Microbial community structure and functions differ between native and novel (exotic-dominated) grassland ecosystems in an 8-year experiment

Authors: SIELAFF, ALEKSANDRA - Iowa State University; UPTON, RACHEAL - Iowa State University; HOFMOCKEL, KIRSTEN - Pacific Northwest National Laboratory; XU, XIA - Iowa State University; Polley, Herbert; WILSEY, BRIAN - Iowa State University

Submitted to: Plant and Soil
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/20/2018
Publication Date: 11/1/2018
Publication URL: http://handle.nal.usda.gov/10113/6168895
Citation: Sielaff, A.C., Upton, R.N., Hofmockel, K., Xu, X., Polley, H.W., Wilsey, B. 2018. Microbial community structure and functions differ between native and novel (exotic-dominated) grassland ecosystems in an 8-year experiment. Plant and Soil. 432:359-372. https://doi.org/10.1007/s11104-018-3796-1.
DOI: https://doi.org/10.1007/s11104-018-3796-1

Interpretive Summary: Disturbances and plant introductions have transformed the plant species composition of grasslands. In many parts of the world, the native species that formerly dominated grasslands have been displaced by introduced (exotic) plant species. This shift to exotic dominance has affected grassland productivity, plant species diversity, and the timing of maximum growth, but effects on the soil microbial community that regulates element cycling and soil carbon storage remains unresolved. We sampled microbial communities in soil beneath different combinations (mixtures) of all exotic or all native perennial plant species that had been grown on the same soil type in central Texas, USA for 8 years. Plant species mixtures either had been irrigated each summer to simulate effects of an anticipated increase in tropical storm activity or not irrigated. Fungal community composition differed consistently between exotic and native plant assemblages. By contrast, native-exotic differences in bacterial communities occurred only in certain years. Differences in fungal composition between native and exotic plant mixtures lead to differences in plant availability of soil nitrogen and phosphorus. Nitrogen and phosphorus availability was higher under native than exotic plant mixtures. Results indicate that conversion of native to exotic grasslands may lead to a marked shift in the composition of soil fungal communities that, in turn, reduces the availability of nitrogen and phosphorus to plants. Results recommend heightened efforts to protect native-dominated grasslands and restore native dominance in exotic-invaded grasslands when practical.

Technical Abstract: Aims - Grasslands dominated by non-native (exotic) species have replaced those dominated by native species in many parts of the world forming ‘novel’ ecosystems. It is still poorly understood how soil microbial communities and their functions are affected between these native- and exotic-dominated sites. Methods - We sampled 64 experimental grassland plots in central Texas with plant species mixtures of either all native or all exotic species; half with summer irrigation. We tested how native vs. exotic plant species mixtures and summer irrigation affected bacterial and fungal community composition and structure, microbial phylotype co-occurrence, and rates of mineralization across sampling years. Results - Plant origin significantly affected fungal community composition and structure, but not diversity, throughout the length of the study, while changes in bacterial communities were limited to certain years. Nitrogen and phosphorus mineralization rates were higher under native plant mixtures, and correlated with changes in particular fungal species. Microbial communities were more structured in exotic than native grassland plots, especially for the fungal community. Conclusions - The results indicate that conversion of native to exotic grasslands will more strongly impact fungal than bacterial communities structure. Furthermore, these impacts can alter ecosystem functioning belowground via changes in nitrogen and phosphorus cycling.