bluuebunny/crossref_metadata_2025_split huggingface dataset:
Selective gopher disturbance influences plant species effects on nitrogen cycling
Authors: Eviner Valerie T. , Chapin, III F. Stuart 
Published: February 2005

Plant species effects on ecosystem processes are mediated by traits such as litter quality and exudation. These same traits also influence the activity and distribution of animals that play key roles in regulating ecosystem dynamics. We planted monocultures of eight plant species commonly found in California grasslands to investigate the relative importance of plant species direct effects on nitrogen cycling, versus their indirect effects mediated by plant interactions with gophers. Plant species differed in their litter C:N ratio, which closely related to species effects on rates of net mineralization and nitrification in undisturbed soil. However, the effect of selective gopher disturbance on N cycling greatly altered these species effects.Plant species differed in their effects on the type and timing of gopher disturbance. Small feeding holes were formed in late spring in plots containing species with high tissue quality. These feeding holes minimally disturbed the soil and did not alter N cycling rates over the short term. Large gopher mounds were formed in the winter and early spring, primarily in plots containing the grass,Aegilops triuncialis, and to a lesser extent in plots containingAvena barbata. These large mounds significantly disturbed the soil and greatly increased net nitrification rates, but had no consistent effects on net N mineralization. In undisturbed soil,Aegilopshad the highest litter C:N ratio and one of the lowest rates of net nitrification. However, gophers preferentially built large mounds inAegilopsplots. Once the effects of gopher burrowing were considered,Aegilopshad one of the highest rates of net nitrification, indicating that the indirect effects of plant species on N cycling can be more important than the direct effects alone. This experiment indicates that it is vital to consider interactions between plants and other organisms in order to predict the ecosystem effects of plant communities.
Is arthropod predation exclusively satiation‐driven?
Authors: Rijn Paul C. J. van , Bakker Frank M. , Hoeven Wietske A. D. van der , Sabelis Maurice W. 
Published: February 2005

Functional response models differ in which factors limit predation (e.g. searching efficiency, prey handling time, digestion) and whether predation behaviour is governed by an internal physiological state (e.g. satiation). There is now much evidence that satiation is a key factor in understanding changes in foraging behaviour, and that many predators are effectively digestion limited. Here, we ask if predation in a predatory arthropod can be explained from satiation‐driven behaviour alone, or if behaviour is also influenced by the density of prey other than via the effect of prey ingestion on satiation. To address this question a satiation‐based predation model is formulated, for which parameters are estimated on the basis of observations on digestion rate, satiation‐related prey searching rate and prey capture behaviour, basically under high prey density conditions. The model predictions are subsequently tested against longer term predation experiments carried out at high and low prey densities. Since satiation can easily be linked with egg production, these tests are carried out both for predation and oviposition.The predator–prey systems under study consist of females of two predatory mite species (Neoseiulus barkeri and N. cucumeris) and the larvae of two thrips species (Thrips tabaci and Frankliniella occidentalis) as their prey. For N. barkeri foraging on T. tabaci, the model gives good predictions at both high (4 larvae cm−1) and low (0.1–1 larvae cm−2) prey densities. For N. cucumeris foraging on F. occidentalis, the predictions hold at the high prey density, but are too low at low prey densities. Thus our analysis indicates that we cannot fully explain density‐dependent predation rates from satiation‐driven behaviour alone. Different mechanisms are suggested on how prey density may affect foraging efficiency other than via satiation.
Applications of ecological stoichiometry for sustainable acquisition of ecosystem services
Authors: Ptacnik Robert , Jenerette G. Darrel , Verschoor Antonie M. , Huberty Andrea F. , Solimini Angelo G. , Brookes Justin D. 
Published: February 2005

