Root and above-ground trait variation across a water availability gradient in woody Fynbos shrubs

Ms Nicola Kühn1, Prof Kathy Willis1, Dr Carolina Tovar, Dr Marc Macias-Fauria1

1University Of Oxford, Oxford, United Kingdom


Trait-based ecology is important for understanding mechanisms of species response to climate change by focusing on the functional traits that mediate plant survival under a set of environmental conditions. There is consensus around which traits are most important in determining plant form and function (Díaz et al. 2016). However, these traits are limited to above-ground parts of the plant due to the difficulties in measuring below-ground traits, even though many studies point to their importance for resource uptake.

We analysed how root and above-ground traits vary along an aridity gradient by comparing dominant woody fynbos shrubs in two sites of different annual precipitation located in the Western Cape (South Africa): wetter site (Stellenbosch, 600-700mm), drier site (Touwsrivier, 200-300mm).Results indicate that water-stress-tolerant traits including greater rooting depth, lower specific leaf area and higher stem-specific density are significantly more prevalent in drier environments (p<0.001), with root to shoot length ratios found to be more than double in the dry site. These results point to a different suite of traits expressed across a water availability gradient for species of the same vegetation and plant functional type.

Further work aims to explore these relationships in terms of how environmental selection acts on allocation of resources to below- and above-ground plant parts across this gradient and thus how environmental change may influence these allocations in the drier future predicted for the Western Cape. Further, our analysis aids the identification of those species inherently more tolerant, as mediated by their trait assemblage, to these future climatic constraints.

Díaz, Sandra, et al. “The global spectrum of plant form and function.” Nature 529.7585 (2016): 167.


Nicola is a PhD candidate at the University of Oxford in the School of Geography and the Environment. She has a background in Ecology, with a BSc undergraduate and BSc postgraduate Honours degree from the University of Cape Town and an MSc in Biodiversity, Conservation and Management from the University of Oxford. Her current research focuses on the role of plant functional traits in determining plant response to climate change, particularly in South African ecosystems expected to become warmer and drier.

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