bluuebunny/crossref_metadata_2025_split huggingface dataset:
An isotopic (15N) assessment of intraclonal regulation in C4 perennial grasses: ramet interdependence, independence or both?
Authors: Derner J.D. , Briske D.D. 
Published: May 2003

1  A series of three experiments was conducted with three C4 perennial grasses, Panicum virgatum (short rhizomes forming distinct clones), Schizachyrium scoparium (caespitose) and Bouteloua gracilis (caespitose), to determine whether intraclonal regulation was characterized by interdependence, independence or a combination of both processes. Specific hypotheses tested were: (i) all ramets within individual clones are physiologically integrated; (ii) ramet hierarchies (several connected generations) within individual clones are capable of acquiring soil nitrogen equally from localized nutrient‐rich pulses; and (iii) nitrogen is retained within individual hierarchies through allocation to sequentially developed ramet generations. 2  Mean 15N atom percent excess values within labelled ramet hierarchies were 10–21‐fold greater than in immediately adjacent ramet hierarchies, and 105–137‐fold greater than in the remaining ramet hierarchies within clones for all three species. This pattern of 15N distribution demonstrates that physiological integration does not occur among all ramets within individual clones and that ramet hierarchies function as integrated physiological individuals. 3  Ramets in closer proximity to a 15N pulse in soils acquired disproportionately greater amounts of the isotope compared to more distant ramets within clones for all three species. Inequitable resource acquisition among ramet hierarchies establishes the potential for asymmetric intraclonal competition below‐ground and the development of size inequalities among hierarchies. 4  Approximately 21.7%, 3.5%, 1.7% and 2.3% of the initial 15N pool was allocated from the first ramet generation to the second and third (spring cohort), third (autumn cohort) and fourth generations, respectively. However, the magnitude of nitrogen allocation from parent to juvenile ramet generations was relatively consistent, with 17–32% of the 15N pool within parental ramets allocated to juvenile ramets. Intergenerational 15N allocation in S. scoparium clones therefore demonstrates a high degree of interdependence within individual ramet hierarchies. 5  Clones of the rhizomatous and two caespitose grasses investigated functioned as assemblages of autonomous ramet hierarchies, but ramet generations within individual hierarchies were effectively integrated. Consequently, intraclonal regulation in these temperate, perennial grasses is characterized by both ramet interdependence and independence. The occurrence of ramet independence throughout much of the life history of perennial grasses demonstrates the ecological importance of clonal fragments to genet and population maintenance and emphasizes that this may be the most relevant scale to investigate further the ecology of this important and widely distributed group of clonal plants.
Consequences of sexually dimorphic timing of emergence and flowering in Silene latifolia
Authors: Purrington Colin B. , Schmitt Johanna 
Published: May 2003

1 Males and females of dioecious plant species often differ in a variety of secondary characteristics, such as size, flower number and flowering time, suggesting that dioecious species have sex‐specific selection histories. However, a potential source of these dimorphic traits is age differences between males and females. By sowing 3000 seeds of the dioecious perennial, Silene latifolia (Caryophyllaceae), on a single day, we were able to assess the contribution of sex differences in emergence time to the development of sexually dimorphic adult traits. 2 Females emerged before males in our experimental field population, but on average males flowered first. Age differences between males and females did not therefore cause the earlier flowering of males. 3 The consequence of the detected differences in emergence and phenology between males and females was explored by path analysis. Emergence time had a strong direct effect on flower production as well as an indirect effect through flowering time. The regression coefficient of flowering time on emergence time was significantly larger for male plants. 4 A phenotypic selection analysis revealed that seedlings emerging early suffered greater mortality than those emerging later. Seedlings emerging early, however, developed into plants with more flowers, indicating that there was a trade‐off between survivorship and reproductive performance. Seeds with intermediate emergence times had the highest total fitness, indicating the presence of stabilizing selection. Despite the strong mortality selection against early emergers, we detected no shift in the sex ratio compared with the sex ratio of seeds matured under low‐mortality greenhouse conditions.
Plant foraging and rhizome growth patterns of Solidago altissima in response to mowing and fertilizer application
Authors: Stoll Peter , Egli Philipp , Schmid Bernhard 
Published: May 2003

