Clonal integration can enable pioneer plants to colonize stressful areas such as coastal foredunes, arguably the most dynamic terrestrial habitats worldwide. Storms can uproot foredune plants, creating barren blowout depressions ripe for recolonization by dune plants like American beachgrass Ammophila breviligulata. We explored the importance of clonal integration among ramets connected by plagiotropic rhizomes expanding into blowouts across growing seasons. In 2017 and 2018, we selected 20 rhizome pairs, equivalent spatially and of similar age as judged by size. We subjected one of each pair to an experimental treatment, where we severed the youngest most distal ramet (Plant I) from its parent (Plant II). For these ramets and for an older ramet (Plant IV) on the same rhizome, we regularly measured physiological stress as fluorescence (Fv/Fm), leaf temperature, and quantified plant growth in height over the growing season along with soil temperature and moisture at 15cm depth and soil surface temperature. Post-experiment, we measured biomass, aspects of root architecture and arbuscular mycorrhizal fungi (AMF) colonization. Lastly, we tracked physiological dyes taken up by roots at a node where there was no shoot, to determine the ramets to which these roots supply water.
Results/Conclusions:
When there were effects of severing the rhizome connecting Plant I to older ramets, performance of Plant I decreased and performance of the older ramets increased, but not all responses were present both years. Specifically, rhizome severance reduced survival and growth of the youngest ramet and increased the biomass of Plant IV without Plant I attached. After controlling for variation in soil temperature and moisture through ANCOVA, severed Plant I showed reduced Fv/Fm, indicating more stress, while older ramets showed increased Fv/Fm. Both years, severance never impacted Plant I root biomass, which regardless of treatment, was greater than older ramets and AMF colonization increased in Plant II when the distal ramet was detached. Water uptake, as tracked by dye, was more often distributed to the youngest ramet but also to older ramets, up to the 13th farthest away. These results suggest that distal ramets are capable of surviving separated from the rhizome independently but are still integrated. Young plant typically viewed as sinks, may serve a foraging role for older ramets as suggested by patterns of AMF colonization. In total, the results support clonal integration as an important mechanism by which plants may come to colonize otherwise inhospitable coastal areas.