bluuebunny/crossref_metadata_2025 huggingface dataset:
Responses of three generations of a xylem‐feeding insect, Neophilaenus lineatus (Homoptera), to elevated CO2
Authors: Brooks G. L. , Whittaker J. B.
Published: March 2003

A population of the xylem‐feeding spittlebug, Neophilaenus lineatus, on blocks of natural vegetation transferred to large hemispherical chambers was studied over two generations with continuous exposure to elevated CO2 (600 ppm). The third generation was transferred from the blocks to potted Juncus squarrosus to enable measurements of fecundity. The principal food plant throughout was Juncus squarrosus. Survival of the nymphs was reduced by more than 20% in elevated CO2 relative to ambient (350 ppm) in both years of the main experiment. Elevated CO2 also delayed development by one or more nymphal instars in each year. Fecundity was not significantly affected.

The C/N ratio of whole Juncus leaves was increased in elevated CO2 and the transpiration rates of the plants were reduced. These changes may have been responsible for the effect of elevated CO2 on spittlebug performance. However, other factors such as plant architecture and microclimate may also be important.
First‐year growth response of trees in an intact forest exposed to elevated CO2
Authors: Naidu Shawna L. , Delucia Evan. H.
Published: March 2003

Although elevated atmospheric CO2 has been shown to increase growth of tree seedlings and saplings, the response of intact forest ecosystems and established trees is unclear. We report results from the first large‐scale experimental system designed to study the effects of elevated CO2 on an intact forest with the full complement of species interactions and environmental stresses. During the first year of exposure to ^ 1.5 Ë ambient CO2, canopy loblolly pine (Pinus taeda, L.) trees increased basal area growth rate by 24% but understorey trees of loblolly pine, sweetgum (Liquidambar styraciflua L.), and red maple (Acer rubrum L.) did not respond. Winged elm (Ulmus alata Michx.) had a marginally significant increase in growth rate (P = 0.069). These data suggest that this ecosystem has the capacity to respond immediately to a step increase in atmospheric CO2; however, as exposure time increases, nutrient limitations may reduce this initial growth stimulation.
UV‐B radiation causes early ripening and reduction in size of fruits in two lines of tomato (Lycopersicon esculentum Mill.)
Authors: Bacci L. , Grifoni D. , Sabatini F. , Zipoli G.
Published: March 2003

An open‐air experiment was performed in Pistoia (Italy) to investigate the possible protective role played by different contents of UV‐B absorbing compounds to realistic UV‐B supplementation and to study its effect on plant fruit production. A mutant line and its normal counterpart of Lycopersicon esculentum Mill, which differ in the content of UV‐B absorbing compounds, were used. Additional UV‐B radiation in the field was supplied to simulate a 20% stratospheric ozone depletion. Two groups of plants were grown: ‘control’, where plants received only natural solar UV‐B radiation, and ‘UV‐B’ treatment, where plants were grown under supplemental UV‐B.

 The results of the experiment showed that the content of UV‐B absorbing compounds of treated plants did not differ from that of the control in both lines. This indicates that natural sunlight, in Mediterranean areas, is saturating for synthesis of these compounds also in plants with normal content of UV‐B absorbing compounds. Consequently, plants are not able to produce significant additional amounts of them, in response to a realistic UV‐B supplementation, in order to protect the plant from additional UV‐B radiation.

 No different responses to the UV‐B supplementation were found between the two lines. The most significant UV‐B effect was an earlier reddening of fruits in comparison with the ‘control’ accompanied by a reduction in the size of mature fruits. No significant effects of UV‐B treatment were observed in biomass accumulation, leaf ontogeny, flowering or productivity.
Carbon dioxide and temperature effects on forage establishment: tissue composition and nutritive value
Authors: Fritschi Felix B. , Boote Kenneth J. , Sollenberger LynN. E. , Hartwell L.
Published: March 2003

Atmospheric CO2 concentration ([CO2]) and temperature are likely to increase in the future and may change plant growth and composition characteristics. Rhizoma peanut (Arachis glabrata Benth.) and bahiagrass (Paspalum notatum Flügge) were grown on a natural field soil in temperature‐gradient greenhouses to evaluate the effects of elevated [CO2] and temperature on tissue composition and digestibility during the establishment year. Carbon dioxide levels were maintained at 365 (ambient) and 640 μL CO2 L–1 air. The temperature‐gradient greenhouses were regulated to obtain air temperature sectors of 0.2, 1.5, 2.9, and 4.5 °C above ambient. Samples were taken of previously undefoliated herbage at 57, 86, 121, 148, and 217 days after planting and entire plots were harvested at 218 days after planting. Elevated [CO2] increased total nonstructural carbohydrate concentration in rhizoma peanut leaves by almost 50%. Rhizoma peanut leaf N concentration was 6% lower at elevated than at ambient [CO2]. The N concentration in new rhizomes of rhizoma peanut was increased by high [CO2], while the N concentration in bahiagrass was not affected by temperature or [CO2]. No effects of [CO2] and temperature were found on neutral detergent fibre in rhizoma peanut leaves or stems; however, elevated [CO2] increased neutral detergent fibre in bahiagrass leaves. Only at season end was in vitro organic matter digestion of rhizoma peanut higher at ambient (623 g kg–1) than at elevated [CO2] (609 g kg–1). Elevated [CO2] had a greater effect on tissue composition of rhizoma peanut than of bahiagrass. These data suggest that elevated temperature and CO2‐induced changes in chemical composition of forage species adapted to humid subtropics will be relatively small, particularly for C4 species.
Decomposition of Metrosideros polymorpha leaf litter along elevational gradients in Hawaii
Authors: Scowcroft Paul. G. , Turner Douglas R. , Vitousek Peter M.
Published: March 2003

