High rock content enhances plant resistance to drought in saline topsoils

Successful mine site restoration in semi-arid regions is limited by availability of topsoil and water, and saline soils are a common feature of these regions and pose an additional stressor to vegetation establishment. We tested the growth and development of a salt-tolerant species on saline topsoil incorporating 25%, 50%, 75% and 88% waste rock, examining soil water content and plant water use to determine how waste rock content affected plant-water relations, growth and development. Under well-watered conditions higher percentages of waste rock lowered the volumetric water content of the total soil mix, causing a reduction in stomatal conductance. Under drought conditions, higher waste rock content reduced rates of water loss and allowed stomatal conductance to be maintained over a longer period. There was no significant or optimal relationship between waste rock content and plant growth, indicating that the addition of waste rock to topsoil has complex effects on plant-water relations and growth. We demonstrate that augmentation of limited topsoil resources with waste rock is a promising option for improving plant resistance to drought in mine site restoration. [Display omitted] •Augmentation of natural topsoil with up to 88% waste rock did not significantly negatively alter plant growth.•The presence of small amounts of rock in soil mixes was beneficial for plant growth.•Increasing rock content reduced declines in plant physiological functions under prolonged water deficit.•Very high rock content in soil reduced water availability, reducing plant physiological functions.