Ecological significance of plant biomass turnover

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Distribution patterns of organisms are largely determined by their ability to cope with different environmental conditions. For plants, the availability of nutrients, water and light plays a major role. Acquisition of these resources is well studied, but equally important for the species ecology, though less studied, is the ability to avoid losses of the resources, once acquired. Resource losses are closely related to leaf and root mortality and turnover. The described research will focus on root turnover. In many ecosystems more than half of plant biomass is below ground. However, below-ground processes are not readily visible, and our knowledge of root turnover still lags behind that of above-ground processes, especially in natural environments. There is increasing evidence that the commonly held views of the ephemeral character of fine roots, and a lack of seasonal patterns in fine root mortality are not always true. In Northern Ontario wetlands many species maintain fine roots over the winter, in other species the roots die synchronously in the fall. The hypothesis underlying this project is that these mortality patterns can be explained by costs and benefits: Cool soil temperatures in the north lower the respiration costs, and site pre-emption by long-lived roots increases a species' competitive ability. In habitats with unlikely winter survival due to disturbance, any investment in survival would be wasted, and the roots are programmed to die in the fall. Root mortality patterns of northern wetland species will be assessed, and related to respiration costs, likelihood of disturbance during the winter, and soil temperatures. It will be investigated whether mild winters might change the mortality patterns. Above-ground mortality patterns will also be assessed, as this is necessary for a proper understanding of the significance of root turnover patterns for the whole plant. The expected results are not only important for our ability to predict species behaviour, but also for accurate predictions of root turnover and the resulting carbon cycling and sequestration in the wetlands which cover large areas in Canada's North.