Effects of waterlogging levels on Holcus lanatus response traits in different created topsoils

- Plant development responded primarily to topsoil type.
- Morphological traits responded positively to intermediate waterlogging treatment.
- Functional traits did not respond clearly to waterlogging levels and different topsoils.
- Amplitude of waterlogging effect was clearly dependent on topsoil tested.
- In wetland restoration experiment including maximization of plant growth, waterlogging and topsoil effects have to be considered together.

The effect of waterlogging was measured on the development of a wet grassland species, Holcus lanatus, grown on four recreated topsoils. Soils used for the experimental setup were collected from wet grasslands of the Seine floodplain to represent contrasting organic matter content and texture. Plants were submitted to no, medium and total waterlogging levels. The no waterlogging level, used as a control, was also performed to estimate the topsoil effects on H. lanatus growth. Morphological and functional response traits (e.g. shoot height, biomass, specific leaf area, nitrogen and carbon contents) were measured on harvested plants at the beginning of the experiment and after 3, 7, 30, and 90 days of waterlogging. As expected, a topsoil effect was immediately recorded on plant development traits (i.e. biomass, number of ramets, and height) and carbon content. On three soils of the four tested, H. lanatus better developed on medium waterlogging level which represents the intermediate level of constraints of the waterlogging gradient tested. Finally, the study demonstrates that the effect of medium waterlogging applied on plants varied among different topsoils. Interestingly, the effect of medium waterlogging was the most beneficial for topsoil conditions where plant initial growth was the lowest.