We examined interactions between temperature, soil development, and decomposition on three elevational gradients, the upper and lower ends of each being situated on a common lava flow or ash deposit. We used the reciprocal transplant technique to estimate decomposition rates of Metrosideros polymorpha leaf litter during a three‐year period at warm and cool ends of each gradient. Litter quality was poorest early in soil development or where soils were most intensely leached and waterlogged. In situ litter decomposition was slowest on the young 1855 flow (k=  0.26 and 0.14 at low and high elevation, respectively). The more fertile Laupahoehoe gradient also supported more rapid in situ decay at the warmer low elevation site (k=  0.90) than at high elevation (k=  0.51). The gradient with the most advanced soil development showed no difference for in situ decay at low and high elevations (k=  0.88 and 0.99, respectively) probably due to low soil nutrient availability at low elevation, which counteracted the effect of warmer temperature. Comparisons of in situ, common litter, and common site experiments indicated that site factors influenced decomposition more than litter quality did. The effect of temperature, however, could be over‐ridden by soil fertility or other site factors. Field gradient studies of this sort yield variable estimates of apparent Q10, even under the best conditions, due to interactions among temperature, moisture, nutrient availability, decomposer communities and litter quality. Such interactions may be as likely to occur with changing climate as they are along elevational gradients.
Carbon and nitrogen pools and mineralization in a grassland gley soil under elevated carbon dioxide at a natural CO2 spring
Authors: Ross D. J. , Tate K. R. , Newton P. C. D. , Wilde R. H. , Clark H.
Published: March 2003

The growth and chemical composition of most plants are influenced by elevated CO2, but accompanying effects on soil organic matter pools and mineralization are less clearly defined, partly because of the short‐term nature of most studies. Herein we describe soil properties from a naturally occurring cold CO2 spring (Hakanoa) in Northland, New Zealand, at which the surrounding vegetation has been exposed to elevated CO2 for at least several decades. The mean annual temperature at this site is ≈ 15.5 °C and rainfall ≈ 1550 mm. The site was unfertilized and ungrazed, with a vegetation of mainly C3 and C4 grasses, and had moderate levels of ‘available’ P. Two soils were present − a gley soil and an organic soil – but only the gley soil is examined here. Average atmospheric CO2 concentrations at 17 sampling locations in the gley soil area ranged from 372 to 670 ppmv.

In samples at 0–5 cm depth, pH averaged 5.4; average values for organic C were 150 g, total N 11 g, microbial C 3.50 g, and microbial N 0.65 g kg−1, respectively. Under standardized moisture conditions at 25 °C, average rates of CO2‐C production (7–14 days) were 5.4 mg kg−1 h−1 and of net mineral‐N production (14 −42 days) 0.40 mg kg−1 h−1. These properties were all correlated positively and significantly (P < 0.10) with atmospheric CO2 concentrations, but not with soil moisture (except for CO2‐C production) or with clay content; they were, however, correlated negatively and mainly significantly with soil pH. In spite of uncertainties associated with the uncontrolled environment of naturally occurring springs, we conclude that storage of C and N can increase under prolonged exposure to elevated CO2, and may include an appreciable labile fraction in mineral soil with an adequate nutrient supply.
A global prognostic scheme of leaf onset using satellite data
Authors: Botta A. , Viovy N. , Ciais P. , Friedlingstein P. , Monfray P.
Published: March 2003

Leaf phenology describes the seasonal cycle of leaf functioning. Although it is essential for understanding the interactions between the biosphere, the climate, and biogeochemical cycles, it has received little attention in the modelling community at global scale. This article focuses on the prediction of spatial patterns of the climatological onset date of leaf growth for the decade 1983–93. It examines the possibility of extrapolating existing local models of leaf onset date to the global scale. Climate is the main variable that controls leaf phenology for a given biome at this scale, and satellite observations provide a unique means to study the seasonal cycle of canopies. We combine leaf onset dates retrieved from NOAA/AVHRR satellite NDVI with climate data and the DISCover land‐cover map to identify appropriate models, and determine their new parameters at a 0.5° spatial resolution. We define two main regions: at temperate and high latitudes leaf onset models are mainly dependent on temperature; at low latitudes they are controlled by water availability. Some local leaf onset models are no longer relevant at the global scale making their calibration impossible. Nevertheless, we define our unified model by retaining the model that best reproduced the spatial distribution of leaf onset dates for each biome. The main spatial patterns of leaf onset date are well simulated, such as the Sahelian gradient due to aridity and the high latitude gradient due to frost. At temperate and high latitudes, simulated onset dates are in good agreement with climatological observations; 62% of treated grid‐cells have a simulated leaf onset date within 10 days of the satellite observed onset date (which is also the temporal resolution of the NDVI data). In tropical areas, the subgrid heterogeneity of the phenology is larger and our model's predictive power is diminished. The difficulties encountered in the tropics are due to the ambiguity of the satellite signal interpretation and the low reliability of rainfall and soil moisture fields.
Photosynthesis, respiration, and net primary production of sunflower stands in ambient and elevated atmospheric CO2 concentrations: an invariant NPP:GPP ratio?
Authors: Cheng Weixin , Sims Daniel A. , Luo Yiqi , Coleman James S. ,   and, Johnson Dale W.
Published: March 2003

