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(Fig. 1A). The order of the four groups of fields (a–d) corresponds to the order of the phases during the crop rotation and thus to the hypothetical temporal trajectory of weed communities. The cyclic trajectory of weed communities was also confirmed by following the individual fields of young and old lucerne and wheat following lucerne in subsequent years (Fig. 1A). Pairwise comparisons showed that weed species composition differed significantly between all treatments (Table 2). Differences were greatest between wheat following annual crops (group a) vs. 2–6 year old lucerne (c) (Table 2). In CDA, these two groups were mainly separated on the first axis (Fig. 1A). The second highest difference appeared between first-year lucerne (b) and wheat following lucerne (d), which was mainly separated on the second CDA axis. Differences were thus stronger between groups lying on opposite sides of the circle and lower, but still significant, between adjacent groups, which would follow each other in the rotation (Table 2, Fig. 1A). Indicator Species Analysis (ISA) showed that nine weed species were significantly associated with wheat following annual crops (a) (see Table 3). First-year lucerne (b) was associated with 16 other species, while most of the 9 species typical for wheat after annual crops had reduced Indicator Values. As a result, species richness and Shannon diversity indices at the field scale (a-diversity) were increased and young lucerne had also a higher dissimilarity between the fields (b-diversity) than wheat following annual crops (Fig. 2). Older lucerne (c) was significantly associated with 10 species and four additional species had similarly high IV in young and old lucerne (Table 3). In contrast, most weed species that were typical of annual crops had further reduced frequencies or disappeared. As a result, mean a-diversity dropped down again to the level of annual crops (about 20 species per field), while mean b-diversity remained high (Fig. 2). Only four species showed highest IV in wheat following perennial lucerne (d), but IV of some species were nearly the same as in group c, demonstrating the similarity between old lucerne and the Table 2 Pairwise comparisons of weed communities in four crop treatments (Table 1). ANOSIM-R varies between 1 (groups do not share any species) and 0 (no differences between groups) (Clarke, 1993) Contrast ANOSIM-R (c) Lucerne 2–6 years vs. (a) wheat after annuals 0.326**** (b) Lucerne 1 year vs. (d) wheat after lucerne 0.171**** (c) Lucerne 2–6 years vs. (d) wheat after lucerne 0.109**** (b) Lucerne 1 year vs. (a) wheat after annuals 0.107**** (b) Lucerne 1 year vs. (c) lucerne 2–6 years 0.062**** (a) Wheat after annuals vs. (d) wheat after lucerne 0.045**** ****P < 0.0001 (Bonferroni-corrected). following annual crops. On the contrary, wheat following lucerne also contained several species typical for annual crops, but always with lower IV (see Table 3). Interestingly, none of the three diversity measures differed between old lucerne and the following wheat; b-diversity was thus significantly higher than in wheat following annual crops (Fig. 2). The weed species which were significant in ISA (P < 0.05 and IVmax ‡ 15) are represented on the CDA plot illustrating the trajectories of individual weed species during the crop rotation (Fig. 1B). Functional groups Relative frequencies of the a-priori defined weed FG varied between the four treatments. Differences were significant for six out of the eight FG (Fig. 3). Relative frequencies of both upright and climbing annual broadleaved species (FG 1 and 2) were highest in wheat after annual crops (a), reduced in young lucerne (b), more strongly reduced in old lucerne (c), and increased again in wheat after annual crops (d), though they did not reach the level of (a). The opposite pattern was observed with four other FG: annuals with rosettes, broad-leaved species with ÔintermediateÕ life cycles, perennial broadleaved species and perennial grasses (FG 4, 5, 6 and 8), which were two to three times more frequent in old lucerne (c) than in wheat after annual crops (a). Two FG did not show any significant difference: annual broadleaved species with ÔotherÕ morphologies (FG 3) and annual grasses (FG 7) (see Fig. 3). Discussion Ó 2010 INRA Journal Compilation Ó 2010 European Weed Research Society Weed Research 50, 331–340 Arable weeds and perennial lucerne 335 This study indicates that weed community dynamics are strongly affected by perennial lucerne. In accordance with Ominski et