Authors: Kim JooN. , Verma Shashi B. , Billesbach David P.
Published: March 2003

The eddy covariance technique was employed with a tunable diode laser spectrometer to quantify methane flux from a prairie marsh dominated by Phragmites australis in north‐central Nebraska, USA. The observations spanned the entire growing season (April to October) and a wide range of weather conditions, allowing a quantitative assessment of the physical and biological controls of methane emission in this ecosystem. Diel patterns in methane emission varied markedly depending on plant growth stage. Prior to plant emergence above water, the rate of methane emission from the marsh was fairly constant throughout the day. After emergence above water, there was a gradual increase in methane emission after sunrise with a peak in late afternoon. Significant changes in diel patterns were observed after tillering. Then, the diel pattern was characterized by a mid‐ to late‐morning peak and a 2‐to 4‐fold increase in methane emissions from night to daytime. In early stages of plant growth, molecular diffusion through dead/live plants and the standing water column seemed to be the primary transport mechanism. After tillering, a transition occurred in the transport mechanism from a molecular diffusion to a convective throughflow, which is a rapid and active gas transport driven by pressure differences. The role of convective throughflow became less important as the plants senesced. Integrated methane emission over the six‐month measurement period (April–October) was about 64 g CH4 m–2. On an annual basis, we estimate the annual methane emission from this ecosystem to be ≈ 80 g CH4 m–2 and that about 80% of the total methane emission occurred between late April and late October.
Fungal root colonization responses in natural grasslands after long‐term exposure to elevated atmospheric CO2
Authors: Rillig Matthias C. , Field Christopher B. , Allen Michael F.
Published: March 2003

Arbuscular mycorrhizae, ubiquitous mutualistic symbioses between plant roots and fungi in the order Glomales, are believed to be important controllers of plant responses to global change, in particular to elevated atmospheric CO2. In order to test if any effects on the symbiosis can persist after long‐term treatment, we examined root colonization by arbuscular mycorrhizal (AM) and other fungi of several plant species from two grassland communities after continuous exposure to elevated atmospheric CO2 for six growing seasons in the field. For plant species from both a sandstone and a serpentine annual grassland there was evidence for changes in fungal root colonization, with changes occurring as a function of plant host species. We documented decreases in percentage nonmycorrhizal fungal root colonization in elevated CO2 for several plant species. Total AM root colonization (%) only increased significantly for one out of the five plant species in each grassland. However, when dividing AM fungal hyphae into two groups of hyphae (fine endophyte and coarse endophyte), we could document significant responses of AM fungi that were hidden when only total percentage colonization was measured. We also documented changes in elevated CO2 in the percentage of root colonized by both AM hyphal types simultaneously. Our results demonstrate that changes in fungal root colonization can occur after long‐term CO2 enrichment, and that the level of resolution of the study of AM fungal responses may have to be increased to uncover significant changes to the CO2 treatment. This study is also one of the first to document compositional changes in the AM fungi colonizing roots of plants grown in elevated CO2. Although it is difficult to relate the structural data directly to functional changes, possible implications of the observed changes for plant communities are discussed.
Biotic, abiotic and performance aspects of the Nevada Desert Free‐Air CO2 Enrichment (FACE) Facility
Authors: Jordan DeaN. N. , Zitzer Stephen F. , Hendrey George R. , Lewin Keith F. , Nagy JohN. , Nowak Robert S. , Smith Stanley D. , Coleman James S. , Seemann Jeffrey R.
Published: March 2003

Arid and semiarid climates comprise roughly 40% of the earth’s terrestrial surface. Deserts are predicted to be extremely responsive to global change because they are stressful environments where small absolute changes in water availability or use represent large proportional changes. Water and carbon dioxide fluxes are inherently coupled in plant growth.

 No documented global change has been more substantial or more rapid than the increase in atmospheric CO2. Free Air CO2 Enrichment (FACE) technology permits manipulation of CO2 in intact communities without altering factors such as light intensity or quality, humidity or wind. The Nevada Desert FACE Facility (NDFF) consists of three 491 m2 plots in the Mojave Desert receiving 550 μL L–1 CO2, and six ambient plots to assess both CO2 and fan effects. The shrub community was characterized as a Larrea–Ambrosia–Lycium species complex. Data are reported through 12 months of operation.
Soil carbon sequestration and land‐use change: processes and potential
Authors: Post W. M. , Kwon K. C.
Published: March 2003

