Natural soil suppressive capacity in a chronosequence of ex-arable fields against three plant pathogenic fungi

Abstract

The restoration of ex-arable fields is a common issue in North-West Europe, having a species rich heathland as a target ecosystem. This is a long process which can take decades due to the different successional stages the system needs to go through. There are many factors playing a role in this secondary succession gradient, as for instance seed bank quality and diversity, abiotic factors as nitrogen or organic matter content and biotic factors as soil biota (which is the living part of the soil and contributes strongly to create the optimal conditions). Soil biota generates a complex soil food web based on multi-trophic interactions, and it has a strong influence in the presence/absence of different species and its abundance, both above and belowground. In this master thesis we wanted to evaluate the importance of soil biota in driving the succession of plants along the restoration process in 9 different ex-arable fields. Mainly, we focused on the effect of different plant pathogenic fungi on early successional wild plant species performance, and whether the impact on the plants is strongly related to the time since agricultural abandonment. The capacity of soil biota to reduce impact of pathogenic fungi on plants is known as suppressive capacity and is mainly expressed in agricultural fields were similar plant species grow generation after generation on the same field. In this study we want to test whether in a natural situation the biotic soil components would also develop from an initial conductive stage to a mature suppressive stage over the course of succession. For this purpose we set up two experiments: the first was a pre-test to find out which plants and fungi were the most appropriate plants and fungal species to be used for the main experiment. In the main experiment we measured the effect of three different fungi (Gaeumannomyces graminis, Botrytiscinerea and Verticillium albo-atrum.) on two plants species (Achillea millefolium and Plantago lanceolata.), on soils from three different successional stages (recent- , mid- and long-term ago taken out of agricultural production). Our hypothesis was that soils belonging to the late successional stage are more suppressive, resulting in lower fungal impact on the plants. We hypothesized that over the course of succession soil biota becomes more diverse and there is more competition due to the fact that easily decomposable organic matter decreases, and suppressiveness might be enhanced undirectly by this fact. The results rejected the hypothesis. Only in the pot where we added Botrytis cinerea there was suppressive capacity by the soil biota on the fungus, but this effect diminished towards later successional soils. The soils showed no soil suppression at all towards the other two soil