Human activities have differentially altered biogeochemical cycling at local, regional and global scales. We propose that a stoichiometric approach, examining the fluxes of multiple elements and the ratio between them, may be a useful tool for better understanding human effects on ecosystem processes and services. The different scale of impacts of the elements carbon, nitrogen and phosphorus and the different nature of their biogeochemical cycles, imply a large variation of their stoichiometric ratios in space and time and thus divergent impacts on biota.In this paper, we examine the effects of anthropogenic perturbations on nutrient ratios in ecosystems in two examples and one case study. Altered stoichiometry in agricultural systems (example 1) can affect not only crop yield and quality but also the interactions between plants and their pollinators, pests and pathogens. Human activities have also altered stoichiometry in coastal ecosystems (example 2). Increased N loading has especially lead to increased N:P and reduced Si:N ratios, with detrimental effects on ecosystem services derived from coastal pelagic food webs, such as fish yield and water quality. The terrestrial–aquatic linkage in stoichiometric alterations is illustrated with a case study, the Mississippi River watershed, where anthropogenic activities have caused stoichiometric changes that have propagated through the watershed into the northern Gulf of Mexico.Coupled with altered stoichiometric nutrient inputs are the inherent differences in variation and sensitivity of different ecosystems to anthropogenic disturbance. Furthermore, the connections among the components of a watershed may result in downstream cascades of disrupted functioning. Applying a multiple element perspective to understanding and addressing societal needs is a new direction for both ecological stoichiometry and sustainability.
Infrequent and intense defoliation benefits dry‐matter accumulation and persistence of clipped Arrhenatherum elatius
Authors: D'Angelo G. H. , Postulka E. B. , Ferrari L. 
Published: February 2005

AbstractThe objective was to determine how the frequency and intensity of defoliation of tall oat grass [Arrhenatherum elatius (L.) Presl.], affected (i) annual dry‐matter (DM) accumulation, (ii) seasonal distribution of the accumulated forage, and (iii) morphological traits related to persistence and vigour. Data were collected twice a year throughout three growing years, beginning the second year after establishment. Two frequencies (A: each time modal height of plants reached 20 cm; B: each time modal height of plants reached 40 cm) and two defoliation intensities (I: 5 cm; II: 10 cm stubble) were arranged in a completely randomized block design with a fully factorial combination and four replicates. Measurements were made of annual DM accumulation, seasonal distribution of accumulated DM and morphological traits related to persistence and vigour, i.e. number of tillers m−2, number of tussocks m−2, crown diameter, and crown area of tussocks. The infrequent defoliation (B) increased annual DM accumulation besides maintaining levels of persistence and vigour. The most productive treatment (BI) had a significantly higher annual DM accumulation than treatments AI and AII. Frequent and severe defoliations (treatment AI) led to plant depletion, which reduced crown diameter, number of tillers m−2 and crown area at the end of the third year compared with infrequent but severe defoliation (treatment BI). Annual DM accumulation was intermediate for less intense defoliations (AII), which produced forage during winter, but resulted in less vigorous plants by the end of the experiment. Crown area was a good indicator of tiller number, particularly under frequent defoliation.
Measurement of above‐ground plant biomass, forage availability and grazing impact by combining satellite image processing and field survey in a dry area of north‐eastern Syria
Authors: Hirata M. , Koga N. , Shinjo H. , Fujita H. , Gintzburger G. , Ishida J. , Miyazaki A. 
Published: February 2005