When agricultural land is no longer used for cultivation and allowed to revert to natural vegetation or replanted to perennial vegetation, soil organic carbon can accumulate. This accumulation process essentially reverses some of the effects responsible for soil organic carbon losses from when the land was converted from perennial vegetation. We discuss the essential elements of what is known about soil organic matter dynamics that may result in enhanced soil carbon sequestration with changes in land‐use and soil management. We review literature that reports changes in soil organic carbon after changes in land‐use that favour carbon accumulation. This data summary provides a guide to approximate rates of SOC sequestration that are possible with management, and indicates the relative importance of some factors that influence the rates of organic carbon sequestration in soil. There is a large variation in the length of time for and the rate at which carbon may accumulate in soil, related to the productivity of the recovering vegetation, physical and biological conditions in the soil, and the past history of soil organic carbon inputs and physical disturbance. Maximum rates of C accumulation during the early aggrading stage of perennial vegetation growth, while substantial, are usually much less than 100 g C m−2 y−1. Average rates of accumulation are similar for forest or grassland establishment: 33.8 g C m−2 y−1 and 33.2 g C m−2 y−1, respectively. These observed rates of soil organic C accumulation, when combined with the small amount of land area involved, are insufficient to account for a significant fraction of the missing C in the global carbon cycle as accumulating in the soils of formerly agricultural land.
Defining the importance of including transient ecosystem responses to simulate C‐cycle dynamics in a global change model
Authors: Van Minnen Jelle G. , Leemans Rik , Ihle Froydis
Published: March 2003

The ability of plant species to migrate is one of the critical issues in assessing accurately the future response of the terrestrial biosphere to climate change. This ability is confined by both natural and human‐induced changes in land cover. In this paper we present land‐cover and Carbon (C) cycle models designed to simulate the biospheric consequences of different types of land‐cover changes. These models, imbedded in the larger integrated assessment model IMAGE 2, were used to demonstrate the importance of considering spatial aspects for global C‐cycle modelling. A gradual‐migration, an unlimited‐migration and a no‐migration case were compared to show the range of possible consequences. Major differences between these cases were simulated for land‐cover patterns and the carbon budget. A large geographical variation in the biospheric response was also simulated. The strongest response was simulated in high‐latitude regions, especially for the migration cases in which land‐cover changes were permitted. In low‐latitudes regions the differences between the migration cases were smaller, mainly due to the effects of land‐use changes. The geographical variation among, and the different responses, the migration cases clearly demonstrate how essential it is to assess biospheric responses to climate change and land use simultaneously. Moreover, it also shows the urgent need for enhanced understanding of spatial and temporal dynamics of the biospheric responses.
Particulate pollution capture by urban trees: effect of species and windspeed
Authors: Beckett K. Paul , Freer‐Smith P. H. , Taylor Gail
Published: March 2003

Particulate pollution is a serious health problem throughout the world, exacerbating a wide range of respiratory and vascular illnesses in urban areas. The use of trees to reduce the effects of these pollutants has been addressed in the literature, but has rarely been quantified. The aim of the present study was to quantify the effectiveness of five tree species − pine (Pinus nigra var. maritima), cypress ( × Cupressocyparis leylandii), maple (Acer campestre), whitebeam (Sorbus intermedia), poplar (Populus deltoides × trichocarpa‘Beaupré’) − in capturing pollutant particles. This was achieved by exposing them to NaCl droplets of approximately 1 μm diameter at a range of windspeeds in two windtunnels. The deposition velocity (Vg) and particle trapping efficiency (Cp) were calculated from these exposures. In addition, a variable dependent on foliage structure [Stokes number (St)] was correlated with Cp to gauge the effect of tree morphology on particle capture. Maximum Cp values ranged from 2.8% for P. nigra, to 0.12% and 0.06% for P. trichocarpa×deltoides and A. campertre, respectively. The finer, more complex structure of the foliage of the two conifers (P. nigra and C. leylandii) explained their much greater effectiveness at capturing particles. The data presented here will be used to model the effectiveness of tree planting schemes in improving urban air quality by capturing pollutant particles.
Global response of terrestrial ecosystem structure and function to CO2 and climate change: results from six dynamic global vegetation models
Authors: Cramer Wolfgang , Bondeau Alberte , Woodward F. Ian , Prentice I. Colin , Betts Richard A. , Brovkin Victor , Cox Peter M. , Fisher Veronica , Foley Jonathan A. , Friend Andrew D. , Kucharik Chris , Lomas Mark R. , Ramankutty Navin , Sitch Stephen , Smith Benjamin , White Andrew , Young‐Molling Christine
Published: March 2003

