Waterlogging in the temperate plantation species Eucalyptus globulus and E. nitens

This project investigated the effect of waterlogging on the productivity of Eucalyptus globulus under field conditions, and the relative tolerance of the two temperate plantation eucalypt species, E. glob ulus and E. nitens, from the subgenus Symphyomyrtus, to waterlogging. In eucalypt plantations across Tasmania, waterlogging is a serious threat to productivity. It is estimated that at least 11 % of all commercial eucalypt plantations in Tasmania are affected to some degree, by waterlogging. The losses incurred by waterlogging during the first 2 years of plantation establishment were found to have significant long-term effects on tree productivity at two sites across the state. In the field, soil indicators of long-term waterlogging, specifically the evidence of greying, in combination with current seasonal waterlogging and development of hypoxic soil conditions were found to be the factors closely associated with severe reductions in tree height and growth. The use of extensive soil mapping and assessment prior to plantation establishment are therefore effective tools in identifying potential waterlogging problems. Under long-term waterlogging, there was no indication of the development of plant water stress during exposure to waterlogging. Waterlogged seedlings of both species exhibited reduced foliar nutrient status, with significantly reduced foliar nitrogen, phosphorus and potassium concentrations. Therefore, waterlogging-induced nutrient deficiency is a mechanism involved in the growth reduction of these species under waterlogged conditions. Various methods of fertiliser application were investigated to determine the most \effective mode in ameliorating waterlogging damage. Soil-based applications of slow release fertilisers applied either prior to or after a waterlogging event were the most successful. Fertiliser application was associated with improved growth foliar nutrition and increased aerenchymatous root production. Reduced availability of nutrients in waterlogged soils and/or reduced uptake of these nutrients are the two possible mechanisms leading to the development of foliar nutrient deficiency of waterlogged plants. It was found that under hypoxic hydroponic culture seedlings with low nutrient status were capable of an increased uptake of nutrients when transferred to high nutrient conditions. This result is significant as it identifies reduced availability of soil nutrients as the primary mechanism responsible for the development of foliar nutrient deficiency in E. globulus and E. nitens under waterlogged conditions. The relationship between aerenchymatous root development and waterlogging tolerance was investigated. It was determined that singular measurements of root adaptive capacity should not be used as the sole measure of tolerance to waterlogging in these species. The regulation of growth and maintenance of relatively high photosynthetic rates are also useful indicators of tolerance. Using this array of measures it was determined that E. nitens was inherently more waterlogging tolerant than E. globulus. Eucalyptus globulus seedlings demonstrated a greater potential for increased waterlogging tolerance by the application of fertiliser regimes."