Abstract
Global temperatures are predicted to increase by 1.5–5.9°C during this century, and this change is likely to impact average rainfall, with predictions that water deficit will perhaps be the most severe threat to sustainable agriculture. In this respect, invasive weeds, which have traits better adapted to drought stress than crops, add to concerns regarding crop sustainability. Lactuca serriola, an aggressive agronomic weed is thought to be a successful weed because of its ability to maintain high water use efficiency under drought conditions. In this study, experiments were conducted to examine the influence of different soil moisture regimes (100%, 75%, 50% and 25% water holding capacity (WHC)) on growth, photosynthetic capacity, leaf biochemistry and reproduction of this species. Soil moisture significantly affected plant’s height, stem diameter, number of leaves and biomass. The highest plant height (115.14 cm ± 11.64), shoot diameter (9.4 mm ± 0.18), leaf area (1206.5 mm2 ± 73.29), plant fresh weight (83.1 ± 3.98) and dry weight (22.38 ± 1.24) were recorded at 75% soil moisture content. A fundamental adaptation to drought was observed as plants in the 25% WHC treatment had the highest root: shoot ratio. Soluble sugars and total phenolic content were highest in the 25% WHC treatment and significantly different to 100% WHC which was a response to soil moisture stress to ameliorate the damaging effects of reactive oxygen species produced under stress conditions. Results also indicate that L. serriola can survive and produce seeds under water stress as more than 6000 seeds were produced per plant in all WHC treatments. In this study, there was no significant difference in the seed weight, number of seeds produced and their germination ability. This can have a huge impact on agricultural systems as the species can survive both under low and high soil moisture conditions. We therefore suggest that the demonstrated ability of L. serriola to complete its life cycle and produce biomass and seeds under water stressed conditions leads to the introduction of strategies that minimize weed survival while maximizing irrigation efficiency for the crop. A clear understanding of the ecological and biological characteristics of this weed will help land managers take appropriate control measures to mitigate the effect of this species on economic crop productivity.
Highlights
Plants undergo or display symptoms of extreme water deficiency when the required levels of moisture are unavailable in their habitat soil
Results obtained from this study show that shoot length, number of leaves, total leaf area, fresh weight and dry weight of L. serriola, all saw a drop when exposed to moisture stress conditions
Exposure of L. serriola to drought stress resulted in decreased growth rate, and reduced biomass production
Summary
Plants undergo or display symptoms of extreme water deficiency when the required levels of moisture are unavailable in their habitat soil This happens when the plants continuously lose water via transpiration or evaporation due to high temperatures and the loss of ground moisture is not refurbished [1]. This extreme dryness, declared as drought, which extends to long periods of time, is prevalent on a global scale. These conditions combine lack of water through rain with high temperatures and radiation, and currently pose the most important environmental threats to plant survival and crop productivity [2]. Prevailing arid conditions is an important factor in weed invasion, as it impacts the competitive establishment, physiology, subsequent growth and reproduction of the mixture of plants in a crop [7], making it an important element of crop production studies
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