The possible responses of ecosystem processes to rising atmospheric CO2 concentration and climate change are illustrated using six dynamic global vegetation models that explicitly represent the interactions of ecosystem carbon and water exchanges with vegetation dynamics. The models are driven by the IPCC IS92a scenario of rising CO2 (Wigley et al. 1991), and by climate changes resulting from effective CO2 concentrations corresponding to IS92a, simulated by the coupled ocean atmosphere model HadCM2‐SUL. Simulations with changing CO2 alone show a widely distributed terrestrial carbon sink of 1.4–3.8 Pg C y−1 during the 1990s, rising to 3.7–8.6 Pg C y−1 a century later. Simulations including climate change show a reduced sink both today (0.6–3.0 Pg C y−1) and a century later (0.3–6.6 Pg C y−1) as a result of the impacts of climate change on NEP of tropical and southern hemisphere ecosystems. In all models, the rate of increase of NEP begins to level off around 2030 as a consequence of the ‘diminishing return’ of physiological CO2 effects at high CO2 concentrations. Four out of the six models show a further, climate‐induced decline in NEP resulting from increased heterotrophic respiration and declining tropical NPP after 2050. Changes in vegetation structure influence the magnitude and spatial pattern of the carbon sink and, in combination with changing climate, also freshwater availability (runoff). It is shown that these changes, once set in motion, would continue to evolve for at least a century even if atmospheric CO2 concentration and climate could be instantaneously stabilized. The results should be considered illustrative in the sense that the choice of CO2 concentration scenario was arbitrary and only one climate model scenario was used. However, the results serve to indicate a range of possible biospheric responses to CO2 and climate change. They reveal major uncertainties about the response of NEP to climate change resulting, primarily, from differences in the way that modelled global NPP responds to a changing climate. The simulations illustrate, however, that the magnitude of possible biospheric influences on the carbon balance requires that this factor is taken into account for future scenarios of atmospheric CO2 and climate change.
Chemistry and decomposition of litter fromPopulus tremuloidesMichaux grown at elevated atmospheric CO2and varying N availability
Authors: King John S. , Pregitzer Kurt S. , Zak Donald R. , Kubiske Mark E. , Ashby Jennifer A. , Holmes William E.
Published: March 2003

It has been hypothesized that greater production of total nonstructural carbohydrates (TNC) in foliage grown under elevated atmospheric carbon dioxide (CO2) will result in higher concentrations of defensive compounds in tree leaf litter, possibly leading to reduced rates of decomposition and nutrient cycling in forest ecosystems of the future. To evaluate the effects of elevated atmospheric CO2on litter chemistry and decomposition, we performed a 111 day laboratory incubation with leaf litter of trembling aspen (Populus tremuloidesMichaux) produced at 36 Pa and 56 Pa CO2and two levels of soil nitrogen (N) availability. Decomposition was quantified as microbially respired CO2and dissolved organic carbon (DOC) in soil solution, and concentrations of nonstructural carbohydrates, N, carbon (C), and condensed tannins were monitored throughout the incubation. Growth under elevated atmospheric CO2did not significantly affect initial litter concentrations of TNC, N, or condensed tannins. Rates of decomposition, measured as both microbially respired CO2and DOC did not differ between litter produced under ambient and elevated CO2. Total C lost from the samples was 38 mg g−1litter as respired CO2and 138 mg g−1litter as DOC, suggesting short‐term pulses of dissolved C in soil solution are important components of the terrestrial C cycle. We conclude that litter chemistry and decomposition in trembling aspen are minimally affected by growth under higher concentrations of CO2.
Mass spectrometric monitoring of gases (CO2, CH4, O2) in a mesotrophic peat core from Kopparås Mire, Sweden
Authors: Beckmann Manfred , Lloyd David
Published: March 2003

Membrane inlet mass spectrometry was used to monitor dissolved gas concentrations (CO2, CH4 and O2) in a mesotrophic peat core from Kopparås, Sweden.

1 A comparison of depth profiles (down to 22 cm) with an ombrotrophic peat core (Ellergower, SW Scotland) investigated previously, revealed major differences in gas concentrations. Thus methane reached concentrations more than twice as high (800 μM) at depths greater than 12 cm in the Kopparås core. As shown previously, the primary determinant of the depth of the oxic zone is the level of the water table. Whereas in the Scottish cores, mass spectrometric detectability of O2 was confined to the first 3 cm below this level, in the Swedish core penetration of O2 was greater (7 cm). CO2 profiles were similar in cores from both locations.

2 A thick layer of Sphagnum mosses dominated the plant cover of the Swedish peat core. A poorly developed deep root system, as distinct from that of the vascular plant cover in Scottish cores, diminished gas exchange rates, and presumably aerobic methane oxidation at depth around roots. These characteristics may contribute to the development of discontinuities in gas profiles at depths greater 15 cm as upward gas transport is established predominantly by diffusion and/or ebullition in the Swedish core.

3 Monitoring gas concentrations at the peat surface and at 2 cm depth after changing water tables showed a delayed response of approximately 4 days as a result of the high water content and moisture‐regulating capacity of mosses.

4 Recovery processes at 2 cm depth after raising the water table revealed final production rates of dissolved CO2 and CH4 in the peat pore water between 0.8 and 4.4 μmol h−1 L−1 and between 0.1 and 1.7 μmol h−1 L−1, respectively. Higher production rates were found during the day, indicating a diurnal rhythm due to plant photosynthetic activity even at the low values of photosynthetically active radiation (PAR: 110 μmol s−1 m−2) used in the experimental set‐up.

