Crop type and within-field location as sources of intraspecific variations in the phenology and the production of floral and fruit resources by weeds

https://doi.org/10.1016/j.agee.2020.107082Get rights and content

Highlights

  • 685 patches of 30 weed species were surveyed in field edges and field cores.

  • Weeds produced more flowers and seeds in field edges earlier in season.

  • Weeds produced less resources and later in cereals than in other crops.

  • Field edges and crop diversity enhance weed resources in the landscape.

Abstract

In arable farming, weeds provide important floral and seed resources that have the potential to support the provision of ecosystem services such as pollination or pest control. Estimating the production of these weed resources in the landscape is however not trivial as large-scale surveys of weed communities are usually conducted once in the season with a timing that may not coincide with the flowering and fruiting stages of all weed species. More, intraspecific variation in the mortality and phenology of individual weed species may arise from differences in the quality of the growing environment of each plant. In this study, we monitored the phenology of 30 common weed species in the field core and the field edge of 64 commercial fields grown with 6 crop types. Our hypothesis was that the production of resources by an individual plant would be modulated by its within-field location and by the crop type where it grows. We quantified floral (proportion, starting date and duration of flowering, dry biomass at flowering as a proxy for the amount of flowers) and seed resource production (proportion and starting date of fruiting). For most species, flowering and fruiting success were higher in field edges than in field cores and were lower in cereal crops than in other crops. Weeds flowered and fruited earlier and the flowering period was longer in field edges, except those of cereal crops. Dry biomass at flowering varied with field location either way, depending on the weed species, but tended to be lower in cereal crops than in other crops. This important intraspecific phenological variability in the production of seed and/or flower or resources should be considered when evaluating the contribution of weed communities to ecosystem services. It also suggests that within an agricultural landscape, the amount, timing and duration of provision of services by weeds could be enhanced by maintaining sufficient lengths of field edges and by growing a diversity of crop types.

Introduction

There is growing evidence that arable weeds provide habitat and resources that are of key value for the maintenance of biodiversity and the delivery of ecosystem services in agroecosystems (Blaix et al., 2018). Weeds are an important source of floral and seed resources for various insects, birds and mammals (Wilson et al., 1999; Petit et al., 2011). Their role as providers of a continuous supply of pollen and nectar is of key importance for the maintenance of pollinators and the provision of the pollination service (Requier et al., 2015; Bretagnolle and Gaba, 2015). Weeds also supply trophic resources for many natural enemies (parasitoids, predators) and are thus contributing to the provision of pest control services (Tylianakis et al., 2004; DiTommaso et al., 2016). Some authors suggest that the decline of many insects and farmland birds is associated with changes in farming practices that adversely affect weeds (Marshall et al., 2003). Weed richness and abundance in arable farming has indeed drastically declined over the last decades as documented in Europe (Andreasen et al., 1996; Baessler and Klotz, 2006). In Northern France, Fried et al. (2009) estimated that weed richness and abundance within arable fields decreased respectively by 44 and 66 % over the last 30 years. These authors also showed that this decline was dependent on the within-field location of weeds, with a much less pronounced decline in crop edges, i.e. the area between the field margin and first row of crop, because this habitat can act as refugia for many weed species (Solé-Senan et al., 2014).

