Simulating changes in cropping practices in conventional and glyphosate-resistant maize. II. Weed impacts on crop production and biodiversity

Environmental Science and Pollution Research, Apr 2017

Overreliance on the same herbicide mode of action leads to the spread of resistant weeds, which cancels the advantages of herbicide-tolerant (HT) crops. Here, the objective was to quantify, with simulations, the impact of glyphosate-resistant (GR) weeds on crop production and weed-related wild biodiversity in HT maize-based cropping systems differing in terms of management practices. We (1) simulated current conventional and probable HT cropping systems in two European regions, Aquitaine and Catalonia, with the weed dynamics model FlorSys; (2) quantified how much the presence of GR weeds contributed to weed impacts on crop production and biodiversity; (3) determined the effect of cultural practices on the impact of GR weeds and (4) identified which species traits most influence weed-impact indicators. The simulation study showed that during the analysed 28 years, the advent of glyphosate resistance had little effect on plant biodiversity. Glyphosate-susceptible populations and species were replaced by GR ones. Including GR weeds only affected functional biodiversity (food offer for birds, bees and carabids) and weed harmfulness when weed effect was initially low; when weed effect was initially high, including GR weeds had little effect. The GR effect also depended on cultural practices, e.g. GR weeds were most detrimental for species equitability when maize was sown late. Species traits most harmful for crop production and most beneficial for biodiversity were identified, using RLQ analyses. None of the species presenting these traits belonged to a family for which glyphosate resistance was reported. An advice table was built; the effects of cultural practices on crop production and biodiversity were synthesized, explained, quantified and ranked, and the optimal choices for each management technique were identified.

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Simulating changes in cropping practices in conventional and glyphosate-resistant maize. II. Weed impacts on crop production and biodiversity

Environ Sci Pollut Res Simulating changes in cropping practices in conventional and glyphosate-resistant maize. II. Weed impacts on crop production and biodiversity Nathalie Colbach 0 1 2 Henri Darmency 0 1 2 Alice Fernier 0 1 2 Sylvie Granger 0 1 2 Valérie Le Corre 0 1 2 Antoine Messéan 0 1 2 Nathalie Colbach 0 1 2 0 INRA, UMR1347 Agroécologie , BP 86510, 17 rue Sully, F-21065 Dijon , France 1 Agroécologie, AgroSup Dijon, INRA, University Bourgogne Franche-Comté , F-21000 Dijon , France 2 Antoine Messéan Overreliance on the same herbicide mode of action leads to the spread of resistant weeds, which cancels the advantages of herbicide-tolerant (HT) crops. Here, the objective was to quantify, with simulations, the impact of glyphosateresistant (GR) weeds on crop production and weed-related wild biodiversity in HT maize-based cropping systems differing in terms of management practices. We (1) simulated current conventional and probable HT cropping systems in two European regions, Aquitaine and Catalonia, with the weed dynamics model FLORSYS; (2) quantified how much the presence of GR weeds contributed to weed impacts on crop production and biodiversity; (3) determined the effect of cultural practices on the impact of GR weeds and (4) identified which species traits most influence weed-impact indicators. The simulation study showed that during the analysed 28 years, the advent of glyphosate resistance had little effect on plant biodiversity. Glyphosate-susceptible populations and species were replaced by GR ones. Including GR weeds only affected functional biodiversity (food offer for birds, bees and carabids) and weed harmfulness when weed effect was initially low; when weed effect was initially high, including GR weeds had little effect. The GR effect also depended on cultural practices, e.g. GR weeds were most detrimental for species equitability when maize was sown late. Species traits most harmful for crop production and most beneficial for biodiversity were identified, using RLQ analyses. None of the species presenting these traits belonged to a family for which glyphosate resistance was reported. An advice table was built; the effects of cultural practices on crop production and biodiversity were synthesized, explained, quantified and ranked, and the optimal choices for each management technique were identified. GM crop; Model; Weed; Glyphosate resistance; Cropping system; Biodiversity; Yield gap; Harmfulness; Agroecology - * Introduction Herbicide-tolerant (HT) crops, particularly those tolerant to glyphosate, are grown on large acreages in some regions of the world (James 2013) . Though these varieties simplify weed management (Bonny 2016; Brookes and Barfoot 2009; Shaner 2000) , the overreliance on glyphosate has led to the development of resistant weeds (Bonny 2016; Heap 2016; Powles 2008) . In contrast to the widespread annual use of glyphosate in HT maize and HT soybean rotations in the USA, the acreage of HT maize in Europe is almost nil today, and maize is often rotated with other crops that are not treated with glyphosate. However, glyphosate is frequently used during summer fallow, and cases of weed resistance to glyphosate have already been detected in arable fields with annual crops (Collavo and Sattin 2014) . Moreover, the introduction of HT crops into the cropping systems may lead to other changes in cultural practices which can also favour the evolution of herbicide resistance, e.g. simplified rotations and/or simplified or no tillage (Beckie 2009; Boerboom 1999; Chauvel et al. 2009; Colbach et al. 2016b; Colbach et al. 2017; Friesen et al. 2000; Lievin et al. 2013; Moss and Clarke 1994; Moss et al. 2007) . This shift to herbicide-resistant biotypes potentially not only increases weed harmfulness for crop production (e.g. yield loss, harvest contamination, field infestion, Mezière et al. 2015 b) but can also impair biodiversity. Indeed, weed flora is a major part of wild plant biodiversity in arable lands and provides habitat and food resources to a range of animals in agricultural landscapes, among which pollinators (Bretagnolle and Gaba 2015) or crop auxiliaries (Taylor et al. 2006) . The management of glyphosate-tolerant crops can also lead to shifts to different weed species, which has already been analysed in recent studies (Bigler and Albajes 2011; Bürger et al. 2015; Heard et al. 2003) . However, the particular effect of herbicide resistance on weed-related functional biodiversity (e.g. weeds as food resources) has yet to be investigated. Because of long-term effects and the multiplicity of the implicated factors, herbicide resistance is increasingly investigated via modelling and simulations (Cavan et al. 2000; Colbach et al. 2016b; Gressel and Segel 1990; Maxwell et al. 1990; Neve et al. 2003; Renton et al. 2014) . These models are, however, limited to a single species and neglect the impact of weeds on crop production and biodiversity. Therefor (...truncated)


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Nathalie Colbach, Henri Darmency, Alice Fernier, Sylvie Granger, Valérie Le Corre, Antoine Messéan. Simulating changes in cropping practices in conventional and glyphosate-resistant maize. II. Weed impacts on crop production and biodiversity, Environmental Science and Pollution Research, 2017, pp. 13121-13135, Volume 24, Issue 14, DOI: 10.1007/s11356-017-8796-9