1  The rhizome growth patterns of the clonal plant Solidago altissima were studied in response to mowing and fertilizer application in a field experiment. Rhizome systems of 120 clonal fragments were harvested in the spring of 1993, after 6 years of mowing (1987–92) and 2 years of fertilizer application (1991–92). The results were interpreted in the light of plant foraging theory. 2  The ages of the individual rhizomes comprising each rhizome system were determined and their length, number of offspring rhizomes, branching angles and the height of emerging shoots measured. Rhizomes were then washed, dried and weighed. 3  Persistent rhizomes, i.e. rhizomes that survived more than 1 year, were shorter and less numerous in mown plots and their dry mass was less than 50% of that in unmown plots. Thus, repeated mowing depleted the rhizomes of their stored resources and has been used as a measure to control the further spread of S. altissima. 4  In contrast, rhizomes established in 1992 produced 10% more daughter rhizomes, which were also 23% longer in mown than in unmown plots. 5  There was little evidence that the length, and no evidence that the number of rhizomes, was increased by fertilizer application. Nevertheless, fertilizer application increased the dry mass and decreased the specific length (length per unit dry mass) of rhizomes. 6  Rhizome branching angles were not consistently altered by the treatments. However, there was a significant interaction, i.e. angles increased in response to fertilizer in unmown but not in mown plots. 7  The observed rhizome growth patterns (3–5) could be explained by adaptive growth plasticity, i.e. foraging, in the first year followed by differential survival of long rhizomes in later years. However, the greater length of newly formed rhizomes in mown plots could also have been due to increased soil temperatures caused by the removal of standing biomass and litter, which increased irradiance at the soil surface. This suggests that the observed growth responses of the rhizome systems to mowing and fertilizer application were due to ‘passive growth’ rather than adaptive foraging.
Abundance–range size relationships in the herbaceous flora of central England
Authors: Thompson Ken , Hodgson John G. , Gaston Kevin J. 
Published: May 2003

1 Using data from a survey of over 10 000 1‐m2 quadrats in a 3000‐km2 area, we examined the relationship between abundance and range for the vascular plant flora of central England. 2 At the level of the whole landscape, abundance was not related to local, regional or national range. Local, regional and national range were closely related to each other. 3 At the level of the whole landscape, range was significantly and positively related to both niche breadth (expressed as the range of habitats exploited) and to habitat availability, although niche breadth appeared to be more important. Abundance was not related to niche breadth or habitat availability. Since specialist species are mainly confined to uncommon habitats (especially wetlands), we conclude that the relationship between range and niche breadth is not an artefact of widespread species passively sampling more habitats. 4 At the level of individual habitat types, significant positive relationships between range and abundance were common. These relationships remained after controlling for the effects of phylogeny. For predominantly annual weed communities, the relationship was linear, but for perennial communities it was markedly ‘upper triangular’, i.e. all combinations of range and abundance were found except wide range/low abundance. The evidence suggests that this difference can be attributed to the greater mobility of annual weeds.
Contrasting ecological breadth of co‐occurring annualPolygonumspecies
Authors: Sultan S. E. , Wilczek A. M. , Hann S. D. , Brosi B. J. 
Published: May 2003