The effect of elevated CO2 on photosynthesis, respiration, and growth efficiency of sunflower plants at the whole‐stand level was investigated using a whole‐system gas exchange facility (the EcoCELLs at the Desert Research Institute) and a 13C natural tracer method. Total daily photosynthesis (GPP), net primary production (NPP), and respiration under the elevated CO2 treatment were consistently higher than under the ambient CO2 treatment. The overall level of enhancement due to elevated CO2 was consistent with published results for a typical C3 plant species. The patterns of daily GPP and NPP through time approximated logistic curves under both CO2 treatments. Regression analysis indicated that both the rate of increase (the parameter ‘r’) and the maximum value (the parameter ‘k’) of daily GPP and NPP under the elevated CO2 treatment were significantly higher than under the ambient CO2 treatment. The percentage increase in daily GPP due to elevated CO2 varied systematically through time according to the logistic equations used for the two treatments. The GPP increase due to elevated CO2 ranged from approximately 10% initially to 73% at the peak, while declining to about 33%, as predicted by the ratio of the two maximum values. Different values of percentage increase in GPP and NPP were obtained at different sampling times. This result demonstrated that one‐time measurements of percentage increases due to elevated CO2 could be misleading, thereby making interpretation difficult. Although rhizosphere respiration was substantially enhanced by elevated CO2, no effect of elevated CO2 on R:P (respiration:photosynthesis) was found, suggesting an invariant NPP:GPP ratio during the entire experiment. Further validation of the notion of an invariant NPP:GPP ratio may significantly simplify the process of quantifying terrestrial carbon sequestration by directly relating total photosynthesis to net primary production.
Partitioning net ecosystem carbon exchange with isotopic fluxes of CO2
Authors: Bowling David R. , Tans Pieter P. , Monson Russell K.
Published: March 2003

Because biological and physical processes alter the stable isotopic composition of atmospheric CO2, variations in isotopic content can be used to investigate those processes. Isotopic flux measurements of13CO2above terrestrial ecosystems can potentially be used to separate net ecosystem CO2exchange (NEE) into its component fluxes, net photosynthetic assimilation (FA) and ecosystem respiration (FR). In this paper theory is developed to partition measured NEE intoFAandFR, using measurements of fluxes of CO2and13CO2, and isotopic composition of respired CO2and forest air. The theory is then applied to fluxes measured (or estimated, for13CO2) in a temperate deciduous forest in eastern Tennessee (Walker Branch Watershed). It appears that there is indeed enough additional information in13CO2fluxes to partition NEE into its photosynthetic and respiratory components. Diurnal patterns inFAandFRwere obtained, which are consistent in magnitude and shape with patterns obtained from NEE measurements and an exponential regression between night‐time NEE and temperature (a standard technique which provides alternate estimates ofFRandFA). The light response curve for photosynthesis (FAvs. PAR) was weakly nonlinear, indicating potential for saturation at high light intensities. Assimilation‐weighted discrimination against13CO2for this forest during July 1999 was 16.8–17.1‰, depending on canopy conductance. The greatest uncertainties in this approach lie in the evaluation of canopy conductance and its effect on whole‐canopy photosynthetic discrimination, and thus the indirect methods used to estimate isotopic fluxes. Direct eddy covariance measurements of13CO2flux are needed to assess the validity of the assumptions used and provide defensible isotope‐based estimates of the component fluxes of net ecosystem exchange.
Productivity overshadows temperature in determining soil and ecosystem respiration across European forests
Authors: Janssens I. A. , Lankreijer H. , Matteucci G. , Kowalski A. S. , Buchmann N. , Epron D. , Pilegaard K. , Kutsch W. , Longdoz B. , Grünwald T. , Montagnani L. , Dore S. , Rebmann C. , Moors E. J. , Grelle A. , Rannik Ü. , Morgenstern K. , Oltchev S. , Clement R. , Guðmundsson J. , Minerbi S. , Berbigier P. , Ibrom A. , Moncrieff J. , Aubinet M. , Bernhofer C. , Jensen N. O. , Vesala T. , Granier A. , Schulze E. ‐D. , Lindroth A. , Dolman A. J. , Jarvis P. G. , Ceulemans R. , Valentini R.
Published: March 2003

This paper presents CO2flux data from 18 forest ecosystems, studied in the European Union funded EUROFLUX project. Overall, mean annual gross primary productivity (GPP, the total amount of carbon (C) fixed during photosynthesis) of these forests was 1380 ± 330 gC m−2 y−1(mean ±SD). On average, 80% of GPP was respired by autotrophs and heterotrophs and released back into the atmosphere (total ecosystem respiration, TER = 1100 ± 260 gC m−2 y−1). Mean annual soil respiration (SR) was 760 ± 340 gC m−2 y−1(55% of GPP and 69% of TER).

Among the investigated forests, large differences were observed in annual SR and TER that were not correlated with mean annual temperature. However, a significant correlation was observed between annual SR and TER and GPP among the relatively undisturbed forests. On the assumption that (i) root respiration is constrained by the allocation of photosynthates to the roots, which is coupled to productivity, and that (ii) the largest fraction of heterotrophic soil respiration originates from decomposition of young organic matter (leaves, fine roots), whose availability also depends on primary productivity, it is hypothesized that differences in SR among forests are likely to depend more on productivity than on temperature.

