Using leaf economics to find appropriate woody species for rain gardens

Abstract: Urban rainwater management faces great challenges in the future, caused by expected increase in precipitation and frequency of storms associated with climate change. Constructions such as rain gardens may be a mean for adaptation to, as well as mitigation of these effects. However, growing conditions in rain gardens are challenging for most vegetation, and in particular woody vegetation, often leading to failing rain garden constructions. By gaining information on the responses of different woody species during conditions found in rain gardens, the probability for a successful decision of vegetation increases. This study was made in connection to a research project led by Anna Levinsson at SLU, Alnarp, researching different responses of nine woody species to waterlogging and drought. The species were chosen based on the categorising work by Niinemets and Valladares (2006), and sorted further according to a few additional criteria. This thesis aim to investigate the possible importance of leaf economics when choosing trees for rain gardens, focusing on the conditions during waterlogging. A literature study explored the current knowledge of waterlogging in urban environments, the effect of waterlogging on trees, and plant strategies centred around Grimes CSR theory and leaf economics. The literature study showed that the most damaging factor to plants during waterlogging is the anoxic conditions created in the soil. Several adaptations exist which may increase the survival-rate for woody species during these conditions, such as the ability for altering root growth, hypertrophied lenticels and a permeable cambium. These adaptations are all associated with the longitudinal transportation of oxygen. The knowledge gathered in the literature study provided the base for the experimental study. Measurements of midday leaf water potential (ψL) and stomatal conductance (gl) were conducted as well as measurements of leaf morphology focusing on the leaf trait Specific leaf area (SLA). The results of the experimental study indicated that the ability for SLA plasticity might be important for the survival of trees during waterlogging, since the species deemed most flood-tolerant displayed significant, or almost significant, effect when kept in a waterlogged state. Furthermore, it showed that these species had a higher ψL and showed no significant effect on gl, indicating that these species seem to be able to upkeep water levels in the leaves and inhibit stomatal closure during waterlogging. This was somewhat contradictory to what was previously described in the literature. Further investigations within the responses of ψL and gl towards waterlogging and how plasticity within leaf economics might be related to this are encouraged. This would possibly increase our understanding in what to search for when choosing woody species for rain beds.