Leif Eklund

Endogenous levels of oxygen, carbon dioxide and ethylene in stems of Norway spruce trees during one growing season

SummaryThe trees sampled in this study came from two stands of Norway spruce, Picea abies (L.) Karst., near Stockholm, Sweden, differing in mean age and height. Holes were bored perpendicular to the stem surface, and gas samples were taken from the outer part of the sapwood throughout one growing season. Endogenous levels of molecular oxygen (O2), carbon dioxide (CO2) and ethylene in the outer sapwood were determined by combined gas chromatography — mass spectrometry (GC-MS) and GC. O2 concentrations began to decrease as growth started in spring. The lowest levels (<5%) were recorded around mid-summer. In the younger stand concentrations remained below 5% until September. In October, O2 concentrations in the sapwood were similar to those of air. Concentrations of CO2 were below 1% in spring, but began to rise in May, peaking a month later at approximately 10%. Thereafter a slow decrease occurred until October, by which time levels had returned to those recorded in spring. Ethylene concentrations in the older stand reached 75 ppm early in May, while levels in the younger stand peaked at around 30 ppm later in May. Thereafter ethylene levels in both stands started to decrease down to ppb levels. The correlation between determined gas levels and physiological events associated with the seasonal growth cycle in temperate zones is discussed.

Ethylene in relation to compression wood formation in Abies balsamea shoots

Abstract The terminal (1-year-old) shoot of dormant, 2-year-old balsam fir [Abies balsamea (L.) Mill.] seedlings was either left vertically oriented or tilted to an angle of 60° from the vertical (tilting experiment), or was ringed with N-1-naphthylphthalamic acid (NPA), an inhibitor of indole-3-acetic acid transport, at a concentration of 0, 1 or 10 mg g−1 lanolin (NPA experiment). After 6 weeks of growth, ethylene evolution from the cambial region was measured by gas chromatography – flame ionization detection, and tracheid production and compression wood formation were determined by microscopy. In vertical seedlings of the tilting experiment and in 0 mg g−1-treated seedlings of the NPA experiment, compression wood was not formed and neither ethylene evolution nor tracheid production varied longitudinally or circumferentially within the stem. Tilting induced compression wood formation and increased ethylene evolution and tracheid production on the lower side of the stem, while decreasing tracheid production on the upper side. Compression wood formation was induced and tracheid production and ethylene evolution were stimulated at and above the point where 1 or 10 mg NPA g−1 was applied, whereas below this point compression wood was not formed and tracheid production was inhibited. In both tilting and NPA experiments, there was a positive correlation between ethylene evolution and tracheid production when data from all seedlings were analyzed, but not when data from seedlings forming compression wood were excluded. The results indicate that cambial region ethylene evolution is enhanced when compression wood is being formed, and that the enhancement is related to compression wood formation per se rather than the associated increase in tracheid production.

Restricted lateral gas movement in Pinus strobus branches

Argon gas was incorporated into the sap flowing through xylem of cut branches, or added to the air in a sealed cuvette surrounding a needle-free portion of the branch to investigate lateral movement of gases in Pinus strobus. Microdialysis was used to sample air in the xylem and evacuated vials were used to collect samples of air from cuvettes attached to branches. Argon concentrations of samples of air were measured by GC-MS. When argon was added through the sap, concentrations of argon in the xylem and in air of chambers enclosing needle stumps was greater than that of controls, but argon concentrations of air in cuvettes enclosing a needle-free portion of the branch were not greater than controls. When argon was added to cuvettes enclosing a needle-free portion of the branch, the argon did not enter the xylem and it was not emitted by needle stumps.

The influence of wind on spiral grain formation in conifer trees

Abstract The correlation between spiral grain formation and crown asymmetry was investigated in 18 Scots pine (Pinus sylvestris L.) and 17 Norway spruce [Picea abies (L.) Karst.] trees selected from clones of each species growing in the south of Sweden. The angle between the longitudinal direction of the tracheids in the outermost year ring compared to the longitudinal direction of the stem was measured by scribing lines which followed the direction of the tracheids. The crown asymmetry was measured by taking photographs of the trees followed by a simple picture analysis of the tree. Wind data for the growing seasons of 1997 and 1998 were obtained from the Swedish Meteorological and Hydrological Institute. The results showed a significant correlation between the angle of the tracheids compared to the stem longitudinal direction going from a left-handed angle if the trees had a crown projected to the north towards a right-handed angle the more the crown projects to the south.

Enhanced growth and ethylene increases spiral grain formation in Picea abies and Abies balsamea trees

Abstract. Spiral grain angle in Norway spruce (Picea abies) trees and balsam fir (Abies balsamea) seedlings was investigated in relation to growth rate, endogenous and applied ethylene. Trees from stands of Norway spruce, which were irrigated and fertilised in order to enhance growth, and trees having different growth rates in non-treated stands were studied. Stem growth rate at the stand level (m3 ha–1 year–1) was measured annually, or by means of microscopy on stem sections as the number and size of tracheids produced. Enhanced growth increased ethylene evolution and maintained a high level of left-handed spiral grain angle in comparison to slower-growing trees. An increased number of earlywood tracheids in fast growing trees was correlated to a more left-handed spiral grain angle. Ethrel, applied to stems of balsam fir seedlings, increased the internal ethylene levels in parallel with increased left-handed spiral grain angle. The results indicate that ethylene regulates the extent of spiral grain angle.