Mycorrhizal symbioses in the Andean paramo.

Abstract

The Andean paramo, hereafter "paramo", is a Neotropical high-mountain region between the treeline and permanent snowline (3500-4800m) and is considered the world's coolest biodiversity hotspot. Because of paramo's high humidity, solar radiation and temperature variation, mycorrhizal symbiosis is expected to be essential for plants. Existing theory suggests that replacement of arbuscular mycorrhizal (AM) by ectomycorrhizal (ECM) and then ericoid mycorrhizal plants (ERM) can be expected with increasing elevation. Previous findings also suggest that non-(NM) and facultatively mycorrhizal (FM) species predominate over obligatory mycorrhizal (OM) species at high elevations. However, these expectations have never been tested outside of the northern temperate zone. We addressed the distribution and environmental drivers of plant mycorrhizal types (AM, ECM and ERM) and statuses (NM, FM and OM) along the paramo's elevational gradient. We used vegetation plots from the VegParamo database, climatic and edaphic data from online repositories, and up-to-date observation information about plant mycorrhizal traits at species and genus level, the latter being proposed as hypotheses. AM plants were dominant along the entire gradient, and ERM plants were most abundant at the lowest elevations (2500-3000m). The share of FM plants increased and that of OM plants decreased with elevation, while NM plants increased above 4000m. Temperature and soil pH were positively related to the abundance of AM plants and negatively to ERM plants. Our results reveal patterns that contrast with those observed in temperate northern-hemisphere ecosystems.