1 Understanding the relative distributions of ecological generalists vs. specialists requires precise characterization of the environmental ranges of closely related taxa. The ecological breadth of four annual species in the genusPolygonumwas determined from field measurements taken from five natural populations per species in a common geographical range.2Significant early and late‐season differences among the species were found for available light (photosynthetically active radiation) at canopy and mid‐canopy levels, and for soil temperature, moisture availability, macronutrient content, pH, cation exchange capacity (CEC) and structure, at two depths. Field sites within each species also differed significantly for these variables.3The field distribution ofP. persicaria covers the broadest range of habitats, from moderate shade with very dark microsites to full insolation, cool to very warm soils, flooded to dry moisture conditions, and organic, high‐nutrient to nutrient‐poor soils.4Polygonum lapathifoliumis comparatively intolerant of shade, particularly early in the growth season. Although this species occurs in flooded to moderately dry conditions and in poor as well as rich soils, its moisture and nutrient ranges do not include such low extremes as those ofP. persicaria, and its range of soil temperatures is also narrower.5Polygonum cespitosumis restricted to low‐light habitats and to consistently moist soils that do not flood. The species is, however, found in a moderately broad range of soil types and macronutrient availabilities.Polygonum cespitosumoccurs in extremely low‐light habitats that are evidently beyond the shade tolerance of the other species.6Polygonum hydropiperis restricted to high‐light sites with highly organic, consistently very moist or flooded soils. Unlike its congeners, this species can tolerate flooded soils during seedling establishment. The species is limited to soils with high early nitrate and calcium content, moderate CEC, and pH close to 6.0, but tolerates a broad range of soil temperatures.7The occurrence of spatial and temporal environmental variability within as well as among field populations ofPolygonumspecies suggests that tolerance of such variability may result from individual phenotypic plasticity rather than from ecotypic adaptation of entire populations.
The occurrence of thermophilous trees in the Scandes Mountains during the early Holocene: evidence for a diverse tree flora from macroscopic remains
Authors: Kullman Leif 
Published: May 2003

1 Macroscopic remains of the fairly thermophilous tree species Alnus glutinosa, Tilia cordata and Betula pendula were recovered in subalpine and adjacent boreal environments far above and beyond their present‐day distributional limits. This establishes that the early Holocene tree flora of the Scandes Mountains in northern Sweden was indeed richer than it is today. 2 Dates ranged between c. 8600 and 7000 radiocarbon years bp. These are much earlier than previous estimates by conventional pollen stratigraphical analyses of the arrival of these species at their maximum geographical limits. This highlights problems in using only pollen data for vegetation reconstruction, and suggests re‐evaluation of earlier records. 3 The results, together with similar macrofossils for Picea abies and Larix sibirica in northern Sweden, suggest that many tree species spread rapidly and became established at their most extended range limits during the early Holocene. Abundances have subsequently varied in accordance with the ecology of individual species as well as with climatic change. 4 Palaeoclimatic inferences may suggest a strongly continental climate, i.e. warmer and drier summers and possibly fairly cold winters between 8600 and 7000 bp relative to the present. Some change towards a more oceanic climate regime with less pronounced seasonal contrasts may have occurred towards the end of the period.
A spatially precise study of Holocene fire history, climate and human impact within the Maurienne valley, North French Alps
Authors: Carcaillet Christopher 
Published: May 2003

1 If, within a vegetation type, fire regimes are climate dependent, then fire patterns should be synchronous at regional scales. If they are not synchronous, then fires may be dependent on local processes such as human‐induced disturbances. 2 Two fire chronologies were developed using 34‐radiocarbon dating measured by accelerator mass spectrometry (AMS) from wood charcoal buried in soil. These charcoal fragments were sampled in two study sites 10 km apart in the Maurienne valley (Southern Vanoise massif, Savoy, France). 3 Asynchronous temporal fire patterns were seen at Aussois and Saint‐Michel‐de‐Maurienne. This demonstrates the dependence of fires on local‐ or stand‐scale environmental forcing; any direct relationship with climate is therefore rejected. 4 Slash‐and‐burn practices are probably the main source of Holocene fires in the Maurienne valley. However, deforestation did not occur throughout a site in any period, nor simultaneously at the same elevation in two different sites 10 km apart. The cultural landscape was shaped as early as the Neolithic and the Bronze Age, between 6000 and 3000 bp. 5 Deforestation at both study sites probably occurred in many stages in many small areas. The fire intervals were c. 500–1000 years. Deforested areas increased in extent over 2000–4000 years, until the present‐day cultural landscape was established. This process stopped c. 2500 bp at Saint‐Michel‐de‐Maurienne but is still active at Aussois.
Can comparative approaches based on plant ecophysiological traits predict the nature of biotic interactions and individual plant species effects in ecosystems?
Authors: Wardle D. A. , Barker G. M. , Bonner K. I. , Nicholson K. S. 
Published: May 2003

