Invasive submerged freshwater macrophytes are more plastic in their response to light intensity than to the availability of free CO₂ in air‐equilibrated water

Abstract

1. The future increase in the atmospheric CO 2 concentration is likely to affect the growth and performance of submerged freshwater macrophytes because of higher concentrations of free CO 2 in the water at air equilibrium. We measured the plastic responses to free CO 2 and light for several traits of four invasive aquatic plants (Elodea canadensis, Egeria densa, Hydrilla verticillata and Ceratophyllum demersum) that use bicarbonate. 2. The plants were grown in standard culture media at either high (HiC, c. 50 lmol L À1 ) or low concentrations of free CO 2 (LowC, c. 19 lmol L À1 ) combined with high (HiL, c. 150 lmol m À2 s À1 ) or low (LowL, c. 21 lmol m À2 s À1 ) light intensity in a 2 9 2 factorial experiment. We compared the relative growth rate (RGR), several morphological traits, the photosynthetic response to light intensity and the bicarbonate uptake capacity of the four species. For every trait measured, we established plasticity indices for light and CO 2 availability. 3. Light intensity had a greater effect than CO 2 concentration on all species. The RGR of all four species was higher at high light intensity, and photosynthetic light responses acclimated to low light with a lower light compensation point, and with higher concentrations of photosynthetic pigments and quantum yield. The bicarbonate uptake capacity was generally highest at the high light intensity and high concentrations of free CO 2 . Plasticity indices for light intensity were consistently higher than for CO 2 availability in all four species. 4. As the growth and photosynthesis of the four invasive bicarbonate users were only slightly affected by the CO 2 availability in air-equilibrated water, the future rise in atmospheric CO 2 is unlikely to exacerbate their invasive behaviour and may even reduce their competitiveness against species unable to use bicarbonate, especially at limiting light.

Invasive macrophytes induce context‐specific effects on oxygen, pH, and temperature in a hydropeaking reservoir

“…In the upper-riverine section, E. densa dominates littoral zones forming large, dense and monospecific beds that are rooted to the bottom and can withstand faster flows (Clayton, Matheson, & Smith, 2009). Although both E. densa and C. demersum are found throughout the year, rapid growth occurs in spring: e.g., 2-10% day −1 and 2-8% day −1 of dry biomass, respectively (Eller et al, 2015). Rapid summer growth leads to peak accumulation of biomass in autumn when both species often reach the water surface (Hofstra & de Winton, 2016).…”

Functional Response (FR) and Relative Growth Rate (RGR) Do Not Show the Known Invasiveness of Lemna minuta (Kunth)

“…[30]), with less attention towards floating macrophytes (e.g., Netten et al . [31], Njambuya, Stiers [14]).…”

Light Availability and Patterns of Allocation to Reproductive and Vegetative Biomass in the Sexes of the Dioecious Macrophyte Vallisneria spinulosa

“…Effects of altered light availability on performance of submerged macrophytes are well known (e.g., Xie et al, 2007; Riis et al, 2012; Yuan et al, 2012; Eller et al, 2015), but sex-specific plasticity in sexual dimorphism in response to varied light levels over an entire growing season has not been well characterized. The present study provides evidence supporting the differential plasticity hypothesis in aquatic environment, particularly in the context of sex-specific resource requirements, with insights into evolution of sexual dimorphism in dioecious macrophytes.…”