Spergula Arvensis Research Articles

Effect of herbicides applied pre- and post-emergence on forestry weeds grown from seed

Weeds growing from seed can cause severe problems in forest nurseries and in woodland establishment by competing for resources with the young trees, leading to reduced growth and survival. Herbicides approved for use on new plantings of farm forestry and forest nurseries were usually developed originally for use in agricultural crops. As a result, information on the susceptibility of weeds that may be a problem in forestry situations rather than the rotational cropping systems used in agriculture is limited. In this series of glasshouse experiments the efficacy of residual and foliar-acting herbicides primarily used on agricultural crops was tested on 14 species of weeds. Cardamine hirsuta, Epilobium ciliatum, Poa annua, Senecio vulgaris, and Spergula arvensis were all effectively controlled by diphenamid, lenacil, metamitron, metazachlor and napropamide when applied immediately after sowing. These species were also controlled when sown into soil sprayed 1 month earlier, indicating persistent phytotoxicity of the herbicides. Cirsium vulgare, E. ciliatum, Senecio jacobaea, Trifolium repens and Urtica dioica grown from seed were well controlled by low dose pre-emergence applications of atrazine, clopyralid+cyanazine, metazachlor and simazine. Ranunculus repens was effectively controlled by pendimethalin and propyzamide. Cyanazine applied early post-emergence also controlled all these species, but their susceptibility to other herbicides varied. Pre-emergence control of the perennial weed species Agrostis stolonifera, Rubus fruticosus and Rumex obtusifolius grown from seed was given by low doses of atrazine, clopyralid+cyanazine, metazachlor and propyzamide. Isoxaben, napropamide and pendimethalin were effective on A. stolonifera and R. obtusifolius. Early post-emergence applications of atrazine and cyanazine controlled all these species; other herbicides varied in efficacy. E. ciliatum, R. repens, S. jacobaea and U. dioica as small seedlings were well controlled by recommended doses of amidosulfuron, pyridate and tribenuron-methyl. T. repens was generally unaffected even at the earliest growth stage. The doses of residual herbicides required for weed control were relatively low, indicating the greater susceptibility of weeds grown in containers compared with field conditions, probably due to restricted rooting depth. The results provide guidance on which herbicides may be worth testing in field conditions for the control of these problem weeds, however diphenamid is no longer commercially available and cyanazine is currently not being supported by the EC Pesticide Review Programme.

Banded herbicides and cultivation for weed control in potatoes (Solanum tuberosum L.)

Increasing costs of production have resulted in intensified efforts to reduce the amount of herbicides applied in potato production. This research evaluated the potential of applying herbicides in 30-cm-wide bands over the potato row in combination with cultivation between the potato rows to achieve weed control. At a moderate to high infestation of quackgrass and annual broadleaf weeds, control of quackgrass, corn spurry and wild radish was as effective with the banded herbicide + cultivation treatments as with the broadcast herbicide treatment. Potato marketable yields from the banded herbicide + cultivation treatments were comparable to the broadcast herbicide application treatment. A single cultivation at 21 d after planting (DAP) (at ground crack), 28 DAP (potatoes 5 to 10 cm tall) or 35 DAP (potatoes 10 to 15 cm tall) did not give adequate weed control, and potato yields were reduced by 30% or more at all times of cultivation compared to herbicide treatments. This study shows that acceptable weed control without effects on marketable yield is possible by using a 30-cm-wide herbicide band over the row followed by cultivation to remove weeds between the row. The amount of herbicide used per hectare with this technique is reduced by 66% compared to a broadcast herbicide application. Key words: Herbicide, potato, quackgrass, Elytrigia repens L. (Nevski), corn spurry (Spergula arvensis L.), wild radish (Raphanis raphanistrum L.), cultivation

Control of Quackgrass (Elytrigia repens) and Broadleaf Weeds and Response of Potato (Solanum tuberosum) Cultivars to Rimsulfuron1

