Impact of two acquisitive plants on N cycle on different soils: The invasive Fallopia japonica does it and so does the native Dactylis glomerata!

Abstract

Invasive plants may alter ecological and ecosystem processes, including the N-cycle. The Fallopia species complex is a well-studied invasive species whose N-resource acquisition traits define it as an acquisitive species. However, the study of the impacts of invasive plants on the N-cycle never considers the N-acquisition strategy as a reference for choosing another suitable plant control. The purpose of this study is to assess the impacts of an invasive species (Fallopia japonicaFJ) on the N-cycle and to compare with those caused by a native acquisitive species (Dactylis glomerataDG), all compared to unplanted soils. A four-months mesocosm experiment was conducted by growing FJ and DG on nine different soils and measuring their impacts on N-cycle microbial activities (free-living nitrogen fixation FLNF, denitrification DEA, nitrification NEA), on N-mineral forms and on functional N-cycle gene abundance (nifH, AOA, AOB, nirS, nirK) as well as the total bacterial community gene (rRNA 16S). The nine soils differ in microbial enzymatic activities, N-mineral form concentrations, physico-chemical factors, texture, and gene abundances. Plant effects on FLNF, NEA and DEA are only soil dependent and no effect of invasive status was found. In addition, the native plant DG generally affected microbial parameters over a wider range of soils than the invasive plant. Stronger impacts of the native DG on microbial gene abundances were found compared to the invasive FJ. A stronger effect of the invasive plant was found for the soil NO3− concentration, with a significant decrease under the FJ than under the DG. Under both FJ and DG, NH4+ concentrations were not significantly affected. In conclusion, the invasive status in the ecosystem of the two plants studied cannot be explained through their impacts on microbial enzymatic activities and gene abundances of the soil N-cycle and the soil N mineral pools.