Polygonum Persicaria Research Articles

New Records of Vascular Plants in the Yukon Territory VIII

Forty-seven taxa, 35 native and 12 introduced, are reported as new to the flora of Yukon and nine taxa previously reported are deleted. The new native taxa are: Artemisia arctica ssp. comata, Botrychium alaskense, Botrychium minganense, Bromus richardsonii, Calamagrostis holmii, Carex incurviformis, Carex mackenziei, Carex microchaeta ssp. nesophila, Carex ramenskii, Carex rariflora var. androgyna, Carex tahoensis, Carex xerantica, Carex × flavicans, Deschampsia sukatschewii, Eleocharis erythropoda, Eleocharis macrostachya, Eleocharis mamillata, Erigeron ochroleucus, Impatiens noli-tangere, Limnorchis huronensis, Nymphaea tetragona, Polygonum douglasii ssp. douglasii, Potamogeton natans, Potentilla crebridens ssp. hemicryophila, Puccinellia tenella ssp. langeana, Rumex beringensis, Salix farriae, Salix glauca ssp. Stipuli fera, Saussurea nuda, Saxifraga hyperborea, Saxifraga rivularis ssp. arctolitoralis, Silene soczavana var. macrosperma, Symphyotrichum subspicatum, Taraxacum hyparcticum, and Zannichellia palustris. The new introduced taxa are: Acer negundo, Avena fatua, Camelina microcarpa, Crepis capillaris, Hippophae rhamnoides, Lamium amplexicaule, Linaria dalmatica, Medicago lupulina, Prunus padus, Rumex pseudonatronatus, Valeriana officinale, and Viola tricolor. Deleted taxa are: Aster laevis var. geyeri, Carex athrostachya, Elatine triantha, Camelina sativa, Erysimum cheiri, Galium palustre, Impatiens capensis, Platanthera hyperborea, and Sonchus oleraceus. Vouchers are cited and general notes on distribution and identification are provided. Four of the native taxa reported here are new to Canada: Botrychium alaskense, Carex microchaeta ssp. nesophila, Potentilla crebridens ssp. hemicryophila and Rumex beringensis.

Contrasting patterns of transgenerational plasticity in ecologically distinct congeners

Stressful parental environments can influence offspring size and development either adaptively or maladaptively, yet little is known about species' differences in this complex aspect of phenotypic plasticity. We performed a reciprocal split-brood experiment to compare transgenerational plasticity in response to drought stress in two closely related annual plant species. We raised inbred replicate parent plants of eight genotypes per species in dry vs. moist soil to generate offspring of each genetic line that differed only in parental environment, then monitored seedling development in both dry and moist conditions. Individuals of the two species expressed contrasting patterns of transgenerational plasticity for traits important to seedling drought tolerance. In Polygonum persicaria, a weedy generalist found in moist, dry, and variably dry sites, drought-stressed plants produced offspring with longer and more rapidly extending root systems and greater biomass when growing in dry soil. In contrast, in P. hydropiper, a non-weedy congener restricted to moist habitats, the offspring of drought-stressed parents had reduced root system development and seedling biomass in dry soil. In P. persicaria, transgenerational and immediate adaptive plasticity combined to produce drought-adapted seedling phenotypes. These results make clear that characteristic patterns of transgenerational plasticity can contribute to ecological diversity among species.

Efficacy of mesotrione used at reduced doses for post-emergence weed control in maize ( Zea mays L.)

Three field experiments were carried out in 2000, 2002 and 2004 in central Italy in order to establish the “minimum dose requirement for a satisfactory efficacy” (ED 90 or ED 95) of mesotrione against several of the most important weeds in maize. Mesotrione was sprayed at four doses in 2000 (150, 100, 50 and 25 g a.i. ha −1) and 2002 (100, 75, 50 and 25 g a.i. ha −1), and at five doses in 2004 (150, 100, 75, 50 and 25 g a.i. ha −1). Untreated and weed-free plots were always added as checks. For each “year–mesotrione–weed” combination, dose–response curves were used to estimate the dose of mesotrione required to obtain 90 and 95% weed control (ED 90 and ED 95 values). Mesotrione phytotoxicity to the maize and the crop grain yield were also assessed. ED values showed that several weeds could be satisfactorily controlled with reduced doses of mesotrione. In particular, mesotrione could be used at 1/6 of the maximum labelled dose (150 g a.i. ha −1) in order to obtain 95% of efficacy against Abutilon theophrasti, Chenopodium album, Solanum nigrum and Xanthium strumarium; while Amaranthus retroflexus and Polygonum persicaria could be satisfactorily controlled (95% weed efficacy) with 40–45 g ha −1 of mesotrione (about 1/4 of the maximum labelled dose). This selective triketone herbicide had to be applied at 90 g a.i. ha −1 to obtain a high efficacy (95%) against Echinochloa crus-galli; while it did not prove effective against Portulaca oleracea even at maximum labelled dose. Thus the ranking among weed species based on their sensitivity to mesotrione was: A. theophrasti = C. album = S. nigrum = X. strumarium > A. retroflexus = P. persicaria > E. crus-galli > P. oleracea. Mesotrione showed a good selectivity to the crop at all application doses; however, some phytotoxicity symptoms, in the form of leaf bleaching, were only transitory and dissipated by 4–5 weeks after treatments with no damage to crop yield.

