Seasonal and latitudinal variation in seagrass mechanical traits across Europe: The influence of local nutrient status and morphometric plasticity

Abstract

Seagrasses are marine flowering plants distributed worldwide. They are however threatened, mostly due to the increase of human activities. Seagrasses have the capacity to adapt their morphological, physiological, and mechanical traits to their local conditions. Mechanical traits have been identified as a good tool to investigate a plant-species capacity to withstand physical forces or disturbances but are still sparsely studied in seagrasses. With this study, we aimed to assess how the mechanical traits of a broadly spread seagrass species vary along a latitudinal gradient in relation to its morphometric plasticity and nutrient status. We found that seagrasses acclimate their mechanical traits in relation to their physiological or morphological traits, both over the growing season and across a latitudinal range: leaves were weaker and thinner in northern areas, particularly at the end of the growing season. Besides the influence of the latitudinal gradient, leaf mechanical strength and stiffness were both strongly affected by their morphometric plasticity. Moreover, we showed that leaves mechanical traits change depending on their nutrient status: leaves were stronger and stiffer in oligotrophic conditions as compared to more eutrophic conditions. Thus, our results imply that, under eutrophication, leaves become weaker and thus more vulnerable to physical forces. This vulnerability is higher in the north at the end of the growing season. The latter is consistent with the more ephemeral character of northern seagrass meadows, in contrast to the more evergreen southern meadows.

Temporal Variability and Within‐Plant Heterogeneity in Blade Biomechanics Regulate Flow‐Seagrass Interactions of Zostera marina

“…As a consequence of the seasonal cycle, all blade biomechanical traits decreased from late summer to spring except material density, which increased. An effect of seasonality on seagrass blade biomechanical traits was also reported by Paul and de los Santos (2019), de los Santos et al 2013and Soissons et al (2018). Focusing on Z. marina, variations in the biomechanical traits reported by Paul and de los Santos (2019) are in general agreement with the findings of the present study, but for a different trend in blade length that they related to the particularly hot climate at their study site.…”

Living in the intertidal: desiccation and shading reduce seagrass growth, but high salinity or population of origin have no additional effect

“…As RGR did not differ between the origins of the populations (e.g., RGR of Saint Jacut was 1.06 times the RGR of Sylt), the size differences at the end of the experiment reflect the differences at the beginning of the experiment. Similar plant size differences between these populations are observed in other years or seasons ( Soissons et al, 2018 ; Govers, 2014 ). Plants originating from the Netherlands (Oosterschelde) were in the middle for all measured traits.…”

“…Perhaps this flexibility may be explained by plants originating from estuarine and shallow coastal conditions (as we used in our experiments) being more used to frequent variations in osmotic stress and thus better able to make fast physiological adaptations, compared to plants from more osmotically stable, true marine environments. Although plants from the three populations differed in plant size and morphology (from big (Saint Jacut), medium (Oosterschelde) to small (Sylt)), in line with the trend over a broader latitudinal gradient for this species (South Spain to Sylt; Soissons et al, 2018 ), their plant size did not influence their ability to cope with emergence or salinity stress.…”

Does Warming Enhance the Effects of Eutrophication in the Seagrass Posidonia oceanica?

“…Carbohydrate reserves in temperate species are fundamental for survival under low-light conditions, especially during winter (Alcoverro et al, 2001;Soissons et al, 2018). A proportion of the carbohydrates used to produce amino acids during nutrient assimilation will certainly go to the production of other compounds such as chlorophylls.…”