Plant functional shifts in Central European grassland under traditional flood irrigation

Abstract

Aims: Lowland meadow irrigation used to be a widespread management practice to improve hay yield in Central European grasslands. Recently, traditional meadow irrigation is being re-established in some parts of Europe. Nevertheless, the consequences of the regular artificial flooding on vegetation of these water meadows remain poorly understood. We studied the impact of flood irrigation on the plant functional and species composition of extensively managed hay meadows. Location: Lowland of River Queich, between Landau and Lustadt, Germany. Methods: We sampled vegetation in 34 meadows that differed in irrigation status (irrigated/non-irrigated) and fertilization (unfertilized/fertilized). Plants were classified into functional groups according to growth forms, N-fixing ability and reproductive strategy. Effects of meadow irrigation on the plant functional composition were analysed using two complementary approaches. In the 'community approach', we analysed total cover of each functional group per meadow with respect to irrigation and fertilization. In the 'species approach', we analysed the mean response to irrigation among the species within the defined functional groups. Results: Total cover of rosettes and semi-rosettes increased relative to graminoids in irrigated meadows. Cover of legumes was three times higher in irrigated compared to non-irrigated meadows. Irrigation enhanced preferences for seed and vegetative reproduction. However, the response of individual species within the functional groups was inconsistent. Fertilization had an overall minor influence on functional composition of the meadows. Conclusions: The higher proportion of plants with basal growth organs in irrigated meadows suggests that irrigation may enhance a more complex vertical structure of the vegetation. Enhancement of rosettes, semi-rosettes and legumes at the cost of graminoids through irrigation was more significant in the community than in the species approach, indicating that the functional group response was amplified by the respective dominant species. This highlights the importance of considering species-level interactions in functional vegetation analysis.