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| Content Provider | Springer Nature Link |
|---|---|
| Author | Klugmann, K. Roloff, A. |
| Copyright Year | 1999 |
| Abstract | In der vorliegenden Arbeit wurde der als Kladoptosis bekannte Prozeß der Zweigabgliederung anQuercus robur L. untersucht. Danach ist die Anlage zur Ausbildung einer Trennungszone während des Knospenstadiums an allen Seitenknospen vorhanden. Dagegen können Triebe, die aus der Terminalknospe entstanden sind, nicht abgegliedert werden. Bei jungen Stiel-Eichen geht unmittelbar nach dem Austrieb der Seitenknospen ihre Abgliederungsfähigkeit verloren. Mit zunehmendem Baumalter verzögert sich die Formation regulären Xylems im Abzweigungsbereich der Seitentriebe.Die Aufrechterhaltung der Trennungszone bewirkt aufgrund ihres histologischen Aufbaus eine Reduzierung der hydraulischen Leitfähigkeit. Die mit einer Trennungzone ausgestatteten Zweige befinden sich in einer indifferenten Phase, in der sie von dem regulären Hydrosystem des Baumes separiert sind. Sie können nachfolgend durch Abgliederung vollständig von ihm getrennt oder durch Eingliederung permanent an das Hydrosystem angeschlossen werden. Bei zusätzlichen negativen Umweltbedingungen steigt der Anteil der nur provisorisch an das Hydrosystem des Baumes angeschlossenen Zweige. In dieser Situation setzt die Eingliederung — Bildung regulären Xylems — nur noch im Abzweigungsbereich der vitalsten Seitenachsen ein.Aufgrund der Reduzierung der hydraulischen Leitfähigkeit wird es dem Baum möglich, das ihm verfügbare Wasser selektiv in der Krone zu verteilen. Eine reduzierte Eingliederungsdynamik der Trennungszone erhöht den hydraulischen Widerstand des daran anschließenden Sprosses. Die in dieser Situation steigende Anzahl der Trennungszonen führt zur Förderung der eingegliederten Leitäste und schützt diese vor unkontrollierter Xylem-Kavitation.The process known as cladoptosis has been investigated inQuercus robur L.. The results show an ontogenetic alteration of the hydraulic architecture which is additionally modified by the vigour of the tree.The preformation of the abscission zone is still present in all lateral buds during bud dormancy. Terminal shoots, however, do not form an abscission zone at their base at any time, which causes their inability to abscise. During juvenile ontogenesis the absciseability of the lateral buds is lost immediately after sprouting. In the further course of ontogenesis the formation of regular xylem (integration) within the stem junctions of the lateral shoots is retarded. The constricted conduits within the abscission zone limit hydraulic conductivity, equivalent to an increase in the hydraulic resistance. However, the absciseable twigs and branches are in an indifferent stage in which they are separated from the regular hydraulic system of the tree. In this stage hydraulically separated shoots are either connected by integration or disconnected by abscission. Negative environmental conditions increase the number of indifferent shoots. In this situation integration only occurs in the junctions of the most vigorous twigs.This special reaction optimizes the hydraulic conductivity by distributing a given water flow selectively within the branching. The hydraulic resistance of the shoot is increased by reduced integration dynamics. The increased number of abscission zones induced by unfavourable environmental conditions enables the tree to avoid runaway embolism during excessive droughts.The active control given by cladoptosis allows the tree to evaluate and control the xylem flow within its branching pattern. The integration and abscission of twigs varies according to environmental conditions. Years with water deficiencies reduce the photosynthesis of the indifferent (less vigorous) twigs and let them cavitate earlier, whereas photosynthesis of the youngest as well as the integrated twigs obviously remains unaffected. |
| Starting Page | 271 |
| Ending Page | 286 |
| Page Count | 16 |
| File Format | |
| ISSN | 00158003 |
| Journal | Forstwissenschaftliches Centralblatt vereinigt mit Tharandter forstliches Jahrbuch |
| Volume Number | 118 |
| Issue Number | 1-6 |
| e-ISSN | 14390337 |
| Language | English |
| Publisher | Springer-Verlag |
| Publisher Date | 1999-01-01 |
| Publisher Place | Berlin, Heidelberg |
| Access Restriction | Subscribed |
| Subject Keyword | twig abscission (cladoptosis) Quercus robur L. hydraulic resistance xylem cavitation decline symptoms Forestry Plant Sciences Plant Ecology |
| Content Type | Text |
| Resource Type | Article |
| Subject | Plant Science Forestry |
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