Impact of plant elicitors on ammonia-oxidizing root and rhizosphere communities in winter wheat

Sammanfattning

Nitrogen is one of the essential nutrients for plants. Nitrogen is taken up as ammonium (NH4+) or nitrate (NO3-) from roots. If not taken up by the plants, nitrate can be lost to the atmosphere by denitrification which contributes to the global warming. Nitrate can leach out in aquatic systems, this can cause eutrophication, thus it’s important to save the nitrogen in soil. Nitrate can be added as fertilizer or produced by a microbial process called nitrification. The first step of nitrification is the oxidation of ammonia, done by ammonia oxidizing archaea, ammonia oxidizing bacteria and comammox (Nitrospira). This first step is also the rate limiting step of this process. Plant elicitors such as cis-jasmone, methyl jasmonate and methyl salicylate are used in pest management but there are also indications that they trigger the production of secondary metabolites that can be found in root exudates and inhibit ammonia oxidizers. However, our knowledge on their effect on soil microbes remains limited. The hypothesis was that treating winter wheat with elicitors will alter the soil ammonia-oxidizing communities without negatively affecting plant performance. The first aim was to determine the abundance, composition and activity of the ammonia oxidizing root and rhizosphere communities. The second aim was to measure plant traits both above- and below ground. The third aim was to assess effects of ammonium availability of the elicitor treated plants. The elicitor treatments showed most effects in the fertilized pots. The elicitors had most significant effects on the ammonia-oxidizing root communities compared to the rhizosphere communities. Methyl jasmonate showed most significant effects and methyl salicylate showed second most significant effects of both decreased microbial abundance and changed community composition. In both cases the plant traits were positively affected except for the shoot biomass. However, it is possible that this effect is temporary and that a longer growth period would allow an increase in the shoot biomass. Cis-jasmone showed no significant effect on microbial abundance but a trend of changed composition. Cis-jasmone positively affected below-ground plant performance. Methyl jasmonate seems to be the most promising elicitor and methyl salicylate is the second promising elicitor. Cis-jasmone is still interesting, showing positive effects on plant performance although limited effect on microbial abundance. Fertilizer as ammonium chloride increase the effects of the elicitor treatments limited to the roots microbial community. We should continue use cis-jasmone, methyl jasmonate and methyl salicylate to see how they can be used in practical agriculture and in different crops.