The mineralization of the organic matter is a very important phenomenon which leads to the release of nutriments used by plants. The rate of transformation of the organic matter depends on several factors and parameters such as climatic factors and biological and physicochemical properties of the soil and the litter. In this study, we investigate the effect of the addition of litter of various species as well as the effect of soil moisture on mineralization of organic matter and on mineral nitrogen release in three soils sampled in three cork oak stands during a period of 41 days under the same laboratory conditions. Carbon mineralization was determined using CO2 respiration method, whereas the mineral nitrogen content was measured at the last day of incubation both in soil samples with added plant leaf material, and in control soil samples without addition under two treatments of moisture (40% and 80% WHC-water holding capacity). Our results show that the addition of leaf litter causes an increase in the microbial activity. Soils without addition were significantly different from the plant leaf added soils in respect to carbon mineralization at the end of the incubation period. Moreover, it is noted that the mineralization of carbon is more marked with moisture at 80% than that of 40%, contrary to that of the nitrogen, which is not influenced by the variation of moisture.

The Mediterranean region is projected to experience severe drying trends and more extreme hydroclimate events as a consequence of anthropogenic climate change over the next century. In some places this signal may have already emerged from natural variability. Here we provide context for recent and future changes with a new high-resolution (0.5$^o$) spatial reconstruction of the Palmer Drought Severity Index (PDSI) using a tree-ring network that spans much of the last millennium. This network provides new information that extends and enhances the existing Old World Drought Atlas (OWDA), and we identify and attribute the differences between the OWDA and our reconstruction. We also reexamine previous conclusions about the severity of recent drought in the context of earlier centuries. We find that, in both the western Mediterranean and the Levant, recent dry periods are indeed the worst in at least the last 500 years, but our assessment of the significance and uncertainty of this finding is affected by differences in the tree-ring networks used for the reconstructions. Long millennium-length hydroclimate reconstructions in the Mediterranean provide the opportunity to understand variability and trends in the hydroclimate of the region, while extant uncertainties arising from the existing tree-ring chronology network and methodological choices call attention to locations that require further proxy collection and statistical scrutiny.

Une étude dendroécologique réalisée dans le nord-ouest de la Tunisie a permis de quantifier l’effet de variables climatiques mensuelles (températures et précipitations) sur la largeur des cernes de cinq populations de merisier (Prunus avium). L’analyse statistique montre que la sécheresse estivale de l’année précédente est le principal (mais non l’unique) facteur limitant la croissance radiale, suivie par la sécheresse de l’automne précédent et enfin le froid hivernal. La variabilité de la réponse dépend plus fortement des précipitations que des températures, une pluviométrie faible conduisant à une sensibilité plus forte au froid hivernal et aux sécheresses estivale et automnale. La croissance de Prunus avium est généralement influencée positivement par les températures maximales (décembre) et les précipitations (d’août à janvier).

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