RESUMEN
New knowledge on soil structure highlights its importance for hydrology and soil organic matter (SOM) stabilization, which however remains neglected in many wide used models. We present here a new model, KEYLINK, in which soil structure is integrated with the existing concepts on SOM pools, and elements from food web models, that is, those from direct trophic interactions among soil organisms. KEYLINK is, therefore, an attempt to integrate soil functional diversity and food webs in predictions of soil carbon (C) and soil water balances. We present a selection of equations that can be used for most models as well as basic parameter intervals, for example, key pools, functional groups' biomasses and growth rates. Parameter distributions can be determined with Bayesian calibration, and here an example is presented for food web growth rate parameters for a pine forest in Belgium. We show how these added equations can improve the functioning of the model in describing known phenomena. For this, five test cases are given as simulation examples: changing the input litter quality (recalcitrance and carbon to nitrogen ratio), excluding predators, increasing pH and changing initial soil porosity. These results overall show how KEYLINK is able to simulate the known effects of these parameters and can simulate the linked effects of biopore formation, hydrology and aggregation on soil functioning. Furthermore, the results show an important trophic cascade effect of predation on the complete C cycle with repercussions on the soil structure as ecosystem engineers are predated, and on SOM turnover when predation on fungivore and bacterivore populations are reduced. In summary, KEYLINK shows how soil functional diversity and trophic organization and their role in C and water cycling in soils should be considered in order to improve our predictions on C sequestration and C emissions from soils.
RESUMEN
The relatively poor simulation of the below-ground processes is a severe drawback for many ecosystem models, especially when predicting responses to climate change and management. For a meaningful estimation of ecosystem production and the cycling of water, energy, nutrients and carbon, the integration of soil processes and the exchanges at the surface is crucial. It is increasingly recognized that soil biota play an important role in soil organic carbon and nutrient cycling, shaping soil structure and hydrological properties through their activity, and in water and nutrient uptake by plants through mycorrhizal processes. In this article, we review the main soil biological actors (microbiota, fauna and roots) and their effects on soil functioning. We review to what extent they have been included in soil models and propose which of them could be included in ecosystem models. We show that the model representation of the soil food web, the impact of soil ecosystem engineers on soil structure and the related effects on hydrology and soil organic matter (SOM) stabilization are key issues in improving ecosystem-scale soil representation in models. Finally, we describe a new core model concept (KEYLINK) that integrates insights from SOM models, structural models and food web models to simulate the living soil at an ecosystem scale.
RESUMEN
Interactions between the saprotrophic animal groups that strongly control soil microbial activities and the functioning of detrital food webs, such as earthworms and mesofauna, are not well understood. Earthworm trophic and engineering activities strongly affect mesofauna abundance and diversity through various direct and indirect pathways. In contrast, mesofauna effects on earthworm populations are less evident; however, their importance may be high, considering the keystone significance of earthworms for the functioning of the soil system. We studied effects of a diverse mesofauna community of a deciduous forest on two earthworm species representing epigeic (Lumbricus rubellus) and endogeic (Aporrectodea caliginosa) ecological groups. In microcosms, the density of total mesofauna or its separate groups (enchytraeids, collembolans, gamasid mites) was manipulated (increased) and responses of earthworms and soil systems were recorded. A rise in mesofauna density resulted in a decrease of biomass and an increased mortality in L. rubellus, presumably due to competition with mesofauna for litter resources. In contrast, similar mesofauna manipulations promoted reproduction of A. caliginosa, suggesting a facilitated exploitation of litter resources due to increased mesofauna activities. Changes of microcosm respiration rates, litter organic matter content and microbial activities across the manipulation treatments indicate that mesofauna modify responses of soil systems in the presence of earthworms. However, similar mesofauna manipulations could induce different responses in soil systems with either epigeic or endogeic lumbricids, which suggests that earthworm/mesofauna interactions are species-specific. Thus, mesofauna impacts should be treated as a factor affecting the engineering activities of epigeic and endogeic earthworms in the soil.
