Linking Restoration and Ecological Succession (Springer ... - Inecol

Chapter 3 Aboveground–Belowground Linkages, Ecosystem Development, and Ecosystem Restoration 59
can control the success of invaders in their new habitats (e.g., Reinhart et al.
2003, Callaway et al. 2004a and b); important shifts occur in belowground
communities associated with plant invaders (e.g., Kourtev et al. 2003, Belnap
et al. 2005, Yourkonis et al. 2005); and soil organisms can be strongly
involved with invader impacts on native flora or ecosystem properties (e.g.,
Wolfe and Klironomos 2005). For example, soil pathogenic fungi or nematodes
are implicated in the failure of new plant species to invade novel habitats
or to subsequently spread (e.g., Mitchell and Power 2003, Reinhart et al. 2003,
van der Putten 2005), whereas soil mutualists such as N-fixing bacteria or mycorrhizal
fungi may promote the success or spread of invaders (e.g., Richardson
et al. 2000, Klironomos 2002, Wolfe and Klironomos 2005). Plant invaders
may increase ecosystem NPP through higher growth rates or per capita inputs
of C and nutrients to the belowground subsystem than do the resident native
species, thus resulting in higher soil microbial biomass and cascading benefits
to other soil trophic levels such as bacterial and fungal feeding nematodes
(Wardle 2002, Knevel et al. 2004). Further, soil organisms are implicated as
either mediating or controlling invader impacts on other plant species, nutrient
availability, or diversity. For example, the forb Centaurea maculosa has been
shown to function as a successful, high-impact invader in western US grassland
systems because of several mechanisms involving belowground communities
including: sequestering P from neighboring plants via mycorrhizal fungi
(Zabinski et al. 2002); suppressing native plants via allelopathic root exudates
(Bais et al. 2003); and escaping soil pathogens and other enemies from its home
range in eastern Europe and Asia (Callaway et al. 2004a and b, Hierro et al.
2005). These studies illustrate the critical role that belowground communities
can have in the successful establishment, spread, and subsequent impacts of
invasive plants on both native species and ecosystem properties (summarized
in Table 3.2).
Feedbacks between the aboveground and belowground components of
ecosystems have received increasing attention over the past decade, in part because
of the critical role that belowground communities play in linking plant invaders
to changes in resource availability, community composition, and ecosystem
properties (Wardle 2002, Callaway et al. 2004b, Wolfe and Klironomos
2005). Feedbacks between plant species and soil communities have been developed
as models for species coexistence or succession (e.g., Bever 2003,
Packer and Clay 2004), and a working hypothesis that remains largely untested
is that invaders may create different feedbacks with the belowground subsystem
than do the native plant species that they displace (e.g., Callaway et al. 2004b).
Feedbacks may also set systems along different successional trajectories if soil
communities differentially facilitate or suppress later successional species, alter
soil fertility levels, or induce vegetation switches (Wilson and Agnew 1992) and
crossing of thresholds of ecosystem states (Suding et al. 2004). Differences in
plant–soil feedbacks between rare and common plant species or between native
and nonnative invasive species are only beginning to be appreciated, (e.g., van
der Putten et al. 1993, Klironomos 2002), although the available evidence supports
the idea that soil communities are an important, if previously neglected,
driver of invader impacts.
Both the impacts of invaders on belowground properties and processes, and
the feedbacks between the above- and belowground components of ecosystems,
are highly relevant for understanding aboveground successional changes and