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What makes a weed a weed ? Towards a functional characterization

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HAL Id: hal-02787982

https://hal.inrae.fr/hal-02787982

Submitted on 5 Jun 2020

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characterization

Bérenger Bourgeois, Pierre Denelle, François Munoz, Guillaume Fried, Sabrina Gaba, Jonathan Storkey, Cyrille Violle

To cite this version:

Bérenger Bourgeois, Pierre Denelle, François Munoz, Guillaume Fried, Sabrina Gaba, et al.. What makes a weed a weed ? Towards a functional characterization. ”Functional Ecology and Environment” Conference, Jul 2017, Toulouse, France. �10.13140/RG.2.2.36807.60321�. �hal-02787982�

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What makes a weed a weed ?

Towards a functional characterization

Bourgeois Bérenger1,2, Denelle Pierre3, Munoz François4,

Fried Guillaume5, Gaba Sabrina1, Storkey Jonathan6 and Violle Cyrille3

Functional Ecology and Environment Toulouse – July 11-12, 2017

1 INRA Dijon, UMR Agroécologie, Dijon 2 CESAB, Aix-en-Provence

3 CNRS – CEFE, Montpellier 4 Université de Montpellier, UMR AMAP

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Context Methods Results Conclusion

From Harlan & deWet, 1965 – Economic Botany

A plant that spontaneously grow on a land modified by humans (Godinho, 1984)

Lack of clear, precise and objective definition

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Context Methods Results Conclusion

Aim

Identify the functional specificities

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Two species lists

Cropland species

= Biovigilance-Flore + LTER ZAPVS

~ 4400 arable fields sampled over 10 years Grassland species

> 51,000 plots in permanent grasslands over France

Nine plant traits

LHS = Height, Seed Mass, Specific Leaf Area

Reproduction = Flowering onset, Flowering duration Autoecology = Ellenberg Nitrogen, Light and Moisture Raunkier biological types

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397 cropland species

924 common species

1374 grassland species

Functional comparisons of species pools

Trait-by-trait: permutational approach or χ² tests

Set of traits: hypervolumes – LHS, reproduction, autoecology

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0 20 40 60 80 0 .0 0 0 .0 1 0 .0 2 0 .0 3 0 .0 4 0 .0 5

Specific Leaf Area

N = 302 Bandwidth = 2.727 D e n si ty 79 cropland species 500 common species 302 grassland species OVERLAP SLA

Cropland vs. Grassland species 80 %

Cropland vs. Common species 86 % Grassland vs. Common species 77 % Resource acquisition

Specific Leaf Area

Weeds:

- have higher SLA

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-4 -2 0 2 0 .0 0 .1 0 .2 0 .3 0 .4 0 .5 0 .6 log(Plant Height) N = 415 Bandwidth = 0.2006 D e n si ty 99 cropland species 628 common species 415 grassland species

Context Methods Results Conclusion

OVERLAP SLA log(Plant Height)

Cropland vs. Grassland species 80 % 86%

Cropland vs. Common species 86 % 85%

Grassland vs. Common species 77 % 93%

Competitive ability

Plant height

Weeds:

- have higher SLA - are taller

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-5 0 5 0 .0 0 0 .0 5 0 .1 0 0 .1 5 0 .2 0 log(Seed Mass) N = 398 Bandwidth = 0.5535 D e n si ty 116 cropland species 680 common species 398 grassland species

OVERLAP SLA log(Plant Height) log(Seed Mass)

Cropland vs. Grassland species 80 % 86% 90 % Cropland vs. Common species 86 % 85% 92 % Grassland vs. Common species 77 % 93% 93 %

Dispersal

Seed mass

Weeds:

- have higher SLA - are taller

- have similar seed mass than grassland species

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Context Methods Results Conclusion

2 3 4 5 6 7 8

Flowering onset (month)

P ro p o rt io n ( % ) 0 10 20 30 40 50 261 cropland species 640 common species 694 grassland species

χ² test Flowering onset

Cropland vs. Grassland species 0.2225 Cropland vs. Common species 0.0537 Grassland vs. Common species 0.0003 Reproductive strategy

Flowering onset

Weeds:

- start flowering

during the same month than grassland species

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χ² test Flowering duration Cropland vs. Grassland species < 0.0001

Cropland vs. Common species 0.0164

Grassland vs. Common species < 0.0001

1 4 5 6 7 8 9 10 11

Flowering duration (months)

P ro p o rt io n ( % ) 0 5 10 15 20 25 30 261 cropland species 640 common species 694 grassland species Reproductive strategy

Flowering duration

Weeds: - flower longer

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Context Methods Results Conclusion

χ² test Ellenberg N

Cropland vs. Grassland species < 0.0001

Cropland vs. Common species 0.6315 Grassland vs. Common species < 0.0001

2 3 4 5 6 7 8 9 Ellenberg Nitrogen P ro p o rt io n ( % ) 0 10 20 30 40 312 cropland species 659 common species 725 grassland species Resource requirements

Ellenberg nitrogen

Weeds: - occur in environment richer in Nitrogen

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χ² test Ellenberg L Cropland vs. Grassland species < 0.0001

Cropland vs. Common species 0.0796 Grassland vs. Common species < 0.0001

4 5 6 7 8 9 Ellenberg Light P ro p o rt io n ( % ) 0 10 20 30 40 50 60 313 cropland species 661 common species 738 grassland species Resource requirements

Ellenberg light

Weeds: - occur in more shaded areas

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Context Methods Results Conclusion

χ² test Ellenberg F

Cropland vs. Grassland species 0.0854 Cropland vs. Common species < 0.0001

Grassland vs. Common species < 0.0001

2 3 4 5 6 7 8 9 Ellenberg Moisture P ro p o rt io n ( % ) 0 10 20 30 40 50 311 cropland species 653 common species 722 grassland species Resource requirements

Ellenberg moisture

Weeds:

- have similar soil moisture requirements

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χ² test Biological type Cropland vs. Grassland species < 0.0001

Cropland vs. Common species 0.0011

Grassland vs. Common species < 0.0001

geophyte hemicryptophyte therophyte

Biological type P ro p o rt io n ( % ) 0 20 40 60 80 415 cropland species 871 common species 1001 grassland species Response to disturbances

Biological types

Weeds:

- are mainly therophytes while grassland species are mainly hemicryptophytes

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Context Methods Results Conclusion Volume Overlap with weeds Centroid distance to weeds Weeds 93 Common 90 68% 0.65 Grassland 142 72% 0.57

LHS hypervolume

Weeds: - have a narrower LHS

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Volume Overlap with weeds Centroid distance to weeds Weeds 115 Common 92 71% 0.60 Grassland 95 73% 0.41

Reproductive hypervolume

Weeds:

- have a larger reproductive niche than grassland species

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Context Methods Results Conclusion Volume Overlap with weeds Centroid distance to weeds Weeds 83 Common 60 73% 0.53 Grassland 112 73% 0.48

Autoecological hypervolume

Weeds:

- have a narrower ellenberg niche than grassland species

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Weeds

Higher SLA Higher height Therophytes Lower Ell-L Higher Ell-N

Longer flowering duration

…compared to grassland species

…but still strongly overlap with grassland species in terms of physiological, reproductive and autoecological niches

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Context Methods Results Conclusion

Synthesis

Higher SLA Higher height Therophytes Lower Ell-L Higher Ell-N

Weeds do not differ that much from grassland species,

but in fact seem better adapted to agricultural disturbances,

like regular tillage, fertilization or competition with crops.

Some species with similar traits are habitat specialists…why ?

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