Soils in transition: dynamics and functioning of fungi
Wal, A. van der
Citation
Wal, A. van der. (2007, October 24). Soils in transition: dynamics and functioning of fungi.
Retrieved from https://hdl.handle.net/1887/12412
Version: Corrected Publisher’s Version
License: Licence agreement concerning inclusion of doctoral thesis in the Institutional Repository of the University of Leiden
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Summary
123 Summary
In Western Europe, arable lands have been abandoned to counteract agricultural overproduction and to increase the area of nature. In the Netherlands, policy makers and nature managers aim to (re)create natural ecosystems, in particular Calluna-dominated heathlands on sandy ex-arable soils. However, the conversion of a nutrient-rich arable land into a heathland is expected to be difficult since the soil conditions on arable land are completely different from those of heathlands. Arable soils do not have an organic matter layer and the pH as well as the availability of nutrients are much higher than in heathland soils.
Fungi have a much stronger contribution to decomposition processes in natural ecosystems than in arable land. Fungi are involved in the formation of soil aggregates, may give protection against nitrogen leaching and sequester more carbon than bacterial-dominated communities. All of these activities of saprotrophic fungi do contribute positively to functioning of soils and may be essential for the development of a natural heathland vegetation on ex-arable soil.
The focus of this thesis is on the dynamics of biomass and functions of saprotrophic soil fungi during conversion from a high input-output agricultural ecosystem into a low input- output natural ecosystem and to asses their effects on soil ecosystem processes. To reach this aim, the development of the fungal biomass along a chronosequence of 26 ex-arable fields that differed in the time since abandonment was studied (Chapter 2). It became clear that neither fungal biomass, nor the organic matter quality and quantity reached the level of a natural ecosystem in the time interval of abandoned fields that was studied (1-34 years). Only during the first 2 years after abandonment fungal biomass values increased. Thereafter a levelling off in fungal biomass was observed. The initial increase in fungal biomass is likely to be due to the stop of soil disturbing agricultural activities. To study the constraints of saprotrophic fungi to increase further in biomass in ex-arable land, the effect of addition of carbon substrate on biomass, activity and composition of soil fungi was determined (Chapter 4). Opportunistic fungi showed to be responsible for the decomposition processes in ex-arable field, and these fungi are stimulated by a high quality of organic matter (low C:N ratio), a large size of substrate and burial of the substrate into soil (Chapter 5).
In Chapter 2 it is described that total phophorous (P) in the upper soil (10 cm) decreased with years of abandonment. To study if this decrease in total P could be due to leaching of large amounts of P from the top soil to lower soil layers, the vertical distribution of total P concentrations at different soil depths in four ex-agricultural fields that differed in time since abandonment was determined (Chapter 3). At each site, total P concentration
Summary
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decreased with increasing depth. Therefore, no large amounts of P seem to leach into deeper soil layers.
Chapter 6 describes a study on the possible factors that enabled the establishment of Calluna vulgaris plants in a recently abandoned arable land, despite high levels of nutrients (P) and the presence of fast-growing forbs and grasses. All roots in Calluna patches were colonized by ericoid mycorrhizal (ERM) fungi and nitrogen mineralization was limited in the soil under these patches, although Calluna plants were not nitrogen limited. Interestingly, Calluna patches had a diameter of 0.70 to 2.0 m and no Calluna seedlings were present in the field, indicating that colonization by new Calluna plants did not take place. The conclusion from this study was that the establishment of Calluna plants between ruderal plants in ex- arable fields could be due to 1) a fast colonization of Calluna immediately after abandonment before the establishment of fast-growing grasses and forbs and 2) the reduction of N- mineralizing microbial activity by toxic compounds produced by Calluna plants in combination with the colonization of Calluna roots by ERM fungi. ERM fungi offer a nutritional benefit for organic nitrogen compared to fast-growing grasses and forbs that do not have this association.
An increase in fungal biomass can be of interest for soil ecosystem restoration. A possibility to trigger the increase in saprotrophic fungal biomass in ex-arable land could be the introduction of large particles of recalcitrant organic matter together with sufficient fungal biomass (Chapter 7). Within the context of the risk of phosphorous leaching after abandonment of arable fields, it appears that attempts to decrease the level of phosphorous are not necessary on ex-arable sandy soils in the central part of the Netherlands (Chapter 3 &7).
The conversion from an arable field into a heathland may be easily achieved by the introduction of Calluna seeds and an inoculum of ericoid mycorrhizal fungi, e.g. soil from a mature heathland, immediately after abandonment of the arable field (Chapter 6 & 7).
