Abstract
Recurrent water level fluctuation and submergence of plants are common in riparian zones. Our study objectives were to test the independent and interactive effects of submergence level and fluctuation frequency on a globally important riparian invasive plant, Alternanthera philoxeroides. To this end, we conducted a greenhouse experiment, in which ramets of the plants, obtained from a wetland in China, were treated with four fluctuation frequencies (0, 3, 6, and 12 cycles over a 96-day experimental period) under three water levels (0, 10, and 30 cm). We found that effects of fluctuation frequency were non-significant, negative, and positive under water levels of 0, 10 and 30 cm, respectively. As fluctuation frequency increased, the effects of increasing water level decreased significantly. When water levels were high, A. philoxeroides allocated greater biomass to shoot production probably in order to elongate and escape from submergence. However, as fluctuation frequency increased, biomass investment in roots and leaves also increased, probably in order to maximize nutrient absorption and photosynthesis, respectively. These results suggest that water level fluctuation may alleviate the effects of submergence on A. philoxeroides. In addition, A. philoxeroides showed significant phenotypic plasticity, adjusting its functional traits, such as number of nodes and leaves per stem, as well as stem diameter and pith cavity diameter, according to recurrent water level fluctuation. We conclude that A. philoxeroides may perform better in shallow water zones under conditions of disturbance that include recurrent water level fluctuation. This ability to adapt to disturbance likely promotes its growth and invasion in disturbed habitats.
Highlights
Fluctuating resources and stress are common in various kinds of habitats and have profound consequences for individuals, populations, communities and ecosystems [1,2,3]
At a water level of 10 cm, total biomass at FF4 was significantly higher than at the other three fluctuation frequencies (FF1, FF2 and FF3; F = 6.013, p < 0.01), at the highest water level (30 cm) total biomass was significantly higher for plants exposed to the highest fluctuation frequency (FF1, 12 cycles of fluctuation) than for those exposed to the other three frequencies (6, 3, and 0 cycles; F = 7.140, p < 0.01)
It is known that submergence can inhibit plant growth [4, 12, 15, 27, 32], our study shows that the effects of water level are dependent on fluctuation frequency
Summary
Fluctuating resources and stress are common in various kinds of habitats and have profound consequences for individuals, populations, communities and ecosystems [1,2,3]. Water level fluctuation occurs frequently due to climate change, and human disturbance [4,5,6,7,8,9,10,11]. Other studies have addressed the response of plants to submergence and de-submergence [9, 19], as well as the effects of the amplitude of water level fluctuation [5, 20,21,22,23]. Recurrent water level fluctuation occurs as a result of extreme weather, such as sudden, heavy rainstorms, and artificial disturbances, such as the construction of dams, which control the release of water into rivers. In the face of increasing submergence and water level fluctuation, research on the effects of such ‘recurrence’ on plants in riparian zones is critical. Despite substantial research on the effects of water level fluctuations on riparian and aquatic plants [5, 14, 17, 23], few studies explore the role of recurrent water fluctuation in influencing their growth
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