At sites where soil disturbance has occurred (e.g. ploughing, drainage), soil espiration was a larger component of the ecosystem C budget and deviated from

the relationship between annual SR (and TER) and GPP observed among the less‐disturbed forests. At one particular forest, carbon losses from the soil were so large, that in some years the site became a net source of carbon to the atmosphere. Excluding the disturbed sites from the present analysis reduced mean SR to 660 ± 290 gC m−2 y−1, representing 49% of GPP and 63% of TER in the relatively undisturbed forest ecosystems.
The cost of living for freshwater fish in a warmer, more polluted world
Authors: Morgan Ian J. , McDonald D. Gord , Wood Chris M.
Published: March 2003

Little of the vast literature on the temperature physiology of freshwater fish is useful in predicting the effects of global warming. In the present review a series of laboratory experiments is reviewed in which rainbow trout (Oncorhynchus mykiss) were exposed to simulated global warming, a 2 °C increment superimposed upon the natural thermal regime, in the presence and absence of two common freshwater pollutants, ammonia and acidity (low pH). Simulated global warming had little effect on the growth and physiology of trout fed to satiation over much of the summer. However, in late summer, when ambient water temperature was at its highest, the addition of 2 °C caused a marked inhibition of appetite and growth, although this impact was not exacerbated by a reduction in food availability. In winter, + 2 °C stimulated metabolism, appetite and growth by approximately 30–60%.

Exposure of satiation‐fed trout to low levels of pollutants produced unexpected results. Ammonia (NH3 + NH4+ = 70 μm) stimulated summer growth and energy conversion efficiency, whilst acidification (pH 5.2) increased appetite and growth but caused no disturbance of electrolyte balance. These pollutant effects were additive upon, but not synergistic with, the effects of + 2 °C. The ability of the fish to acclimate to the experimental conditions was tested with acute lethal temperature and/or toxicant challenges. Fish exposed to + 2 °C had a slightly (0.2–1.0 °C) but significantly higher lethal temperature than those exposed to ambient temperature when fed to satiation. However, there was no evidence of acclimation to either ammonia or low pH. It is concluded that the impact of global warming on freshwater fish will vary seasonally. The additional temperature may provide growth benefits in winter, but may threaten fish populations living towards the upper end of their thermal tolerance zone in (late) summer.
Organic carbon and carbon isotopes in modern and 100‐year‐old‐soil archives of the Russian steppe
Authors: Torn Margaret S. , Lapenis Andrei G. , Timofeev Anatoly , Fischer Marc L. , Babikov Boris V. , Harden Jennifer W.
Published: March 2003

Archived soils can provide valuable information about changes in the carbon and carbon isotope content of soils during the past century. We characterized soil carbon dynamics in a Russian steppe preserve using a 100‐year‐old‐soil archive and modern samples collected from the same site. The site has been protected since 1885 to the present, during which time the region has experienced widespread conversion to cultivation, a decrease in fire frequency, and a trend of increasing precipitation. In the preserve, the amount of organic carbon did not change appreciably between the 1900 and 1997 sampling dates, with 32 kg C/m2 in the top meter and a third of that in the top 20 cm. Carbon and nitrogen stocks varied by less than 6% between two replicate modern soil pits or between the modern sites and the archive. Radiocarbon content decreased with depth in all sites and the modern SOM had positive Δ values near the surface due to nuclear weapons testing in the early 1960s. In the upper 10 cm, most of the SOM had a turnover time of 6–10 years, according to a model fit to the radiocarbon content. Below about 10 cm, the organic matter was almost all passive material with long (millennial) turnover times. Soil respiration Δ14CO2 on a summer day was 106–109‰, an isotopic disequilibrium of about 9‰ relative to atmospheric 14CO2. In both the modern and archive soil, the relative abundance of 13C in organic matter increased with depth by 2‰ in the upper meter from δ13C = ‐‐26‰ at 5 cm to ‐‐24‰ below a meter. In addition, the slope of δ13C vs. depth below 5 cm was the same for both soils. Given the age of the soil archive, these results give clear evidence that the depth gradients are not due to depletion of atmospheric 13CO2 by fossil fuel emissions but must instead be caused by isotopic fractionation between plant litter inputs and preservation of SOM. Overall, the data show that these soils have a large reservoir of recalcitrant C and stocks had not changed between sampling dates 100 years apart.
A meta‐analysis of elevated [CO2] effects on soybean (Glycine max) physiology, growth and yield
Authors: Ainsworth Elizabeth A. , Davey Phillip A. , Bernacchi Carl J. , Dermody Orla C. , Heaton Emily A. , Moore David J. , Morgan Patrick B. , Naidu Shawna L. , Yoo Ra Hyung‐shim , Zhu Xin‐guang , Curtis Peter S. , Long Stephen P.
Published: March 2003

