Fine Root Traits Are Correlated with Flooding Duration while Aboveground Traits Are Related to Grazing in an Ephemeral Wetland

Functional traits affect species ranges, but it is unclear how above and below-ground traits determine species responses to flooding and herbivory in wetland communities. We analyzed community-weighted means (CWM) of nine functional traits along a hydrological gradient inside and outside of grazing exclosures in an ephemeral wetland in New Zealand. Root traits exhibited the strongest relationships with the flooding gradient. Root aerenchyma increased linearly as flooding increased but plateaued in the ungrazed treatment. Root dry matter content and root tissue density decreased non-linearly as flooding increased. Grazing reduced the strength of the trait-flooding relationships for all traits except root tissue density, specific root length, and aboveground dry matter content. Specific leaf area decreased non-linearly and height increased linearly with flooding in the ungrazed treatment. Our results indicate that fine root traits can provide more information about the functional adaptation of plants to variation in flooding duration than aboveground traits, but traits such as height and specific leaf area responded to the exclusion of herbivores. Altered hydrological dynamics driven by changes in precipitation regimes will induce shifts in species ranges. Fine root traits, especially aerenchyma, can be used to predict how wetland species will respond to changes in soil hydrology.