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To determine sequestration rates of carbon dioxide (C[O.sub.2]) we calculated the carbon (C) storage rate in humus layers of Swedish forests with Podsolic soils, which account for 14.2 x [10.sup.6] ha of the 22.7 x [10.sup.6] ha of forested land in Sweden. Our data set covered 41 years of humus inventories and mean humus layer thickness in 82513 plots. We analysed three forest types: (i) all combinations of tree species, (ii) forests dominated (>70%) by Norway spruce (Picea abies (L.) Karst.), and (iii) forests dominated (>70%) by Scots pine (Pinus sylvestres L.). To relate changes in humus layer thickness to land area we used the intersections in 25 km x 25 km grids and used kriging interpolation, permitting calculations for each forest type. For each intersection mean humus thickness for each year was calculated and regressed against time to obtain the rate of change. This rate, humus bulk density, and humus C concentration were used to calculate sequestration rates. The mean sequestration rate was 251 kg C x [ha.sup.-1] x [year.sup.-1], which is higher than theoretical values. The sequestration rate was positively related to temperature sum, albeit including effects of forest management. The pine-dominated forest type had a mean rate of 283 kg C x [ha.sup.-1] x [year.sup.-1], and the spruce-dominated had a mean rate of 239 kg C x [ha.sup.-1] x [year.sup.-1]. Under similar site conditions, pine sequestered more C than spruce (difference of 71 kg C x [ha.sup.-1] x [year.sup.-1]; p < 0.0001), showing the importance of this type of ecosystem for C sequestration. Pour determiner le taux de sequestration du dioxyde de carbone (C[O.sub.2]), nous avons calcule le taux de stockage du carbone (C) dans la couche d'humus des forets suedoises etablies sur un sol podzolique qui representent 14,2 x [10.sup.6] ha des 22,7 x [10.sup.6] ha de foret. Nos donnees couvraient 41 annees d'inventaire de l'humus incluant la profondeur moyenne de la couche d'humus dans 82 513 placettes. L' analyse a porte sur trois types de forets : (i) les forets composees de toutes les combinaisons d'especes d'arbres; (ii) les forets dominees (>70 %) par l'epicea commun (Picea abies (L.) Karst.); (iii) les forets dominees (>70 %) par le pin sylvestre (Pinus sylvestres L.). Pour relier les variations de profondeur de l'humus a la superficie du terrain, nous avons utilise les intersections dans des grilles de 25 km x 25 km et le krigeage, ce qui permettait de faire le calcul pour chaque type de forets. A chaque intersection, la profondeur moyenne de l'humus a ete calculee pour chacune des annees et une courbe de regression a ete etablie en fonction du temps, ce quia permis d'obtenir le taux de variation. Ce taux, la densite apparente de l'humus et la concentration de C dans l'humus ont ete utilises pour calculer le taux de sequestration. Le taux moyen atteignait de 251 kg C x [ha.sup.-1] x [an.sup.-1], ce qui est plus eleve que la valeur theorique, et l'augmentation etait positivement reliee a la somme des temperatures, bien que les effets de l'amenagement forestier soient inclus. Le taux moyen etait respectivement de 283 et 239 kg C x [ha.sup.-1] x [an.sup.-1] dans le groupe de forets domine par le pin et dans le groupe domine par l'epicea. Dans des conditions similaires de station, le pin sequestrait plus de C que l'epicea (difference de 71 kg C x [ha.sup.-1] x [an.sup.-1]; p < 0,0001), ce qui montre l'importance du type d'ecosysteme pour la sequestration de C. [Traduit par la Redaction], Introduction Although soil organic matter (SOM) holds the largest carbon (C) pool on land (1.5 x [10.sup.15] kg, three times that of vegetation), little is known about the current net [...]

Romanian populations of Norway spruce are induced to set terminal budsby four inductive cycles of 8 h light/16 h darkness. To distinguish betweencircadian and hourglass timekeeping for the photoperiodic control of budset,seedlings were raised in continuous light at 300 μmol m[sup -2] s[sup -1] at 20°C for 10 weeks. They were then exposed to anextended night regime consisting of three cycles of 8 h light/40 h dark with4-h or 1-h nightbreaks (120 μmol m[sup -2] s[sup -1] )applied to groups of plants at intervals during the extended night. Followinga final cycle of 8 h light/16 h dark to maximize budset, the plants were transferredto continuous light. Budset was delayed when the night-break was applied closeto the critical nightlength (CNL) of 6–7 h or about 22–23 h laterin the extended night, consistent with circadian rather than hourglass timekeeping.Confidence intervals were calculated for the times to maximum effect of thenight-breaks. [ABSTRACT FROM AUTHOR]