1 The development of general principles regarding biotic interactions involving plants, or plant species effects in ecosystems, is best achieved through simultaneous evaluation of several species. We utilized a comparative approach involving 20 dicotyledonous herbaceous species, to explore possible relationships between several plant ecophysiological traits and plant litter decomposition, interactions involving competition and herbivory, and plant species effects on soil properties.2 Decomposition rates of plant stem and leaf litter were negatively related to plant mass, time until flowering and vegetative growth rate, and positively related to stem nitrogen content. Root decomposition was also related to several traits. Multiple regression relationships showed that 74% and 84% of the variation across species for stem and root litter decomposition, respectively, could be predicted by plant traits; this suggests that plant traits may be powerful predictors of decomposition and have potential as alternative predictors to the litter quality characteristics that previous studies have concentrated on.3Palatability of both seedlings and leaf discs by the invertebrate herbivoresDeroceras reticulatumandListronotus bonariensiswere frequently related to plant traits. Those traits that showed the strongest relationships with the palatability data included various vegetative growth characteristics and (for the leaf disc data) nitrogen concentrations of flowering plant stems.4Competitive effects of the dicotyledonous species against a phytometer species, the grassLolium perenne, were negatively related to leaf nitrogen concentration, and multiple regression relationships involving this trait in combination with others explained over 50% of the variation across species. The competitive response of both plant mass and total seed production toL. perennewas poorly related to plant traits.5The effects of plant species on soil properties including microbial biomass and activity, pH, nitrate concentration and total nitrogen were often closely related to various plant traits. Multiple regression relationships revealed that combinations of several traits were often important in determining these effects; the strongest relationships found were for effects of senescent plants on soil respiration and for the effects of flowering plants on soil nitrate. Plant traits were therefore clearly important in determining plant species effects on soils.6Our study emphasizes the importance of plant traits in understanding (and predicting) species interactions and effects in communities and ecosystems, and shows that properties considered at the whole plant level have the potential to manifest themselves over much larger scales. We therefore conclude that there are clear linkages between plant ecophysiological traits, biotic interactions involving plants, and ecosystem level properties and processes.
Migration of vascular plants to secondary woodlands in southern Sweden
Authors: Brunet Jörg , Von Oheimb Goddert 
Published: May 2003

1 We studied the migration of field layer plants across ecotones between ancient woodlands and recent deciduous woods on former arable land varying in age between 30 and 75 years. 2 Number and percentage cover of woodland species in recent woods decreased with increasing distance to the ancient woods, and increased with the age of the recent woods, indicating dispersal limitation during secondary succession. 3 Colonization by typical woodland plants was observed in 183 of 200 species × site combinations. In 72 combinations, a colonization front was characterized by logarithmic or linear decrease in species cover, indicating establishment of isolated individuals and gradual infill of gaps. This pattern was most common in ant‐dispersed species and less frequent in species with adhesive or ingested seeds. 4 Migration rates were calculated for 49 woodland species. Mean migration rates based on maximum cover in recent woods varied from 0.00 to 1.00 m year−1 between species, with a median migration rate of 0.30 m year−1. Migration rates calculated on occurrence of the farthest individual ranged from 0.00 to 1.25 m year−1, with a median rate of 0.53 m year−1. 5 Ant‐dispersed species had lower migration rates based on maximum cover compared with species with adhesive or ingested seeds. No differences between dispersal modes were found when comparing migration rates based on the farthest individuals. Most of the calculated migration rates (84%) exceeded the rate of possible vegetative spread of woodland species. 6 Establishment of a field layer vegetation in secondary woods comparable to that of the adjacent ancient stands proceeded at a rate of c. 0.3–0.5 m year−1. We conclude that scale and intensity of temperate forest management should be adjusted to the relatively slow migration of the field layer flora in order to enable complete recovery during a management cycle.
Disturbance‐induced density‐dependent seed set in Shorea siamensis (Dipterocarpaceae), a tropical forest tree
Authors: Ghazoul Jaboury , Liston Katharine A. , Boyle T. J. B. 
Published: May 2003

