Xylem formation in Fagus sylvatica during one growing season

The study analyses the activity of cambium and the increment of wood during one growing season of European beech (Fagus sylvatica L.) in the central part (region) of the Drahanská vrchovina, Czech Republic. The research plot was situated at an altitude of 630ma.s.l. The following parameters were studied: the beginning and end of cambial activity, differentiation of wood fibres and vessels and the total increment of wood during the growing season in six trees. Samples were taken during the growing season of 2010 in weekly intervals from the beginning of April to the end of October. The dormant cambium consisted of 5.3 cells on average; their number rose gradually after reactivation. The maximum number of cells (10 to 14, 9.1 on average) in the cambial zone persisted for 8 weeks; in mid-August the cambium ended its division activity, while the differentiation process continued till mid-September. The first fully lignified vessels were formed 5 to 6 weeks after their formation in the cambial zone. Vessels and adjacent wood fibres were the first elements to become fully lignified. The maximum production of cells (wood increment) was recorded from June 11 to June 24. 57% of the total ring width was formed in June. The mean ring width calculated by means of Gompertz function is 1777 μm (ranging from 1226 μm to 2423 μm)

Monitoring of xylem formation in Picea abies under drought stress influence

The effect of drought stress on regular cambium activity and wood formation in stems of two different clones of Norway spruce (Picea abies (L.) Karst.) was investigated. Tissue samples were taken during the growing season from May to September 2010. Artificial drought stress, induced by long-term sheltering of the soil, was significantly manifested in clone 15. In the stressed individual, the period of cambium activity was shorter, the total number of formed cells was lower and the resulting tree ring was narrower. The number of cells in the phases of postcambial growth and secondary cell wall formation was significantly lower in comparison to the control tree. The tracheid lignification process was slower in the tree stressed by water deficit and the first mature tracheids were observed later. On the other hand, in clone 18 probably genetic dispositions played an important role as no considerable deviations in the cambium activity and new wood cells production were observed. Fitting xylem increments to the Gompertz function showed that the period of the most intensive cell formation was at the turn of June and July and the maximum daily production of new cells was higher in non-stressed individuals than in the stressed ones. The results of the experiment lead us to the conclusion that drought stress can significantly affect the cambium activity of some clones, the differentiation process of anatomical elements, and thus also the resulting tree ring width

The cambial response of Scots pine trees to girdling and water stress

We monitored six healthy dominant trees and six girdled Scots pine trees for two successive growing seasons (2014 and 2015) to investigate the seasonal dynamics, cambial activity, and morphology of the new xylem and phloem cells formed under environmental stress when girdling was applied during the dormant period (15 January 2014). Microcore (1.8 mm) samples were collected weekly using a Trephor tool above and below the girdling area, and weather data were measured on site. Drought stress in combination with girdling reduced the total number of differentiation days cell formation. In 2014, no significant differences in tracheid dimensions were observed between the girdled area and the control trees, while in 2015, the control trees showed significantly smaller cell wall thickness and radial dimensions of the latewood tracheids (LW) compared to 2014 and girdled trees had no occurrence of LW. Under stressful heat waves and prolonged periods of no precipitation, the trees tended to reduce the number of tracheids that were formed and exhibited smaller radial dimensions (narrower tree rings) to increase their hydraulic efficiency. Trees responded to limited water availability by forming intra-annual density fluctuations (IADFs L) in the zone of the LW to overcome stressful conditions. Although xylem cell differentiation was affected by stressful conditions, no significant variability in phloem cell dimensions was observed. Thus, the phloem tissue was less sensitive to exogenous factors. © 2020 International Association of Wood Anatomists

How needle phenology indicates the changes of xylem cell formation during drought stress in Pinus sylvestris L.

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Woody biomass production lags stem-girth increase by over one month in coniferous forests

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The 2018 European heatwave led to stem dehydration but not to consistent growth reductions in forests

Heatwaves exert disproportionately strong and sometimes irreversible impacts on forest ecosystems. These impacts remain poorly understood at the tree and species level and across large spatial scales. Here, we investigate the effects of the record-breaking 2018 European heatwave on tree growth and tree water status using a collection of high-temporal resolution dendrometer data from 21 species across 53 sites. Relative to the two preceding years, annual stem growth was not consistently reduced by the 2018 heatwave but stems experienced twice the temporary shrinkage due to depletion of water reserves. Conifer species were less capable of rehydrating overnight than broadleaves across gradients of soil and atmospheric drought, suggesting less resilience toward transient stress. In particular, Norway spruce and Scots pine experienced extensive stem dehydration. Our high-resolution dendrometer network was suitable to disentangle the effects of a severe heatwave on tree growth and desiccation at large-spatial scales in situ, and provided insights on which species may be more vulnerable to climate extremes