5 In the water‐logged mesotrophic Kopparås core changes of dissolved gas concentrations (DGC) at 3 and 14 cm depth were surface temperature‐dependent rather than light dependent. This suggests that changes of air temperature alters the covering vegetation to increase the conductivity for dissolved gases through vascular plants and to facilitate gas transport by diffusion and/or ebullition.
Effect of elevated atmospheric CO2and vegetation type on microbiota associated with decomposing straw
Authors: Frederiksen Helle B. , Rønn Regin , Christensen Søren
Published: March 2003

Straw from wheat plants grown at ambient and elevated atmospheric CO2concentrations was placed in litterbags in a grass fallow field and a wheat field. The CO2treatment induced an increase in straw concentration of ash‐free dry mass from 84% to 93% and a decrease in nitrogen concentration from 0.43% to 0.34%. After five months of decomposition, less than 50% of the straw was decomposed. The content of ash‐free dry mass remaining in straw from plants grown at elevated CO2was significantly higher than that from plants grown at ambient CO2(4.02 vs. 3.69 g AFDM per litterbag in the fallow field and 3.40 vs. 2.67 g AFDM per litterbag when buried in the wheat field). The immobilization of nitrogen during decomposition was significantly higher in the ambient straw, and there was a significant negative correlation between the content of organic matter remaining per litterbag and the nitrogen concentration in the recovered straw samples. After five months of decomposition, hyphal biomass was significantly lower in straw from plants grown at elevated CO2(− 30% and −13% in the fallow and wheat field, respectively). Bacterial biomass was not significantly affected by the CO2induced changes in the litter quality, but the lower decomposition rate and fewer bacterial grazers in the straw from plants grown at elevated CO2together indicate reduced microbial activity and turnover. Notwithstanding this, these data show that growth at elevated atmospheric CO2concentration results in slower decomposition of wheat straw, but the effect is probably of minor importance compared to the effect of varying crops, agricultural practise or changing land use.
Modelling the effects of loss of soil biodiversity on ecosystem function
Authors: Hunt H. W. , Wall D. H.
Published: March 2003

There are concerns about whether accelerating worldwide loss of biodiversity will adversely affect ecosystem functioning and services such as forage production. Theoretically, the loss of some species or functional groups might be compensated for by changes in abundance of other species or functional groups such that ecosystem processes are unaffected.

 A simulation model was constructed for carbon and nitrogen transfers among plants and functional groups of microbes and soil fauna. The model was based on extensive information from shortgrass prairie, and employed stabilizing features such as prey refuges and predator switching in the trophic equations. Model parameters were derived either from the literature or were estimated to achieve a good fit between model predictions and data. The model correctly represented (i) the major effects of elevated atmospheric CO2 and plant species on root and shoot biomass, residue pools, microbial biomass and soil inorganic nitrogen, and (ii) the effects on plant growth of manipulating the composition of the microbial and faunal community. The model was evaluated by comparing predictions to data not used in model development.

 The 15 functional groups of microbes and soil fauna were deleted one at a time and the model was run to steady state. Only six of the 15 deletions led to as much as a 15% change in abundance of a remaining group, and only two deletions (bacteria and saprophytic fungi) led to extinctions of other groups. Functional groups with greater effect on abundance of other groups were those with greater biomass or greater number of consumers, regardless of trophic position. Of the six deletions affecting the abundance of other groups, only three (bacteria, saprophytic fungi, and root‐feeding nematodes) caused as much as 10% changes in indices of ecosystem function (nitrogen mineralization and primary production). While the soil fauna as a whole were important for maintenance of plant production, no single faunal group had a significant effect. These results suggest that ecosystems could sustain the loss of some functional groups with little decline in ecosystem services, because of compensatory changes in the abundance of surviving groups. However, this prediction probably depends on the nature of stabilizing mechanisms in the system, and these mechanisms are not fully understood.
North Atlantic Oscillation signatures in aquatic and terrestrial ecosystems—a meta‐analysis
Authors: Blenckner Thorsten , Hillebrand Helmut
Published: March 2003

Climate variations over the Northern Hemisphere are to a substantial proportion associated with the North Atlantic Oscillation (NAO). Recently, many studies revealed the impacts of the NAO on the dynamics of organisms in different ecosystems but the results in the single studies were inconsistent. Here, we used meta‐analysis techniques for a quantitative synthesis of results. We tested the influence of the NAO on the timing of life history events, on biomass of organisms, and on biomass of different trophic levels. We found a clear NAO signature in freshwater, marine, and terrestrial ecosystems. The response of life history events to the NAO was similar in all environments but less pronounced at higher latitudes. The magnitude of the biomass response was significantly related to the NAO, either positively in aquatic or negatively in terrestrial ecosystems. The response depended on longitude, the effect being less pronounced in Eastern Europe. The results stressed that a meta‐analysis is a valuable tool in the field of climate‐driven ecosystem responses and can identify more general ecological responses than single studies. We recommend the inclusion of nonsignificant results in order to archive an objective view of the strength of NAO and climate impacts in general.
Foliar resistance to simulated extreme temperature events in contrasting plant functional and chorological types
Authors: GURVICH DIEGO E. , DÍAZ SANDRA , FALCZUK VALERIA , HARGUINDEGUY NATALIA PÉREZ‐ , CABIDO MARCELO , THORPE P. CHRISTOPHER
Published: March 2003

We analysed leaf resistance of 41 Angiosperms belonging to a wide range of plant functional (PFTs) and chorological types (PCTs) to simulated frost and high‐temperature extreme events (EE). Leaf resistance was estimated as percentage of membrane electrolyte leakage under heating and freezing treatments in the lab.

