No abstract

Summary — The purpose of this study was to explain large differences in growth and decline of the pedunculate oak (Ouercus robur L) and the sessile oak (Q petraea Liebl) observed in the forest as a result of drought. In addition, northern red oak (Q rubra L) was compared with the 2 indigenous oaks. The effects of controlled soil water deficits on growth and water relations of young plants of these 3 species grown in large boxes have been studied. The plants were old enough to have developed normal root systems. Two species were planted in each box, and submitted to very similar patterns of water stress. Predawn leaf water potential, stomatal conductance, net assimilation rates, shoot elongation and mortality were monitored. The effect of an overall improvement in mineral nutrition on these parameters was also tested. During water deficit (decrease in predawn leaf water potential), the pattern of decrease of gas exchange was similar for the 3 species. Thus, their ability to limit water deficit by reduction of transpiration was similar. On the other hand, shoot growth of Q rubra was more reduced than that of Q robur for similar predawn leaf water potential; growth of Q petraea was the least sensitive. However, increase of mineral nutrition improved the growth of both Q robur and Q rubra, but not that of Q petraea. For the 3 species, no mortality was noted as long as predawn leaf water potentials remained > -3.6 MPa. Below this limit, the mortality rate was highest in Q robur, Q petraea and lowest in Q rubra. These differences in mortality between species are due to differences in tolerance to water stress, not in avoidance.drought / growth I gas exchange I dieback I fertilization I Quercus Résumé — Différences dans la résistance à la sécheresse de 3 espèces de chêne à feuilles caduques, cultivées en conteneurs.

-The aim of this study was to examine the influence of long-term soil water deficit on growth and physiological processes of two black pine varieties (Pinus nigra ssp. laricio var.Corsicana and Pinus nigra ssp. laricio var. Calabrica). Three-year-old seedlings grown in larges boxes (volume: 1.62 m 3 ) were subjected to a prolonged summer drought (99 days from the end of June until the end of September) and photosynthesis (A)

No abstract

Summary — When investigating historical alterations of the soil chemistry, it could be interesting to determine the mineral content of the successive annual tree rings. The study reported here aimed at verifying this assumption. Oak heartwood was selected in order to minimize the disturbance due to element translocations in the wood. This study was carried out in a forest included in a floristic and edaphic survey performed earlier throughout northeast France. Xylem cores were extracted from the boles of five over 60-year-old pedunculate oaks in each of 68 plots. The analysis showed on average an increase in nitrogen and aluminum, a decrease in phosphorus, potassium and magnesium, and no change for calcium, in the rings corresponding to the last 30 years of the heartwood . These results are consistent with those of the floristic and edaphic survey, which had shown an increase in nitrogen and a trend towards acidification in most of the soils between 1970 and 1990, mainly due to atmospheric deposition (Thimonier et al, 1992