Abstract
Melinis minutiflora is an invasive species that threatens the biodiversity of the endemic vegetation of the campo rupestre biome in Brazil, displacing the native vegetation and favouring fire spread. As M. minutiflora invasion has been associated with a high nitrogen (N) demand, we assessed changes in N cycle under four treatments: two treatments with contrasting invasion levels (above and below 50%) and two un-invaded control treatments with native vegetation, in the presence or absence of the leguminous species Periandra mediterranea. This latter species was considered to be the main N source in this site due to its ability to fix N2 in association with Bradyrhizobia species. Soil proteolytic activity was high in treatments with P. mediterranea and in those severely invaded, but not in the first steps of invasion. While ammonium was the N-chemical species dominant in plots with native species, including P.mediterranea, soil nitrate prevailed only in fully invaded plots due to the stimulation of the nitrifying bacterial (AOB) and archaeal (AOA) populations carrying the amoA gene. However, in the presence of P. mediterranea, either in the beginning of the invasion or in uninvaded plots, we observed an inhibition of the nitrifying microbial populations and nitrate formation, suggesting that this is a biotic resistance strategy elicited by P. mediterranea to compete with M. minutiflora. Therefore, the inhibition of proteolytic activity and the nitrification process were the strategies elicited by P.mediterranea to constrain M.munitiflora invasion.
Highlights
The Serra do Rola Moça State Park (PESRM), located in the state Minas Gerais (Brazil), covers an area of 3,924 ha and hosts one of the most important preserved areas of the campo rupestre biome
One of the most reported strategies elicited by invasive species is the increase in soil nitrate, which has been related with a positive feedback for the AOA17, and the ammonia-oxidising bacteria (AOB) nitrifying community[3,15,16] and or by a negative feedback via the inhibition of the denitrifying microbial community[14]
The 16S rRNA gene sequences of the isolated strains were compared with those kept in EzBiocloud, a database containing the sequences of the 16S rRNA genes of the type strains of all bacterial species, and the results showed that they belonged to the genus Bradyrhizobium
Summary
The Serra do Rola Moça State Park (PESRM), located in the state Minas Gerais (Brazil), covers an area of 3,924 ha and hosts one of the most important preserved areas of the campo rupestre biome. Melinis minutiflora displayed a positive feedback with the nitrogen cycle by increasing nitrate and the AOB-nitrifying community in an invaded campo rupestre site[3] These authors found that the main nitrogen source for the site was represented by biological nitrogen fixation performed by the prevalent leguminous species Mimosa pogocephala, which was associated with Burkholderia nodosa, assuring soil N fertility. We hypotized that (1): the N-fixing leguminous species are the main N source in the campo rupestre, making the ammonium-N, the predominant chemical species available to other plants, and that (2) M.minutiflora disrupts the soil N cycling by increasing soil nitrate via a positive feedback over nitrifying microorganisms as a general mechanism of invasion. The overall aim of this study was to understand the general mechanism of M. minutiflora invasion in order to develop adequate management strategies for the control of this species in the campo rupestre
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