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Abstract
Soils are key to the delivery of ecosystem services yet, until recently, the concept and measurement of soil quality was focused on the delivery of primary productivity. Soils can deliver several functions simultaneously, but which functions are delivered or have the potential to be delivered depends on soil properties, environmental conditions and associated soil management practices. The processes that determine the delivery of one soil function can play a role in the delivery of other functions leading to the existence of synergies and trade-offs between soil functions that we do not yet fully understand, due in part to the difficulty of measuring several soil functions simultaneously. In order to sustainably meet agronomic objectives, it is important that we understand the trade-offs and synergies that occur between soil functions, as well as what management decisions and environmental conditions promote multifunctionality.
Soil biota play an important role in the delivery of soil functions and yet the intensification of agricultural land is one of the largest threats to soil biodiversity in Europe. The loss of specialist species as a consequence of land use intensity has been documented for many above ground organisms. This is a problematic issue, since it leads to the loss of functional diversity, which could (in the soils) translate to a change in soil functions. And yet, we do not know whether the impacts associated with agricultural practices have a larger effect on soil specialists than generalists, amongst others because the quantification of niche width in soil organisms is very complex.
The main objective of this thesis was to study the effects of land use on different aspects of the soil system, particularly the effects on soil biodiversity. More specifically, I calculated the habitat niche width of nematodes and enchytraeids and classified them from specialists to generalists (i), studied the effect of land use intensity on the community weighted specialisation of soil organisms (ii), studied the effects of long-term agricultural practices on biological soil quality (iii), and studied the multifunctionality of agricultural soils, and the synergies and trade-offs that occur between biodiversity, primary productivity and nutrient cycling (iv).
In Chapter 2 I calculated the realised niche width for soil nematodes using cooccurrence data mostly collected by the Netherlands Institute for Health and the Environment (RIVM). I then calculated the nematode taxon richness, diversity and abundance as well as an index of community specialisation (ICS) and explored the differences in these indicators due to land use intensity. Contrary to our expectations, the lowest ICS was found in soils with the lowest human intervention (shrubland-woodland ecosystems), while grasslands, dairy farms, and arable farms had an overall higher level of specialisation. The lowest abundances were found on shrubland-woodland systems. Assessing niche widths via co-occurrence matrices opens the door to estimating the soil community’s niche breadth.
In Chapter 3 I classified enchytraeid species according to their degree of habitat specialisation and tested the robustness of the calculated niche widths to scenarios designed test sampling and legacy-effects. I used data gathered from 81 sites across Europe in three land use types of increasing land use intensity (forestry, grassland and arable land). I then calculated the enchytraeid ICS for each site and tested whether increasing land use intensity led to changes in the ICS. Cognettia sphagnetorum was the most specialised enchytraeid species and Enchytronia parva the least. Tolerance to pH might explain at least the position of these two extreme species in the generalist to specialist scale. The resulting niche width ranks were robust to scenarios simulating under-sampling. Land use intensity did not have an effect on the level of community specialisation of enchytraeids, revealing how much there is still to understand regarding the niche width and community level specialisation of soil organisms.
In Chapter 4 I investigated how and whether biological soil quality (as measured by the nematode community) has developed over time in cropping systems situated on two contrasting soil textures and under different management regimes, using time-series analyses. I gathered data from two experimental farms and 20 commercial farms that have been sampled throughout time. I found changes in the nematode community through time in all three systems, but these were not consistent across the systems or treatments. Additionally, very few trends were affected by land management (organic or conventional) or by treatment (conventional tillage or minimum tillage). In both experimental sites I observed an increase in nematode richness, and in SHE I also observed an increase in the structure and enrichment indices over time. This trend was not matched by commercial farms, where we found an overall decrease in the nematode structure and an increase in the ICS, indicating a widespread decrease in the soil’s food-web structure possibly associated with an increase in land use intensity.
In Chapter 5 I evaluated the supply of primary productivity (PP), nutrient cycling (NC) and biodiversity and habitat provision (B-HP) of 31 grasslands and 21 croplands in the Netherlands using models developed by the Landmark project. I used data gathered by the RIVM and Wageningen Economic Research on soil parameters and economic performance respectively. 38% of the farms had a medium to high supply of all three soil functions, whereas only one cropland had a high supply for all three. 48% of the farms were characterized by a high supply of PP and NC. We observed a clear trade-off between these two functions and B-HP. Higher organic inputs combined with a lower mineral fertilization concur with higher biodiversity scores while maintaining a medium delivery of PP and NC. Multifunctionality can be achieved in agricultural soils; however, without specifically managing for it, biodiversity might come at a loss.
Chapter 6 addresses the main findings of my thesis and provides a discussion regarding the issue of multifunctionality, the effects of agricultural impacts on soil biodiversity, the role of the ICS as a biological indicator as well as the niche width of soil organisms as quantified using co-occurrence matrices. I also provide suggestions for future study.
Original language | English |
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Qualification | Doctor of Philosophy |
Awarding Institution |
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Supervisors/Advisors |
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Award date | 1 Jun 2021 |
Place of Publication | Wageningen |
Publisher | |
Print ISBNs | 9789463956178 |
DOIs | |
Publication status | Published - 1 Jun 2021 |
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Dive into the research topics of 'The fate of biological soil quality: Functional diversity and realised niche width'. Together they form a unique fingerprint.Projects
- 1 Finished
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SQUASH - A Soil Quality Universally Applicable Soil Health assessment system.
Vazquez Martin, C. (PI), Creamer, R. (CoI), de Goede, R. (CoI), Vazquez Martin, C. (PhD candidate), Creamer, R. (Promotor) & de Goede, R. (Co-promotor)
1/10/15 → 1/06/21
Project: PhD