AbstractField survey and satellite image processing methods were used to estimate the total available forage over an area of 95 034 ha in north‐eastern Syria, and to assess grazing impact on the area. The above‐ground plant biomass was measured by a quadrat method at three sites in each of eight vegetation classes. Available forage was measured by excluding woody parts of shrubs from the whole aerial plant parts. The total above‐ground plant biomass and available forage were estimated by extrapolating the measured point data to the whole target area using classified vegetation data by satellite image processing. Grazing impact was assessed by calculating the differences between the total available forage at the end of growing season and the end of dry season. The values for the estimated total available forage (s.e. of mean) in the area were 55 628 000 (12 920 000) kg DM and 30 007 000 (2 437 000) kg DM at the end of growing season and dry season respectively. Although the area of the cereal fields covered only 0·315 of the area, about 0·69 and 0·82 of the available forage existed in the harvested cereal fields at the ends of growing season and dry season respectively. The integration of cereal fields and rangeland is a normal land use system for livestock management in the area. The higher cover of herbaceous vegetation types showed higher grazing impacts which reduced the total available forage at the end of the growing season by 0·817 (0·199) at the end of the dry season. Although these dense herbaceous vegetation types could possibly produce more available forage, they would incur more intensive grazing impact. On the contrary, lighter grazing impact would occur with a higher cover of shrub vegetation types. The importance of maintaining plant cover over the rangeland area to protect the land against soil erosion is stressed.
Potential of imaging spectroscopy as tool for pasture management
Authors: Schut A. G. T. , Lokhorst C. , Hendriks M. M. W. B. , Kornet J. G. , Kasper G. 
Published: February 2005

AbstractThe use of imaging spectroscopy to predict the herbage mass of dry matter (DM), DM content of herbage and crude fibre, ash, total sugars and mineral (N, P, K, S, Ca, Mg, Mn, Zn and Fe) concentrations was evaluated. The experimental system used measured reflectance between 404 and 1650 nm at high spatial (0·28–1·45 mm2) and spectral resolution. Data from two experiments with Lolium perenne L. mini‐swards were used where the degree of sward damage or N‐fertilizer application varied. Regression models were calibrated and validated and the potential reduction in prediction error with multiple observations was estimated. The mean prediction errors for DM mass, DM content and N, total sugars, ash and crude fibre concentrations were 235–268 kg ha−1, 9·6–16·8 g kg−1, 2·4–3·4 g kg DM−1, 16·2–27·7 g kg DM−1, 5·8–6·5 g kg DM−1 and 8·4–10·4 g kg DM−1 respectively. The predictions for concentrations of P, K, S and Mg allowed identification of deficiency levels, in contrast to the concentrations of Na, Zn, Mn and Ca which could not be predicted with adequate precision. Prediction errors of DM mass may be maximally reduced to 95–142 kg ha−1 with 25 replicate measurements per field. It is concluded that imaging spectroscopy can provide an accurate means for assessment of DM mass of standing grass herbage. Predictions of macronutrient content and feeding value were satisfactory. The methodology requires further evaluation under field conditions.
The effects of treading by dairy cows during wet soil conditions on white clover productivity, growth and morphology in a white clover–perennial ryegrass pasture
Authors: Menneer J. C. , Ledgard S. F. , McLay C. D. A. , Silvester W. B. 
Published: February 2005

AbstractSingle pugging events, which involve remoulding of the soil around the hooves of livestock during treading, of moderate or severe pugging intensity were imposed in plots in a long‐term white clover‐ryegrass pasture during spring, by using dairy cows at varying stocking rates (4·5 cows 100 m−2 for 1·5 or 2·5 h respectively). Changes in the growth and morphology of white clover were investigated over the following 12 months. Defoliation at approximately 3‐week intervals was carried out by mowing. Annual herbage production was reduced following moderate and severe pugging proportionately by 0·16 and 0·34 compared with the non‐pugged control treatment. The corresponding decreases in white clover production were 0·09 and 0·52 respectively. Annual perennial ryegrass production was reduced by 0·37 under severe pugging. Pugging had an immediate adverse effect on growth of white clover which persisted for up to 156 d, and coincided with a large decrease in the proportion of white clover in herbage over the same period (e.g. 0·40 vs. 0·12, in control and severely pugged treatments, respectively, on day 112). In comparison, recovery in ryegrass growth was apparent after 50 d in severely pugged treatments, indicating that white clover is more vulnerable to severe pugging than perennial ryegrass. Analysis of individual white clover plants extracted from turves (300 mm × 300 mm) showed that direct hoof damage, fragmentation and burial of stolons were the major factors which reduced white clover production, rather than the changes in soil physical properties measured. Morphological characteristics associated with plant size (e.g. stolon length, growing points, and leaf numbers) all decreased under pugging. The situation had reversed by late summer, with larger plants dominating pugged plots, and coincided with the recovery of the proportion of white clover in herbage. Strategic pasture management practices, such as restricted grazing and the use of stand‐off pads when soils are overly wet, are suggested as means of minimizing treading damage to pasture and reducing negative impacts on the growth and productivity of white clover.
Forage yield and persistency of Trifolium repens × Trifolium nigrescens hybrids under rotational sheep grazing
Authors: Marshall A. H. , Williams T. A. , Olyott P. , Abberton M. T. , Michaelson‐Yeates T. P. T. 
Published: February 2005

