Life history traits in contrasting environments - intraspecies variation in stress tolerance

Seeds are the next generation of a plant and the transition from seed to seedling is germination that begins with the absorption of water. Germination is controlled by several environmental factors, such as water availability, temperature, light and soil chemistry and the resulting combination of germination requirements is the germination niche, a key aspect of the plant regeneration. The knowledge of such descriptors are of outmost importance in order to select the apropriate species according the location environments in a restotation context. Seed germination characters do not necessarily predict seedling emergence and the timing of plant development, the latter seemingly an ecological function of ‘biology x environment’ and an essential requirement of restoration ecology effort. The effects of temperature, droght stress, exogenous nitrate, seed and soil nitrogen forms content, soil gravimetric water content and seed mucilage quantity in the germination and seedling performance of Plantago albicans, P. coronopus, P. lagopus and P. lanceolata were adressed in the present work. The first aim of this work was test the seed germination and the seedling development in temperature and water stress conditions in order to predict its effects on species in the environment restoration context. Using 30 accessions of P. coronopus, and P. lanceolata in temperature and water stress conditions, experiments showed that P. coronopus germination and normal seedling development physiologic traits differed significantly among the species tested, showing a clear species-specific temperature and minimum water requirement for germination and seedling development. Seed performance refers to the seed germination capacity under various environmental conditions and represents a critical component of the plant life cycle which is of imminent ecological importance. Dormancy is a mechanism by which species can bet, or spread the risk of starting the life cycle by ensuring a degree of non-germination even when conditions are good for germination. Nitrate and light has being described to break seed dormancy in several species but little is known about the interplay between temperature and nitrate in the germination improvement. Our second aim was: 1) evaluate the contribution of temperature regimens and exogenous nitrate to, and its interaction in seed germination improvement; 2) evaluate the effect of the different forms of nitrogen and carbon present in seeds and soils and the contribution of these nutrients to the germination and extrapolate to the ecosystems and 3) evaluate the impact of the exogenous nitrate on the germination cardinal base temperature and thermal time requirement. Using seeds and soil samples of 22 accessions of the four above referred Plantago species, results showed that exogenous nitrate is more effective at constant temperatures, loses effectiveness at supra-optimum temperatures and cooler temperatures and nitrate interaction could interfere positively with the dormancy.