N availability does not modify plant-mediated responses of Trichoplusia ni to elevated CO2

Aims Elevated CO2 and increased N availability can alter a variety of plant physiological processes leading to changes in the nutritional quality of leaf tissue for herbivores. Numerous experiments have examined the responses of herbivores to environmental change; however the potential effects of simultaneous change in multiple factors on leaf-chewing insect herbivores are less well understood. The plant-mediated effects of elevated CO2 and high N on the performance of a generalist leaf-chewing insect herbivore, Trichoplusia ni, were investigated. Methods Newly hatched T. ni larvae were introduced to Amaranthus viridis and Polygonum persicaria plants grown under ambient and elevated CO2 and low and high N conditions. Insect performance was assessed by measuring larvae weight after ten days of feeding. Plant photosynthesis, biomass, leaf area and specific leaf weight were measured to determine the effects of elevated CO2, N and insect feeding on plant performance. Important Findings Elevated CO2 did not have strong effects on plant or insect performance, only affecting a few responses under low or high N conditions, but not both. Growth under high nitrogen improved almost all measures of plant performance.Trichoplusiani performed significantly better onAmaranthus viridis (C4 )c ompared toPolygonum persicaria (C3), despite similar leaf C:N ratios in both species. The performance ofT.ni caterpillars was only improved by the high nitrogen treatment when they were feeding on P. persicaria, the host they performed poorly on. The only interactions between N and CO2 affecting plant performance were seen for leaf photosynthesis of P. persicaria and leaf area of A. viridis. Contrary to the predictions, there were no significant CO2 by N interactions affecting T. ni performance.

Flat fan and air induction nozzles affect soybean herbicide efficacy

Fifteen field experiments were conducted from 2002 to 2005 to determine the influence of the nozzle type, spray volume, spray pressure, and herbicide rate on herbicidal efficacy in soybean. There was no effect of the nozzle type on herbicidal efficacy with fomesafen, bentazon, glyphosate, and cloransulam‐methyl when applied at the manufacturer's recommended rate. The control of Echinochloa crus‐galli (barnyardgrass) with quizalofop‐p‐ethyl was improved when applied with flat fan (FF) nozzles compared with air induction (AI) nozzles. There was an increase in weed control with the FF nozzles compared with the AI nozzles in four of the 13 comparisons when the herbicides were applied at half the recommended rate, while in two situations, application with the AI nozzles resulted in improved weed control. With the FF nozzles, there was no effect of the water carrier volume on weed control with bentazon, glyphosate, and cloransulam‐methyl. The control of Abutilon theophrasti (velvetleaf) and Chenopodium album (common lambsquarters) with fomesafen and E. crus‐galli with quizalofop‐p‐ethyl was improved at the higher water carrier volume. With the AI nozzles, the control of A. theophrasti and Ambrosia artemisiifolia (common ragweed) with fomesafen and E. crus‐galli with quizalofop‐p‐ethyl was improved at the higher water carrier volume, while the control of A. theophrasti and Polygonum persicaria (ladysthumb) was improved with glyphosate at the lower water carrier volume. With the AI nozzles, the control of C. album with bentazon and E. crus‐galli with quizalofop‐p‐ethyl was improved at the higher spray pressure. There was no effect of the nozzle type on the soybean yield with glyphosate, cloransulam‐methyl, and quizalofop‐p‐ethyl. The use of the FF nozzles compared with the AI nozzles to apply fomesafen and bentazon increased the soybean yield by 6 and 7%, respectively. Based on this study, the optimum nozzle type, water carrier volume, and spray pressure is herbicide‐ and weed species‐specific.

