排序方式: 共有63条查询结果,搜索用时 15 毫秒
61.
Marion Durand-Gillmann Maxime Cailleret Thomas Boivin Louis-Michel Nageleisen Hendrik Davi 《Annals of Forest Science》2014,71(6):659-673
? Context
In recent decades, there have been increasing reports of forest decline, especially in Mediterranean forest ecosystems. Decline in tree vitality is usually due to complex interactions between abiotic factors and biotic agents that attack weakened trees.? Aims and methods
Estimating dendrometrical characteristics [basal area increment (BAI), age at DBH from tree ring counting, social status, height, and diameter], tree health status, and a competition index, we investigated the individual vulnerability of a French declining silver fir forest to both mistletoe (Viscum album L. ssp. abietis) and bark beetles (Pityophthorus pityographus Ratz., Pityokteines vorontzovi Jac., and Pityokteines spinidens Reitt.).? Results
BAI was negatively correlated with both mistletoe infection (via mistletoe biomass) and bark beetle attack (number of insects per square meter), but there was evidence of divergence in tree choice between two groups of parasites. Mistletoe preferentially infected isolated and dominant trees that showed higher past growth rates than non-infected ones. Conversely, bark beetles mainly attacked defoliated and preferably declining trees with diameter (DBH) lower than 44.5 cm and slower past growth.? Conclusion
While successive severe drought periods are thought to greatly weaken southern silver fir populations, mistletoe and bark beetles may contribute actively to their decline processes as inciting and contributing factors, respectively. 相似文献62.
63.
Valérie Maxime Karine Pichavant Gilles Boeuf Guy Nonnotte 《Fish physiology and biochemistry》2000,22(1):51-59
Variations in respiratory and acid-base status were studied in turbot (Scophthalmus maximus) during progressive severe hypoxia followed by recovery under normoxic conditions. The first behavioural strategy of turbot under hypoxia was an increase in amplitude and frequency of ventilation. Consequently, standard O2 consumption remained unchanged over a broad range of O2 tensions, until a low critical level of 30 mmHg. The hyperventilation induced a moderate blood alkalosis, compensated by a lactic acidosis. The fact that blood pH did not decrease below control values could be explained by the retention in white muscle of most of the lactate produced and by a high capacity for H+ excretion. During the recovery period, the marked increase in O2 uptake corresponding to an oxygen debt repayment, was partly related to the lactate elimination. When total energy contributions of aerobic and anaerobic processes were assessed in terms of ATP, the anaerobic contribution, estimated at the deepest hypoxia level, was higher than 20% of the total energy budget and appeared to totally compensate for the decline in aerobic metabolism. Moreover, the high value of O2 tension in arterial blood in normoxia and during recovery from hypoxia showed high diffusing capacity of gills in turbot. Our results explain the high tolerance of turbot for O2 deficient waters. 相似文献