The effects of elevated [CO2] on 25 variables describing soybean physiology, growth and yield are reviewed using meta‐analytic techniques. This is the first meta‐analysis to our knowledge performed on a single crop species and summarizes the effects of 111 studies. These primary studies include numerous soybean growth forms, various stress and experimental treatments, and a range of elevated [CO2] levels (from 450 to 1250 p.p.m.), with a mean of 689 p.p.m. across all studies. Stimulation of soybean leaf CO2 assimilation rate with growth at elevated [CO2] was 39%, despite a 40% decrease in stomatal conductance and a 11% decrease in Rubisco activity. Increased leaf CO2 uptake combined with an 18% stimulation in leaf area to provide a 59% increase in canopy photosynthetic rate. The increase in total dry weight was lower at 37%, and seed yield still lower at 24%. This shows that even in an agronomic species selected for maximum investment in seed, several plant level feedbacks prevent additional investment in reproduction, such that yield fails to reflect fully the increase in whole plant carbon uptake. Large soil containers (> 9 L) have been considered adequate for assessing plant responses to elevated [CO2]. However, in open‐top chamber experiments, soybeans grown in large pots showed a significant threefold smaller stimulation in yield than soybeans grown in the ground. This suggests that conclusions about plant yield based on pot studies, even when using very large containers, are a poor reflection of performance in the absence of any physical restriction on root growth. This review supports a number of current paradigms of plant responses to elevated [CO2]. Namely, stimulation of photosynthesis is greater in plants that fix N and have additional carbohydrate sinks in nodules. This supports the notion that photosynthetic capacity decreases when plants are N‐limited, but not when plants have adequate N and sink strength. The root : shoot ratio did not change with growth at elevated [CO2], sustaining the charge that biomass allocation is unaffected by growth at elevated [CO2] when plant size and ontogeny are considered.
Long‐term land‐cover changes in the Belgian Ardennes (1775–1929): model‐based reconstruction vs. historical maps
Authors: Petit C. C. , Lambin E. F.
Published: March 2003

Understanding long‐term human‐environment interactions requires historical reconstruction of past land‐cover changes. The objective of this study is to reconstruct past land‐use and land‐cover changes in a rural municipality of the Belgian Ardennes over the last 250 years. Two approaches were compared. The first approach produced backward projections based on a mechanistic model which computes the demand for different land uses under the assumption of an equilibrium between the production and consumption of resources. The second approach involved using a series of historical maps to extract directly land‐use areas. A stochastic Markov chain model was also used to project backward missing land‐cover data in the time series. The consistency between the results obtained with the different approaches suggests that land‐use area can be successfully reconstructed on the basis of the mechanistic model, under conditions of a subsistence farming system and a closed economy. Land‐use/cover changes in the Belgian Ardennes from 1775 to 1929 were more driven by the interventionist measures of the Belgian government and by technological progress than by the ‘pressure’ of the growing population and livestock. Thanks to agricultural intensification, a decrease in land under human use was supporting increasing human and livestock populations from 1846 to 1880. Reforestation has accelerated since the mid‐19th century. This case study illustrates the highly dynamic and non‐linear character of land‐use change trajectories over long time periods and their strong interactions with the history of societies.
Effects of ultraviolet‐B radiation on growth, mycorrhizas and mineral nutrition of silver birch (Betula pendula Roth) seedlings grown in low‐nutrient conditions
Authors: De La Rosa Tania M. , Aphalo Pedro J. , Lehto Tarja
Published: March 2003

The effects of increased ultraviolet‐B (UV‐B) radiation on the growth, mycorrhizas and mineral nutrition of silver birch (Betula pendula Roth) seedlings were studied in greenhouse conditions. Seedlings—planted in a birch‐forest top soil and sand substrate—were grown without additional nutrient supply. Ultraviolet treatment started immediately after the seedlings emerged and the daily integrated biologically effective UV‐B irradiance on the UV‐B‐treated plants was equivalent to a 25% depletion of stratospheric ozone under clear sky conditions. Visible symptoms of UV‐B damage or nutrient deficiency were not observed throughout the experiment. Seedling height and dry weight (DW) (measured after 58 days and 76 days of treatment) were not affected by increased UV‐B. However, a significant shift in DW allocation toward roots resulted in a lower shoot/root ratio and leaf area ratio in UV‐B‐treated plants compared to control plants. At the first harvest (after 58 days of treatment), the percentage of various mycorrhizal morphotypes and the number of short roots per unit of root length or weight were not affected by increased UV‐B despite significantly increased DW allocation toward roots. Subtle reduction in the allocation of nitrogen (N) to leaves and increased allocation of phosphorus (P) to roots may suggest cumulative effects that could affect the plant performance over the long‐term.
Abiotic constraints on the establishment ofQuercusseedlings in grassland
Authors: Danner Brett T. , Knapp Alan K.
Published: March 2003

High evaporative demand and periodic drought characterize the growing season in midwestern grasslands relative to deciduous forests of the eastern US, and predicted climatic changes suggest that these climatic extremes may be exacerbated. Despite this less than optimal environment for tree seedling establishment, deciduous trees have expanded into adjacent tallgrass prairie within the last century leading to a dramatic land cover change. In order to determine the role of light and temperature on seedling establishment, we assessed carbon and water relations and aboveground growth of first‐yearQuercus macrocarpaseedlings exposed to one of three conditions: (1) intact tallgrass prairie communities (control), (2) aboveground herbaceous biomass removed (grass removal), and (3) shade plus biomass removal to reduce light (PFD) to levels typical of the grassland‐forest ecotone (shade). In the 2000 growing season, precipitation was 35% below the long‐term average, which had a significant negative effect on oak seedling carbon gain at midseason (photosynthesis declined to 10% of maximum rates). However, net photosynthesis and stomatal conductance in the shade treatment was ca. 2.5 and 1.5 times greater, respectively, than in control treatment seedlings during this drought. During this period, leaf and air temperatures in control seedlings were similar whereas leaf temperatures in the shade treatment remained below air temperature. A late‐season recovery period, coincident with decreased air temperatures, resulted in increased net photosynthesis for all seedlings. Increased photosynthetic rates and water relations in shaded seedlings compared to seedlings in full sun suggest that, at least in dry years, high light and temperature may negatively impact oak seedling performance. However, high survival rates for all seedlings indicate thatQ. macrocarpaseedlings are capable of tolerating both present‐day and future climatic extremes. Unless historic fire regimes are restored, forest expansion and land cover change are likely to continue.
Effects of sward structure on the diet selected by guanacos (Lama guanicoe) and sheep (Ovis aries) grazing a perennial ryegrass‐dominated sward
Authors: Bakker M. L. , Gordon I. J. , Milne J. A.
Published: March 2003

