Aim To identify temperatures at which cell division and differentiation are active in order to verify the existence of a common critical temperature determining growth in conifers of cold climates. Location Ten European and Canadian sites at different latitudes and altitudes. Methods The periods of cambial activity and cell differentiation were assessed on a weekly time-scale on histological sections of cambium and wood tissue collected over 2 to 5 years per site from 1998 to 2005 from the stems of seven conifer species. All data were compared with daily air temperatures recorded from weather stations located close to the sites. Logistic regressions were used to calculate the probability of xylogenesis and of cambium being active at a given temperature. Results Xylogenesis lasted from May to October, with a growing period varying from 3 to 5 months depending on location and elevation. Despite the wide geographical range of the monitored sites, temperatures for onset and ending of xylogenesis converged towards narrow ranges with average values around 4-5, 8-9 and 13-14 degrees C for daily minimum, mean and maximum temperature, respectively. On the contrary, cell division in the cambium stopped in July-August, when temperatures were still high. Main conclusions Wood formation in conifers occurred when specific critical temperatures were reached. Although the timing and duration of xylogenesis varied among species, sites and years, the estimated temperatures were stable for all trees studied. These results provide biologically based evidence that temperature is a critical factor limiting production and differentiation of xylem cells in cold climates. Although daily temperatures below 4-5 degrees C are still favourable for photosynthesis, thermal conditions below these values could inhibit the allocation of assimilated carbon to structural investment, i.e. xylem growth

Heating and cooling can influence cambial activity and cell differentiation in Norway spruce. However, at the ultrastructural and topochemical levels, no changes were observed in the pattern of secondary cell-wall formation and lignification or in lignin structure, respectively.

No abstract

In trees with broader annual rings, the final steps of differentiation of the youngest latewood tracheids near the cambium still continued during autumn, but were finished prior to winter. It was concluded from structural observations that duration of cambial activity is longer in trees with broad annual rings than in trees with narrow rings.

To investigate the potential of Norway spruce (Picea abies L. Karst) as a palaeoclimate archive in the southeastern European Alps, tree ring chronologies were developed from trees growing at two sites in Slovenia which differed in their ecological and climatological characteristics. Ring width, maximum latewood density, annual height increment and latewood cellulose carbon isotope composition were determined at both sites and the resulting time-series compared with and verified against instrumental climate data for their common period (AD 1960-AD 2002. Results indicate that ring width sensitivity to summer temperature is very site-dependent, with opposing responses at alpine and lowland sites. Maximum density responds to September temperatures, indicating lignification after cell division has ceased. Stable carbon isotopes have most potential, responding strongly to summer temperature in both alpine and lowland stands. Height increment appears relatively insensitive to climate, and is likely to be dominated by local stand dynamics.

No abstract

Nuclear magnetic resonance (NMR) enables an instantaneous determination of the proton density in liquids and is thus convenient for determining the moisture content (MC) of wood. We demonstrated that the MC of a wood sample can be determined instantaneously on the basis of its mass (m) and the amplitude of its NMR free-induction-decay (FID) signal. The measurement is based on the assumption that the only liquid in the wood is water and that the relationship between the amplitude of the FID signal (S) and the mass of the water (m w ) in the sample is linear, i.e., S=k m w +k′ (m-m w ), and can be precisely calibrated for a given NMR probe and NMR spectrometer setup (in our case k=105 AU g-1 and k/k′ =34). With the FID signal converted into the mass of water, the MC is calculated as: MC=(S-m k′)/(m k-S). After the initial calibration of the FID signal with respect to the content of water, the correctness of the method was verified on samples of different wood species with various MCs. The results confirmed that the proposed method is comparable in terms of accuracy and reliability to the gravimetric method, regardless of the species of wood. As the method is instantaneous, it might become the method of choice in applications where a short measurement time combined with a high accuracy is demanded.

High-definition automated optical analysis was used to observe the morphological changes of bleached hardwood dissolving pulp during oxidation mediated by (2,2,6,6-tetramethylpiperidn-1-yl)­oxyl (TEMPO). The effects of TEMPO treatment kinetics on fiber morphology and fibrillation degree at a constant reagent loading were studied. The pulp underwent significant swelling, and carboxyl groups were introduced in which the fiber cell walls loosened, which contributed to fibrillation and subsequently nanocellulose dispersion quality in terms of both viscosity and visible light transmittance. The use of an automated optical fiber analyzer facilitates process control, as it allows controlling the fiber morphology and preventing major losses in the form of pulp fines stemming from an unnecessarily long TEMPO oxidation time.