Clonal intergration of Arundo donax in the riparian zone

Background/Question/Methods

Physiological integration, the sharing of water, carbohydrate, or nutrient resources through interconnected rhizomes, is an important component for clonal growth. The effects and levels of physiological integration can be different among species, size of ramets, and resource availability. This study focused on the invasive riparian reed grass, Arundo donax L., a clonal plant of the family Poaceae that is widely distributed in North America. It is a typical invader with large rhizomes and long groundwater-reaching roots. This study was directed to find out whether A. donax used physiological integration to transport water through interconnected rhizomes as a mechanism to increase growth. Both a rhizome severing experiment and a deuterium labeling experiment were conducted on a naturally-populated, continuous monoculture of A. donax. Five sets of 1-m² paired plots were selected in a randomized complete block design and aboveground plants were removed. On the plot margins of half of the plots we severed rhizomes to 30-cm depth and compared plant growth-related parameters after 3, 7, and 11 weeks. Labeled water (1800‰) was applied to three 1-m² area over 3 successive days. Twenty-five rhizome and three soil samples were collected at distances of 1, 1.5, 2, and 4 m from the watering zone in 5 directions after 5, 24, and 48 hours of last watering. Water from soil and rhizome samples was extracted using a cryogenic vacuum distillation method and the extracted water analyzed by TC/EA-IRMS.

Results/Conclusions

We found evidence of physiological integration in A. donax. Labeled water was transported distances of at least 1.5 m through connected rhizomes; however, we did not detect any at 4.0 m. Rhizome severing stimulated 97% higher ramet propagation initially (p <0.05), while over longer periods, intact rhizomes produced 67% taller stems (p <0.05) with 49% greater diameter (p <0.05) and higher flood tolerance (42% of mortality in isolated plots and 22% in intact plots after flooding, p = 0.072). However, plot-level biomass was similar among plots with severed and intact rhizomes after 11 weeks of re-growth. This implies that A. donax can establish and grow in a new habitat without the support from neighboring ramets, but physiological integration may further increase growth rates, enhance competitive abilities, and strengthen its capability to re-colonize disturbed areas.