Complexity of soil faunal communities in relation to ecosystem functioning in coniferous forest soil : a disturbance oriented study

Abstract

Soil fauna are known to exert a significant influence on soil processes. However, little is known about the importance of the complexity of soil decomposer communities for ecosystem functioning, and the ability of these systems to withstand disturbances. The objective of the thesis was to relate complexity of soil faunal communities - using (i) functional complexity, (ii) species richness, and (iii) species identity as criteria - to the rate of ecosystem processes (i.e. primary production and nutrient leaching) and the system's susceptibility to disturbances. In addition, the impact of disturbances on soil biota was assessed. Abrupt increase in soil pH (due to wood ash application), and drought were used as disturbances. The experiments were conducted in the field, in field lysimeters, and in laboratory microcosms. The experiments showed that primary production and nutrient leaching and the ability of soils to resist and recover from disturbances were virtually unaffected by the functional complexity and the species richness of soil fauna. Apparently, the functional redundancy among soil fauna is high, and hence, only a small number of species is necessary for soil systems to maintain their functions. However, the enchytraeid, Cognettia sphagnetorum, had a significant effect on nutrient mineralisation and plant growth, but whether the effect was stimulative or retarding was largely dependent on environmental factors (i.e. ash-free/ ash-treated soil; plant species growing in the microcosms). Soil fauna, in general, were rather resistant to disturbances. However, C. sphagnetorum clearly suffered from both wood ash application and drought, but the impact of drought on enchytraeid populations appeared to be temporary. It seems that due to the high resiliency of soil biota, short-term disturbances, such as drought, do not have major consequences on the functions of soil fauna. However, long-lasting perturbations, such as wood ash application, can cause significant changes in the functioning of soils, but the direction of such changes is likely to be context dependent.