Studies were conducted from 1992 to 1995 to determine the effect of rimsulfuron on corn spurry, wild radish, narrowleaf goldenrod, and quackgrass and potato cultivars. Rimsulfuron alone gave 100% control of wild radish, 68 to 70% control of corn spurry, and 75 to 90% control of narrowleaf goldenrod. Rimsulfuron plus metribuzin gave 99 to 100% control of wild radish and 85 to 100% control of corn spurry. Quackgrass control varied from 51 to 90% between experiments, indicating that environmental and plant factors affected the activity of the herbicide. Tank mixes with metribuzin slightly reduced the control of quackgrass but resulted in greater foliar injury than that of rimsulfuron to potato. Slight injury to potato plants disappeared within 2 to 3 wk, and tuber yields were not reduced. Russet Burbank, Shepody, and Kennebec potato cultivars had slight (2 to 8%) injury from rimsulfuron. Injury to Shepody (14 to 20%) and Russet Burbank (11%) increased when rimsulfuron was applied with metribuzin. Rimsulfuron had no effect on the number or the fresh weight of sprouts on daughter tubers tested the next spring after application.Nomenclature: Metribuzin; rimsulfuron; corn spurry, Spergula arvensis L. #3 SPRAR; narrowleaf goldenrod, Solidago canadensis L. # SOLCA; quackgrass, Elytrigia repens Nevski # AGRRE; wild radish, Raphanus raphanistrum L. # RAPRA; potato, Solanum tuberosum L. # SOLTU ‘Russet Burbank’, ‘Shepody’, ‘Kennebec’.Additional index words: Daughter tuber sprouting, DPX E-9636.Abbreviations: GC, ground crack; lf, leaf; PEI, Prince Edward Island; POST, postemergence; PRE, preemergence; RH, relative humidity.

Weeds as a source of plant growth promoting rhizobacteria in agricultural soils.

The influence of plant growth promoting (PGP) activity of bacterial communities recovered from each of six weed species (barnyard grass (Echinochloa crusfalli (L.) Beauv.), corn spurrey (Spergula arvensis L.), goldenrod (Sonchus sp.), Italian ryegrass (Lolium multiflorum L.), lamb's-quarters (Chenopodium album L.), and quack grass (Agropyron repens (L.) Beauv.)) was examined in relation to the effect it had on the growth of the potato cultivar Russet Burbank. Bacterial species composition and community structure were compared, species-abundance relationships were determined, and those members conferring positive benefits for potato growth and development were identified. Of the genera identified, Bacillus, Arthrobacter, Stenotrophomonas, Acinetobacter, and Pseudomonas were the most common, and Stenotrophomonas maltophilia was the most frequent species recovered across all sources. Significantly higher population densities were found in the root zones of quack grass, compared with Italian ryegrass and lamb's-quarters. There were no significant differences in species richness among the root zones; however, evenness indices (species distribution) were significantly lower in corn spurrey (P = 0.05). Significantly higher diversity indices (Hill-1 and Hill-2 numbers) (P = 0.05) were found in the root zone soil communities of potato and goldenrod, indicating a decrease in the proportional abundance of common and very abundant species, respectively, while in barnyard grass, corn spurrey, and Italian ryegrass the reverse was the case. In both years of the study, Italian ryegrass and corn spurrey were consistently better sources of PGP rhizobacteria for potatoes, significantly (P < 0.001) increasing the mean wet weight of shoots and roots in in vitro bacterization studies. Barnyard grass was a consistently poor source of such isolates. Species-abundance measures of root zone bacterial biodiversity were not found, in this instance, to be a particularly good predictor of the presence or absence of PGP rhizobacteria. We consider that the study of complementary crops and soil-conditioning treatments should not preclude the examination of weed species as possible beneficials, as alterations in rhizobacterial biodiversity and functional versatility can influence the numbers and types of PGP bacterial strains, and consequently may serve to improve soil quality.