Leaf resistance to heating or freezing was not significantly correlated with the main resource‐use characteristics that defined PFTs, such as leaf specific area, toughness, N concentration or thickness. Leaf resistance to heating differed among PFTs (graminoids and bromeliads were the more resistant groups), but not among PCTs. In contrast, leaf resistance to freezing significantly differed among PCTs. Along a steep regional climatic gradient, climate variables (annual mean temperature, mean minimum temperature, mean maximum temperature and number of frost‐free months) at the locations where the given species were most abundant were also significantly correlated with freezing resistance. Species from colder habitats both at the sub‐continental and regional scales showed the highest leaf resistance to freezing. Our work indicates that leaf resistance to climatic EE and resource‐use strategy (assessed in previous studies) represent two different, partially decoupled axes of plant specialisation. It also suggests that changes in the frequency of very low temperature events might have regional‐scale impacts on vegetation, whereas changes in the frequency of very high temperature events might have more influence at the local scale.
Effects of climate change on labile and structural carbon in Douglas‐fir needles as estimated by δ13C and Careameasurements
Authors: HOBBIE ERIC A. , GREGG JILLIAN , OLSZYK DAVID M. , RYGIEWICZ PAUL T. , TINGEY DAVID T.
Published: March 2003

Models of photosynthesis, respiration, and export predict that foliar labile carbon (C) should increase with elevated CO2but decrease with elevated temperature. Sugars, starch, and protein can be compared between treatments, but these compounds make up only a fraction of the total labile pool. Moreover, it is difficult to assess the turnover of labile carbon between years for evergreen foliage. Here, we combined changes in foliar Carea(C concentration on an areal basis) as needles aged with changes in foliar isotopic composition (δ13C) caused by inputs of13C‐depleted CO2to estimate labile and structural C in needles of different ages in a four‐year, closed‐chamber mesocosm experiment in which Douglas‐fir (Pseudotsuga menziesii(Mirb.) Franco) seedlings were exposed to elevated temperature (ambient + 3.5 °C) and CO2(ambient + 179 ppm). Declines inδ13C of needle cohorts as they aged indicated incorporation of newly fixed labile or structural carbon. Theδ13C calculations showed that new C was 41 ± 2% and 28 ± 3% of total needle carbon in second‐ and third‐year needles, respectively, with higher proportions of new C in elevated than ambient CO2chambers (e.g. 42 ± 2% vs. 37 ± 6%, respectively, for second‐year needles). Relative to ambient CO2, elevated CO2increased labile C in both first‐ and second‐year needles. Relative to ambient temperature, elevated temperature diminished labile C in second‐year needles but not in first‐year needles, perhaps because of differences in sink strength between the two needle age classes. We hypothesize that plant‐soil feedbacks on nitrogen supply contributed to higher photosynthetic rates under elevated temperatures that partly compensated for higher turnover rates of labile C. Strong positive correlations between labile C and sugar concentrations suggested that labile C was primarily determined by carbohydrates. Labile C was negatively correlated with concentrations of cellulose and protein. Elevated temperature increased foliar %C, possibly due to a shift of labile constituents from low %C carbohydrates to relatively high %C protein. Decreased sugar concentrations and increased nitrogen concentrations with elevated temperature were consistent with this explanation. Because foliar constituents that vary in isotopic signature also vary in concentrations with leaf age or environmental conditions, inferences ofci/cavalues fromδ13C of bulk leaf tissue should be done cautiously. Tracing of13C through foliar carbon pools may provide new insight into foliar C constituents and turnover.
Effects of elevated CO2 and cutting frequency on plant community structure in a temperate grassland
Authors: Teyssonneyre Florence , Picon‐cochard Catherine , Falcimagne Robert , Soussana Jean‐François
Published: March 2003

Monoliths of a fertile, N limited, C3 grassland community were subjected (or not) to an atmospheric CO2 enrichment (600 µmol mol‐‐1) using a Mini‐FACE system, from August 1998 to June 2001 and were subjected to two contrasting cutting frequencies (3 and 6 cuts per year). We report here the effects of the CO2 and cutting frequency factors on the plant community structure and its diversity.

Species‐specific responses to elevated CO2 and cutting frequency were observed, which resulted in significant changes in the botanical composition of the grassland monoliths. Elevated CO2 significantly increased the proportion of dicotyledones (forbs + legumes) and reduced that of the monocotyledones (grasses). Management differentiated this response as elevated CO2 increased the proportion of forbs when infrequently and of legumes when frequently defoliated. However, among the two dominant forbs species only one was significantly enhanced by elevated CO2. Moreover, not all grass species responded negatively to high CO2. At a low cutting frequency, the observed decline under ambient CO2 in species diversity (Shannon‐Weaver index) and in forb species number was partly alleviated by elevated CO2.

