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Importance of soil microbial communities for restoration

Soil microorganisms are essential for soil functioning, particularly organic matter decomposition and nutrient cycling. They are a key factor in the regulation of plant productivity and community dynamics and for soil structural generation. Their study should be an essential part of any project related to ecosystem restoration. However, soil microbes have only recently become a focus of study in restoration ecology.

Carpobrotus edulis (L.) N. E. Br. (Aizoaceae)

Carpobrotus edulis (L.) N. E. Br. (Aizoaceae), native to South Africa, is one of the most invasive plants of rocky shorelines and dunes in many parts of the world. It is also one of the most thoroughly studied invasive species. It was originally introduced to Europe, California and Australia to stabilize coastal sand dunes in the early 20th century.

The functional capacity of soil microbial community varies among soils dominated by different plant species. Consequently, when the species composition of a community is substantially changed due to the invasion of an alien plant, there are often profound changes in nutrient cycling processes. C·I·B post-doc Ana Novoa and her co-workers studied this phenomenon and its implications (mainly as part of her PhD thesis at the University of Vigo) to inform plans to restore several areas invaded by the succulent species Carpobrotus edulis (L.) N.E.Br. in the Iberian Peninsula.

Carpobrotus edulis, a perennial clonal plant native to South Africa, is novel in many respects compared to the native plants in the ecosystems it has invaded: it differs in size, spatial distribution, litterfall dynamics, decomposition rate and overall functionality. These differences bring about important changes in the quality of soil microsites. Until now, soils in areas invaded by C. edulis were thought to have lower pH and a higher percentage of organic matter and more available nitrogen than those unaffected by C. edulis. Research by Novoa et al. has showed that responses of soils to C. edulis invasion depend on the initial characteristics of the invaded ecosystems. For example, during the absorption of nutrient ions, roots of C. edulis roots release H+ or OH- depending on the initial soil pH, in order to maintain electrical neutrality. Soil pH levels have a direct influence on the availability of phosphorus and nitrogen.

Just how such effects affect plant community composition, diversity, succession, microbial communities, and what this means for restoration, was poorly understood before these studies were done. The research showed that these effects influence the function of soil microbial communities and constrain the establishment of native plant species in dune vegetation. Moreover, after the removal of the invasive species, regenerating dunes are occupied by opportunistic ruderal species that, thanks to the invasion-induced changes to soil characteristics, compete with native dune plants of conservation value, restricting their establishment.

These studies have provided important insights into the difficulties encountered by managers dealing with this invasive species. The results should serve not only to enhance restoration strategies in areas invaded by C. edulis, but also to improve the understanding of soil residual effects in restoration projects in general.




Read the papers:

Novoa, A., Rodríguez, R., Richardson, D., & González, L. (2013) Soil quality: a key factor in understanding plant invasion? The case of Carpobrotus edulis (L.) NE Br. Biological Invasions (doi: 10.1007/s10530-013-0531-y).

Novoa, A., González, L., Moravcová, L., & Pyšek, P. (2013). Constraints to native plant species establishment in coastal dune communities invaded by Carpobrotus edulis: Implications for restoration. Biological Conservation, 164, 1-9.

Novoa, A., González, L., Moravcová, L., & Pyšek, P. (2012). Effects of soil characteristics, allelopathy and frugivory on establishment of the invasive plant Carpobrotus edulis and a co-occurring native, Malcolmia littorea. PloS one, 7(12), e53166.

For more information, contact Ana Novoa at anan@sun.ac.za