Investigation into the drought tolerance of broadleaf street trees using chlorophyll fluorescence

Abstract

Water stress extensively contributes to the high tree mortality rates experienced in urban areas. This gives rise to direct costs due to replacement, but also indirect ones linked to the loss of ecosystem services delivery. Still, there is limited knowledge on how different species, commonly used in UK street plantings, rate in their tolerance to successive drought events. This study aims to compare young specimens of broadleaf tree species for their drought response and to establish how a species response varies as a result of prior exposure to drought. Results presented here are from a preliminary experiment carried out in the UK, where two-year old trees from nine species underwent two drought and recovery cycles. Responsiveness to the different periods was evaluated by changes in maximum quantum yield of photosystem II (Fv/Fm). Species varied in their Fv/Fm reduction while in drought and in the time it took Fv/Fm to recover to a pre-drought level once trees were watered. Populus tremuloides and Robinia pseudoacacia showed the greatest Fv/Fm reduction during the first cycle, they also lost many leaves and so they were excluded from the second cycle. All other species showed a greater Fv/Fm reduction in the second cycle than in the first one, particularly Betula pendula, Quercus robur and Acer platanoides. Quercus robur and A. platanoides also took the longest to recover from drought. Results suggest that selected tree species differ in their suitability to be used in water restrictive urban sites.