Clonal Integration and the Expansion of Phragmites australis

Abstract

The recent expansion of the reed Phragmites australis in western Atlantic salt marshes has become a conservation concern. Historically, Phragmites was restricted to the terrestrial border of marshes, but now it aggressively invades lower elevations. To explore factors influencing this expansion, we examined (1) the effects of physical factors and competitive interactions on the performance of Phragmites and (2) the role of clonal integration on the ability of Phragmites to invade low marsh habitats.We transplanted Phragmites into vegetation along an elevation gradient, with and without neighboring plants. Phragmites died when transplanted to the lowest marsh zone but survived and expanded in higher marsh zones. This suggests that the low oxygen availability characteristic of waterlogged soils limits Phragmites growth in the low marsh. Neighboring vegetation reduced Phragmites growth in all zones, and severing Phragmites rhizomes invading the low marsh reduced the survivorship and photosynthetic rate of ramets.These results suggest that Phragmites may invade low marsh habitats by initially establishing itself in the high marsh and then expanding into lower, less favorable habitats using clonal integration. This has important implications for understanding the changing dynamics of New England salt marsh plant communities and developing management strategies for the control of Phragmites.

Long-term effects of a Phragmites australis invasion on birds in a Lake Erie coastal marsh

“…The rhizomes of P. australis are resilient to a number of stressors and are able to withstand temperature lows of -20 o C, fire, disease, predators, and water stress (Mal and Narine, 2004), allowing them to disperse large distances. Vegetative growth also allows P. australis to expand into areas with deeper water than seeds could germinate in (Amsberry et al, 2000).…”

Interactions among Plant Species and Microorganisms in Salt Marsh Sediments

“…Changes in soil physicochemical conditions that occur because of nutrient enrichment or increasing disturbance due to human activities can alter the pattern of plant zonation. Increased levels and availability of nitrogen, for example, might facilitate the growth of invasive plant species like the highly competitive C 3 grass Phragmites australis, which is capable of exploiting enhanced nutrient resources (2), and result in the displacement of native plant species, such as S. patens.…”

Morphometric structural analysis ofPhragmites australisstands in Lake Balaton

“…Basic morphological units of Phragmites (ramets) are not considered a discrete entity due to physical (and thus physiological) interconnections with other ramets via associated rhizomes. The interconnected clone represents the basic physiological unit of Phragmites, which is able to independently interact with the given environment (Pitelka and Ashmun, 1985;Hara et al, 1993;Amsberry et al, 2000). This hierarchical structure of reed stands is well established, but is often overlooked in morphological studies.…”

“…As a result of the rationalized distribution of nutrients and photosynthates within a clone, the physiological interaction of ramets leads to the standardization of morphological properties: ramets in need and growing shoots are supported by plants with greater access to resources (Pitelka and Ashmun, 1985;Hara et al, 1993;Amsberry et al, 2000). Although this is not a reed-specific feature (Stueffer et al, 1996;Schwinning and Weiner, 1998;Oborny et al, 2000), Phragmites is one of the few species that is able to efficiently exploit the capabilities of physiological integration and thus grow in monocultures.…”

“…One of the most important structuring features of clonal Phragmites is the physiological integration of genets (clones), which facilitates intraclonal cooperation (Pitelka and Ashmun, 1985;Hara et al, 1993;Amsberry et al, 2000), and thus substantially influences competition within a reed stand. Biotic and abiotic factors, together with predominantly vegetative reproduction shape the borders between clones within a reed stand (Ailstock and Center, 2000;Santamarı´a, 2002).…”