Redistribution of Phosphate into the soil via hydrological processes explained by functional traits in scattered trees of different species in the tropical Andes.

Andean ecosystems exhibit a natural limitation in nutrients such as Phosphorus that, potentially, affect the entire ecosystem´s metabolism, function and resilience to environmental perturbation. Due to this limitation in the soil, atmospheric inputs via wet or dry deposition become a determinant source of nutrients to the ecosystems. In highly disturbed Andean forests, scattered trees that remain in the landscape after forest conversion into other land uses, have been designated as key structures due to the ecological functions they have relative to the area they occupy, allowing to improve the biophysical and biogeochemical conditions of the place. On a Landscape-scale, they modify spatial heterogeneity, and contribute ecological connectivity that helps plant species dispersal. Previous studies have demonstrated the importance of precipitation for nutrient inputs into forests where various tree species differ in their responses because of their specificity, trait configuration, and changes in plant community competitive hierarchies. However, few studies have quantified the response of functional traits for different species of trees, evaluating their ability to intercept and move phosphorus through the relationship with hydrological processes. We determined the interception and input of phosphorus into the ecosystem through the study of twenty individuals from five scattered tree species in a modified Andean landscape: Croton magdalenensis, Tibouchina lepidota, Vismia Baccifera, and Quercus humboldtii, which are dominant and native to the Northern Andes, as well as a common exotic species in the area Eucaliptus globulus, generally planted for timber. In all individuals, we measured functional traits that relate, and potentially explain rainfall interception, and quantified concentrations of phosphate PO4 in precipitation, throughfall, and stemflow in all individual trees for a group of 16 individual rain events that varied in their hydrological characteristics. In general, PO4 concentrations in precipitation were low, although variation associated with hydrological characteristics of precipitation (intensity, duration, magnitude and cumulative precipitation in the previous days) was generally observed. In most cases were concentrations of PO4 were observed in precipitation, throughfall and stemflow had similar concentrations in most trees, highlighting the potential role of these hydrological processes in redistributing nutrients into the root zone.  Notably, one particular species, Croton magdalenensis, a pioneer species that generally dominates early forest recovery in disturbed areas, had significantly higher values of PO4 concentration in throughflow and stemflow compared to concentration in oncoming precipitation, as well as in the same fluxes on the other species. This condition potentially results from a particularly higher epiphyte load in these trees, which potentially facilitate biogeochemical exchange and enhances ecological functions associated with early stages of forest recovery.  Overall, our results highlight the complex biogeochemical interactions that occur in these highly biodiverse ecosystems where plant functional traits can be useful to describe ecosystem function at the landscape scale.  More generally, our results can be useful for restoration processes where ecosystem function, and particularly biogeochemical processes related to limiting nutrients (such as Phosphorous), need to be prioritized.

Keywords: precipitation, phosphorus interception, nutrients limitation, scattered tree, functional traits.