1 The reproductive output of Shorea siamensis, a widespread dipterocarp tree, was assessed in relation to disturbance and tree density at three sites in western Thailand during the 1996 and 1997 flowering seasons. The locations were similar except in disturbance history, which was reflected in decreasing tree density from undisturbed via moderately disturbed to disturbed sites. 2 Hand pollination experiments showed S. siamensis to be partially self‐incompatible due to differential pollen tube growth and abortion of inbred fruit. Although more than 90% of flowers from trees at all sites were pollinated, pollen tubes developed in only a small proportion of these flowers. Both pollen tube development and initial fruit production were highest at the undisturbed site. Many fruit, presumably selfed, were aborted during development at all sites, but significantly more fruit were aborted at the disturbed site, resulting in lowered production of mature fruit. 3
Shorea siamensis was pollinated by small Trigona bees, which exhibited significant declines in intertree movements with increasing distance between flowering trees. As resource availability did not differ between sites, differences in mature fruit set were considered to be mediated by changes in pollinator foraging behaviour at differing tree densities. Variation in seed set was found to be negatively correlated with distance to nearest conspecific both within and between sites. 4 At the two least disturbed sites observed seed set values corresponded with those expected by calculation. However, seed set at the disturbed site was significantly lower than expected. 5 Our results suggest that high reproductive success of S. siamensis is dependent upon cross‐pollination which, through pollinator behaviour, is a function of tree isolation. This species may thus be subject to the Allee effect, where population viability is reduced disproportionately with a decline in population size or, as in this study, population density. The implications of these results for population recovery and genetic structure following disturbance are discussed.
Cleistogamy as a bet‐hedging strategy in Oxalis acetosella, a perennial herb
Authors: Berg Henrik , Redbo‐torstensson Peter 
Published: May 2003

1 Phenology and reproduction were studied in three populations of the cleistogamous herb Oxalis acetosella during three growing seasons, in order to see how the balance between chasmogamous (CH) and cleistogamous (CL) reproduction varies with temporal and spatial environmental variation and with plant size. The numbers of CH and CL flower buds, flowers, immature capsules and mature capsules were counted per ramet, ramet sizes were estimated, and mature capsules were collected for seed counts. 2 Both CH and CL flower numbers were positively correlated with ramet size expressed as leaf number, but the correlation was much stronger in the CL phase. CL flower production also varied significantly between years and sites. Thus, CL production in O. acetosella was not independent of resources and climatic variation. 3 When the effects of year and site were taken into account, the probability of an individual flower developing into a mature fruit was not higher in the CL phase than in the CH phase. 4 CL production was affected by fertilization success in the CH phase. Ramets with one or more CH flowers left unfertilized generally produced more CL buds than ramets with all their CH flowers fertilized. The former group also tended to have more seeds per CL capsule. 5 Since reproductive success in the two phases varies in different temporal and spatial patterns, cleistogamy in O. acetosella is considered to be a bet‐hedging strategy optimizing reproductive output in fluctuating environments. 6 The findings of this study are in conflict with the general view on cleistogamy as a fail‐safe mechanism for back‐up seed production, unaffected by variations in resource supply and environmental conditions.