The effect of three different vertical structures of a perennial ryegrass‐dominated sward, defined by pseudostem heights (cm) — 1·3 low (L), 2·5 medium (M) and 3·5 high (H) — on the bite depth and selection of plant parts within the grazed horizon of the sward by sheep and guanacos was studied. The bite depth (cm) was similar between sheep and guanacos across the different swards (L, 1·5; M, 3·6; H, 3·8) and was related to pre‐grazing sward surface height rather than to pseudostem height. There were differences in diet composition between species that were related to differences in selection for plant parts. Sheep had a higher proportion of green leaf in the diet than did guanacos in L (0·84 vs. 0·71, P < 0·05) and M (0·75 vs. 0·59, P < 0·05) swards, and possibly selected this plant part in H swards in which the proportion of green leaf in the grazed horizon was low (0·45–0·50). Guanacos had a higher proportion of dead leaf and sheath in the diet than did sheep in L (0·23 vs. 0·09, P < 0·05) and M (0·30 vs. 0·18, P < 0·05) swards, and possibly selected this plant part on these swards, in which the proportion of green leaf in the grazed horizon was high (0·70–0·95). The proportion of pseudostem in the diet of sheep and guanacos was similar across all swards (0·03) and was generally much lower than that in the grazed horizon (0·01–0·18). Guanacos had a higher proportion of dead stem in the diet than did sheep (0·06 vs. 0·02, P < 0·05) across all swards, but the proportion was similar to that in the grazed horizon of each sward.
Changes in contribution of white clover to canopy structure in perennial ryegrass/white clover swards in response to N fertilizer
Authors: Laidlaw  , Withers
Published: March 2003

Twelve plots were laid down on an existing perennial ryegrass/white clover sward, one plot in each of six replicated blocks receiving 100 kg  N ha−1 (100N) and one plot receiving no N (0N). Biomass, canopy development (stratified cuts and point quadrat records at 2–4‐week intervals) and changes in stolon population density were recorded during one 8‐week regrowth period (25 July–23 September) to investigate the likely causes of N effects on white clover in mixed swards.

Over the period, N fertilizer resulted in an increase of 74% in perennial ryegrass biomass and a reduction of 24% in white clover biomass. There was also a reduction of 44% in stolon growing point density, mainly due to lower density of younger stolon branches. White clover's contribution to the upper three leaf area index (LAI) units (taken as an estimate of the proportion of photosynthetically active radiation (PAR) intercepted) was, on average, 70% at 0N producing 74% of the sward biomass, compared with 46% contribution to interception and 37% contribution to biomass at 100N.

While there was no evidence of overtopping, it is concluded that N fertilizer application increased the LAI of perennial ryegrass in the upper layers of the canopy thereby reducing the share of available PAR to white clover. This, coupled with a lower radiation use efficiency at high N and lower population density, results in white clover's reduced performance in mixed swards receiving N fertilizer.
A study of the nutritive value of white clover (Trifolium repens L.) in relation to different stages of phenological maturity in the primary growth phase in spring
Authors: Ayres  , Nandra  , Turner
Published: March 2003

This paper reports the effects of onset of phenological maturity on the nutritive value of white clover (Trifolium repens L.). The study comprised (i) examination of an extensive data set on nutritive value and (ii) investigation of the constituents of nutritive value, in vivo feeding value, protein degradability and metabolizable protein content of white clover harvested at three stages of maturity (early‐flowering, full‐flowering, ripe seed stages) during the primary growth phase in spring in Australia. The data set on nutritive value showed a consistent pattern of high nutritive value during cool season months, progressive decline through spring and uniformly lower nutritive value over summer. Results from laboratory determinations, in sacco degradability studies and a digestibility trial on white clover harvested at early‐flowering, full‐flowering and ripe seed stages were consistent with results from the data set on nutritive value. Onset of maturity during the primary growth phase in spring was accompanied by large changes in nutritive value: neutral‐detergent fibre (NDF) increased from 184 to 301 g kg−1 dry matter (DM), nitrogen (N) declined from 36 to 20 g kg−1 DM, in vitro digestibility declined from 0·74 to 0·65 and metabolizable protein content declined from 144 to 67 g kg−1 DM from early‐flowering to ripe seed stage. These nutritive value changes were accompanied by a decline of in vivo digestibility at the rate of 0·0032 d−1 and an 0·2 reduction in voluntary intake.
The implications of controlling grazed sward height for the operation and productivity of upland sheep systems in the UK. 4. The effect of seasonal pattern of nitrogen fertilizer application and annual stocking rate
Authors: Maxwell  , Sibbald  , Dalziel  , Agnew
Published: March 2003

