Leaf water relations for 23 angiosperm species from steppe grasslands and associated habitats in Hungary

Pressure-volume (p-V) analysis, instantaneous transpiration rate and relevant leaf structural information were used to compare leaf water relations for 23 angiosperm species from semiarid temperate loess-, sand- and saline steppe grasslands and several associated habitats representing a water availability gradient. For the species studied, the most marked differences occurred between grasses and dicots. Grasses in our survey possessed low (highly negative) osmotic potential both at water saturation and at turgor loss, moderate transpiration rate, relatively high leaf dry matter proportion (DMP) and - except for the sclerophyllous Festuca species - high specific leaf area (SLA, area per unit dry mass). In contrast, dicots had lower bulk tissue elasticity, higher (less negative) osmotic potentials, intense transpiration, and lower SLA andDMP than grasses. Therefore, grasses mainly invest in osmotic potential to extract water from drying soil, while dicots rely on relatively inelastic tissue that decreases water potential by a rapid drop of turgor with turgor loss occurring at relatively high water content. Habitat effects were significant for osmotic parameters only. Osmotic potential at full turgor and at turgor loss decreased in the following order: loess grassland ? sand grassland ??saline grassland ? loess wall. Life form influenced leaf structure only, since annuals possessed markedly higher SLA and lower DMP than perennials. Comparison of habitat specialist species within the same genus revealed that certain congeners (Achillea and Aster spp.) do not differ significantly in leaf water relations, thus they might rely on similar water supply in the three steppes. Other congeners (Festuca, Kochia and Plantago spp.) differed considerably, thus for these plants leaf function and structure must be different to ensure survival under the contrasting water regime. For the two generalist grasses (Cynodon dactylon and Dactylis glomerata) habitat-specific populations showed a tendency of increasing capacity for water extraction from soil (more negative water potential) with increasing habitat dryness, although differences were significant only between the extremes of the water availability gradient.