Impact of Competition and Mycorrhizal Fungi on Growth of Centaurea Stoebe, an Invasive Plant of Sand Dunes

Article excerpt

ABSTRACT.-

Soil biota such as arbuscular mycorrhizal fungi (AMF) have been shown to increase invasive plant species success in a wide variety of systems by providing both direct and indirect benefits to the invader. For example, Centaurea stoebe invasion in the western US is at least partially due to AMF networks allowing Centaurea to parasitize some native plant species. Centaurea also invades sand dune systems of the northern Great Lakes region, which often have reduced or altered soil communities compared to other grasslands. In these habitats, AMF may play a different role in invasion success of this species. We conducted a greenhouse experiment to compare effects of soil biota and AMF on competitive interactions between Centaurea and two varieties of Ammophila breviligulata, a dominant native grass of Great Lakes sand dunes. We found that Centaurea growth was slowed by the presence of Ammophila competitors, while AMF had no direct or indirect effect on growth. Both Ammophila varieties were uninhibited by the presence of Centaurea. The commercially available Cape variety of Ammophila had more than twice the inhibitory effect of a native Michigan variety on Centaurea growth. It does not appear that Centaurea takes advantage of AMF networks in this dune system. Indeed, since Centaurea growth is actually reduced in direct competition with Ammophila, we suspect that invasion of dunes by this species is a result of disturbance. For land managers, planting Ammophila in open areas as part of a restoration plan may slow spread of Centaurea in this system.

INTRODUCTION

Soil biota such as arbuscular mycorrhizal fungi (AMF) have been shown to increase invasive plant species success in a wide variety of systems (Richardson et al., 2000; Bray et al., 2003; Fumanal et al., 2006). AMF can provide direct benefits to invasive plants by increasing nutrient and water uptake (Smith and Read, 1997) and can also provide indirect benefits to plants by altering competitive hierarchies with native species, or even directly transferring resources or carbon between plants (Chiariello et al., 1982; Meding and Zasoski, 2008). However, the generality of these benefits, even for a given plant species, is unknown.

AMF have been shown to have a potential role in the invasion success of Centaurea stoebe L. (formerly C. maculasti or C. biebersteinu; referred to throughout this paper as Centaurea) in the western United States. Centaurea is one of the most problematic invasive species in North America, infesting nearly 7million ha of rangeland in the western United States (Sheley et al., 1998), as well as invading lower productivity prairie, savanna grasslands, and sand dunes in the mid-western US (Emery and Gross, 2005; Marshall and Storer, 2008). In the western US, Centaurea has been known to form near-monocultures in previously grass-dominated rangeland, leading to altered nutrient cycling, desertification, and erosion problems (Rice et al., 1997; Herron et al., 2001) as well as loss of economically important grazing areas. While a more recent invasion, and so less studied, in Great Lakes sand dunes Centaurea appears to overstabilize dune habitat, reducing native plant biodiversity (Marshall and Storer, 2008). For these reasons, Centaurea is actively managed as an invasive species in several state and national parks in the region and is listed as a prohibited noxious weed in Michigan (Michigan Department of Agriculture, 1990). Several greenhouse and field studies have shown that Centaurea gets little or no direct benefit from AMF but may use AMF networks to parasitize some native plant species in western US grasslands (Marier et al., 1999; Callaway et al., 2004; Carey et al., 2004). However, nothing is known about whether similar interactions occur in Great Lakes sand dunes.

As primary successional ecosystems, sand dunes are one of the few habitats where AMF are not ubiquitous. AMF are virtually absent from young or unvegetated dunes (Sylvia, 1986), with AMF diversity and abundance generally increasing with successional age (Koske and Gemma, 1997) and buildup of soil organic matter (Olsson and Wilhelmsson, 2000). …