Summary The biological and functional diversity of ectomycorrhizal (ECM) associations remain largely unknown in South America. In Patagonia, the ECM tree Nothofagus pumilio forms monospecific forests along mountain slopes without confounding effects of vegetation on plant–fungi interactions. To determine how fungal diversity and function are linked to elevation, we characterized fungal communities, edaphic variables, and eight extracellular enzyme activities along six elevation transects in Tierra del Fuego (Argentina and Chile). We also tested whether pairing ITS1 rDNA Illumina sequences generated taxonomic biases related to sequence length. Fungal community shifts across elevations were mediated primarily by soil pH with the most species‐rich fungal families occurring mostly within a narrow pH range. By contrast, enzyme activities were minimally influenced by elevation but correlated with soil factors, especially total soil carbon. The activity of leucine aminopeptidase was positively correlated with ECM fungal richness and abundance, and acid phosphatase was correlated with nonECM fungal abundance. Several fungal lineages were undetected when using exclusively paired or unpaired forward ITS1 sequences, and these taxonomic biases need reconsideration for future studies. Our results suggest that soil fungi in N. pumilio forests are functionally similar across elevations and that these diverse communities help to maintain nutrient mobilization across the elevation gradient.

No abstract

The effects of tillage on soil structure, physiology, and microbiota structure were studied in a long-term field experiment, with side-to-side plots, established to compare effects of conventional tillage (CT) vs. no-till (NT) agriculture. After 27 years, part of the field under CT was switched to NT and vice versa. Soil texture, soil enzymatic profiles, and the prokaryotic community structure (16S rRNA genes amplicon sequencing) were analysed at two soil depths (0–5, 5–10 cm) in samples taken 6, 18, and 30 months after switching tillage practices. Soil enzymatic activities were higher in NT than CT, and enzymatic profiles responded to the changes much earlier than the overall prokaryotic community structure. Beta diversity measurements of the prokaryotic community indicated that the levels of stratification observed in long-term NT soils were already recovered in the new NT soils thirty months after switching from CT to NT. Bacteria and Archaea OTUs, which responded to NT were associated with coarse soil fraction, SOC and C cycle enzymes while CT responders were related to fine soil fractions and S cycle enzymes. This study showed the potential of managing the soil prokaryotic community and soil health through changes in agricultural management practices.

Nodulation kinetics were analysed in two nitrogen-fixing actinorhizal symbioses that show different pathways for infection: Alnus acuminata H. B. K., which is infected by Frankia ArI3, and Discaria trinervis (Hooker et Arnot) Reiche, which is infected by Frankia BCU110501. Both pairs are incompatible in cross-inoculation experiments. The dose–response effects in nodulation were studied in A. acuminata seedlings using different concentrations of compatible and incompatible bacteria in co-inoculation experiments. Restriction fragment length polymorphism PCR analysis and plant-trapping analysis showed no co-occupation in A. acuminata nodules when plants were co-inoculated with Frankia BCU110501 and Frankia ArI3. Despite the lack of co-occupation, the noninfective BCU110501 could modify the nodulation parameters of the non-host A. acuminata when infective ArI3 was present in the inoculum. The results suggest that although BCU110501 was not able to induce nodulation in A. acuminata, its interaction with the plant could induce autoregulation as if some level of infection or partial recognition could be achieved. We explored the possibility that physiological complementation of the heterologous Frankia BCU110501 for nodulation of A. acuminata originated in the homologous Frankia ArI3 in the presence of compatible root exudates. Despite the possibility of full activation between bacteria and the host, there was no co-infection of Frankia BCU110501 in Alnus or of Frankia ArI3 in Discaria either. These negative results suggest a physical recognition barrier in actinorhizal symbiosis that operates after early interactions, involving something other than root exudates and diffusible factors of bacterial or plant origin, regardless of the infection pathway.