| 1. |
- Anbari, Saghi, et al.
(författare)
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Effects of root fragmentation on generative reproduction of Sonchus arvensis
- 2016
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Ingår i: Acta Agriculturae Scandinavica, Section B - Soil and Plant Science. - : Informa UK Limited. - 0906-4710 .- 1651-1913. ; 66, s. 391-398
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Tidskriftsartikel (refereegranskat)abstract
- To develop better mechanical management strategies, more information on the impact of root partitioning on generative reproduction of Sonchus arvensis L. is needed. Therefore, an outdoor experiment was performed in Sweden in 2008, to evaluate the effect of root fragmentation on generative reproduction of S. arvensis. Two artificial populations of S. arvensis with the same total root length per area but with different initial root lengths and different numbers of root fragments were planted. Cumulative numbers of flower receptacles which had shed mature seeds over the season were assessed. Changes in the number of seeds per flower receptacle and average seed weight were monitored over time during the late season. Plants from long root fragments produced more flower receptacles than plants from short ones. Per area, however, the number of mature flower receptacles did not differ. The number of seeds per flower receptacle and individual seed weight were not affected by initial root length for the first cohort of shoots which sprouted from the initially planted roots. A second cohort, from roots produced during the season, resulted, irrespective of its initial root length, in fewer flower receptacles per plant and per area, with less seeds per receptacle, but with the same average seed weight as the first cohort. The number of seeds per flower receptacle was higher in mid-September than earlier or later. Average seed weight slightly decreased over time. The weight of seeds produced in early September was inversely related to the number of seeds per receptacle, but this trade-off disappeared over time. Root fragmentation alone in pure populations of S. arvensis does not impede generative reproduction, but is likely to decrease input of seeds to the seed bank, when combined with crop competition.
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| 2. |
- Anbari, Saghi, et al.
(författare)
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Population dynamics and nitrogen allocation of Sonchus arvensis L. in relation to initial root size
- 2016
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Ingår i: Acta Agriculturae Scandinavica, Section B - Soil and Plant Science. - : Informa UK Limited. - 0906-4710 .- 1651-1913. ; 66, s. 75-84
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Tidskriftsartikel (refereegranskat)abstract
- To develop better mechanical management strategies, more information on the impact of root partitioning on changes in the population dynamics of Sonchus arvensis is needed. Therefore, the effects of root fragmentation of S. arvensis on shoot height frequency distributions, biomass production and nitrogen allocation were studied in an outdoor experiment in Sweden in 2008. Three artificial populations of S. arvensis of different initial root lengths but with the same total root length per area were planted. Shoot heights were measured at the onset of flowering and dry weight and nitrogen content of leaves, stems, buds and roots were quantified twice during the season. Height frequency distributions of the populations were bimodal, indicating the existence of two generations distinctly different in height growth pattern. Shorter root fragments produced shoots with a lower mean height compared to longer fragments. Plants originating from longer root fragments had higher dry weight and more nitrogen compared to plants from shorter root fragments. Dry matter production per square meter did not differ between the populations. The proportion of dry matter and nitrogen allocated to the different plant components (leaves, stems, buds and roots) at harvest did not differ between the populations. Over time, nitrogen was reallocated from leaves and stems to roots. Our results show that initial root length of S. arvensis per square meter, rather than the number of root fragments per square meter, is a good predictor of biomass at harvest, and that the degree of root fragmentation does not affect nitrogen allocation patterns. Root fragmentation, however, leads to a lower average canopy height for S. arvensis, and thus may be an effective weed control measure in combination with a crop which is competitive for light.
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| 3. |
- Anbari, Saghi
(författare)
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Population dynamics of the perennial weed species Sonchus arvensis L.
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Sonchus arvensis L. is a perennial weed that is widely prevalent in annual crops in northern Europe and can cause substantial yield losses. The abundance of S. arvensis has increased recently, primarily due to expansion of organic farming and increased use of reduced tillage. This thesis assessed the effect of mechanical control measures on the population dynamics of S. arvensis and sought to predict the impact of temperature on sprouting of S. arvensis under variable climate conditions. An outdoor box experiment was performed to evaluate the effect of initial root fragment size on subsequent growth of S. arvensis. Four artificial populations of S. arvensis with differing initial root length but with the same total root length per area were planted (20 roots of 5 cm, 10 roots of 10 cm, 20 roots of 5 cm and 4 × 20 cm + 4 × 5 cm roots). A pot experiment was performed in darkness to assess the impact of initial root length (5 and 10 cm), temperature (4, 8 and 18 °C) and planting depth (3, 10 and 17 cm) on belowground shoot elongation and emergence time of S. arvensis shoots. The data from this pot experiment were used to model shoot emergence rate as a function of temperature and to predict emergence time under different climate scenarios. Degree of root fragmentation was found to strongly infl uence plant performance in terms of shoot emergence time, shoot numbers, rosette size, flowering, biomass production and seed production. Compared with larger root fragments, small root fragments of S. arvensis produced more numerous but smaller-sized shoots, which emerged later in the beginning of the growing season and had lower generative capacity in terms of seed and root production. Root fragmentation by mechanical control measures resulted in a change not only in the frequency of shoots originating from S. arvensis root fragments, but also in the height of these shoots. Temperature significantly affected sprouting and emergence time of S. arvensis, with an increase in temperature causing an increase in the rate of S. arvensis shoot elongation. Variations in temperature between years under field conditions (in central Sweden) resulted in larger variations in emergence time than differences in root fragment weight. An average increase in mean air temperature of about 3 °C would cause earlier emergence, approximately equal to the difference between the earliest and latest year in the present climate.