INFLUENCE OF HERBICIDES ON WEED MANAGEMENT IN TRUE POTATO

The results obtained showed that there was severe competition between potato and the predominant weed species Coronopus didymus, Chenopodium album, Fumaria parviflora, Melilotus indica and Spergula arvensis. Competition by other weed species was nominal. The maximum reduction in tuber yield due to weed competition was 50.5% in 1997–98 and 63.4% in 1998–99. Weed control treatments lowered the weed density and weed biomass and scaled up tuber yield in both the years, but their effect on weed species differed. Metribuzin killed all the Chenopodium album plants and gave excellent control of Coronopus didymus (94%) and effective control of other weed species. Pendimethalin inhibited the germination of Chenopodium album, gave good control of arvensis and lowered the density of other weed species. Fluchloralin completely inhibited the germination of Fumaria parviflora and gave good control of Chenopodium album and Spergula arvensis, but was least effective against other weed species. The highest yield was recorded in the weed-free treatment, which was significantly superior to all other treatments. Hand weeding + earthing up, isoproturon (1.0 kg/ha), metribuzin and pendimethalin caused an identical increase in tuber yield, which was significantly higher than the increase in the rest of the treatments. Atrazine at 0.25 kg ha –1 resulted in a higher increase than when applied at 0.5 kg ha –1 . Fluchloralin, paraquat and paddy straw mulch boosted up production, but the increase in tuber yield was not significant.

Quantitative analysis of emergence of seedlings from buried weed seeds with increasing soil depth

Abstract Trials were carried out to investigate the effects of seed burial depth on seedling emergence rate of 20 weed species. Marked depth-mediated variation in emergence ability of the different species was observed, together with a general pattern of decreasing emergence with increasing soil depth. At 10 cm, only johnsongrass, velvetleaf, catchweed bedstraw, and cutleaf geranium emerged, albeit only in limited numbers. Species most severely inhibited by burial depth were buckhorn plantain, large crabgrass, common purslane, chickweed, and corn spurry, none of which emerged from beyond 6 cm. In all species, depth-mediated inhibition was found to be sigmoidal (polynomial regression). In addition, the number of seedlings and rate of seedling emergence decreased when depth of burial increased. The depth at which the number of emerged seedlings was halved varied by species and ranged from 3.6 cm for common purslane and chickweed to 7 cm for velvetleaf and catchweed bedstraw. Excessive burial depth generally...

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.

Modelling field emergence patterns in arable weeds.

A model was developed to simulate weed emergence patterns after soil cultivation. In the model, the consecutive processes of dormancy release, germination and pre-emergence growth were modelled in separate modules. Input variables of the model were: date of soil cultivation, soil temperature and soil penetration resistance. Output variables of the model were: seedling density and timing of seedling emergence. The model was parameterized for Polygonum persicaria, Chenopodium album and Spergula arvensis with data from previous field and laboratory experiments. The model was evaluated with data from an experiment, in which emergence of P. persicaria, C. album and S. arvensis was monitored in field plots that were cultivated once only, at one of five dates in the spring. At the same time as the field observations on seedling emergence, seasonal changes in seed dormancy of the buried weed seeds were assessed by testing the germination of seed lots that were buried in envelopes. From a comparison between field observations and simulated data, it appeared that the model overestimated the rate of dormancy release in spring, whereas germination and pre-emergence growth were simulated well. In general, therefore, both the numbers of emerging seedlings and the timing of emergence could be predicted accurately, when dormancy was not simulated but introduced from experimental data. Improvement of predictions of field emergence of weeds should mainly focus on increasing the precision of the simulation of dormancy release. Close correlations were found between seedbed temperature and both the extent and rate of seedling emergence, but analysis with the simulation model revealed that they were only partly based on causal relationships, so that they have limited predictive value.