al. (1999), wheat fields following pluriannual lucerne (d) vs. several years of annual crops (a) showed strong differences in weed species composition. These differences were consistent with, and may thus be explained by, the weed community trajectories during the perennial crops (b and c), which, to our knowledge, have not been shown to date. Below we compare the observed community shifts to findings in previous studies and discuss possible underlying mechanisms. Lucerne had strong negative impacts on broad-leaved weeds with an upright morphology (FG 1, e.g. Mercurialis annua L., Chenopodium album L., Solanum nigrum L.) and on species climbing on neighbouring plants (FG 2, e.g. Galium aparine L., Fallopia convolvulus (L.) A ´ . Lo¨ve). In previous studies, species with similar morphologies, including Abutilon theophrasti Medik., Amaranthus sp., C. album, and G. aparine, reacted in a similar way
336 H Meiss et al. Table 3 Indicator Species Analysis (ISA) of the four groups of fields (a–d) representing key stages of the rotation (Table 1) Weed species Code Group (treatment) (a) Wheat after annuals (Ominski et al., 1999; Teasdale et al., 2004; Albrecht, 2005; Heggenstaller & Liebman, 2006). Upright and climbing broad-leaved plants may be particularly vulnerable to frequent cutting removing large parts of leaves and also buds ⁄ meristems needed for resprouting. Therefore, such plant types are likely to have slowest regrowth and highest mortality rates in frequently cut crops, such as lucerne. In contrast, cutting may cause less damage in (b) Lucerne 1 year (c) Lucerne 2–6 years P-value (d) Wheat after Lucerne P-value Indicators of wheat after annuals (a) Mercurialis annua MERAN 30 6 0 25 0.0008 Veronica hederifolia VERHE 35 9 2 25 0.0002 Fallopia convolvulus POLCO 40 12 1 26 0.0002 Galium aparine GALAP 32 10 2 13 0.0004 Polygonum aviculare POLAV 32 9 2 19 0.0010 Viola arvensis + tricolor + sp. VIOTR 28 9 1 15 0.0022 Chenopodium album CHEAL 20 5 0 16 0.0134 Cirsium arvense + sp. CIRAR 22 9 6 6 0.0196 Solanum nigrum + sp. SOLNI 10 0 0 1 0.0156 Indicators of lucerne 1 year (b) Stellaria media STEME 10 24 7 11 0.0120 Sinapis arvensis SINAR 17 19 1 4 0.0418 Sonchus oleraceus SONOL 0 38 2 1 0.0002 Reseda lutea + sp. RES 0 31 0 0 0.0002 Kickxia spuria + sp. KICSP 2 24 1 0 0.0002 Malva neglecta + sylvestris + sp. MAL 0 19 5 0 0.0004 Festuca rubra + sp. FES 0 15 1 0 0.0004 Lamium amplexicaule LAMAM 3 15 5 6 0.0470 Lapsana communis + sp. LAPCO 1 14 0 0 0.0044 Atriplex patula + prostrata + sp. ATX 1 40 10 0 0.0002 Picris echioides PICEC 0 27 17 1 0.0004 Picris hieracioides PICHI 3 17 15 0 0.0266 Sonchus asper SONAS 1 51 23 4 0.0002 Capsella bursa-pastoris CAPBP 1 33 32 0 0.0004 Lactuca serriola LACSE 1 18 18 0 0.0092 Calepina irregularis CPAIR 0 12 12 0 0.0236 Indicators of lucerne 2–6 years (c) Veronica arvensis + polita VERAR 1 14 17 9 0.0270 Crepis sancta + vesicaria + sp. CVP 0 7 30 2 0.0002 Poa trivialis POATR 2 4 20 8 0.0098 Bromus sterilis + mollis + sp. BRO 2 5 19 6 0.0210 Rumex crispus RUMCR 0 5 18 3 0.0046 Myosotis arvensis + sp. MYOAR 2 9 17 8 0.0472 Cerastium arvense + glomeratum CER 0 2 13 5 0.0174 Geranium rotundifolium GERRT 1 2 13 0 0.0210 Silene latifolia MELAL 0 15 18 15 0.0484 Veronica persica VERPE 7 17 35 24 0.0002 Indicators of wheat after lucerne (d) Taraxacum officinale TAROF 0 4 34 39 0.0002 Poa annua POAAN 4 0 3 27 0.0006 Falcaria vulgaris FALVU 1 0 2 11 0.0198 Fumaria officinalis + sp. FUMOF 15 2 0 18 0.0136 High indicator values (IV) are shaded in darker grey with three levels: IV ‡ 10, IV ‡ 20 and IV ‡ 30. They appear mostly in one or two adjacent groups of fields, showing that the weed species are not randomly distributed but follow a trajectory during the long crop rotation. Only weed species with IV max ‡ 10 and P < 0.05 are shown. broad-leaved species with rosettes and in grasses, since buds and leaves are located nearer to the soil surface. This mechanism has been suggested by experiments on individual plants (Meiss et al., 2008). The present study is, to our knowledge, the first one testing this hypothesis for weed communities in real fields. Our results also indicate that lucerne favours perennial broad-leaved species. Increased occurrences of the Ó 2010 INRA Journal Compilation Ó 2010 European Weed Research Society Weed Research 50, 331–340
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Diversifying crop rotations with te
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In Chizé, I am indebted to all the
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Talks . ...........................
