Comportement des semis de Pin d'Alep sous contraintes thermiques.

Abstract

In Algeria, the pine forests are concentrated mainly in arid and semi arid regions where the climatic conditions limit the production potential seriously. Due to the unpredictable nature of thermal stress, tolerance is the most effective strategy in situations of severe and prolonged stress. At the time of this tolerance one attends modifications of structures or functions which increase the probability of being useful and production plants in these conditions. In this study, seedlings of Aleppo pine are conducted according to two tests, first under semicontrolled conditions and under natural conditions. We fixed as objective to evaluate the effect of thermal stress from the biochemical markers such as the synthesis of proline, sugars, chlorophyll, proteins and to examine differences in these parameters between the organ (old needles and young shoots, stems and roots). The accumulation of various osmolytes under natural conditions showed that the sugars and proline, are much more concentrated in shoots (needles), stems and roots, but the winter period (hardness) and spring (active growth period) that give the greatest rate, the values of chlorophyll observed significant falls. The intensity of stress is positively correlated with proline, soluble sugars, and negatively with chlorophylls in winter and summer. At leaf level, high temperatures are manifested by a change in gas exchange following the closure of stomatal bands which may reflect an adaptation of the needles of Aleppo pine to heat stress. Thus, the biochemical parameters measured after the application of heat treatments also reflect a tolerance to low and high temperatures. These conditions have resulted in seedlings of Aleppo pine a reduction of chlorophyll content, an accumulation of osmoticums including proline and sugars as well as an increase in protein synthesis. Chlorophyll is negatively correlated with the other metabolites, which are correlated with each other. The results show that the concentrations of these compounds vary depending on the seedling organ and the severity of stress with thermal limits between -10 °C and 42 Ä°C. On the morphological plan, growth of seedlings of Aleppo pine is greatly weakened by the winter conditions. However, the rate of recovery is improved during the spring season and reaches a maximum value during the summer season. In conclusion, the study revealed the thermophilous character of seedlings of Aleppo pine and shows that these last used the same strategies of tolerance opposite to the thermal stress but the only difference is in the synthesis rates of the studied markers.