Clinical hypocalcaemia associated with Yarr (Spergula arvensis) ingestion

extract Spergula arvensis (Spurrey, known locally as Yarr) is a fine- stemmed, viscid, erect or sprawling annual up to 30cm tall, with small white flowers and narrow, needle-shaped leaves in whorls at each stem node. It is a common weed of recently cultivated pastures. We have found no record of toxicity associated with ingestion of this plant, apart from a suggestion of illness when fed to caged birds (Roy et al., 1998). One of the authors (JDH) can recall a calcium-responsive recumbency in a small number of ewes grazing a poorly established swede crop in summer in which Yarr was the predominant green feed available.

Biosynthesis of plant phenolic compounds in elevated atmospheric CO2

SummaryExperiments were carried out to determine the effects of elevated atmospheric carbon dioxide (CO2) on phenolic biosynthesis in four plant species growing over three generations for nine months in a model plant community. Results were compared to those obtained when the same species were grown individually in pots in the same soils and controlled environment. In the model herbaceous plant community, only two of the four species showed any increase in biomass under elevated CO2, but this occurred only in the first generation for Spergula arvensis and in the second generation for Poa annua. Thus, the effects of CO2 on plant biomass and carbon and nitrogen content were species‐ and generation‐specific. The activity of the principle phenolic biosynthetic enzyme, phenylalanine ammonia lyase (PAL), increased under elevated CO2 in Senecio vulgaris only in Generation 1, but increased in three of the four plant species in Generation 2. There were no changes in the total phenolic content of the plants, except for P. annua in Generation 1. Lignin content decreased under elevated CO2 in Cardamine hirsuta in Generation 1, but increased in Generation 2, whilst the lignin content of P. annua showed no change, decreased, then increased in response to elevated CO2 over the three generations. When the species were grown alone in pots, elevated CO2 increased PAL activity in plants grown in soil taken from the Ecotron community after nine months of plant growth, but not in plants grown in the soil used at the start of the experiment (‘initial' soil). In P. annua, phenolic biosynthesis decreased under elevated CO2 in initial soil, and in both P. annua and S. vulgaris there was a significant interaction between effects of soil type and CO2 level on PAL activity. In this study, plant chemical composition altered more in response to environmental factors such as soil type than in response to carbon supply. Results were species‐specific and changed markedly between generations.

The effects of elevated CO2 and light environment on growth and reproductive performance of four annual species.

To predict changes in the range and density of plant species as a consequence of elevated atmospheric CO2 , it is essential to characterize the effect of elevated CO2 on key components of plant life history stages such as rate of establishment and maturation of individuals, reproductive output and offspring fitness. We measured vegetative response, phenology, reproductive output and seed quality of four annual C3 plant species, grown from seed to senescence under ambient and elevated (ambient+200 ppm) CO2 and ambient and reduced (33% shade) light. Few previous studies have included all stages of a plant's life as well as characteristics of the next generation. Elevated CO2 had no effect on the vegetative attributes of Cardamine hirsuta, Spergula arvensis or Poa annua whereas Senecio vulgaris produced longer leaves and greater biomass. Both Senecio and Poa had faster maturation times. The vegetative response of Senecio was not translated into increased seed output, although seed mass and carbon∶nitrogen ratios were significantly increased. By contrast, Poa showed no vegetative response to elevated CO2 , but had significantly increased seed production. Thus we found no evidence for a simple translation from vegetative response to elevated CO2 into reproductive response. There was also no consistent light-mediated response to elevated CO2 among the four species. However, the effect of reduced light (33% shade) on vegetative and reproductive output was consistent across the four species and significantly stronger than the effect of elevated CO2 . On the basis of this glasshouse study, we predict that Poa would be most likely of the four species to show significant increases in population size and migration potential, as a result of increased reproductive output, under elevated atmospheric CO2 . However, this response may be relatively small compared with variation in growth and reproduction as a result of environmental heterogeneity in resources such as light.

