Although the structure and composition of plant communities is known to influence the functioning of ecosystems, there is as yet no agreement as to how these should be described from a functional perspective. We tested the biomass ratio hypothesis, which postulates that ecosystem properties should depend on species traits and on species contribution to the total biomass of the community, in a successional sere following vineyard abandonment in the Mediterranean region of France. Ecosystem-specific net primary productivity, litter decomposition rate, and total soil carbon and nitrogen varied significantly with field age, and correlated with community-aggregated (i.e., weighed according to the relative abundance of species) functional leaf traits. The three easily measurable traits tested, specific leaf area, leaf dry matter content, and nitrogen concentration, provide a simple means to scale up from organ to ecosystem functioning in complex plant communities. We propose that they be called ''functional markers,'' and be used to assess the impacts of community changes on ecosystem properties induced, in particular, by global change drivers.

Summary1. The impact of sample preparation, rehydration procedure and time of collection on the determination of specific leaf area (SLA, the ratio of leaf area to leaf dry mass) and leaf dry matter content (LDMC, the ratio of leaf dry mass to fresh mass) of mature leaves was studied in three wild species growing in the field, chosen for their contrasting SLA and LDMC. 2. Complete rehydration was achieved 6 h after samples were placed into water, but neither of the procedures tested -preparation of samples before rehydration or temperature applied during rehydration -had a significant effect on the final values of SLA or LDMC. 3. As expected, water-saturated leaves had a lower LDMC than non-rehydrated leaves; more surprisingly, their SLA was also higher. The impact of rehydration on SLA was especially important when the SLA of the species was high. 4. There was no significant effect of time of sampling on either trait in any species over the time period covered (09·00-16·30 h). 5. These results suggest that SLA and LDMC obtained on water-saturated leaves (SLA SAT and LDMC SAT ) can be used for species comparisons. We propose a standardized protocol for the measurement of these traits. This would allow for better consistency in data collection, a prerequisite for the constitution of large databases of functional traits.

Summary• Specific leaf area (leaf area to dry mass ratio), leaf dry matter content (leaf dry mass to saturated fresh mass ratio) and leaf nitrogen concentration (LNC) have been proposed as indicators of plant resource use in data bases of plant functional traits.• We tested whether species ranking based on these traits was repeatable by studying spatio-temporal variations in specific leaf area and leaf dry matter content of water-saturated leaves (SLA SAT and LDMC SAT ), as well as in LNC, for 57 herbaceous and woody species (or subsets thereof) growing under the Mediterranean climate of southern France.• Interseason and intersite variations were more pronounced than interannual variations, but species ranking for a given trait remained mostly consistent in space and time. Classifications based on LDMC SAT were generally more repeatable across years and sites, whereas those based on SLA SAT were more stable over seasons. LNC usually gave the least repeatable classifications.• Species rankings were not completely similar for the three traits. Discussion of reproducibility, ease of trait measurement, as well as trait-function relationships led us to propose that measurements of the leaf traits, SLA SAT and/or LDMC SAT , were the most suitable in large screening programmes.