Greyface (Border Leicester × Scottish Blackface) ewes, mated in October, were housed in winter and turned out after lambing in late March to one of four treatments replicated three times on perennial ryegrass (Lolium perenne)‐dominated pastures. On three of the treatments the stocking rate was 12·5 ewes plus lambs ha−1 annum−1 (SR12·5), whereas on the fourth it was 15·0 ewes plus lambs ha−1 annum−1 (SR15·0). There were two levels of applied fertilizer nitrogen (N), 152 kg N ha−1 annum−1 (N152) and 205 kg N ha−1 annum−1 (N205). Three patterns of nitrogen application were used: predominantly in spring (E), predominantly in autumn (L), and mainly in spring and autumn (E + L). Grazed sward surface height was controlled within the range 3·5–5·5 cm during spring and summer, and supplementary feed was offered when sward height was below 3·5 cm.

The effects on animal performance, yield of silage and requirement for supplementary feed were measured over 3 years (1986–88). Management of the sward height within the specified limits resulted in similar levels of individual animal performance for all treatments, but treatment SR15·0N205E + L produced a significantly (P < 0·05) greater output of lamb per hectare. There was no evidence to suggest that, by increasing the amount of N fertilizer applied in the autumn, ewe reproductive performance was increased. Neither the treatment with the lower level of N applied in the spring (SR12·5N152L) nor the high stocking rate treatment (SR15·0N205E + L) was self‐sufficient in winter feed (silage) production. SR15·0N205E + L also required more supplementary feed in both the lactation (38·1 kg ewe−1) and the mating (9·1 kg ewe−1) periods. SR12·5N152L required the second greatest amount of supplementary feed during lactation (36·1 kg ewe−1), whereas SR12·5N205E + L required the least supplementary feed over both periods (27·8 kg and 4·8 kg ewe−1). Taking all treatments together, there were significant (P < 0·05) differences between years in lamb weaning weight (kg), lamb output (kg ha−1), yield of silage (kg ewe−1) and supplementary feed required (kg ewe−1), arising mainly from a lower level of herbage production in one year. Treatment SR12·5N152E generated the highest gross margin per hectare.
The infection of Festuca rubra by the fungal endophyte Epichloë festucae in Mediterranean permanent grasslands
Authors: Zabalgogeazcoa  , Aldana B. R. Vázquez de , Criado B. García , Ciudad A. García
Published: March 2003

The purpose of this work was to determine the frequency of infection by fungal endophytes in Festuca rubra plants from Mediterranean permanent grasslands (dehesas). Plants infected with the fungal endophyte Epichloë festucae were detected in all twenty‐seven populations studied in the province of Salamanca, Spain. Infection frequencies in six selected populations ranged from 44% to 92% (average, 70%) of the plants. Infected plants were almost always symptomless. These results suggest that the association between E. festucae and F. rubra is common and occurs at a high frequency in Mediterranean permanent grasslands.
Severity of damage to Trifolium repens leaves by certain invertebrate species in mixed perennial ryegrass/white clover swards: response to cultivar, cutting frequency and sward characteristics
Authors: Fengrui Li
Published: March 2003

The severity of damage by certain invertebrate species to white clover (Trifolium repens) leaves on the main stolons of plants grown in mixed perennial ryegrass/white clover swards was examined in a field experiment in the Netherlands in which two cutting frequencies (high and low) and three white clover cultivars (Retor, Alice and Gwenda) were used. The damage to the leaves was described in terms of the numbers of damaged leaves and the extent of that damage (slight <20%, moderate 20–50% and heavy >50%). The relationships between leaf damage and sward characteristics (white clover content, above‐ground biomass and sward height) were evaluated throughout the growing season.

Over the whole experimental period, 23·7% and 27·4% of the total number of leaves produced per stolon were damaged by slugs and weevils in the low‐ and high‐frequency cutting treatments respectively. High‐frequency cutting increased the number of leaves in the total leaf damage and moderate leaf damage categories by 21·4% and 34·8%, respectively, compared with the low‐frequency cutting. The cv. Retor (medium‐leaved) experienced the most severe damage by invertebrates. It had much higher leaf damage than cvs Alice (large‐leaved) and Gwenda (small‐leaved) at either cutting frequency, both in the total number of damaged leaves and in the different damage categories. Differences among cultivars in the number of damaged leaves and relative leaf damage occurred primarily in spring, late summer and autumn, but did not differ during the early‐ and mid‐summer months.

