| Terrestrial ecosystems are characterized by an intricate relationship between plants and soils that influence ecosystem and community level processes and properties. At the ecosystem level, plants (producers) provide organic carbon to the decomposer subsystem and obligate root-associated organisms once they die. In turn, the decomposer subsystem breaks down dead plant material and ultimately returns this carbon to the atmosphere. At a lower level of ecological organization, litter can have profound impacts on plant-plant interactions through physical and/or chemical effects. I investigated the role that litter plays at these two levels of ecological interaction.;Decomposition varied as function of site and was higher for root than shoot litter. Clipping intensity had no effect on decomposition across all sites. In contrast, drought significantly hampered decomposition whereas warming significantly decreased shoot decomposition but increased root decomposition, although insignificant. Drought generally reduced litter quality consequently retarding decomposition and this effect was further enhanced under drought condition. These findings suggest that in the short-term temperature and precipitation may have direct consequences on carbon storage in these systems.;Second, I studied the interactive effects between litter, root competition and belowground chemical interaction, as well as the effect of root exudates on plant growth, competition and evenness. The nature of belowground interaction switched from negative when aboveground litter was left intact to positive when removed. Root exudates enhanced plant growth, modified competition and enhanced evenness. These results show the existence of other potential non-resource mechanisms that may play a role in the organization of natural plant communities.;First, I conducted a short-term factorial decomposition study testing the interactive effects of warming, drought, and land use practice (simulated grazing) on root and shoot litter decomposition. The study was carried out over a 2-year period at three sites across the Canadian Prairie Provinces. I manipulated temperature using open-top chambers (OTCs), reduced precipitation using rainout shelters, and manually clipped vegetation at varied levels consistent with grazing practices in the region. Additionally, I studied the effect of litter quality on decomposition, whereby litter material pre-exposed to climate manipulations were placed in plots of origin (in situ) or in untreated standard plots. |