Ocena rozwoju osobniczego (ontogenezy) chwastów w łanie lnu włóknistego

The study was conducted according to observations of ontogenesis of weeds found in the field of fibrous flax conducted in 2005–2006. The field experiments were conducted at INF Experimental Farms Stary Sielec and P tkowo (wielkopolskie district). Experiments were set on two types of soil: grey brown podsolic and black earth. The phenological development of flax and weeds was evaluated according to BBCH scale. 
 On black earth soil (good wheat agricultural soil complex) the full ontogenesis was recorded for the following taxa: Geranium pusillum L., Viola arvensis Murr., Stellaria media Vill., Chenopodium album L., Matricaria maritima L. ssp. inodora (L.) Dostal, Galium aparine L., Polygonum lapathifolium L., Capsella bursa-pastoris (L.) Med., Euphorbia cyparissias L., Galinsoga parviflora Cav. and Elymus repens (L.) Goud. On grey brown podsolic soil (good rye agricultural soil complex) few weed species reached flowering or green maturity stage (BBCH 60–73): Chenopodium album L., Polygonum aviculare L., Polygonum persicaria L. and Anthemis arvensis L. Most weeds senesced before completion of full development cycle on the lighter soil. Environmental conditions had stronger effect on development of weeds than on ontogenesis of fibrous flax.

Progress in the detection of costs of phenotypic plasticity in plants

Progress in the detection of costs of phenotypic plasticity in plants

Are pre‐spraying growing conditions a major determinant of herbicide efficacy?

SummaryTo evaluate the effect of pre‐spraying growing conditions on herbicide efficacy, two years of experimentation were conducted in which Persicaria maculosa plants were exposed to different light intensities for 1–4 days before metribuzin treatment. Specific leaf area, rather than plant growth rate or plant size, was the only parameter that correlated well with herbicide efficacy in both years of experimentation. The negative relationship between the ED50 and the specific leaf area indicates that leaf characteristics might be an important determinant of herbicide efficacy, for instance through an effect on herbicide uptake. In the third year of experimentation this hypothesis was further investigated by raising six cohorts of weed plants at a 1‐week interval and thus exposing them to a range of weather conditions. Clear relationships between uptake and herbicide efficacy were found for a combination of four plant species (Solanum nigrum, Senecio vulgaris, Chenopodium album and Brassica napus) and two herbicides (phenmedipham and bentazone). For phenmedipham, uptake was negatively correlated with global radiation and positively correlated with relative humidity. For the herbicide bentazone the opposite was found. These results were not species‐specific. This study shows the importance of the sensitivity of herbicide × species combinations and indicates that pre‐spraying weather information is relevant for the development of reduced dose rate recommendations.

Smoke derived from burnt vegetation stimulates germination of arable weeds

A commercially available smoke-water solution (Seed Starter (R)) stimulated the germination of caryopses and intact florets of Avena fatua L. The solution was most effective when diluted (5-50%) and presented to intact or dehulled grain that had received a short period of dry after-ripening. It was less effective when applied at full strength or to grains that had been freshly harvested. The same stimulatory effect was observed in par-fly after-ripened caryopses of nine different wild oat biotypes obtained from three different cropping regions of the world. When freshly harvested caryopses were re-tested with the commercial solution (100%) for just 7 days prior to placement on to distilled water, a much higher germination percentage was possible than seen with continuous smoke-water incubation. The stimulatory ability of smoke water was more closely matched to that of gibberellic acid than to potassium nitrate, which had little or no effect on freshly harvested caryopses. The smoke-water solution (5-100%) was tested on the germination of 18 other cool temperate arable weed species. All monocotyledonous species tested (viz. Avena sterilis ssp. ludoviciana L., Alopecurus myosuroides, Sorghum halepense, Phalaris paradoxa) responded positively, while those of the dicotyledonous species were either strongly stimulated (greater than or equal to 40% stimulation Malva neglecta), moderately stimulated (greater than or equal to 20% stimulation Galium aparine, Veronica persica), slightly stimulated (Polygonum persicaria, P pennsylvanicum, Fallopia convolvulus), unaffected (P. aviculare, Sinapis arvensis, Heracleum sphondylium, Angelica sylvestris, Mercurialis annua, Veronica hederifolia) or inhibited (Lamium purpureum). The optimal concentrations required to stimulate germination of the monocotyledonous species were similar to those observed for A. fatua (5-10%). However, for the dicotyledonous species slightly stronger solutions were required (10-20%). When the unaffected species were retested using a 10-day pre-chilling treatment, smoke water showed a small promotive response in three (S. arvensis, P. aviculare and V hederifolia) of the six species. When four different smoke-water solutions (Seed Starter (R), Regen 2000 (R), charred-wood solution and wheat-straw solution) were tested on two representative species (A. fatua and M. neglecta), three formulations were effective in promoting the germination of both species, while the fourth (charred-wood solution) was only active on A. fatua. The active concentrations were different for the four solutions. Three solutions were active in the 2-20% dilution range, while the fourth (Regen 2000 (R)) was only active in the 1-2% dilution range and was inhibitory at higher concentrations. These observations are discussed in the context that smoke may play an important ecological role in the management and control of introduced weeds in native and arable communities.

