Functional response of graminoid species to changing summer water availability: insight into the effects of climate change in sub-Mediterranean meadows

We measured leaf area, dry mass and plant height and calculated SLA on randomly collected leaf samples of dominant graminoid species (three replicates for each treatment with different watering frequency), at three times of one growing season, and tested the effect of treatments on these variables, controlling for phenological state of plant, leaf state and time of data collection. We found that in some perennial late spring/early summer-flowering species (i.e. Cynosurus cristatus and Lolium perenne), reduced rainfall, jointly with phenological phase and time, affected in the same direction both leaf area and dry mass, leaving SLA values substantially unchanged during the growing season. Additional rain increased significantly SLA in Cynosurus cristatus, due to a higher increase in leaf area than in dry mass. In other perennial species (i.e. Arrhenatherum elatius and Elymus repens) with later reproductive cycle, increase in drought caused a significant decrease in SLA, associated to a reduction in leaf area, especially at the end of the treatment (summer end), indicating a shift of plant strategy to a lower efficiency in resource acquisition and use. Contrariwise, the increase in drought within a growing season, had a modest influence on plant height. These results suggest that response patterns of leaf traits to reduced water availability are species-specific and are probably linked to species’ functional structure.