Environmental changes in biodiversity hotspot ecosystems of
South Ecuador: RESPonse and feedback effECTs (FOR2730)

Abstract:

In undisturbed tropical montane rainforests massive organic layers accommodate the majority of roots and only a small fraction of roots penetrate the mineral soil. We investigated the contribution of vegetation to slope stability in such environments by modifying a standard model for slope stability to include an organic layer with distinct mechanical properties. The importance of individual model parameters was evaluated using detailed measurements of soil and vegetation properties to reproduce the observed depth of 11 shallow landslides in the Andes of southern Ecuador. By distinguishing mineral soil, organic layer and aboveground biomass, it is shown that in this environment vegetation provides a destabilizing effect mainly due to its contribution to the mass of the organic layer (up to 973 t ha
1 under wet conditions). Sensitivity analysis shows that the destabilizing effect of the mass of soil and vegetation can only be effective on slopes steeper than 37.9. This situation applies to 36% of the study area. Thus, on the steep slopes of this megadiverse ecosystem, the mass of the growing forest promotes landsliding, which in turn promotes a new cycle of succession. This feedback mechanism is worth consideration in further investigations of the impact of landslides on plant diversity in similar environments.

Abstract:

Natural ecosystems across the globe are already modified in their structure and composition. This often leads to a decline of biodiversity which can in turn affect important ecological functions. Species richness as a measure of biodiversity ignores almost 89% of the overall diversity and many traits of species show a phylogenetic signal. Therefore, phylodiversity is often a better indicator of functional processes than species richness. To better understand changes in ecosystem functionality it is thus essential to study and compare taxonomic and phylogenetic diversity patterns across environmental gradients such as elevation. In this study I therefore analyse the effects of elevation and soil parameters on the taxonomic and phylogenetic diversity of tree communities in an Andean mountain rainforest in southern Ecuador. 427 tree species were recorded on 54 plots at three elevation levels at 1000, 2000 and 3000 m, with phyloalpha diversities ranging between -1.91 and 2.20. There was no distinct pattern of over- or underdispersed phyloalpha diversities along the gradient. Elevation affected both the alpha taxonomic and phylogenetic tree species diversity: While taxonomic diversity declined along the elevation gradient, phyloalpha diversity showed a humped relationship with highest phylodiversity values at mid-elevations. I assume environmental filtering to reduce the taxonomic diversity at high elevation. Simultaneously, I suppose the occurrence of facilitator species to enable a nevertheless phylogenetic diverse tree community to persist at high elevations. At low elevations my findings indicate neutral or stochastic processes to shape the phyloalpha dispersion. Elevation had the strongest direct effect on the phyloalpha diversities. Moreover, it influenced soil parameters which explained an additional amount of the phyloalpha diversities. The pattern of phylobeta diversity supported the idea of facilitator species at high elevations and revealed two phylogenetic distantly related tree communities to exist at low and high elevation levels. The ranges of both species sets overlap at mid elevations where phylodiversities are most diverse, corresponding to a mid-domain effect at the phylogenetic scale. Drawing conclusions from phylodiversity to functional traits suggests an ecosystem with a high functional trait space along the gradient with a peak at mid-elevations. Altogether, the analysis of phylodiversity patterns revealed a much more complex picture of the diversity distribution than taxonomic diversity. Furthermore, phylodiversity permitted to find the evolutionary biotic and abiotic processes which shaped the diversity structure.

Abstract:

Previous research from the tropics indicates that AMF may be well adapted to organic soils and even represent the dominant mycorrhizal form, though the extraradical part of the symbiosis was omitted as in most other tropical studies. Our study aims at characterizing the extraradical part of arbuscular mycorrhizal fungi (AMF) in a highly organic tropical montane forest soil in Southern Ecuador. Based on recent studies on the interaction of AM fungal hyphae and litter we hypothesized that within the organic layer AM hyphae grow in close contact with decomposing material. To test this idea, AM fungal hyphal distribution in the organic layer was determined by directly staining roots and decomposing leaves and extracting hyphae from the remaining particulate organic material. AM and non-AM fungal hyphae were analyzed, as well as root colonization patterns. Our results showed that AMF indeed represented the dominant mycorrhizal form with an average root colonization of 43%. The extraradical AM hyphal length ranged from 2 to 34 m g?1 soil with a mean of 10.4 m g?1 soil (equals 3.1 m cm?3 soil), and therefore exceeded root length about 13-fold. As hypothesized, 29% of AM extraradical hyphae were closely attached to decomposing leaves. These hyphae were mainly located at the leaf surface, though in some parts leaf veins and inner leaf tissues were colonized. More than half of AM hyphal biomass was detected on the root surface, a pattern potentially driven by the predominant Paris-type AMF. Non-AM fungal hyphae colonized decomposing material to a significantly greater extent, though hyphal length attached to roots was equal. This study supports the adaptation of AMF to highly organic soils in the tropics and the existence of a widespread extraradical mycelium, which is not readily detectable by standard methods. The close association with decomposing leaves most likely improves direct nutrient uptake from decomposed material and points to a potential indirect contribution of AMF to the decomposition process.