Evaluating the capacity of agroecosystems to provide key resources and how this capacity is affected by farming management is of prime importance to enhance the ecological functioning of agricultural systems. Yet, there are few examples of such assessment at large spatial scales. Evans et al. (2011) evaluated the biomass and energy provided by berries and seeds at a farm scale in relation to the trophic value of such resources for farmland birds. Similarly, Vialatte et al. (2017) estimated the pollen resource provision within an agricultural landscape for hoverflies through the aggregation of mean provision values estimated by plant surveys in different types of semi-natural and cultivated habitats. Many studies have documented weed communities in different agricultural or landscape settings, yet, to our knowledge, no assessment of weed floral and seed resources within an agricultural landscape is yet available. One reason is that most arable weed surveys conducted at large scale are designed to assess the effect farming management or environmental conditions on weed communities (for a review, see Hanzlik and Gerowitt, 2016). The timing of the weed sampling is therefore often driven by agronomic considerations such as the completion of weed management measures (e.g. Hawes et al., 2010) or crop phenology (e.g. Andreasen and Stryhn, 2008). Weeds are often described once in the season, at an earlier or unspecified phenological stage (Hanzlik and Gerowitt, 2016). Such methodology is thus not tailored to assess the production of weed resources within an agricultural landscape. Between earlier phenological stages and the flowering and fruiting stages that are key in the provision of resources to other taxa, weed plant survival and development is likely to be impacted by the environment where it grows. The competition for resources (nutrients, water, light) exerted by the crop on weeds can significantly affect weed survival and growth (Kaur et al., 2018), with an effect often considered as weaker in field edges than in field cores (Cordeau et al., 2012; Perronne et al., 2014) and variable according to the type of crop grown. In addition, even after the completion of weed management operations, farming practices such as nitrogen fertilization can affect weed development (Bàrberi et al., 1997; Kleijn and van der Voort, 1997). The timing, frequency and intensity of these farming practices vary across farming systems and crop types and their adverse effect on weed development likely to be less intense in the edges of the field (Marshall and Moonen, 2002). One can thus expect that the chance for a weed plant to reach the next phenological stages will vary much within the same agricultural landscape, depending on the local plant growing conditions. Assessing this intraspecific variability in weed phenology thus appears a necessary step for assessing the production of weed resources within an agricultural landscape.

In this paper, we assessed the intraspecific phenological variability of 30 weeds species commonly found in arable farming in response to their location in the field (hereafter ‘within-field location’, i.e. field core vs. field edge) and to the crop grown. We monitored the phenology of 685 weed seedling patches across 64 commercial fields and 6 crop types over 6 months. We developed survival curves and estimated indicators of floral resources production (flowering success, starting date and duration of flowering and dry biomass at flowering as a proxy for the amount of flowers) and seed resource production (fruiting success, starting date of fruiting). We tested for the effect of within-field location, crop type and their interaction on the phenological indicators. We expected higher success and higher resource production in the field edge as this within-field location is less affected by farming practices and by crop competition. We also expected weed phenology to respond to the crop grown as the crop tested differed in terms of competitive ability, morphological traits and response to farming management.

Section snippets

Study area

The study was conducted in the monitoring study area of Fénay, a 1000 ha arable farming area located in a plain 10 km south of Dijon in eastern France (47°13′N, 5°03′E). Climatic conditions are continental (mean annual temperature 10.7 °C and precipitation 744 mm) and land use is dominated by arable cropping, i.e. mostly rapeseed/cereals-based rotations. Climatic and soil conditions are quite homogeneous across the area, and such a low variability in pedoclimatic conditions across sampled

Results

The proportion of light reaching the soil surface was significantly higher in field edges than in field cores for all crop types but mustard and oilseed rape. It did not differ between crop types, whether in crop edges or in field cores (Supp. Mat. Fig. S2).

Discussion

A first rationale for this phenological survey was to assess the proportion of plants recorded at seedling stage, and after the completion of weed management operations, that would reach a stage where they provide floral and seed resources. Our results indicate that on average, only 60 % of plants flowered and 50 % fruited; this was mostly due to weed mortality which highly varied among the 30 species. We also expected resource production of individual weed species to be modulated by their

Conclusion

This study provides field-based evidence that the production of trophic resources by 30 individual weed species that are commonly found in arable farming is not a constant. Rather, we evidenced important intraspecific variability in the success of reaching phenological stages that are key to resource provision as well as in the timing of the production of resources in response to within-field location and crop type. It is important to account for this intraspecific variability when evaluating

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

We want to thank the two reviewers who provided many constructive comments on a previous version the manuscript. We thank the staff of UMR Agroécologie who have contributed to the long-term weed monitoring in the Fenay study area (Emilie Cadet, Bruno Chauvel, Emeline Felten, Eric Vieren). We are also grateful to the farmers for granting us access to their fields. This work was funded by the European Union's Horizon 2020 research and innovation program under grant agreement No 727321 (IWM

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