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C.II.4.1 Differences between crop t
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INDEX OF FIGURES Fig. 1: Population
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ABSTRACTS (ENGLISH, FRENCH & GERMAN
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Extended summary in English Résum
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Extended summary in English Résum
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CONTEXT AND FUNDING This thesis is
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THESIS ORGANISATION This thesis ent
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8) Meiss, H., Lagadec, L. L., Munie
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Posters . 1) Meiss, H., Waldhardt,
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2007). Agriculture is increasingly
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term considerations (Munier-Jolain
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problematic for the production of d
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Newton, 2004). Several bird species
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A.III APPROACHES TO ALLEVIATE THE
Page 35 and 36: and higher production costs or even
Page 37 and 38: competitive yield loss (Cousens, 19
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Page 47 and 48: Clay & Aguilar (1998) compared the
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Page 53 and 54: A.V DIVERSIFIED CROPPING SYSTEM CON
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Page 61 and 62: B OVERWIEW OF THE MATERIALS & METHO
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Page 67 and 68: B.III.2.4 Cutting height In 2008, t
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Page 73 and 74: Contrasting weed species compositio
Page 79 and 80: Mean frequency in perennial lucerne
Page 81 and 82: C.I.2 Article 2: Meiss, H., Médiè
Page 83 and 84: 332 H Meiss et al. communities (Boo
Page 85: 334 H Meiss et al. functional group
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Page 111 and 112: At the end of the experiment in spr
Page 113 and 114: Difference sown - unsown (plants m
Page 115 and 116: Cumulated BM production (g m -2 ) 1
Page 117 and 118: Weed biomass (g m -2 ) 500 400 300
Page 119 and 120: Table 12: Factors differing between
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Page 123 and 124: Table 13: Mechanisms causing the im
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Page 127 and 128: • Weed biomasses decreased in sum
Page 129 and 130: Our results show that different mec
Page 131 and 132: including exotic species (Palmer an
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XIII ème COLLOQUE INTERNATIONAL SU
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irradiation,…), and (ii) biotic i
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Table I: Species included in the ex
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Fig. 2: Mean biomass (harvestable d
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When both treatments were combined,
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C.IV WEED SEED PREDATION C.IV.1 Art
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XIII ème COLLOQUE INTERNATIONAL SU
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produites restent à la surface du
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Tableau 1 : Liste des espèces adve
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Insectes prédateurs Les principaux
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C.IV.3 Article 8: Meiss, H., Lagade
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Table 1 Studies investigating the i
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Table 2 Overview showing (i) mean s
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higher weed seed losses (e.g., Mena
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D GENERAL DISCUSSION Data from weed
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The first two limits could be addre
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composition that may be compared to
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Frequency in field experiment (Epoi
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crops (Clay and Aguilar, 1998; Card
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Such diversified crop rotations cou
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the leaves (needed for photosynthes
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field margin strips (compare Articl
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1) The absence of soil tillage and
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D.III.2 Predicting weed regrowth af
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Future studies must determine the s
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(illustrated in Fig. 24). Later, re
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D.III.3 Factors determining weed se
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governing the presence and abundanc
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natural conditions, weed species po
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This PhD research project documente
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area needed for crop production. Gl
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seed characteristics, tillage and s
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Fried G., S. Petit, F. Dessaint, X.
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at the Eastern base of the Meissner
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Lindegarth M., L. Gamfeldt. (2005)
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Murphy S.D., D.R. Clements, S. Bela
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affected by experimental substrate.
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Vincent G., M. Ahmim. (1985) Note o
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ANNEXES ANNEXE 1: KEY WORDS IN ENGL
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genetically modified crop varieties
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ANNEXE 3: WEED SPECIES OF THE LARGE
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Name of species /genera Code Freq.
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Name of species /genera Code Freq.
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ERKLÄRUNG (DECLARATION FOR THE GIE
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