Decomposition and Invasive Species

Decomposition and Invasive Species 

Terrestial ecosystems are changed by an invasive species's litter decomposition rate.

Studies have shown than on the average, invasive species have 117% higher decomposition rate in comparison to native plants (Ehrenfeld 2010).  Generally, more litter mass is associated with higher input of elements to the soil.  

Invasive plant litter decomposes more quickly because their litter is generally of higher quality with lower carbon:nitrogen and lignin:nitrogen ratios.  Whether due to increased litter mass or increased decomposition rate, the invasive plants frequently have higher net flux of carbon to the soil (Ehrenfeld 2010).

           

There have been several studies that have shown that invasive plants have somewhat faster decomposing litter and nitrogen loss; studies have repeatedly shown faster decomposition and nitrogen cycling for both native and invasive species when they are grown together at a site growing invasive species.  The implication is that in addition to the nature of the litter, there are soil changes caused by the invasive plants that are not well-understood, but seem to favor recycling of all species.  For example, one study in Hawaii compared the invasive nitrogen-fixing tree, Falcataria molucanna, to the native tree that did not fix N₂, Metrosideros polymorpha, and found that following invasion by a Falcataria stand, the litter decomposition rates of both trees increased six times over what it had been in native soil (Hughes 2006).

                                           F. molucanna                             M. polymorpha

                                     

Garlic mustard (Alliaria petiolata) is an invasive plant that is able to suppress competition by secretion of numerous secondary compounds, such as glucosinolates, that suppress spore formation by arbuscular mycorrhizal fungi, a common symbiotic fungus of native plants (Wolf, Klironomos 2005).  Surprisingly, despite the secondary antimicrobial compounds, garlic mustard green rosette leaves consistently accelerated the decomposition of native tree litter and nitrogen immobilization, while it increased soil N and P availability, soil pH, and base cation availability.  Plant tissue volatiles and root exudates had little impact on soil properties or fungi other than AMF’s (Rodgers et al 2007).

Alliaria petiolata

                        

While you might think the larger biomass would lead to higher litterfall mass, this situation does not always occur because of other factors, such as relative carbon allocation to leaves and decomposition rate.  Florida’s invasive tree, Melaleuca, has monoterpene-rich leaves that decompose slowly.  These plant chemicals probably served a protective role against herbivores or disease in their native countries.  The oil content of trees growing in Florida is less than that found in tree of Australia (Ehrenfeld 2003).

Melaleuca quinquenervia

The preceding examples show that invasive species' litter decomposition rates change terrestrial ecosystems.                                                   

References

1. Ehrenfeld, Joan G. (2010). Ecosystem Consequences of Biological Invasions. Annual Review of Ecology, Evolution, and Systematics. 41:59-80.

2. Ehrenfeld, Joan G. (2003). Effects of Exotic Plant Invasions on Soil Nutrient Cycling Processes. Ecosystems. 6:503-523.

3. Hughes, R. Flint, Uowolo, Amanda. Impacts of Falcataria molucanna Invasion on Decomposition in Hawaiian Lowland Wet Forests: The Importance of Stand-level Controls. Ecosystems. Vol. 9:977-991.

4. Rodgers, Vikki L., et al. (2008). The Invasive species Alliaria petiolata (garlic mustard) increases soil nutrient availability in northern hardwood-conifer forests.

Oecologia. 157:459-471.

5. Wolfe, Benjamin E. and John N. Klironomos. (2005). Breaking New Ground: Soil Communities and Exotic Plant Invasion. BioScience. Vol. 53 No. 6:477-487.