Diversity and functional responses of nitrogen-fixing microbes to three wetland invasions

Abstract

Impacts of invasive species on microbial components of wetland ecosystems can reveal insights regarding functional consequences of biological invasions. Nitrogen fixation (acetylene reduction) rates and diversity of nitrogen fixers, determined by genetic fingerprinting (T-RFLP) of the nifH gene, were compared between native and invaded sediments in three systems. Variable responses of nitrogen fixing microbes to invasion by a non-native mussel, Musculista senhousia, and mangrove, Avicennia marina, in Kendall FrostNorthern Wildlife Preserve (Mission Bay) and salt cedar, Tamarisk (Tamarix spp.) in Tijuana Estuary suggest microbes respond to both species-and sitespecific influences. Structurally similar invaders (the mangrove and salt cedar) produced different effects on activity and diversity of nitrogen fixers, reflecting distinct environmental contexts. Despite relative robustness of microbial community composition, subtle differences in total diversity or activity of nitrogen fixers reveal that microbes are not immune to impacts of biological invasions, and that functional redundancy of microbial diversity is limited, with significant consequences for functional dynamics of wetlands.

Environmental tolerances of rare and common mangroves along light and salinity gradients

“…However, the widespread native species Avicennia and Rhizophora were only slightly more sensitive to alterations in light and salinity, and they too have proven to be effective invaders outside their native range. Avicennia germinans has recently spread north through the Texas Gulf Coast and Florida salt marshes (Stevens et al 2006;Perry and Mendelssohn 2009;Cavanaugh et al 2014), and A. marina, intentionally introduced from New Zealand to Mission Bay in San Diego, CA, USA in 1968, became invasive during the 1970s and again in 2006, despite removal efforts (Moran 1980;Sauer 1988;Moseman et al 2008). Rhizophora mangle was introduced to Hawaii in 1902, where it is now well established and vigorously expanding its local distribution (Krauss and Allen 2003;Chimner et al 2006), as is R. stylosa, which was introduced to two of the Society Islands of French Polynesia in about 1946 (Taylor 1979;Smith 1996).…”

Microbial community shifts influence patterns in tropical forest nitrogen fixation

“…Previous research suggests that the distribution and activity of both symbiotic and free-living N-Wxers are regulated by temperature (Hicks et al 2003) and moisture (Roskoski 1980), and by the availability of both micro-and macro-nutrients (Vitousek and Howarth 1991), particularly phosphorus (P) (Eisele et al 1989;Benner and Vitousek 2007;Reed et al 2007b). Physiological diVerences among N-Wxing organisms can also regulate N Wxation rates in natural settings (Sprent and Sprent 1990); however, investigations of organismal controls over terrestrial N Wxation rates typically include studies of legumes and the microbial N-Wxing organisms residing in their roots (but see Yeager et al 2004;Hsu and Buckley 2009;Moseman et al 2009). While symbiotic N Wxation may provide the dominant input of biologically Wxed N to some ecosystems (Cleveland et al 1999), research suggests that free-living organisms can account for a signiWcant proportion of total N Wxation (Cleveland et al 1999), particularly in temperate and tropical forests (Parkin 1987;Gehring et al 2005;Perez et al 2008;Reed et al 2007a).…”

“…However, a growing body of evidence suggests that microbial community composition also regulates fundamental ecosystem processes (Balser and Firestone 2005;Waldrop and Firestone 2006;Reed and Martiny 2007;Strickland et al 2009), and links between microbial community structure and function have been demonstrated for soil processes such as denitriWcation (Cavigelli and Robertson 2000), nitriWcation (Carney et al 2004), and methanotrophy (Gulledge et al 1997). Relationships between N-Wxer communities and N Wxation rates have been investigated for soils in temperate wetlands (Moseman et al 2009), desert systems (Yeager et al 2004), and in agricultural lands (Hsu and Buckley 2009), yet links between community and free-living N Wxation rates in tropical ecosystems remain poorly studied. Furthermore, we are aware of no study that has explicitly explored the N-Wxing communities occupying N Wxation hotspots.…”

Are mangroves in the tropical Atlantic ripe for invasion? Exotic mangrove trees in the forests of South Florida

“…Despite eradication attempts, this mangrove persists and its population is expanding. The invasion of the salt marsh by mangroves caused changes in nitrogen cycling in the sediments (Moseman et al 2009). The cycling of the detrital material produced by mangrove forests, essential to coastal food webs in South Florida, may be altered by the presence of B. gymnorrhiza and Lumnitzera racemosa.…”