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Accueil du site → Doctorat → Espagne → 2004 → Effects of dispersal and competition with "Avena Sterilis" L. on the spatial structure and dynamics of "Lolium rigidum" Gaudin in dryland cereal fields

Universitat de Barcelona (2004)

Effects of dispersal and competition with "Avena Sterilis" L. on the spatial structure and dynamics of "Lolium rigidum" Gaudin in dryland cereal fields

Blanco Moreno, José Manuel

Titre : Effects of dispersal and competition with "Avena Sterilis" L. on the spatial structure and dynamics of "Lolium rigidum" Gaudin in dryland cereal fields

Auteur : Blanco Moreno, José Manuel

Université de soutenance : Universitat de Barcelona

Grade : Doctorat de Biologia Vegetal 2004

This thesis focuses on different spatial issues in relation to the commonest weed species ("Avena sterilis" L. and "Lolium rigidum" Gaudin) in dryland cereal crops. A 3-year detailed study of "L. rigidum" and "A. sterilis" mixed weed community at contrasting scales offered an insight on the various factors that affect weed distribution across space and time. "A. sterilis" showed fairly constant spatial structure of its population across time at large scale, with well-defined patches. "L. rigidum" showed poorly defined patches that were not stable across time. Interaction between species explained to some degree the spatial distribution at large scale : there was a progressive replacement of "L. rigidum" by "A. sterilis". At fine scale both species showed a clear interaction effect from primary dispersal (more important in "A. sterilis") and secondary dispersal from combine harvesting (more important in "L. rigidum") which generated a clearly banded pattern in L. rigidum populations but not in "A. sterilis". Many attempts have been made to characterise the competition against wheat from "L. rigidum" and "A. sterilis", but no attention has been paid to within field spatial and temporal variation. The stability of competition in crop-weed mixtures dominated by "L. rigidum" and "A. sterilis" across time and location was examined. "A. sterilis" was more competitive than "L. rigidum", and this relationship was stable over time and location. However, "L. rigidum" performed better in a dry season, whilst its effect was hardly noticeable in a wetter one. The competitive relationships between weeds and this changes in competitive ability could explain to some degree the spatial distribution of weeds and the replacement of "L. Rigidum" by "A. sterilis" that was found. Dispersal behaviour had been reported for "A. sterilis", but not for "L. rigidum". Therefore, the relationship between the dispersal of seeds and the distribution pattern of weeds at fine scale was only analysed for "L. rigidum". Primary dispersal of "L. rigidum" seeds occurs in a very limited space around the parent plants, but the density of seed is low since most seeds do not spontaneously fall from spikes. In contrast, many seeds are spread by combine harvesters. Maximum dispersal distance exceeded 18 m from established stands in cereal fields, although most seeds remained within the established stands. In addition, the action of the combine harvesters tended to accumulate "L. rigidum" seeds predominantly under the straw swath, with some lateral movement. This action could explain the fine scale banded pattern of "L. rigidum" in cereal fields. Seed dispersal equations were included in a demographic model in order to assess the population dynamics and the spread of "Lolium rigidum" from a point source. The model was used to describe the behaviour of "L. rigidum" populations in the absence of control practices and to predict the effect of various control strategies. The sensitivity of the model to variation in demographic parameters was low except for seed production, for which sensitivity was up to 99%. Spread rate was hardly affected by changes in demographic parameters except fecundity, which at its lowest limit keeps the population at a critical size and leads to occasional extinction. Thus, the management practices with the greatest influence on population growth would be those affecting seed production or seed losses during dispersal. However, factors most affecting patch spread would be weed phenology (mainly rate of spontaneous seed shed at harvest) and disruption of the cereal cycle (fallow), but not demographic parameters, since these do not affect dispersal distance. The contribution of dispersal to spatial patterning was clear, since the simulation model predicted a fine scale banded-pattern similar to that found in the field.

Mots clés : Conreus de secà, Cereals, Males herbes

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Page publiée le 11 mars 2008, mise à jour le 13 février 2019