This experiment shows that the botanical composition of temperate grasslands is likely to be affected by the current rise (+ 0.5% per year) in the atmospheric CO2 concentration, and that grassland management guidelines may need to be adapted to a future high CO2 world.
Site and temporal variation of soil respiration in European beech, Norway spruce, and Scots pine forests
Authors: BORKEN WERNER , XU YI‐JUN , DAVIDSON ERIC A. , BEESE FRIEDRICH
Published: March 2003

Global warming and changes in rainfall amount and distribution may affect soil respiration as a major carbon flux between the biosphere and the atmosphere. The objectives of this study were to investigate the site to site and interannual variation in soil respiration of six temperate forest sites. Soil respiration was measured using closed chambers over 2 years under mature beech, spruce and pine stands at both Solling and Unterlüß, Germany, which have distinct climates and soils. Cumulative annual CO2fluxes varied from 4.9 to 5.4 Mg C ha−1 yr−1at Solling with silty soils and from 4.0 to 5.9 Mg C ha−1 yr−1at Unterlüß with sandy soils. With one exception soil respiration rates were not significantly different among the six forest sites (site to site variation) and between the years within the same forest site (interannual variation). Only the respiration rate in the spruce stand at Unterlüß was significant lower than the beech stand at Unterlüß in both years. Soil respiration rates of the sandy sites at Unterlüß were limited by soil moisture during the rather dry and warm summer 1999 while soil respiration at the silty Solling site tended to increase. We found a threshold of −80 kPa at 10 cm depth below which soil respiration decreased with increasing drought. Subsequent wetting of sandy soils revealed high CO2effluxes in the stands at Unterlüß. However, dry periods were infrequent, and our results suggest that temporal variation in soil moisture generally had little effect on annual soil respiration rates. Soil temperature at 5 cm and 10 cm depth explained 83% of the temporal variation in soil respiration using the Arrhenius function. The correlations were weaker using temperature at 0 cm (r2 = 0.63) and 2.5 cm depth (r2 = 0.81). MeanQ10values for the range from 5 to 15 °C increased asymptotically with soil depth from 1.87 at 0 cm to 3.46 at 10 cm depth, indicating a large uncertainty in the prediction of the temperature dependency of soil respiration. Comparing the fitted Arrhenius curves for same tree species from Solling and Unterlüß revealed higher soil respiration rates for the stands at Solling than in the respective stands at Unterlüß at the same temperature. A significant positive correlation across all sites between predicted soil respiration rates at 10 °C and total phosphorus content and C‐to‐N ratio of the upper mineral soil indicate a possible effect of nutrients on soil respiration.
Methane (CH4) release from littoral wetlands of Boreal lakes during an extended flooding period
Authors: JUUTINEN SARI , ALM JUKKA , LARMOLA TUULA , HUTTUNEN JARI T. , MORERO MICAELA , SAARNIO SANNA , MARTIKAINEN PERTTI J. , SILVOLA JOUKO
Published: March 2003

Lake littoral zones have a transitional nature and dynamic conditions, which are reflected in their CH4 emissions. Thus, detailed studies are needed to assess the littoral CH4 emissions in a regional scale. In this study, CH4 fluxes were followed during the ice‐free seasons in 1998 and 1999 by using the static chamber method in the littoral zone of two lakes in Finland. An exceptionally high water level in 1998 caused an unusually long inundation in otherwise ephemerally flooded zone. The flooding was normal in year 1999. The factors controlling CH4 emissions were examined and statistical response functions were constructed. Further, the effect of extended flooding on the littoral CH4 budged was estimated. The methane flux was primarily regulated by the water level in grass and sedge dominated eulittoral zone, but not in infralittoral reed and water lily stands. Methane emissions in the sedge dominated zone decreased significantly, when the flood was high enough to submerge the venting structures of the plants. Besides water level, sediment temperature determined CH4 emission. The cumulative CH4 emissions from the whole littoral wetlands in wet year were 1.1 times (L. Kevätön), or 0.61 and 0.79 times (L. Mekrijärvi) those in dry year. The crucial factor was the discrepancy between the exceptional and the average water level. The extension of inundated area does not necessarily increase CH4 emissions if the flood reaches infrequently inundated areas, which apparently have low CH4 production potential. This is the case especially, if the emissions in lower zones simultaneously decrease due to high water level. Our study analyses these complex responses between CH4 emissions and water level.
Sodium fertilizer application to pasture. 6. Effects of combined applications with sulphur on herbage production and chemical composition in the season of application
Authors: Chiy P. C. , Phillips C. J. C.
Published: March 2003