In vitro digestibility, neutral detergent fibre, lignin and cell wall thickness in plant parts of three forage species

In order to learn more about some of the reasons for differences between forage plant species in nutritive value, plant parts of three contrasting species, Onobrychis viciifolia Scop., Spergula arvensis L. and Lolium multiflorum Lam., were examined. In vitro digestibility was recorded in milled and in chopped (1 cm lengths) material, neutral detergent fibre (NDF) and lignin were recorded in milled material and the proportions of thick-walled, thin-walled and epidermal cells and the thickness of the cell walls were recorded in cross-sections. Early harvesting was compared with later harvesting in each of two years. The plants were grown in a heated glasshouse in spring-summer.In O. viciifolia the petioles had much higher concentrations of NDF and lignin, a higher proportion of thick-walled cells and generally thicker cell walls than the leaflets, but the petioles were, if anything, slightly more digestible than the leaflets. The leaflets of O. viciifolia had cell walls of similar thickness to those of Trifolium repens and Medicago sativa. The leaves of S. arvensis had generally thin cell walls and a high proportion (0·84) of thin-walled cells. The stems of S. arvensis had high concentrations of NDF (633 g/kg) and lignin (94 g/kg) and a high proportion of thick-walled cells, but the walls of these cells were not particularly thick (1·4 μm). The leaflets and petioles of O. viciifolia and the stems of S. arvensis were much less digestible than the leaf blades or leaf sheaths of L. multiflorum. L. multiflorum leaf blades and leaf sheaths were low in lignin (16–18 g/kg) and had rather thin cell walls; the sheaths were lower in NDF than the blades and tended to be more digestible than the blades, despite thicker epidermal cell walls.

Influence of elevated atmospheric CO2 concentration on common weeds in Scandinavian agriculture

This study investigated the influence of elevated CO2 on three perennial weed species (Achillea millefolium, Leontodon autumnalis and Rumex acetosa) and seven annual species (Chenopodium album, Matricaria matricarioides, Poa annua, Polygoniini persicaria, Senecio vulgaris, Spergula arvensis and Stellaria media). The study was carried out during the period 3 May to 5 August in ten field chamber units of 9 m2 in a cool (12.6°C) maritime climate under long days (15.8–18.1 h day‐1) on the south‐west coast of Norway (59° N, 6° E). Dry weights of the seven annual species were not significantly affected by the CO2 concentration. Of the three perennial species, L. autumnalis increased in dry weight by 27% and A. millefolium by 19% at elevated compared with ambient CO2 concentration. Plant height increased by 8% in L. autumnalis and decreased by 12 and 10% in M. matricarioides and P. annua respectively. Leaf size increased by 32% and specific leaf area decreased by 23% in P. persicaria at elevated CO2, while the other species were unaffected. The results are discussed in relation to competition between species and the influence of climate on the CO2 responses.

Sensitivity of Selected Vegetable and Weed Seedlings to Ultraviolet-B Radiation

Relative sensitivity of selected vegetable and weed seedlings to ultraviolet-B (UV-B) radiation (280–320 nm) was investigated. Seedlings were grown for 4 weeks in a greenhouse, in chambers equipped with UV-B-emitting fluorescent tubes and Mylar (control) and cellulose acetate (UV-B) filters. UV-B radiation reduced seedling height, leaf area, and leaf fresh weight in tomato (Lycopersicon esculentum `Cour Di Bue'), broccoli (Brassica oleracea var. Italica `Purple Sprouting'), cabbage (Brassica oleracea var. Capitata `Red Drumhead'), and cucumber (Cucumis sativus `Straight Eight'), leaf area and leaf fresh weight in beet (Beta vulgaris `Cylindra' and `Early Wonder'), seedling height and leaf area in spinach (Spinacia oleracea `Long Standing Bloomsdale'), lettuce (Lactuca sativa ``Red Salad Bowl Everest') and `Savoy' cabbage, and seedling height in `Chinese Tip Top' cabbage and lettuce (`Saladin'). `Winterton' cabbage was not affected. UV-B radiation decreased leaf area and leaf fresh weight in common chickweed (Stellaria media) and corn spurry (Spergula arvensis) and seedling height in green foxtail (Setaria viridis) and redroot pigweed (Amaranthus retroflexus). Tillering was stimulated in response to UV-B in green foxtail. There was no effect of UV-B on lady's-thumb (Polygonum persicaria) growth. Leaf number was not affected by exposure to UV-B in any species. The differential morphological sensitivity of vegetable and weed seedlings may result in altered competitive relationships under enhanced UV-B levels expected with the depletion of the earth's ozone layer.

