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

Chapter 3 Aboveground–Belowground Linkages, Ecosystem Development, and Ecosystem Restoration 47
effects. These changes in vegetation composition have important consequences
for resource input to the soil. For example, in the first few years of primary
succession, nitrogen input often increases rapidly as a result of colonization by
plant species that are capable of forming symbiotic relationships with bacteria
that fix atmospheric N2(Bradshaw and Chadwick 1980). This is apparent,
for example, through colonization of Lupinus spp. on Mt. St. Helens (Morris
and Wood 1989), Alnus spp. on fresh floodplains (Luken and Fonda 1983),
and Carmichaelia on newly created gravel outwashes (Bellingham et al. 2001).
Concomitant with this are rapid increases in net primary productivity (NPP) and
net accumulation of organic matter in the soil (Schlesinger et al. 1998). This
accumulation is made possible through the steady accumulation of microbial
residues and humified materials, which facilitate soil moisture availability and
nutrient cycling.
Over the past few years, a growing number of studies have investigated how
plant species and community composition affect the community composition
of the soil biota (e.g., Wardle et al. 1999, Porazinska et al. 2003). There is also
recognition that traits of dominant plant species have important indirect consequences
for the belowground subsystem (Wardle et al. 1998, Eviner and Chapin
2003), including the densities and community composition of soil organisms
(De Deyn et al. 2004, Vitecroft et al. 2005). These impacts are especially relevant
for understanding belowground changes that occur during either primary
or secondary vegetation succession, as this literature suggests that changes in
the functional composition of vegetation during succession should be matched
belowground. As such, microbial communities during ecosystem development
in both herbaceous and woody systems show shifts from bacterial to fungal
domination (e.g., Ohtonen et al. 1999), an attribute that is frequently associated
with greater conservation of nutrients (Coleman et al. 1983). Other changes in
soil communities that have been identified during succession include shifts in
nematode taxa from those known to be r-selected to those that are K -selected
(Wasilewska 1994), shifts from domination by arbuscular mycorrhizal fungi to
ectomycorrhizal fungi (Dighton and Mason 1985), increases in the length of
soil food chains (Verhoeven 2002), and enrichment of diversity within trophic
groups (Sigler and Zeyer 2002, Dunger et al. 2004). There is also evidence
that during vegetation succession, changes in the community structure of at
least some belowground groups may be deterministic and consistent across
succession (Hodkinson et al. 2004). It is, therefore, apparent that changes in
the quantity and quality of resources present in soils during the course of vegetation
succession will have important, and often predictable, consequences for
belowground communities.
Just as the aboveground biota influences the belowground biota, so the belowground
biota influences what we see aboveground. Soil organisms affect plant
communities both through a direct pathway and an indirect pathway (Wardle
et al. 2004a, van der Putten 2005) (Fig. 3.1). The direct pathway involves those
organisms that affect plants through being intimately associated with plant roots
(e.g., mycorrhizal fungi, root herbivores, root pathogens) while the indirect
pathway involves decomposer biota that indirectly affect plant growth through
mineralizing or immobilizing plant-available nutrients. Although the literature
is replete with examples that show how both pathways may affect plant growth,
few studies have investigated how belowground community composition affects
plant communities. However, soil pathogens affect successional trajectories in