The flexural rigidity and bending modulus of kelp, Laminaria hyperborea, collected at the MarGate area (https://www.awi.de/en/science/special-groups/scientific-diving/margate.html) north of Heligoland, Germany (latitude: 54° 11.700'N, longitude: 7° 52.600'E) was determined from measurements performed at the Alfred Wegener Institute (AWI) Helmholtz Centre for Polar and Marine Research. Scientific divers from the Biological Institute Helgoland, AWI, collected nine kelps (Laminaria hyperborea) from the MarGate area on 21.06.2022. The collected kelps were transported into the laboratory in boxes filled with seawater from the site and stored in laboratory sinks filled with running aerated seawater from the North Sea during the experiments. The measurements were carried out on 23.06.2022, 25.06.2022, and 27.06.2022. They consisted of cutting strips 20 cm in length (L) and 2.5 cm in width (b) from the blades close to the stipe of each kelp. The cut-out strips were towel-dried, and their thickness (t, mm) and weight in grams were measured. The weight in grams was converted to weight per unit area (w, N/m²) to compute the flexural rigidity per unit width (J, Nm). A standard ruler with precision for the nearest millimeter was used to measure the length (L), width (b), and cantilever length (l) of strips. The thickness (t) of the strip was measured with a caliper gauge that measured to the nearest 0.01 millimeter. The weight of the strip was measured by a weighing scale (Sartorius, LE323S), which had a precision of 0.001 grams. The cut-out strips from each kelp form the nine samples tested for the bending properties. Each sample is used to repeat the cantilever test four times, i.e., both sides' ends, as Henry (2014) recommended to improve the accuracy. An apparatus consisting of two planes, one angled at 45° (θ = 45°) and the other parallel to the horizontal, was used for the test. The device was clamped onto a table on the horizontal plane. The experimental protocol consists of laying each strip onto the apparatus with the strip's edge coinciding with the apparatus's angled edge. After that, the strip is slowly moved forward with a ruler, with the ruler's zero coinciding with the strip's edge. This is done until the tip of the strip touches the inclined plane. The horizontal projection of the length of the hanging strip is equal to the distance between the ruler's tip and the apparatus's angle, termed the cantilever length (l). The flexural rigidity per unit width (J, Nm) and the bending modulus (Eb, N/m²) are then calculated with the second moment of area (I, m⁴) as in Henry (2014).
Our current understanding of the ecology of lianas and their role in natural ecosystems falls well behind that of most of other plant groups. This gap in current knowledge has potentially serious consequences because (1) climbing plants are known to show significantly enhanced growth under CO2 enrichment (2) many climbing plant species are serious invasive elements in both tropical and temperate ecosystems and cultivated areas and (3) recent censuses of tropical lianas suggest that recent changes in climbing plant growth dynamics might be actually changing vegetation communities in the tropics. These issues therefore beg for detailed studies on the effects of CO2 enrichment on invasive climbing plants. The main aim of this study was to analyse the effects of elevated CO2 concentration on the development, biomass and mechanical properties of two selected invasive climbing species (Ipomoea triloba, Momordica charantia) and an agricultural C4 host plant (Sorghum bicolor) with a new approach on the interface of biophysics and ecophysiology. We investigated a) the effect of elevated CO2 on sorghum without climbers, b) the effect of elevated CO2 on developmental traits of the two invasive species and c) the effect of elevated CO2 on the interaction and crop/climbing plant competition with the effects on growth and yield. Sorghum bicolor plants were grown with two invasive climbing species under ambient (380 ppm) and elevated CO2 (750 ppm) in glasshouse conditions. The results are summarized in three main articles in preparation: First, Sorghum grown alone showed significant differences in biomass allocation between ambinet and elevated CO2, particularly between vegetative and reproductive components and a significant decrease in yield under elevated CO2. In terms of mechanical architecture sorghum plants grown without climbers showed no change in the stiffness of the leaf sheath at elevated CO2 despite increases in vegetative biomass. Second, both liana species showed changes in mechanical, morphological and photosynthetic traits under elevated CO2 resulting in enhanced growth (length + branching). Third, the results from the crop/climbing plant competition experiment demonstrated that the sorghum host plants are more affected under elevated CO2 than ambient CO2 leading to a weakened mechanical architecture and a decrease in panicle biomass and stem carbohydrate production. The results of this study provide fundamental knowledge for the effects of climate change on weed/crop competition and liana growth. Elevated CO2 can potentially increase the invasive climber threat for crops in future which should be taken in account for agricultural management.