Thigmomorphogenesis: a dose response to flexing in Ulmus americana seedlings

Abstract

Six-week-old half-sib seedlings of Ulmus americana L. were subjected to different amounts of flexure daily for 3 weeks under controlled greenhouse conditions. The daily flexure treatments were: no flexing in a staked stem, minimal flexing in a non-staked stem, and five, 10, 20, 40, and 80 flexures. Seedling height and diameter growth and average leaf area were determined before and after the treatments. The ratio of the change in height growth (DeltaH) to the change in diameter growth (DeltaD; (DeltaH:DeltaD)) before and after the 3-week treatments were calculated. At the end of the 3-week experiment, staked seedlings were significantly taller and had smaller stem diameters than all of the flexed seedlings. Height growth tended to decrease exponentially with increased flexure, with significant differences between the extremes of treatment. All of the flexure treatments significantly increased stem diameter compared to staked seedlings. The DeltaH:DeltaD ratio exhibited an exponential function in response to increased flexure. Average leaf area decreased with increased flexure, and seedlings in the 40x and 80x flexure treatments had significantly less leaf area than seedlings in all of the other treatments. These data are similar to the dose responses previously observed in herbaceous species. The finding that trees exhibit greater sensitivity to low doses of flexure than to high doses of flexure indicates that slight exposure to wind may result in a large initial alteration in stem morphology, producing a thigmomorphogenetic effect. Trees will continue to respond to increasing amounts of mechanical stress, but at an exponentially declining rate. Declining leaf areas in response to increasing amounts of mechanical stress may result in a decrease in available photosynthate, resulting in a tree of smaller stature compared to trees exposed to lower amounts of mechanical loading.

Effects of induced drought and tilting on biomass allocation, wood properties, compression wood formation and chemical composition of young Pinus radiata genotypes (clones)

“…While our results showed that T tilting does not affect growth and R/S ratios significantly, wind or other mechanical perturbations such as flexing had a direct effect of increasing radial growth, reducing stem elongation, and decreasing total biomass above ground (Telewski and Jaffe 1986;Stokes et al 1997;Telewski and Pruyn 1998;Kern et al 2005). Significant clonal differences were seen in the R/S ratio (Table 3).…”

RELATIONSHIP BETWEEN LIGNIN CONTENT AND QUALITY OF Pinus taeda SEEDLINGS1

“…In the month prior to planting, the accumulated rainfall was 230 mm, and during the evaluation period the cumulative value was 502 mm, with an air temperature of 20.8 ± 1.1 °C and relative humidity of 68.8 ± 3.7%. However, during the same period wind speed peaked between 62.6 to 85 km h which are capable of altering plant growth (TELEWSKI, 2012). Thus, under those conditions, the mechanical stimulus applied in the nursery triggered mechanisms of tolerance to external stimuli, resulting in greater success in establishing P. taeda seedlings, as growth at ninety days after planting were strongly influenced by the frequency of swayings applied in the nursery and the wind velocity was on the average higher than that recommended by Telewski (2012).…”

“…Response of plant growth to mechanical disturbance was coined as thigmomorphogenesis by Jaffe (1973) which causes reduction of primary growth (TELEWSKI; PRUYN, 1998;COUTAND et al, 2010), changes biomechanical properties of wood (CORDERO, 1999) and stimulates biosynthesis and chemical composition of lignin (KERN et al, 2005;HAMANN et al, 2009;SAIDI et al, 2011;RAMOS et al, 2012).…”

Neighbor and Height Effects on Crown Properties Associated with the Uniform-Stress Principle of Stem Formation

“…In trees, mechanical stimulation of the stems will increase their elasticity, requiring a larger cross section to maintain stiffness [21,88]. Trees will also slow height growth when exposed to wind [88,89]. Lundqvist and Elfin [90] worked with a Scot's pine (Pinus sylvestris L.) plantation where the trees had been planted using a repeated pattern of various spacings, thus creating a range of repeated spacings within the stand.…”