The effect of sulphur and sodium fertilizers on the response of a perennial ryegrass (Lolium perenne) sward was examined over 2 years. Sulphur fertilizer was applied as ammonium sulphate at 0 or 97·5 kg S ha−1 year−1 and sodium fertilizer as sodium nitrate at 0 (nil), 31 (low), 62 (medium) or 94 (high) kg Na ha−1 year−1, with nitrogen input balanced across all treatments. Both sulphur and sodium increased herbage yield. Sodium fertilizer increased herbage sulphur concentration and sulphur fertilizer slightly increased herbage sodium concentration, but there were no major interactions between the two fertilizers on herbage yield or composition in the season of application. Sodium fertilizer increased dry‐matter digestibility, water‐soluble carbohydrate concentration and the live proportion of the herbage. Herbage sodium and magnesium concentrations were increased and potassium concentration decreased by sodium fertilizer. Sulphur fertilizer increased herbage dry‐matter digestibility and water‐soluble carbohydrate concentration. Sulphur and potassium concentrations were also increased and non‐protein nitrogen, magnesium and phosphorus concentrations decreased in response to sulphur fertilizer. It is concluded that, although there was evidence of facilitation of sodium uptake by sulphur fertilizer and vice versa, this was not sufficient to produce synergistic effects on herbage growth in the season of application.
Bovine faeces as a source of micro‐organisms for the in vitro digestibility assay of forages
Authors: Akhter  , Owen  , Theodorou  , Butler  , Minson
Published: March 2003

The aim of this study was to investigate whether bovine faeces could replace rumen liquor collected from fistulated sheep in the determination of organic matter digestibility (OMD) of forages in vitro. The first experiment compared two inocula that had been prepared by mixing 83 and 333 g of cattle faeces with 1 litre of artificial saliva according to the first stage of the in vitro technique of Tilley and Terry (Journal of the British Grassland Society,18, 104–111, 1963). Inocula made from 333 g of faeces gave higher values of OMD than that prepared from 83 g of faeces and was used in subsequent studies. When a 48‐h acid pepsin digestion, the second stage of the
Tilley and Terry (1963) technique, was included, the OMD values and the ease of filtering of undigested residues were increased. The second experiment compared digestibility determined with inocula produced from faeces with that produced from rumen liquor. The OMD of a ryegrass hay determined with an inoculum prepared from faeces was 0·468 compared with 0·528 when using an inoculum prepared from rumen liquor. The third experiment investigated the accuracy of estimating the OMD of eight contrasting forages determined using rumen liquor from three sheep (y) and faeces from two cows (x). All regressions were significant (P < 0·001) and had residual standard deviations (r.s.d.) of between ±0·019 and ±0·022. The final study compared faeces collected from cattle fed with either hay or concentrates. The OMD of forage was higher from the hay‐fed animals, but the r.s.d. values of the regressions were similar. It was concluded that cattle faeces shows potential as an alternative to rumen liquor collected from rumen‐fistulated sheep for use in the in vitro digestibility assay of forages.
Sodium fertilizer application to pasture. 8. Turnover and defoliation of leaf tissue
Authors: Chiy  , Phillips
Published: March 2003

The effects of application of sodium fertilizer on the turnover and defoliation of leaf tissue were investigated in a perennial ryegrass (Lolium perenne) pasture grazed by dairy cows. Eight plots were allocated to treatments either with or without sodium fertilizer, with the former receiving 32 kg Na ha–1 applied in five applications of NaNO3 over the grazing season. An equivalent amount of nitrogen was given to the controls as ammonium nitrate, the application of which was reduced in the sodium treatment to equate nitrogen fertilizer applications for the two treatments. In nine periods between April and September, marked tillers were recorded to measure leaf turnover, leaf lamina growth and specific leaf weight and, when combined with tiller density measurements, gave an estimate of herbage flux for the sward. The defoliation and net growth of the marked tillers were monitored at 3‐day intervals and the data were combined with tiller density and specific leaf weight data to determine the intake of the expanding, penultimate and oldest live leaf laminae. Sodium fertilizer application did not affect the rate at which leaves appeared, but it retarded their rate of disappearance. The extension rate and the specific weight of green laminae were both increased by sodium fertilizer application and therefore the net gravimetric growth rate was increased. Tiller density was not affected by sodium fertilizer application and hence the estimated herbage growth and net herbage flux were increased by sodium fertilizer application. Application of sodium fertilizer did not affect lamina length, and in both treatments the penultimate laminae were approximately twice as long as expanding and oldest live laminae. Defoliation frequency decreased from the expanding to the oldest live laminae in the control treatment without sodium. Sodium fertilizer application increased the frequency of defoliation of the oldest live leaf and also increased the length of the expanding leaf that was defoliated. For penultimate leaf laminae sodium fertilizer application reduced the defoliation frequency and length of foliage grazed. The dry‐matter (DM) intake of the oldest live laminae was increased by the application of sodium fertilizer. It is concluded that sodium fertilizer application increases net herbage growth both by increased extension rate of leaf laminae and specific leaf weight and by delayed laminae senescence, and that it increases herbage DM intake by increasing the defoliation frequency of the oldest live leaf laminae.
Implications of nitrogen fertilizer applications and extended grazing for the N economy of grassland
Authors: Laidlaw  , Watson  , Mayne
Published: March 2003

The response of swards which have been previously grazed to N fertilizer applied in early February was studied in two experiments in Northern Ireland. The effect of N fertilizer applied at a range of dates in autumn and spring on swards for out‐of‐season utilization was studied in a further experiment. Deep soil coring was also undertaken, subsequent to grazing with dairy cows, in grazed and protected areas in November and March to investigate the effect of out‐of‐season grazing on soil mineral N levels.