The importance of tillage depth in relation to seedling emergence in stale seedbeds

Stale seedbeds can be used in arable farming to reduce the density of weeds in the crop. This type of tillage before crop sowing can contribute to a successful weed management in systems where no herbicides are used, e.g. organic farming. The population dynamics of weeds in response to stale seedbeds is, however, hardly understood, and therefore possibly not optimised. The relevance of tillage depth in relation to seedling emergence is explored with a simple, deterministic model. We systematically examined the effect of seedling emergence and subsequent weed control on weed population dynamics, starting by considering the seed bank as one soil layer, and continued by considering a depth-structured seed bank. Whether the widely used tillage regime consisting of shallow tillage, again shallow tillage, and ultimately deep tillage, is preferred above the regime we propose (i.e. deep, shallow and ultimately shallow tillage) depends on the proportion emergence specific for each soil layer, the proportion of seeds that is moved from one layer to the other, and the seed distribution in the soil. A case study based on characteristics of the population dynamics of the weed Polygonum persicaria showed that the proposed tillage regime could give reductions in weed density of up to 32% compared to the conventional tillage regime of stale seedbeds. The tillage regime that we propose requires techniques that restrict soil compaction to fixed traffic lanes, giving large zones favourable for crop growth. Because of ongoing processes in precision farming technology with respect to controlled traffic systems, this regime has realistic opportunities to become widely used in the future.

The effect of competition from different weed species on the growth of Betula pendula seedlings

The identification of less competitive weed species and infestation rates might allow weeding operations to be better targeted, help conserve local plant biodiversity, and facilitate reductions in the amount of herbicide used to achieve woodland regeneration. Therefore, the effect of competition from pure stands of Cirsium vulgare (Savi) Ten., Epilobium ciliatum Raf., Holcus lanatus L., Poa annua L., and Persicaria maculosa Gray on Betula pendula Roth was investigated over 2 years. All weed species reduced tree growth significantly compared with weed-free plots, but there were no significant differences among species. When Lolium perenne L., Rumex obtusifolius L., and Cirsium vulgare were established at four densities in plots containing newly planted B. pendula over a 1-year period, all weed species reduced tree growth, but Lolium perenne was the most competitive. Weed density had no significant effect, indicating that even sparse weed growth can have a major impact on tree performance. None of the treatments affected B. pendula survival. These results confirm the inhibitory effects of a range of weed species on tree growth, but not survival, and the capacity of B. pendula to recover in the second year after planting from an initial check in growth. Percent cover was a good explanatory variable for models developed to describe the effects of weeds on tree growth, and preliminary competition indices for the different species are presented.

New Records of Vascular Plants in the Yukon Territory VII

Based on field reconnaissance mainly in 2003 in Kluane National Park but also many other areas throughout the Yukon, information is provided on geographically significant plant occurrences. Thirteen native taxa, Agrostis humilis, Blysmopsis rufa, Carex bebbii, C. lenticularis var. dolia, C. nigricans, C. sartwellii, C. siccata, Diphasiastrum sitchense, Najas flexilis, Oxytropis arctica var. arctica, Oxytropis arctica var. murrayi, Saxifraga nelsoniana ssp. carlottae and Swertia perennis and two introduced taxa, Bromus japonicus and Leymus mollis ssp. mollis s.l. are reported new to the flora of the Yukon Territory. Significant range extensions for 109 native and eight introduced taxa are included and three species, Clematis occidentalis, Polygonum persicaria, and Verbena hastata are deleted from the flora.

