Speaker
Description
Introduction
Weeds are the most damaging pest for yields in arable crops, as they compete with the crops for light, minerals and water (Oerke, 2006). Because of climate change, crop-weed competition for water is expected to increase.
As water use and crop-weed competition depend on plant morphology (Moreau et al., 2022), we investigated the interspecies diversity in morphological responses to water stress on five weed species (Abutilon theophrasti Medik., Alopecurus myosuroides Huds., Avena fatua L., Geranium dissectum L., Tripleurospermum inodorum (L.) CH Schultz) and two crop species (Triticum aestivum L. - soft wheat and Brassica napus L. - rapeseed), that co-exist in temperate arable cropping systems and pedoclimates.
We focused on traits involved in light competition (Colbach et al., 2019):
- Leaf area to leaf biomass ratio (SLA): efficiency to produce leaf area (for photosynthesis and transpiration) from a given leaf biomass.
- Height to aboveground biomass ratio (HBR): ability to grow taller from a given aboveground biomass (for radiation interception above the canopy).
- Leaf to aboveground biomass ratio (LBR): leaf production efficiency from aboveground biomass.
- Root to total biomass ratio (RBR): propensity to explore soil to uptake water and nutrients.
Material and methods
A greenhouse experiment was performed on a platform equipped with automatic watering systems. Plants were grown in nutrient-rich individual pots, with seven levels of water availability, ranging from 10% to 95% of field capacity. For each species × water treatment combination, five plants were sampled at two phenological stages (early and late vegetative or early vegetative and flowering, depending on the species). Morphological traits were analysed in response to a water stress index. Generic non-linear regressions were fitted, whose response parameters were to characterise interspecies diversity.
Results
For all species, SLA decreased whereas HBR increased with increasing water stress index. RBR and LBR varied less. For most species × stage combinations, the proportion of biomass allocated to roots (vs aboveground organs) increased. LBR response to water stress depended on the combinations (increase, no effect or decrease). G. dissectum and A. theophrasti were the most responsive species for all traits, especially at the flowering stage.
Most species × stage combinations enhanced water uptake ability (RBR increase) and lowered water demand per unit leaf biomass, but some favoured one mechanism. At low stress levels, G. dissectum and flowering A. theophrasti favoured water uptake ability (RBR increase without SLA decrease) whereas early vegetative T. inodorum only reduced demand per unit leaf biomass (SLA decrease without RBR increase). Late vegetative rapeseed and A. fatua kept a better light-interception potential (high HBR).
The species effect explained most of the variability in parameter values, followed by growth stage. In contrast to weeds, water-stressed crop species tended to increase the proportion of biomass allocated to their roots. Most water-stressed dicotyledonous species increased the proportion of aboveground biomass allocated to leaves whereas monocotyledons favoured stems.
Discussion
This study provides new insights on comparative ecology of crop and weed responses to water limitation, and is the first to compare the morphological plasticity of such a wide range of weed species. Trait responses are consistent with the literature (Monaco et al., 2005; Chahal et al., 2018; Moreau et al., 2022). Species × stage combinations had diverse behaviours, which involved different response mechanisms to water stress, in line with Basu et al. (2016)'s plant classification from ‘water savers’ (that reduce transpiration) to ‘water spenders’ (that maximise water uptake). To our knowledge, no studies identified clade- nor status-dependence of RBR and LBR responses to water stress. Additional research is needed to characterise other species and identify generic trends to predict the behaviour of a wider range of weeds. Our formalisms will feed a 3D mechanistic model (Colbach et al., 2021) to predict the outcomes of future climate-dependent crop-weed interactions (Cournault et al. 2024, second presentation in this congress).
References
Basu, S. et al., 2016. https://doi.org/10.12688/f1000research.7678.1
Chahal, P.S. et al., 2018. https://doi.org/10.1017/wsc.2018.47
Colbach, N. et al., 2019. https://doi.org/10.1016/j.fcr.2019.04.008
Colbach, N. et al., 2021. https://doi.org/10.1016/j.fcr.2020.108006
Cournault, Q. et al., 2024. 18th ESA congress, Rennes
Monaco, T.A. et al., 2005. https://doi.org/10.1111/j.1365-3180.2005.00480.x
Moreau, D. et al., 2022. https://doi.org/10.1111/wre.12554
Oerke, E.-C., 2006. https://doi.org/10.1017/S0021859605005708
| Keywords | Morphological plasticity; Water stress; Crop/weed competition; Climate change; Biomass allocation |
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