Abundance of Microbes Involved in Nitrogen Transformation in the Rhizosphere of Leucanthemopsis alpina (L.) Heywood Grown in Soils from Different Sites of the Damma Glacier Forefield

Abstract

Glacier forefields are an ideal playground to investigate the role of development stages of soils on the formation of plant-microbe interactions as within the last decades, many alpine glaciers retreated, whereby releasing and exposing parent material for soil development. Especially the status of macronutrients like nitrogen differs between soils of different development stages in these environments and may influence plant growth significantly. Thus, in this study, we reconstructed major parts of the nitrogen cycle in the rhizosphere soil/root system of Leucanthemopsis alpina (L.) HEYWOOD: as well as the corresponding bulk soil by quantifying functional genes of nitrogen fixation (nifH), nitrogen mineralisation (chiA, aprA), nitrification (amoA AOB, amoA AOA) and denitrification (nirS, nirK and nosZ) in a 10-year and a 120-year ice-free soil of the Damma glacier forefield. We linked the results to the ammonium and nitrate concentrations of the soils as well as to the nitrogen and carbon status of the plants. The experiment was performed in a greenhouse simulating the climatic conditions of the glacier forefield. Samples were taken after 7 and 13 weeks of plant growth. Highest nifH gene abundance in connection with lowest nitrogen content of L. alpina was observed in the 10-year soil after 7 weeks of plant growth, demonstrating the important role of associative nitrogen fixation for plant development in this soil. In contrast, in the 120-year soil copy numbers of genes involved in denitrification, mainly nosZ were increased after 13 weeks of plant growth, indicating an overall increased microbial activity status as well as higher concentrations of nitrate in this soil.

The role of microorganisms at different stages of ecosystem development for soil formation

“…2), where the N content is still low but plant coverage has already strongly increased, which hints at a competition between microbes and plants for N (Brankatschk et al, 2011;Duc et al, 2009). This theory is further corroborated by results from Töwe et al (2010), where the abundance of nifH carrying microbes was highest in the rhizosphere of L. alpina planted in a 10 yr soil, which was connected with the lowest C / N ratios of plant biomass. However, during incubation the N content of L. alpina grown in the 10 yr soil strongly increased while plant and root biomass stayed stable, as shown in Fig.…”

“…The phenomenon of enhanced microbial activity and abundance in the rhizosphere of plants is known as the "rhizosphere effect" (Butler et al, 2003;Hartmann et al, 2008). Regarding the Damma Glacier the rhizosphere effect is generally more pronounced at initial sites compared to developed ones (Töwe et al, 2010;Edwards et al, 2006). This observation seems to be a general effect independent of plant species, bedrock material or climatic conditions.…”

“…Several studies at the Damma Glacier showed that pioneering plants display a nutrient hotspot at initial sites (Töwe et al, 2010;Duc et al, 2009;Miniaci et al, 2007). Thus, much higher abundances and activities of microbes were detected in the rhizosphere of pioneering plants.…”

Abundances and potential activities of nitrogen cycling microbial communities along a chronosequence of a glacier forefield

“…In the last decades, different studies at glacier forefields focused on the dynamic of selected processes and transformation steps of the N cycle Kandeler et al, 2006;Duc et al, 2009;Towe et al, 2010a) because N as a macronutrient is essential for ecosystem development, but most bedrocks do not contain any N.…”

Chemical and microbiological changes in Norway spruce deadwood during the early stage of decomposition as a function of exposure in an alpine setting

“…To build the standard curves we used as templates the purified PCR products of known concentrations of the following pure cultures: Fusarium solani (DSMZ 10696), fungi, and Azospirillum irakense (DSMZ 11586), nifH gene. The primer pairs were FF390/FR1 (fungi; Prévost-Bouré et al 2011) and nifHf/nifHr (nifH gene; Töwe et al 2010). Stock concentration (gene copies µL −1 ) was determined via PicoGreen measurement and was freshly prepared for each run.…”