Resistance against uprooting in carrots ( Daucus carota) and annual weeds: a basis for selective mechanical weed control

Trials were carried out in order to investigate ways in which to achieve selectivity in mechanical weed control. The influence of soil type, uprooting angle and development stage on the uprooting force of some annual weeds and carrot was studied. Spergula arvensis L., Urtica urens L., Chenopodium album L. and carrot (Daucus carota L.) were sown in soil bins filled with four different soil types. The plants were uprooted when they had two true leaves. Soil type significantly influenced the uprooting force needed by all four species. The forces required to uproot U. urens and C. album differed significantly between peat and loamy sand. In loamy sand, Capsella bursa‐pastoris (L.) Med., Stellaria media (L.) Vill, Chamomilla suaveolens (L.) Pursh Buch. and Viola arvensis Murr. could all be uprooted by less force than it took to uproot carrot. The uprooting angle (0°, 45° and 90°) had no significant influence on the uprooting force for carrot at the studied developmental stage. C. album, S. arvensis, U. urens, Matricaria inodora, Thlaspi arvense L. and carrot could all be uprooted by less than 1 N when they had two true leaves. Carrots required a greater uprooting force than the weeds at the three early developmental stages studied. This indicates that it should be possible to develop selective mechanical weed control methods.

Economic thresholds for wild radish, wild oat, hemp-nettle and corn spurry in spring barley

The yield response of spring barley (Hordeum vulgare L. 'Morrison') to a range of densities of wild radish (Raphanus raphanistrum L.), wild oat (Avena fatua L.), hemp-nettle (Galeopsis tetrahit L.), and corn spurry (Spergula arvensis L.) was investigated in field experiments on Prince Edward Island from 1991 through 1994. Barley yield was modelled as a function of both barley and weed density. In the absence of weed competition, barley seed yield, number of main shoots, number of heads, and thousand-kernel weight varied significantly during the 4 yr of the study. Increasing densities of wild radish and wild oat reduced the number of barley heads primarily by interfering with tillering, but wild oat also reduced barley thousand-kernel weight. Hemp-nettle and corn-spurry at densities up to 200 plants m−2 had little effect on barley yield, except in a year of low barley yield potential. Estimated economic thresholds for wild radish, wild oat, hemp-nettle and corn spurry at a barley population of 250 plants m−2 were 37, 45, 122 and 297 plants m−2, respectively, assuming a weed-free yield of 4 t ha−1, a crop price of $100 t−1, and weed control costs of $30 ha−1. Key words: Avena fatua, Galeopsis tetrahit, Hordeum vulgare, Raphanus raphanistrum, Spergula arvensis, yield loss, weed interference, economic threshold

Variation in seed dormancy among mother plants, populations and years of seed collection

AbstractVariation in dormancy level was tested in seeds of four species, each collected from three populations in 1994 and 1995 (experiment 1). Germination was tested in light and darkness on recently-harvested seeds and on those after-ripened in dry storage for one year. In addition, seeds from each of eight individual plants within each of eight populations were tested for germination when recently harvested and after warm stratification or cold stratification followed by a drying period (experiment 2). Seeds from the two years differed in dormancy level in Silene noctiflora, Sinapis arvensis and Spergula arvensis. Germination percentage differed significantly among populations in Sinapis arvensis and Spergula arvensis in both experiments and in Thlaspi arvense in experiment 2. Furthermore, dormancy level in seeds from different mother plants also varied in the three species tested in experiment 2. Variations at the three levels tested (year, population and mother plant) indicate that these species have a random pattern of variation in dormancy level. It is concluded that variation in seed dormancy among mother plants, populations and years must be taken into account when testing the germination characteristics of a species and also when attempting to model weed seed bank dynamics.