Shade tolerance plasticity in response to neutral vs green shade cues in Polygonum species of contrasting ecological breadth

Here we examined species differences in perception and response to two distinct types of shade cue, reduced photosynthetically active radiation (PAR) with and without reduced red : far red ratio (R : FR), in Polygonum persicaria and Polygonum hydropiper, two closely related annuals of contrasting ecological breadth. We compared plasticity data for light-gathering traits from glasshouse experiments at equivalently reduced PAR under neutral shade (R : FR 1.03) and green shade (R : FR 0.702). Species shared the ability to distinguish between the two types of shade, as shown by the ability of each to respond differently to neutral vs green shade for one or more traits. However, the species' responses to these cues differed significantly. Polygonum persicaria expressed stronger shade-tolerance responses (increased leaf allocation and leaf area ratio) to reduced PAR alone than to green shade. By contrast, P. hydropiper expressed slightly less plasticity for these traits in neutral than in green shade. The pronounced plastic response of P. persicaria to neutral shade may contribute to the range of habitats this widespread species can occupy, which includes neutral-shade environments such as urban settings.

Population Differentiation and Plastic Responses to Drought Stress in the Generalist AnnualPolygonum persicaria

We tested the generalist annual plant Polygonum persicaria (Polygonaceae) for adaptive differentiation in drought responses. Populations from one consistently moist and two variably dry sites were grown in moist and drought conditions in a greenhouse. Physiological, morphological, and reproductive data were collected. All three populations maintained similar levels of fitness in both drought and moist conditions, indicating that these populations may be equally drought tolerant. Also, the three populations had similar water use efficiency and root biomass responses to soil moisture, indicating that substantial phenotypic plasticity is present in all the populations, including a population from a consistently moist site. The magnitude of plastic responses for specific traits varied among the populations; i.e., the physiological and morphological means by which these plants maintained reproductive homeostasis across moisture conditions was population dependent. In particular, the moist‐site population had t...

Weed seed production, crop planting pattern, and mechanical weeding in wheat

Experiments were carried out to investigate weed seed production in widely spaced spring wheat crops that received aggressive mechanical weed control (hoeing and harrowing) compared with that in narrowly spaced crops receiving less aggressive mechanical control (harrowing only). Three species (wild buckwheat [Polygonum convolvulus], ladysthumb [Polygonum persicaria], and common chickweed [Stellaria media]) were studied in three row-spacing treatments (10, 20, and 30 cm) and two sowing densities (140 and 180 kg ha−1). Average seed production per surviving plant was up to three times higher in the 30-cm treatments compared with the 10-cm treatments. Taking into account the 40–50% weed mortality resulting from control in the 30-cm treatments, seed production per seedling was still higher in the 30-cm treatments than in the 10-cm treatments. Differences in wheat yield were not found among treatments. From the perspective of long-term weed population management, using a narrow row spacing would be more effective in spring wheat on the basis of experiments with the weed species considered here.

Differential susceptibility of agricultural weeds to ultraviolet-B radiation

Differential morphological sensitivity of weed species to ultraviolet-B (UV-B) radiation (290–320 nm) may alter competitive relationships among weeds and associated crop species as the level of this radiation changes. In order to determine relative sensitivity of common chickweed [Stellaria media (L.) Vill.], green foxtail (Setaria viridis L.), lady's-thumb (Polygonum persicaria L.), lamb's-quarters (Chenopodium album L.), redroot pigweed (Amaranthus retroflexus L.), and shepherd's-purse (Capsella bursa-pastoris L.) to this radiation, seedlings were grown under 0, 7, and 11 kJ m-2 d-1 of biologically effective UV-B radiation in a greenhouse for 6 wk. The influence of UV-B radiation on seedling growth and morphology was investigated. UV-B radiation reduced shoot height in green foxtail (by up to 41%), lamb's-quarters, and redroot pigweed, and increased tillering in green foxtail seedlings. Leaf area and leaf biomass in common chickweed, green foxtail, lamb's-quarters, and shepherd's-purse, and stalk biomass in common chickweed, green foxtail, lamb's-quarters, redroot pigweed and shepherd's-purse declined in response to UV-B radiation. In common chickweed, leaf area was reduced by 74% at 11 kJ m-2 d-1. Root biomass was reduced by UV-B radiation in all species (up to 68% at 11 kJ m-2 d-1 in common chickweed) except lady's-thumb. Specific leaf weight increased and leaf area ratio declined in response to UV-B radiation in common chickweed and shepherd's-purse. Exposure to UV-B radiation increased the leaf weight ratio in common chickweed. Shoot:root ratios increased in response to UV-B radiation in common chickweed and redroot pigweed. Scanning electron microscopy revealed collapsed epidermal cells in occasional necrotic regions on adaxial leaf surfaces of redroot pigweed grown under 11 kJ m-2 d-1 UV-B radiation. Morphology and growth of lady's-thumb were not affected by UV-B radiation. This study suggests that common agricultural weeds have differential morphological and growth responses to UV-B-enhanced environments. Sensitivity to UV-B radiation was greatest for common chickweed and least for lady's-thumb and redroot pigweed. Key words: ultraviolet-B, Amaranthus retroflexus, Capsella bursa-pastoris, Chenopodium album, Polygonum persicaria, Setaria viridis, Stellaria media

