Aspects of Invasiveness of Ludwigia and Nelumbo in Shallow Temperate Fluvial Lakes

Abstract

The relationship between invasive plant functional traits and their invasiveness is still the subject of scientific investigation, and the backgrounds of transition from non-native to invasive species in ecosystems are therefore poorly understood. Furthermore, our current knowledge on species invasiveness is heavily biased toward terrestrial species; we know much less about the influence of allochthonous plant traits on their invasiveness in aquatic ecosystems. In this paper, we present the results of a study on physiological and ecological traits of two introduced and three native macrophyte species in the Mantua lakes system (northern Italy). We compared their photophysiology, pigment content, leaf reflectance, and phenology in order to assess how the invasive Nelumbo nucifera and Ludwigia hexapetala perform compared to native species, Nuphar lutea , Nymphaea alba , and Trapa natans . We found L. hexapetala to have higher photosynthetic efficiency and to tolerate higher light intensities than N. nucifera and the native species especially at extreme weather conditions (prolonged exposure to high light and higher temperatures). Chlorophyll a and b, and carotenoids content of both allochthonous species were substantially higher than those of native plants, suggesting adaptive response to the ecosystem of Mantua lakes system. Higher variability of recorded data in invasive species was also observed. These observations suggest advanced photosynthetic efficiency of the invasive species, especially L. hexapetala , resulting in faster growth rates and higher productivity. This was supported by the evaluation of seasonal dynamics mapped from satellite remote sensing data. This study provides empirical evidence for the relationship between specific plant physiological traits and invasiveness of aquatic plant species, highlighting the importance of trait studies in predicting ecosystem-level impacts of invasive plant species.

Impact of invasive alien plants on native plant communities and Natura 2000 habitats: State of the art, gap analysis and perspectives in Italy

“…Bolpagni (2013aBolpagni ( , 2013b and Bolpagni et al (2017) found that Lagarosiphon major and Elodea nuttallii create extensive submerged meadows that almost completely replace native macrophyte communities belonging to N2000 habitats 3140 and 3150. Nelumbo nucifera and Ludwigia hexapetala seem to actively compete with native species (Bolpagni et al, 2014b;Villa et al, 2017Villa et al, , 2018Tóth et al, 2019) due to their enhanced competitive ability for limiting resources and their tolerance to edaphic conditions variability (Tóth et al, 2019). Some studies focused on the impact of Lemna minuta on freshwater ecosystems.…”

Leaf reflectance can surrogate foliar economics better than physiological traits across macrophyte species

“…The Superior, Middle and Inferior lakes are characterized by high turbidity and eutrophic conditions, and the water level is kept fixed to prevent flooding the city of Mantua. Macrophyte communities in the system are populated by both native ( T. natans, N. lutea , N. alba in open water areas, and P. australis in wetlands) and alien species [ 46 , 59 , 60 ]: Nelumbo nucifera Gaertn., introduced into the lake around a century ago, and Ludwigia hexapetala (Hook. & Arn.)…”

“…Leaf reflectance in the visible to shortwave infrared range (350–2500 nm, with a spectral resolution of 3 nm for wavelengths under 1000 nm, and < 8 nm up to 2500) was measured using a portable full range spectroradiometer (SR-3500, Spectral Evolution, Lawrence, USA), following the protocol described in Tóth et al [ 60 ]. After 20-min dark adaptation, leaves were laid on a flat neoprene plate (reflectance factor < 5%) to minimize background reflection of light transmitted through the leaves.…”

“…Data were collected occasionally between 09:00 and 15:00, standard solar time. Relevant fluorescence yield data (initial fluorescence yield—F 0 , maximal fluorescence yield—F m ) were measured following the protocol described in Tóth et al [ 60 ] on mature, healthy-looking leaves after a dark-adapting period of 20 min with a pulse of a saturated light (630 nm, intensity 3000 μmol m −2 s −1 ). Photochemical PSII efficiency (F v /F m ), coefficient of photochemical quenching (qP), coefficient of non-photochemical quenching (qN), maximum electron transport rate of the photosystem II (PSII) (ETR max ), theoretical saturation light intensity (I k , and maximum quantum yield for whole chain electron transport (α were calculated using fluorescence yield data and a light response curve—with ETR measured as a function of photosynthetically active radiation (PAR; 11 steps between 5 and 787 μmol m −2 s −1 )—described by an exponentially saturating equation [ 62 ].…”

“…Half of the discs sampled were stored at – 20 °C in a freezer, to be used for pigments extraction, following the protocol described in Tóth et al [ 60 ]. Upon extraction, they were homogenised in liquid N 2 in a grinder, subsequently extracted in acetone solution (80%), and stored in a fridge overnight.…”