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Title: Cambial activity and wood formation of Maritime pine in a drought-prone environment: the effect of growth rate, size and climate
Authors: Vieira, Joana 
Orientador: Nabais, Cristina
Rossi, Sergio
Freitas, Helena
Issue Date: 13-Dec-2013
Project: info:eu-repo/grantAgreement/FCT/5876-PPCDTI/111675/PT 
Abstract: The formation of tree rings is a slow and complex process. The year-to-year climatic variability and the constant interaction between the internal and external factors controlling cambial activity create the conditions that make each tree ring unique. In order to capture the dynamics of cambial activity and wood formation during the growing season, it is necessary to monitor wood development in narrower time intervals (from minutes to weeks). Most of the studies performed on cambial activity and wood formation were held in cold environments, however, in other environments, such as drought-prone areas, it still remains poorly understood. In order to understand cambial activity and wood formation in a drought-prone environment, timings and dynamics of cambial activity were monitored in maritime pine (Pinus pinaster Ait.) growing in the Mediterranean region for two years (2010 and 2011). Anatomical observations of the cambial zone and differentiating xylem were made and stem radial increment monitored using manual and automatic dendrometers. The studies described in this thesis were carried out in Perimetro Florestal Dunas de Cantanhede, a managed plantation of maritime pine located in the west coast of Portugal. The cambial activity and wood formation of maritime pine trees with the same age and size but different growth rates in the period 2009-1994 (classified as fast and slow trees), were monitored throughout 2010, to determine whether the observed differences in tree-ring width were triggered by timings of cambial activity or by rates of cell production. Anatomical observations of the cambium and developing xylem determined that the timing of cambial activity was similar in both growth rate classes. However, fast-growing trees presented higher rates of cell production than slow-growing trees. The band dendrometer readings revealed a bimodal pattern of stem radial increment, with two peaks of increment, one more pronounced in spring and another in autumn. Although the bimodal pattern is typical of trees growing in the Mediterranean region, the combined analysis of anatomical observations and band dendrometers showed that the second period of radial increment corresponded mostly to the re-hydration of the stem, since no resumption of cambial activity was observed in autumn. In order to determine if differences in stem diameter were due to different rates of cell production or xylogenesis timings, the cambial activity of even-aged trees belonging to two diameter classes was monitored throughout 2011. The timings of cambial onset and differentiation were the same in both diameter classes. However, enlargement and cell wall deposition lasted longer in large trees. Besides the different durations, large trees also showed a higher rate of cell production. Thus, revealing that the differences in diameter observed between the trees were due to the rates of cell production. In both diameter classes, the cambium was active from March to July, and quiescent from August to November, suggesting that in the Mediterranean region trees are under a double climatic control: low temperatures and reduced photoperiod in the winter and high temperatures associated with low water availability in the summer. Summer quiescence was broken in late October, when precipitation re-hydrated the stem. In November, cambial divisions were observed, indicating that maritime pine has the ability to form new xylem cells after the summer drought. The influence of climate on the cambial activity and wood formation of maritime pine was studied over two dry years (2010 and 2011). It was found that cambial onset started earlier in response to a warmer late-winter and stopped earlier in response to a drier spring and summer, confirming that Mediterranean conifers are under a double climatic control. Low water availability during spring and summer limited cell production, which affected tree-ring width. Drier conditions also triggered an earlier start of latewood formation, leading to the development of fewer tracheids with smaller lumen area. It was also observed that the duration of xylogenesis was not dependent on cambial onset. In fact, an earlier onset of xylogenesis did not trigger a longer duration of cambial activity. To ascertain the influence of water availability on the stem radial increment of maritime pine, hourly variations of stem radial increment and tree water deficit were monitored throughout 2010 using automatic dendrometers. The seasonal cycle was divided in five periods of distinct physiological activity: winter dormancy, spring growth, pre-summer contraction, summer quiescence and autumn re-hydration. The stem cycle approach was then used to divide the daily cycles in contraction, recovery and increment phases. Continuous positive radial increment started in spring and reached its maximum by the end of June, time at which a shrinking period was observed. The stem contraction observed in June was due to the inability of trees to recover the water lost by transpiration, contracting from one cycle to the next. In autumn, a period of re-hydration and rapid expansion was observed after precipitation. Daily variations in stem radius of maritime pine were mainly determined by the course of transpiration and thus, highly dependent on temperature and water availability. Overall, the results obtained in this dissertation provided a detailed insight on the dynamics of maritime pine cambial activity in a drought-prone environment, the Mediterranean region. It was observed that cell production rate was the main responsible for the differences in tree-ring width and ultimately in stem diameter. Within an even-aged and managed forest, different individuals can present different cellular production rates (fast and slow trees) that in time will be translated in different stem diameters (larger and smaller trees). Growth onset was not influenced by tree size, but a longer duration of wood formation was observed in fast-growing and larger trees. In both years (2010 and 2011), the radial increment of all studied trees presented a clear bimodal pattern, with two increment peaks, as observed in other Mediterranean species. The first and more pronounced peak occurred in spring and a second less pronounced peak in autumn. The second growth peak corresponded mainly to a re-hydration of the stem after the summer drought, since the anatomy study did not reveal the formation or differentiation of new xylem cells. Climate played an important role in maritime pine cambial activity and wood formation, low temperatures and reduced photoperiod in winter and high temperatures associated with low water availability in the summer limited tree growth by imposing a dormant period.
Rights: openAccess
Appears in Collections:I&D CFE - Teses de Doutoramento

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