This study indicates that variations in leaf damage among clover cultivars were associated with differences in measured sward characteristics. Both the number of damaged leaves and the relative leaf damage were strongly negatively correlated with white clover content and biomass in spring, late summer and autumn under each cutting treatment. White clover content and biomass explained 65%, 59% and 50% of the variation in the number of damaged leaves in spring, late summer and autumn, respectively, and 58%, 57% and 45% of the variation in relative leaf damage in these three periods. Thus, sward characteristics may play a role in regulating the severity of invertebrate damage to clover leaves in addition to the primary effects of HCN.
Effect of combined insecticide and fungicide treatments on newly sown swards of Italian and perennial ryegrass using two methods of sowing, two rates of seed and N fertilizer, with and without herbicide
Authors: Lewis  , Clements
Published: March 2003

The effects of six factors, each at two levels and in all combinations, on herbage yield and weed content of perennial (Lolium perenne) and Italian (L. multiflorum) ryegrass were assessed in four autumn sowings of field plots, in 3 years and at two sites. The factors were (i) perennial (PRG) or Italian (IRG), (ii) normal or low seed rate, (iii) drilling or broadcasting the seed, (iv) normal or low N fertilizer rate, (v) ryegrass fungicide seed treatment and post‐emergence insecticide sprays (F + I) or untreated, and (vi) herbicide treatment or untreated. Overall, herbage yield at the first harvest was increased by F + I and IRG (all sowings), and the higher rates of seed (three sowings) and N (two sowings). Variable results were obtained for the other two factors. Increased yield was often associated with reduced weed content. Significant interactions between factors were obtained at two sowings; in particular, F + I increased yield of IRG by 12% and 22%, but had no effect on PRG. A second harvest, in the following spring, was taken for two sowings and there was no effect of F + I or the higher rates of seed and N. Thus, it is concluded that the desired aim when establishing grass swards of an adequate plant population without excessive competition from weeds appeared to be obtained even with plots receiving the least inputs.
The effects of wilting grass before ensiling on silage intake
Authors: Dawson  , Ferris  , Steen  , Gordon  , Kilpatrick
Published: March 2003

Herbage, predominantly perennial ryegrass (Lolium perenne) grown in Northern Ireland, was harvested at four dates from June to October 1996 (H1, H2, H3 and H4). At each harvest approximately one‐fifth of the grass harvested was artificially dried and pelleted (G). The remainder of the grass was either wilted for 28–52 h (W), depending on the weather conditions, or ensiled directly, i.e. unwilted (UW). Within the W and UW treatments an inoculant or formic acid additive was applied to the herbage before ensiling. After a minimum ensiling period of 10 weeks, sixty steers, mean initial live weight 432 (s.d. 37) kg, were offered the twenty forages in a four‐period partially balanced changeover design experiment. Each period was of 2 weeks’ duration. Dry‐matter (DM) intakes were recorded daily, with intakes in the second week of each period used in the statistical analysis of the data. The digestibility of each of the forages was also determined in vivo using four castrated male sheep per silage. Wilting increased the DM content of the silage and the pH, the largest increase in DM content occurring at the second harvest. On average, wilting proportionally increased silage DM intake by 0·21 compared with the unwilted silage (P < 0·001), but the intake of the wilted silage was not significantly different from that of the artificially dried and pelleted grass (P > 0·05). The intake of the wilted silage was higher than that of the unwilted silage at each harvest, the proportional increases being 0·22 (P < 0·001), 0·41 (P < 0·001), 0·19 (P < 0·001) and 0·05 (P > 0·05) at harvests H1, H2, H3 and H4 respectively. Treatment of the grass with formic acid before ensiling resulted in a proportional increase in silage intake of 0·08 compared with the inoculant‐treated silage (P < 0·05). Compared with the inoculant‐treated silage, formic acid increased silage intake by 0·08, 0·02, 0·14 and 0·10 at harvests H1 (P > 0·05), H2 (P > 0·05), H3 (P < 0·01) and H4 (P < 0·05). The results of this study indicate that the effect of wilting on silage intake varies across different harvests and additive treatments. The difference in response to wilting across different harvests is mainly a result of the prevailing weather conditions during wilting.
The effects of incorporating sugar beet pulp with forage maize at ensiling on silage fermentation and effluent output using drum silos
Authors: Hameleers  , Leach  , Offer  , Roberts
Published: March 2003

The effects of incorporating sugar beet pulp with forage maize at ensiling on silage fermentation, effluent output and pollution potential of the effluent was investigated using 200‐litre drum silos. A forage maize crop (Zea mais) was harvested on four different dates, generating four different stages of maturity [dry‐matter (DM) content 154–235 g kg−1 DM], and molassed sugar beet pulp (MSBP) was added at five different rates (0, 2, 7, 13, 18 kg MSBP 100 kg−1 fresh maize crop). A total of fourteen treatments (each replicated three times) were evaluated. The chemical analysis of the maize silages and the mixtures produced showed that MSBP addition increased DM, ash, neutral cellulase gaminase digestibility (NCGD) and metabolizable energy (ME) contents of the mixture significantly (P < 0·01) for all harvesting dates except for harvest date 1. Silage fermentation in terms of final pH was unaffected by MSBP addition, although lactic acid concentration of the effluent tended to increase with increased MSBP addition. When no MSBP was included, large volumes of effluent were produced, ranging from 200 g kg−1 to 100 g kg−1. MSBP addition significantly (P < 0·01) decreased effluent production except for the driest material. A curvilinear equation was fitted to predict effluent production from DM of the forage maize and pressure applied to the sample (adjusted r2=0·95). In addition, a curvilinear equation was fitted to predict the MSBP addition rate required to prevent effluent production (adjusted r2=0·65). For harvest dates 1, 2 and 3, the biological oxygen demand for 5 days (BOD5) and the chemical oxygen demand (COD) concentration of the effluent were significantly increased (P < 0·05) with increased levels of MSBP addition. However, the pollution potential per kg of material ensiled was significantly reduced (P < 0·05) with increased MSBP addition, since less effluent was produced. The experiment indicates that ensiling low DM silages with appropriate levels of MSBP produces nutritionally valuable silages with reduced pollution potential.