Using stomatal conductance capacity during water stress as a tool for tree species selection for urban stormwater control systems

Improving our understanding of how different tree species function in urban stormwater management systems is important, as tree pits may provide a temporary reservoir for stormwater and as trees have the potential to actively reduce stormwater runoff by transpiration. While urban tree planting pits are increasingly used for shortterm water storage during stormwater runoff events, this storage can have negative effects on both tree vitality and water removal capacity, since stress from waterlogging result in stomatal closure. However, sensitivity to water stress varies by species. It is therefore important to determine which tree species can maintain long-term vitality and continued transpiration even under water stress, and thus are suitable for such locations. Here, we studied how nine different tree species, varying in expected tolerance to water stress, were affected by short-term and seasonal waterlogging, in a greenhouse experiment. The seedlings (Magnolia x loebneri, Tilia tomentosa, and Sorbus torminalis - low water logging tolerance; Cercidiphyllum japonicum, Rhamnus cathartica, and Fraxinus ornus - medium water logging tolerance; Quercus palustris, Acer saccharinum, and Fraxinus pennsylvanica - high water logging tolerance) were exposed to two days, five days and seasonal waterlogging. The treatments reflected best practice (optimal), suboptimal and total lack of tree pit drainage, using Swedish standards. Stomatal conductance and leaf water potential were determined regularly over a period of 71 days, and morphological adjustments were registered. Four of the species were affected already after two days of waterlogging, with reduced stomatal conductance either during the waterlogging or immediately after, and only the most waterlogging tolerant species were unaffected by the five-day treatment. However, all plants survived waterlogging for almost 30 days before the estimated permanent wilting was reached in some plants. We suggest that tree species selection for stormwater management systems should consider the species' capacity to maintain high stomatal conductance during waterlogging, as there were clear differences between species. The effectiveness of the selected species could have an important impact on the stormwater management capacity of cities, as well as on other aspects of ecosystem service delivery from urban trees

Evaluation of Alnus subcordata for urban environments through assessment of drought and flooding tolerance

The urban environment is stressful and trees experience multiple stresses, including drought, flooding, and extreme heat, all of which are likely to increase under future climate warming and increasing urbanisation. In the selection of tree species to maximise ecosystem services, tolerance to site characteristics such as flooding and severe drought is of critical importance. This study evaluated the suitability of a rare species, Mims subcordata C.A. Mey (Caucasian alder) from the Hyrcanian forests of southern Azerbai-jan, for its functionality as an urban tree.A total of 48 pot-grown, two-year-old saplings of A. subcordata were tested in a greenhouse experiment using a complete randomised block design. Each block contained four replicates of three treatments (waterlogging, drought, control), with 16 plants per treatment. Height differences between treatments were measured, and water status was estimated by determination of midday leaf water potential (psi(L)) and stomatal conductance (g(s)). To estimate drought tolerance reaction in the treatments, leaf water potential at turgor loss (psi(P0)) was used together with broken-stick modelling of water status over time.A. subcordata plants showed no height increase, while plants in both the waterlogged and control treatments increased in height during the nine-week experiment. Over 63 days of flooding, plant water status was slightly more negative in the waterlogging treatment, but did not deviate essentially from the control. In the drought treatment, plant water status rapidly deviated from the control. There was a significant difference in psi(P0) between treatments, with drought-treated plants showing the lowest value (-2.31 MPa).This study demonstrated that A. subcordata has limited tolerance to drought and seems to rely more on water loss-avoiding strategies. However, the species may be usable at periodically waterlogged sites, due to its high tolerance to flooding. It could therefore be recommended for wet urban environments and stormwater management facilities, for which reliable guidance on suitable trees is currently lacking

Nulägesanalys trädgård

Rapporten Nulägesanalys - trädgård har genomförts inom ramen för projektgruppen Insatsstyrka trädgård. Syftet med inventeringen har varit att ge svar på vem som jobbar med trädgårdsvetenskap, vilka forskargrupper och med vilka forskningsämnen, samt identifiera framtida arbetsfält inom ämnet trädgårdsvetenskap och därmed ge uppslag för framtida utveckling av forskningsfält, utbildning och samverkan. I detta ingår att kartlägga trädgårdsvetenskaplig forskning, utbildning och samverkan vid SLU. Nulägesanalysen förväntas därmed ge en grund för fortsatt strategiskt arbete med att utveckla ämnet trädgårdsvetenskap (Horticultural Science) utifrån inventerade resurser och förutsättningar