Weed invasion in East Africa: insights from herbarium records

The invasion process was documented from data on the labels of specimens stored in the East African Herbarium at the National Museums of Kenya. We analysed data from seven abundant alien plant species: Ageratum conyzoides L. (Asteraceae), Capsella bursa‐pastoris (L.) Med. (Brassicaceae), Datura stramonium L. (Solanaceae), Galinsoga parviflora Cav. (Asteraceae), Tagetes minuta L. (Asteraceae), Spergula arvensis L. (Caryophyllaceae) and Stellaria media (L.) Vill. (Caryophyllaceae) and compared these data with the spread of two native weeds: Cynoglossum coeruleum A.DC. (Boraginaceae) and Senecio discifolius Oliv. (Asteraceae). Although all investigated species had been already recorded before the Second World War, most specimens were collected between 1960 and 1980. This regional spread is correlated with a change in the agricultural systems of Kenya. The early records of alien weeds were restricted to higher altitudes. With the increasing human population and the associated increase of agricultural activities (e.g. irrigation in arid areas) the weed species from South America were able to spread to lower altitudes.

Isolation and Structural Identification of Sucrose Esters from Corn Spurrey ( Spergula arvensis ); Inhibition of Seed Germination

Polar as well as nonpolar extracts of Spergula arvensis (corn spurrey) were shown to cause inhibition of seed germination. The polar methylene chloride extracts were subjected to solvent partitioning and separations by a combination of silicic acid and Sephadex LH-20 column chromatography. All chromatographic fractions were monitored by a proso-millet seed germination assay, which resulted in the isolation of a group of sucrose esters (SE). The identity of the ester acids was determined by gas chromatography (GC) of their butyl esters. Further characterization of the SE by GC-mass spectrometry of their trimethylsilyl derivatives showed the presence of four different SE groups with two to seven acyl groups attached to sucrose. The SE isomers in greatest abundance contained either octanoic or dodecanoic acid along with two smaller branched-chain acids (butanoic and pentanoic acids). All four SE groups were inhibitory to seed germination. This is the first report of SE outside the family Solanaceae.

The response of soil microorganisms and roots to elevated CO2 and temperature in a terrestrial model ecosystem

We investigate the response of soil microorganisms to atmospheric CO2 and temperature change within model terrestrial ecosystems in the Ecotron. The model communities consisted of four plant species (Cardamine hirsuta, Poa annua, Senecio vulgaris, Spergula arvensis), four herbivorous insect species (two aphids, a leaf-miner, and a whitefly) and their parasitoids, snails, earthworms, woodlice, soil-dwelling Collembola (springtails), nematodes and soil microorganisms (bacteria, fungi, mycorrhizae and Protista). In two successive experiments, the effects of elevated temperature (ambient plus 2 °C) at both ambient and elevated CO2 conditions (ambient plus 200 ppm) were investigated. A 40:60 sand:Surrey loam mixture with relatively low nutrient levels was used. Each experiment ran for 9 months and soil microbial biomass (Cmic and Nmic), soil microbial community (fungal and bacterial phospholipid fatty acids), basal respiration, and enzymes involved in the carbon cycling (xylanase, trehalase) were measured at depths of 0–2, 0–10 and 10–20 cm. In addition, root biomass and tissue C:N ratio were determined to provide information on the amount and quality of substrates for microbial growth.