Response of leaf respiration to water stress in Mediterranean species with different growth forms

The aim of the present study was to undertake a comparative analysis of the effects of water stress on leaf respiration rates and carbon balance, including a wide variety of Mediterranean species with different growth forms and evolutionary history. Plant water relations, photosynthetic and respiration rates, and specific leaf area were measured in plants grown in pots and subjected to different levels of water stress, the most severe followed by re-watering. A high range of variation was observed in maximum leaf respiration rates, largely related to differences among plant growth forms. Leaf respiration rates decreased under drought in most but not all species. Such decline also resulted growth form-dependent, with herbs showing both the highest proportional decrease and the highest recovery after re-watering, and evergreens the lowest, reflecting differences in respiration requirements due to different life span and growth carbon costs between growth forms. The decline in respiration in response to drought occurred at a stomatal conductance threshold which is coincident with that observed to induce down-regulation of the activity of many other metabolic components, suggesting that decreased respiration is part of a systemic metabolic response, which occurs under conditions where drought severely restricts CO2 availability inside leaves.