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

Abstract:

Forest site classification adapted to the respective site conditions is one prerequisite for sustainable silviculture. This work aims to initiate the forest site classification for pine plantations in the southern Andean region of Ecuador. Forest productivity, estimated by the dominant height of 20-year-old trees (DH20), was related to data from climate, topography, and soil using 23 plots installed in pine plantations in the province of Loja. Forest site productivity was classified as: low (class C: 13.4 m), middle (class B: 16.6 m), and high (Class A: 22.3 m). Strong determinants to differentiate the forest site classes were: the short to medium term available Ca and K stocks (organic layer + mineral soil standardized to a depth of 60 cm), soil acidity, the C:N ratio, clay and sand content, forest floor thickness, altitude, and slope. The lowest forest productivity (Class C) is mainly associated with the lowest short to medium term available K and Ca stocks. Whereas, in site classes with the highest forest productivity, pines could benefit from a more active microbial community releasing N and P, since the soil pH was about 1 unit less acidic. This is supported by the lowest forest floor thickness and the narrowest C:N ratio.

Abstract:

The increasing anthropogenic influence on the environment on a global scale has led to a shift in nutrient cycles which are not fully understood yet. These shifts could alter the properties of ecosystems and therefore change habitats and species composition. Therefore it is crucial to understand nutrient cycles and how ecosystems react to these nutrient availability shifts. Especially the phosphorus and nitrogen cycles are highly important because of their direct influence on plant growth as primary macronutrients. Even in some so far undisturbed regions, a human caused rise in atmospheric input of phosphorus-containing particles is expected. One of the reasons therefor is land-use change in rural areas with associated combustions, from which the particles are transported downwind. This study simulates the prognosticated increased nutrient input and focuses on the following fate of the phosphorus in soil. For this, in 2008 a nutrient manipulation experiment was established to fertilize an old-growth tropical montane forest with moderate phosphorus (10 kg P ha-1 yr-1) and/or nitrogen additions (50 kg N ha-1 yr-1). This experimental setup was conducted for the first time at three altitudes (1000m a.s.l., 2000m a.s.l., 3000m a.s.l.) to compare the effects along an altitudinal gradient. After seven years the total phosphorus and bioavailable phosphorus concentrations of these locations were investigated in litterfall, the organic layer and in mineral soil to see if the added phosphorus is retained and enriched. The results showed that the application of the phosphorus fertilizer resulted in increased total and bioavailable phosphorus concentrations mainly in the organic layer. The phosphorus increase in mineral soil was not significant and indicated that the added phosphorus is not leached, but retained in the ecosystems. There were no effects on phosphorus concentrations after nitrogen addition. The altitudinal gradient referred to a pronounced difference between 1000m and the other altitudes (2000m and 3000m), due to the accumulated organic matter at the higher altitudes. Overall this study shows that the sustainable anthropogenic phosphorus increase may cause a change in the ecosystem’s characteristics and nutrient cycles.

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.