The influence of root traits on soil reinforcement and erosion mitigation

Burak, Emma and Dodd, Ian and Quinton, John (2019) The influence of root traits on soil reinforcement and erosion mitigation. PhD thesis, Lancaster University.

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Abstract

Soil erosion is a global concern as it reduces the quality of the soil and restricts its ability to provide essential ecosystem services such as supplying the nutrients and substrate for the majority of the world’s food. Without the fertile top soil, more fertilisers are needed to achieve the same yield. Additionally, the displaced soil clogs waterways, increasing both the risk and magnitudes of flooding and landslides. Plant roots have beneficial traits that can reinforce the soil and mitigate erosion. However, there is a large gap in the knowledge regarding the relative contribution of individual root traits. Root hairs can bind soil particles at the root soil interface and anchor roots during growth, but their influence on wider reinforcement of soil and erosion mitigation has not yet been evaluated. This thesis subjected root systems with varying traits to erosion events and evaluated which traits are more beneficial to preventing erosion. Initially, pot experiments evaluated the ability of root hairless mutants of barley (brb), maize (rth3), and L. japonicus (Ljrhl1) to bind soil at the root soil interface and form a rhizosheath. Root exudate adhesiveness and root hair traits were compared with wild type (WT) genotypes. Root hair development proved to be the most influential trait for rhizosheath formation. Pots containing one each of the barley and maize genotypes were subjected to shear stress in a laboratory shearing rig to establish which root traits most influenced the root system's ability to reinforce the soil. The presence of roots significantly increased soil reinforcement, but unlike with rhizosheath development, root hairs showed no propensity to influence this. Root diameter was the trait most dominant in determining a root system’s effectiveness as soil reinforcement. A mesocosm experiment evaluated the impact of root hairs on erosion mitigation under a controlled laboratory environment. Multiple barley plants were grown in mesocosms modified to collect eroded sediment and subjected to a gravity fed laboratory rainfall simulator. The presence of roots significantly decreased the yield of sediment in the runoff in comparison to the unplanted mesocosms and the presence of root hairs enhanced this reduction. Lastly, barley genotypes were grown in field plots and subjected to simulated rainfall from a portable field rainfall simulator. The presence of roots significantly reduced the yield of sediment in the runoff. However, under the less controlled field conditions, there was no correlation with soil yield and increasing root presence. Consequently the influence of root hairs was swamped by other uncontrolled variables. Thus, it was concluded that in a small scale homogenous environments root hairs can enhance a root system's ability to mitigate soil erosion, however their contribution is small and can easily become overshadowed by more dominant forces such as larger roots or intense rainfall so that in some scenarios their contribution is negligible.