Gas exchange and crop yield of the reproductive organs in hybrid larch (Larix decidua x L. kaempferi) in relation to the vegetative carbon demand

Horn

2005

S. 179-193

9 Abb., 1 Tab., 42 Lit. Ang.

Artikel aus einer ZeitschriftUnselbständiges Werk

200138869

Little is known about the gas exchange of naturally growing, reproductive organs in larch trees, in particular, in comparison with the vegetative carbon (C) demand. The study focuses on the hybrid between European and Japanese larch, known for high capacities in stem growth and flower-ing. Male flowering mass can be as high as 1.6 mg cm[-][1], i.e. per unit length of twig section, while respiring 1.2 mg CO[2] g[-][1] h[-][1] at 15°C. The respiratory C release during the short flowering period in early April was about 11% of the C content of male flowers. The dark respiration rate of cones was, in July, only half as high as in male flowers, however, up to 60 % of the respired CO[2] was photo-synthetically refixed in cones under high-light and moderate temperature conditions. Cone photo-synthesis, being saturated at 900 μmol photons m[-][2] s[-][1] and declining with increasing temperature, lowered the daily respiration by about 22 % under variable light conditions. While overheating three times as much above the ambient air temperature as did larch needles, cones displayed a lower transpiration rate and water vapour conductance, the latter being insensitive to the climatic factors. The annual cone yield related to reduction in the radial stem increment, whereas radial branch growth was hardly affected. Reserves for male flowering appeared to be accumulated during preceding years favourable to stem growth. The carbon respired by the short-lived male flowers only demanded a minor portion of the annual, whole-tree C balance. However, at high cone yield of about 25 % of the biomass of radial stem increment, C costs of cones including respiration become significant in the tree's C balance. The abundant flowering of hybrid larch may be regarded as another expression of heterosis, as the high annual C gain apparently ensures ample reproduction. Given the high reproductive biomass, CO[2] refixation of cones alleviates the C balance at the whole-tree level.