Dry‐matter (DM) yield response to early spring N application in previously grazed swards was low, with no effect on DM yield in February or March. Progressively delaying N application (and commencement of herbage accumulation) in autumn from 8 September until 18 October reduced herbage availability in late autumn and early spring but increased leaf lamina content. The greater the amount of herbage accumulated to 1 December, the lower the tiller density in the following April.

N fertilizer had a greater impact on soil mineral N in spring than in late autumn/early winter, suggesting that fertilizer N was more prone to loss in the latter. Soil mineral N was not significantly affected by out‐of‐season grazing.

It is concluded that in well‐fertilized, previously grazed swards response to N for out‐of‐season herbage is low and the probability for N loss is increased. Herbage quality will decline and the sward may be damaged if about 2 t DM ha−1 or more of harvestable herbage accumulates for use in winter or in early spring.
Differences in the nitrogen use efficiency of perennial ryegrass varieties under simulated rotational grazing and their effects on nitrogen recovery and herbage nitrogen content
Authors: Wilkins  , Allen  , Mytton
Published: March 2003

Eight varieties of perennial ryegrass (six new varieties and two old ones) grown at five levels of applied fertilizer (100, 200, 300, 400 and 500 kg of N ha–1) were cut monthly during two growing seasons (March to October in 1997 and 1998) and their herbage dry‐matter (DM) yield and nitrogen (N) content were determined. Herbage leaf content and the N content of young fully expanded leaves were also measured in 1997, and monthly recovery of applied N was determined in both the first and second harvest years by using 15N.

The rank order of varieties was similar for annual yield of DM and N at all five fertilizer levels. Proportional differences between varieties in DM yield were greatest in the first cut of each year, the late‐heading candidate variety Ba12151 out‐yielding the old late‐heading variety S23 by more than 70%. However, differences in annual DM yield were much more modest than in early spring yield, up to 10% in 1997 and up to 21% in 1998. The relatively small differences in total annual DM yield were attributed to only a small proportion of the applied N being recovered during a single regrowth period, most of the remainder becoming available for uptake in subsequent regrowth periods.

There were small but highly statistically significant differences among varieties in the N content of their leaves, leaf N content being inversely related to yield of DM and N. This lends further support to the hypothesis that the metabolic cost of protein synthesis and turnover is a key factor controlling genetic variation both in leaf yield and in annual DM and N yield under frequent harvesting. Seasonal variation in herbage N content was much greater than differences among varieties in mean N content over all harvests. In May of both years at all applied fertilizer levels, herbage N content fell below the 20 g N kg–1 DM level required by productive grazing animals.
The effect of a silage additive and level of concentrate supplementation on silage intake, animal performance and carcass characteristics of finishing beef cattle
Authors: Agnew  , Carson
Published: March 2003

An experiment was carried out to examine silage fermentation, effluent production and aerobic stability in unwilted grass silage, which was either ensiled without additive or with a commercially available blend of ammonium hexamethanoate, ammonium hexapropionate and octanoic acid (6 l t−1, Maxgrass, BP Chemicals Ltd., Northwich, UK) and to determine alternative approaches to obtaining the same performance in finishing beef cattle.

Seventy‐two Limousin × Friesian and Charolais × Friesian steers (mean initial live weight 424 kg s.d. 28·3) were blocked into groups of nine according to live weight and previous performance and offered silage, either with or without the additive, and supplemented with 0, 1·5, 3·0 or 4·5 kg d−1 of a concentrate with a crude protein content of 150 g kg−1 DM or allocated to a pre‐experimental slaughter group to enable calculation of daily carcass gain. Daily silage intakes were recorded for 112 days. At the end of the experiment, all cattle were slaughtered and daily carcass gain, omental, mesenteric, perinephric and retroperitoneal fat depots [kidney‐knob and channel fat (KKCF)], fatness, conformation, subcutaneous fat depth over M. longissimus dorsi muscle and carcass fat, protein and bone contents were assessed.

Across all levels of supplementation, cattle offered the silage with the additive showed significantly (P < 0·001) higher daily DM intakes than those offered the silage without additive. Cattle offered the silage with the additive but unsupplemented had significantly (P < 0·001) higher daily carcass gains than those offered the silage without additive and unsupplemented. The response in carcass gain was 76 and 35 g kg−1 additional concentrate for the silages with and without the additive respectively.