AbstractIntrogression of reproductive traits from the annual, profuse flowering, ball clover (Trifolium nigrescens Viv.) into white clover (Trifolium repens L.) is one breeding strategy to improve seed yields of T. repens that must be achieved without sacrificing agronomic performance and persistency under grazing. The yield and persistency of hybrids between white clover and T. nigrescens were compared under rotational sheep grazing over three harvest years. The hybrids included the backcross (BC) 2 and 3 generations produced using white clover as the recurrent parent. The large‐leaved T. repens variety Olwen, medium‐leaved varieties AberDai and Menna and the small‐leaved variety S184 were sown as controls. Hybrids and control varieties were sown with a perennial ryegrass companion; between April and the end of October in each harvest year the plots were rotationally grazed with sheep with clover and perennial ryegrass (DM) yield and the proportion of clover present measured over the growing season. The clover and total DM yields of the BC2 and BC3 were generally comparable with the small‐ and medium‐leaved varieties within the experiment and significantly greater than the yields of the large‐leaved variety Olwen. Throughout the 3 years of the experiment the BC2 maintained a clover content above 0·30 and comparable with the small‐leaved varieties, while the clover content of the BC3 was comparable with the small‐ and medium‐leaved varieties in the first and third harvest years. No significant difference in perennial ryegrass production was observed when grown with the backcrosses or the control varieties. Differences in stolon and growing‐point density were observed at the end of the experiment with the density of the BC2 and BC3 less than the small‐leaved variety S184 but, in common with the medium‐leaved varieties, greater than the large‐leaved variety Olwen. The implication of these results for the use of this material in future experiments and in the white clover breeding programme is discussed.
Transition through the taprooted growth stage in white clover as related to temperature
Authors: Bonesmo H. , Bakken A. K. 
Published: February 2005

AbstractMorphology and phenology, including stolon disintegration, of white clover were studied at two sites in the first three years after sowing. The plants reached their maximum size in late summer in the first year after sowing, and the populations contained at that time mainly taprooted plants. The subsequent fragmented plants were smaller in most of the investigated characteristics. A function describing the daily transition rate from taprooted to fragmented plants in relation to daily mean temperature is presented. Deviations between the recorded and the calculated proportion of taprooted plants were small; the overall root mean square error was 0·057. The data indicated that there is a low temperature requirement that must be met prior to the onset of transition. It is also suggested that, in further modelling of the response of white clover to temperature, the effect of daylength should be accounted for, particularly if the data are collected from sites with a considerable latitudinal spread.
The productivity of oats and berseem clover intercrops. II. Effects of cutting date and density of oats on annual forage yield
Authors: Ross S. M. , King J. R. , O'Donovan J. T. , Spaner D. 
Published: February 2005

