Aboveground succulence in woody plants is related with drought survival in green roof modules and not their degree of anisohydry or water use

Abstract

Background and aims

On green roofs, water and depth limitations reduce woody plant survival due to shallow free-draining substrates. Succulents like Sedum spp. are commonly used on green roofs as succulence improves drought survival. Succulence refers to water storage in plant tissues and plants can use succulence to maintain physiological function under drought as ‘utilisable water’ or to buffer changes in water potential to prevent dehydration. The amount of water used to buffer one unit change of water potential is termed ‘capacitance’. Succulence also exists in woody plants, but it is unclear whether this can improve survival on green roofs as their total water use (evapotranspiration) and their drought tolerance will also affect survival.

Methods

We evaluated survival of seven woody plant species in a 23-month (from establishment) green roof module experiment. Survival analyses determined time until 75% survival of each species. Survival was related to succulence (degree of leaf succulence and organ water content normalised by dry mass), utilisable water, capacitance, total water use and degree of anisohydry, which were determined previously in a glasshouse experiment.

Results

On green roofs during summer drought, plants with higher levels of leaf and stem succulence had greater survival. However, survival was not related to utilisable water, capacitance or water use and degree of anisohydry.

Conclusion

Greater aboveground succulence leads to better drought survival in woody plants and could be used to improve plant selection and broaden species used on green roofs.