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| 4. |
- Anbari, Saghi, et al.
(författare)
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Sprouting and shoot development of Sonchus arvensis in relation to initial root size
- 2011
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Ingår i: Weed Research. - : Wiley. - 0043-1737 .- 1365-3180. ; 51, s. 142-150
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Tidskriftsartikel (refereegranskat)abstract
- To assess the effects of initial root size of Sonchus arvensis on sprouting and shoot development, an outdoor box experiment was performed in Sweden in 2008. Shoot emergence time, shoot numbers, rosette size and flower production were quantified as functions of root length and weight. Emergence of the first shoot per root and of later cohorts was delayed with decreasing root length and weight. Number of shoots per root increased with root length and weight, but per unit root length and weight, short roots produced more shoots. The first emerging rosettes were, for rosettes of a given age, larger for longer roots. Total rosette area per root 5 weeks after planting increased with increasing root length and weight. The number of flowers and production of mature seeds were positively related to root length and weight, because of delayed sprouting of short and light roots. The proportion of flowers leading to mature seeds declined with shoot emergence time. By clarifying relationships between root size and growth parameters, this study showed that fragmenting of S. arvensis roots delays phenological development and hampers reproduction by seeds. The information may be used to refine mechanical weed control strategies for S. arvensis.
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| 5. |
- Torssell, Bengt, et al.
(författare)
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Modelling below-ground shoot elongation and emergence time of Sonchus arvensis shoots
- 2015
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Ingår i: Acta Agriculturae Scandinavica, Section B - Soil and Plant Science. - : Informa UK Limited. - 0906-4710 .- 1651-1913. ; 65, s. 582-588
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Tidskriftsartikel (refereegranskat)abstract
- To assess emergence time of shoots from roots of the perennial weed Sonchus arvensis as a function of root weight and soil temperature, we performed an experiment to which linear models were fitted. Root parts of three distinct initial weight classes were grown in pots in the dark at constant temperatures of 4, 8 and 18 degrees C, respectively. During five harvest occasions, prior to or at shoot emergence, below-ground shoot length was measured. Root planting depth (3, 10 and 17 cm) did not influence shoot elongation rate. The below-ground shoot elongation rate for a given initial root-weight class was estimated from the observations to be constant with time, but to increase with temperature and initial root weight. By expressing shoot length for a given day as a linear function of the number of days from planting date, and elongation rate as a linear function of temperature, we calculated (1) the accumulated temperature-sum requirement for emergence, (2) emergence time for variable temperature conditions in a clay soil using soil temperature recordings at 5-cm depth for seven seasons in central Sweden and (3) the emergence time at three elevated temperature levels and initial root-weight classes. The accumulated temperature-sum requirements for below-ground shoots of S. arvensis to reach soil surface are independent of temperature regime for roots of a given initial weight but lower for heavier than lighter roots. The temperature limit for below-ground shoot elongation to occur is about 2.0-2.5 degrees C. Between-year variations in temperature under field conditions cause larger variation to emergence time than initial root-weight differences. An average temperature increase of 3 degrees C would cause an earlier emergence time, in the same range (about 2 weeks) as the difference between the earliest and latest year in the current weather conditions.
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| 6. |
- Verwijst, Theo, et al.
(författare)
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Weight loss in overwintering below-ground parts of Sonchus arvensis under current and temperature-elevated climate scenarios in Sweden
- 2013
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Ingår i: Weed Research. - : Wiley. - 0043-1737 .- 1365-3180. ; 53, s. 21-29
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Tidskriftsartikel (refereegranskat)abstract
- Weight loss in overwintering below-ground parts of perennial weeds has been attributed to respiration, but neither its temperature dependence nor its relevance for biomass dynamics under changing climate conditions have been investigated. In two experiments, we quantified weight loss of the perennial weed Sonchus arvensis, by measuring weight changes over time of sprouting roots in dark rooms at temperatures of 4, 8 and 18 degrees C. Dry weight loss rates were 0.47, 0.64 and 1.47% day-1 at 4, 8 and 18 degrees C, respectively, giving a half-life time of 149, 110 and 47 days, respectively. A factor by which weight loss rates increase for every 10 degrees rise in temperature (Q10) was equal to about 2.3. Cumulative weight loss may comprise >40% of the below-ground biomass during overwintering periods. Applying weight loss rates and Q10 to elevated soil temperature projections showed that losses during winter seasons in central Sweden will remain basically constant, the effect of increased weight loss at higher temperatures being balanced by shorter winters. This implies that need for control of S. arvensis in a changing climate will persist, but that shorter winter seasons will provide a longer time window for control of S. arvensis prior to sowing crops.
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