AbstractAnnual forage yields of intercrops of berseem clover (Trifolium alexandrinum L.) and oats (Avena sativa L.), as affected by timing of initial harvest and sowing rate of oats, were investigated. Berseem clover was intercropped with oats at 0, 30, 60, 90 and 240 plants m−2 of oats in 1999 and 2000 in Alberta, Canada. Cutting date treatments involved initial harvest at 10‐d intervals between 35 and 88 d after planting (DAP), and one or two subsequent harvests of regrowth. Total intercrop dry‐matter (DM) yield averaged 12·9–13·3 t ha−1 with proportions of 0·21–0·43 of berseem clover in the forage. Treatments with an initial cut at the silage stage of oats (76 DAP in 1999, 88 DAP in 2000, at about soft‐dough stage of oats) had greater yields of oats, lower yields of berseem clover, and lower proportions of berseem clover in total annual yields than treatments with an earlier initial cut. Total crude protein (CP) yield was greater with an initial cut at 65–66 DAP than with a silage‐stage initial cut. With an initial cut at 35 DAP (before stem elongation of oats) or after 65 DAP (after heading of oats), yield potential of oats was sometimes reduced compared with silage‐stage treatments, but this was balanced by a greater yield of berseem clover. The impact of harvest timing on total yield decreased as the proportion of berseem clover in the intercrops increased. With decreasing density of oats, DM yield of first‐cut intercrops and total DM yield of oats decreased, while regrowth and total DM yields of berseem clover increased. Intercrops with oats at 60 plants m−2 had equal or greater total DM and CP yields than intercrops with 240 plants m−2 of oats. For intercrops with oats at 60 plants m−2, with initial cuts at 65–66, 75–76, or 88 DAP, yields of regrowths were 0·30–0·35, 0·16–0·26 and 0·09 of the total yield respectively. Oats–berseem clover intercrops showed potential to manipulate the pattern of annual forage yield and to provide flexibility of harvest without reducing annual yields.
The productivity of oats and berseem clover intercrops. I. Primary growth characteristics and forage quality at four densities of oats
Authors: Ross S. M. , King J. R. , O'Donovan J. T. , Spaner D. 
Published: February 2005

AbstractBerseem clover (Trifolium alexandrinum L.) was sown as an intercrop with oats (Avena sativa L.) at 0, 30, 60, 90 and 240 oats plants m−2 in May in 1999 and 2000 in Alberta, Canada. Forage yield and quality were measured at 10‐d intervals between 35 and 88 d after planting (DAP). Yield is defined as the biomass above 6 cm of the soil surface. The dry‐matter (DM) yield of berseem clover in sole crops increased by 5–10 g m−2 d−1 between 35 and 55 DAP and then increased by 21–28 g m−2 d−1 between 55 and 75 DAP. The DM yields of oats sown at 240 plants m−2 increased by 26–28 g m−2 d−1 over the whole period from 35 to 75 DAP. Oats were the dominant component in the intercrops, even at low densities of oats. Berseem clover grown with 60 oats plants m−2 received only 0·24 of the incident light when shading by oats peaked at 65 DAP. DM yields of berseem clover in intercrops with 60 oats plants m−2 averaged 0·14–0·32 of the yields of berseem clover sole crops. Between 35 and 88 DAP in 2000, the crude protein (CP) concentration of berseem clover sole crops declined linearly from 310 to 180 g kg−1 DM, and the CP concentration of oats exhibited a quadratic response, declining from 350 g kg−1 DM at tillering to 110 g kg−1 DM at the soft dough stage. The mean CP concentration of berseem clover in intercrops with 60 oats plants m−2 was 25 g kg−1 less than in berseem clover sole crops, indicating that competition by oats reduced the CP concentration of berseem clover. At later sampling dates, CP and DM yields of intercrops with oats at 60 plants m−2 equalled those with oats at 240 plants m−2. The addition of berseem clover to oats in intercrops at 60 oats plants m−2 reduced the neutral‐detergent fibre concentration by 30 g kg−1 DM compared with oats alone. Oats were very competitive as a companion crop for berseem clover. Adding berseem clover to oats increased forage quality and may provide for increased intake and digestibility of forage to support higher livestock productivity.