Are morpho-functional traits reliable indicators of inherent relative growth rate for prealpine calcareous grassland species?

Abstract

Relative growth rate (RGR) is a fundamental trait for comparative plant ecology but cannot be measured in situ, leading to problems in interpreting vegetation function. However, the components of RGR (net assimilation rate (NAR), leaf area ratio (LAR), leaf weight ratio (LWR), and specific leaf area (SLA)) can be calculated for wild plants from morphological measurements (leaf area, leaf dry mass, whole plant dry mass), which potentially reflect RGR. Seeds of 19 species from Italian prealpine calcareous grasslands were collected and seedlings were cultivated under controlled conditions. RGR, NAR, LAR, LWR and SLA were analysed. The results demonstrated that RGR was positively correlated with SLA and LAR (p < 0.01). Furthermore, LAR was positively correlated with LWR and negatively with NAR (p < 0.05). Monocotyledons showed significantly higher LAR, LWR and NAR than dicotyledons, as the latter allocated a greater proportion of biomass to stems, but RGR and SLA showed no such phylogenetic constraint. Therefore SLA is the most reliable indicator of RGR in ecological and functional surveys of prealpine calcareous grasslands, and has the additional advantage that it can be measured from leaf material alone. Lower mean RGR and SLA for calcareous grassland species suggests that this vegetation is less likely to recover from the effects of disturbance than meadows and dry meadows.

Key words:

• Calcareous grasslands
• functional ecology
• hard trait
• leaf economics spectrum
• soft trait

Acknowledgements

The research was financially supported by Centro Flora Autoctona of Lombardy and is partially included in the Life Project Natura 2000 “Integrated management of Insubric-Prealpine habitats” (LIFE00NAT/IT/7258). We would like to thank Prof. Rod Hunt and Prof. Donato Chiatante for helpful suggestions on data analysis and comments on an early version of the manuscript. We are also pleased to acknowledge the consistent support of Christian Cammareri during plant cultivation.