WEED POPULATIONS AND CROP ROTATIONS: EXPLORING DYNAMICS OF A STRUCTURED PERIODIC SYSTEM

The periodic growing of a certain set of crops in a prescribed order, called a crop rotation, is considered to be an important tool for managing weed populations. Nevertheless, the effects of crop rotations on weed population dynamics are not well understood. Explanations for rotation effects on weed populations usually invoke the diversity of environments caused by different crops that a weed population encounters. Using a periodic matrix model, we show that the number of different crops is not the sole factor, and that the sequence of a given set of crops can play an important role. In the model the weed population is structured by seed depth in the soil, and plowing moves seeds between layers. For illustration of concepts, we use parameter values thought to be characteristic for Polygonum persicaria growing in carrots (crop A) and spring wheat (crop B) in the Netherlands. We systematically examine the population growth rates for P. persicaria and their sensitivity to changes for all rotations of 2–6 years based on crops A and B. We include eight scenarios that differ in the effects of plowing and seed survival over winter. Differences between rotations can be striking. For example the weed population growth rate in the baseline rotation AABB (assuming 100% winter survival) is nearly 25% lower than in rotation ABAB. The elasticity (a measure to quantify the effect of proportional changes in model parameters on population growth) to seedling survival is nearly 75% higher in the B years of rotation ABAB than in the B years of rotation AABB. Changing parameter values changes the relation between population dynamics and rotation organization, but not the conclusion that there are consequences for population dynamics and management due to choice of a rotation. While our example is an agronomic one, the question “Does sequence matter?” and the methods applied should be of interest to researchers and managers concerned with the periodic management of other ecosystems.

Population variation in Persicaria salicifolia (Brouss. ex Willd.) Assenov (Polygonaceae) in Nigeria

AbstractStudy of six living population samples and herbarium specimens of Persicaria salicifolia from Nigeria revealed considerable variability in vegetative and floral characters. Two subspecies, one of which is a new one (subsp. nova, p. 516), are recognised. Experimental cultivation showed that the combination of distinguishing characters for each subspecies remains intact under uniform conditions in the botanical nursery.

Persilben, a new carboxystilbene from Polygonum persicaria

A new stilben isolated from herbs of Polygonum persicaria L. has been characterised as 2-carboxy-3,5-methoxy-E-stilbene and named persilben. Its structure was elucidated by 1H NMR, 13C NMR and HR-MS method.The correctnes of 13C assignment was verified by DFT GIAO calculation.

A simulation model for seasonal changes in dormancy and germination of weed seeds

A model has been developed to simulate the annual dormancy cycle of seeds of light-requiring species in the seed bank and the germination of exhumed seeds after irradiation. Simulation of dormancy and germination is based on a physiological model concerning the action of phytochrome in the seed. Dormancy is related to the amount of a hypothetical phytochrome receptor, which fluctuates in an annual pattern. Relief of dormancy is equivalent to an increase in the amount of receptor, and induction of dormancy is equivalent to a decrease in the amount of receptor. Annual changes in temperature are the driving force for annual changes in the amount of phytochrome receptor in seeds that are buried in the seed bank. From the average amount of phytochrome receptor in the seeds of a population, the model calculates the germination percentage that is reached when a seed sample from the population is exhumed, irradiated and incubated at a given temperature in darkness. In the model, relief of dormancy results in a widening of the range of temperatures over which germination can occur, and induction of dormancy results in a narrowing of this range. Model parameters were estimated by fitting the model to data from a burial experiment with seeds of Polygonum persicaria L., Chenopodium album L. and Spergula arvensis L. At regular time intervals during 3 years, subsamples of these seeds were exhumed and tested for germination in the laboratory. The simulation model gave a good description of the observed cyclic changes in germinability of exhumed seeds.