The role of root system characteristics in plant responses to flooding and drought.

摘要

The importance of wetlands is increasingly being recognized yet changing hydrological patterns threaten their existence. To understand how wetland plant communities will respond, aspects of flooding and drought tolerance of several plant species were investigated. Under flooded conditions oxygenation of submerged organs is critical to their ability to function. I identified experimentally a novel pathway for oxygen transport, via an aerenchymatous phellem in Lythrum salicaria. Many plants produce adventitious roots along submerged parts of stems when flooded. If they are also colonized by AM fungi, three pathways for resource uptake exist: adventitious roots, AM hyphae and the primary root system. Using L. salicaria as a test species, I found that if the ability of one or more of these pathways to acquire resources is compromised, the remaining pathway(s) compensate. In terrestrial systems, arbuscular mycorrhizal (AM) fungi improve phosphorus nutrition of their host plant; their importance in aquatic systems was unclear. By assessing the performance of AM inoculated and non-inoculated L. salicaria plants grown under inundated conditions at 5 levels of phosphorus availability, I found that AM fungi do not significantly improve plant performance and, as in terrestrial systems, higher levels of P reduced AM colonization levels. Establishing predictive models of plant community response to perturbation based on functional group responses is a current trend in plant community ecology. Anatomical and morphological traits of root systems of 17 wetland species from five families were investigated for their potential in defining functional groups; many root system traits are hypothesized to confer flooding and/or drought tolerance. A functional group approach to predicting wetland plant community response to changing hydrological conditions was not feasible. Several assumptions implicit in this approach were not met; the traits that define groups varied across levels of water availability and species, and traits were not consistently correlated with performance among species or levels of water availability. Further, responses and their contribution to performance did not agree with predictions based on current literature. I conclude that traits that contribute to flooding and drought tolerance are species specific and that the relationship between traits performance are more complex than currently believed.