Waterlogging duration: Interspecific comparison ofLeptospermum scoparium(Forst et Forst.f.), Acacia melanoxylon(R. Br.), Nothofagus cunninghamii(Hook.) andEucalyptus obliqua(L’Herit)

Abstract

Abstract The effect of the duration of waterlogging on the pre‐dawn water potential, gas exchange, biomass accumulation and survival was investigated on four species,Leptospermum scoparium(Forst et Forst.f.),Acacia melanoxylon(R. Br.), Eucalyptus obliqua(L’Herit) andNothofagus cunninghamii(Hook.). These species co‐occur, but are restricted to particular microsites. The three waterlogging treatments applied to potted seedlings were: four cycles of 15 days, two cycles of 30 days or one 60‐day cycle, followed by an equal period in freely drained conditions. Water potential, gas exchange, biomass accumulation and survival were not significantly affected by the duration of waterlogging inL. scopariumorA. melanoxylon.With increased waterlogging duration,N. cunninghamiihad progressively decreased survival, had less biomass accumulation in all waterlogging treatments and more negative water potential after the 60‐day waterlogging cycle. In contrast,E. obliquahad low survival under the 15‐day waterlogging cycle treatment, although survival, biomass accumulation and maximum net photosynthesis were decreased by all waterlogging cycle treatments. Water potential was significantly lower (more negative) inE. obliquathan other species after the 30‐ and 60‐day waterlogging cycle treatments only. When exposed to oxygen deficit in hypoxic nutrient culture for 5 days,L. scopariumhad 100% survival and maximum net photosynthesis was not affected.Acacia melanoxylonhad 80% survival and decreased photosynthesis from 2 days of exposure onwards.Nothofagus cunninghamiiandE. obliquahad 70% and 30% survival, respectively, and their photosynthesis was significantly depressed after 1 day of exposure to hypoxic conditions. Relative tolerance of the species examined to waterlogging and hypoxia was consistent with adaptation to conditions of seasonal variation in water table height and soil oxygenation concentration observed at the microsites occupied by the respective species. The results indicate that duration of waterlogging may be a major determinant in the microsite distribution of the co‐occurring species investigated.