Effect of an invasive grass on ambient rates of decomposition and microbial community structure: a search for causality

Abstract

In situ decomposition of above and belowground plant biomass of the native grass species Andropogon glomeratus (Walt.) B.S.P. and exotic Imperata cylindrica (L.) Beauv. (cogongrass) was investigated using litter bags over the course of a 12 month period. The above and belowground biomass of the invasive I. cylindrica always decomposed faster than that of the native A. glomeratus. Also, belowground biomass of both species decomposed at a consistently faster rate when placed within an invaded area consisting of a monotypic stand of I. cylindrica as opposed to within a native plant assemblage. However, there was no similar such trend observed in the aboveground plant material. The microbial communities associated with the invaded sites often differed from those found in the native vegetation and provide a possible causal mechanism by which to explain the observed differences in decomposition rates. The microbial communities differed not only compositionally, as indicated by ordination analyses, but also functionally with respect to enzymatic activity essential to the decomposition process. This study supports the growing consensus that invasive plant species alter normal ecological processes and highlights a possible mechanism (alteration of microbial assemblages) by which I. cylindrica may alter an ecosystem process (decomposition).

Cogongrass (Imperata cylindrica) invasions in the US: Mechanisms, impacts, and threats to biodiversity

“…Disturbance and allelopathy were the most often tested mechanisms, and while disturbance appears to enhance cogongrass spread, considerable uncertainty remains regarding the relative importance of allelopathy due to limited evidence of below-ground chemical transfer and a lack of trials on native plant species. Observational studies have suggested that cogongrass invasions impact native plant diversity and fine fuel loads (Brewer, 2008;Platt and Gottschalk, 2001), and experimental evidence indicates that cogongrass can alter nitrogen cycling and decomposition rates (Daneshgar and Jose, 2009a;Hagan et al, 2013a;Holly et al, 2009). However, we found no studies on how cogongrass invasions impact arthropod diversity, soil microbial communities, carbon cycling, or hydrology, which are all possible effects of plant invasions (Powell et al, 2013;Pyšek et al, 2012;van Hengstum et al, 2014).…”

“…The putative impacts of cogongrass invasions include community-level effects on native plant diversity and performance (Brewer, 2008) and ecosystem-level impacts on nutrient cycling (Daneshgar and Jose, 2009a), disturbance regimes (Platt and Gottschalk, 2001), and decomposition (Holly et al, 2009). Because cogongrass is a federally listed noxious weed (USDA and NRCS, 2005), and appears to spread rapidly and significantly impact communities (reviewed by MacDonald, 2004), establishing management strategies based on reliable data is a critical step toward conserving vulnerable habitats and native biodiversity.…”

Non‐additive effects of invasive tree litter shift seasonal N release: a potential invasion feedback

“…As a consequence, many have suggested that invasive plants benefi t from strong soil nutrient feedbacks (Allison and Vitousek 2004, Liao et al 2008, Ehrenfeld 2010, Lee et al 2012. While these feedbacks are often attributed to altered microbial communities (Hawkes et al 2005, Holly et al 2009, Lee et al 2012), a growing body of literature suggests that the decomposition of leaf litter also contributes to positive feedbacks (Wolkovich et al 2009, Eppinga et al 2011, Castro-D í ez et al 2012.…”

No apparent effects of soil inoculum on green frog (Lithobates clamitans Latreille) tadpole performance

“…Having this information would allow us to better understand why tadpoles responded to our treatments the way they did. Several studies show that plant invasions alter microbial community composition and function (Kourtev et al 2002;Hawkes et al 2005;Hawkes et al 2006;Holly et al 2009). It is important to note that we did not assess differences in microbial communities among our soil inocula.…”

“…Plant invasions often increase rates of litter decomposition (reviewed by Liao et al 2008, but see Godoy et al 2010, and recent research suggests that invasive plants may cultivate microbial communities that specialize in breaking down their own litter (Holly et al 2009). In this study, we examined whether establishment of introduced European genotypes of Phragmites australis (common reed, Saltonstall 2002), a widespread wetland plant invader (for a synopsis of documented and suspected ecosystem impacts see Marks et al 1994;Weis and Weis 2003;Meyerson et al 2008), would affect the function of wetlands as larval habitat for a widespread North American amphibian (Lithobates clamitans Latrielle, green frog).…”