The Influence of Plant Diversity on Soil Physical Properties in Grasslands.

Gould, Iain James (2014) The Influence of Plant Diversity on Soil Physical Properties in Grasslands. PhD thesis, Lancaster University.

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Abstract

The scale of biodiversity loss facing our planet has prompted many scientists to explore the potential consequences for ecosystems, and the goods and services that they provide. A favoured approach for investigating such impacts of species loss is to experimentally address the result of a reduction in species numbers on multiple ecosystem functions. Such studies of biodiversity-ecosystem function (BEF) relationships have generated a wealth of knowledge on the consequences of diversity loss for a range of ecosystem processes, such as primary productivity, nutrient cycling and the stability of communities under environmental change. However, virtually nothing is known about the response of soil physical properties to plant biodiversity change, which represents a serious gap in our knowledge given the key role soil physical structure has in providing an essential medium for plant growth; microbial activity; carbon storage; nutrient cycling; water retention; and gas flow. The potential negative effects of species loss on the degradation of soil physical properties could have adverse consequences for a host of ecosystem functions, and thus conservation of both biodiversity and soil physical integrity has potential to work hand in hand to regulate services essential to our survival. The overarching goal of this thesis is to address this gap in our understanding, by investigating the impact of shifts in plant biodiversity on a range of soil physical properties. Grassland plant communities influence soil erosion factors through their rooting properties. Plant roots can act to stabilise the soil, create hydrological pathways and release organic exudates to benefit soil aggregation. Different grassland species exhibit contrasting root traits. For example, some species produce vast expanses of fine roots, enmeshing the soil and supporting binding mechanisms, whilst other species invest in fewer, yet thicker, roots, which create anchorage and aid water flow. Grassland communities that encapsulate a large variety of plant species will exhibit a wider array of root traits, and therefore have potential for multiple beneficial effects on soil stability. Here, a pot experiment, experimental plot sampling, and a field survey, were employed, alongside an extensive review, to investigate the influence of plant diversity, and grassland community dynamics, on soil physical properties. Plant species richness was found to have strong effects over soil aggregate stability. Plant functional group and species identity also impacted on soil strength and hydraulic regimes, often with legumes and grasses displaying contrasting behaviour. The impact of changes in rooting structure, and their associated inputs to the soil, was significant in all of these relationships. This represents the first time such a relationship have been revealed at a range of scales, and provide valuable insight into a new direction for biodiversity-ecosystem function studies.