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Low temperature induces different cold sensitivity in two poplar clones (Populus×canadensis Mönch ‘I-214’ and P... Article in Journal of Experimental Botany · July 2009 DOI: 10.1093/jxb/erp212 · Source: PubMed
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Journal of Experimental Botany, Vol. 60, No. 13, pp. 3655–3664, 2009 doi:10.1093/jxb/erp212 Advance Access publication 30 June, 2009
RESEARCH PAPER
Low temperature induces different cold sensitivity in two poplar clones (Populus3canadensis Mo¨nch ‘I-214’ and P. deltoides Marsh. ‘Dvina’) Claudia Cocozza1, Bruno Lasserre1, Alessio Giovannelli2, Gaetano Castro3, Giuseppe Fragnelli3 and Roberto Tognetti1,* EcoGeoFor Lab, Dipartimento di Scienze e Tecnologie per l’Ambiente e il Territorio (STAT), Universita` degli Studi del Molise, Contrada Fonte Lappone, 86090 Pesche, Italy 2 Laboratorio Xilogenesi, Istituto Valorizzazione Legno e Specie Arboree, IVaLSA-CNR, Via Madonna del Piano, 50019 Sesto Fiorentino (FI), Italy 3 Unita` di Ricerca per le Produzioni Legnose Fuori Foresta-CRA, Strada per Frassineto, 15033 Casale Monferrato (AL), Italy Received 10 March 2009; Revised 19 May 2009; Accepted 3 June 2009
Abstract Changes of stem diameter were continuously monitored during winter in two field-grown poplar clones, using automatic point dendrometers. The objective of this study was to find an analytical solution to seasonal synchronization of stem diameter oscillations and low air temperatures. The study identified to what extent and with what frequency low air temperature induced stem diameter variation in ‘Dvina’ (P. deltoides) and ‘I-214’ (Populus3canadensis) poplar clones, after exposure to summer drought. The patterns of reversible stem shrinkage were related to the cycles of low air temperature. Hourly and daily evidence showed that ‘I-214’ was more sensitive to low air temperatures than ‘Dvina’. The analysis of raw data and graphic details implemented with the study of derivative tests allowed an increase in the general sensitivity of the investigation applied to describe the response of poplar clones to environmental conditions. Given these diameter fluctuation patterns, automatic point dendrometers were confirmed to be a reliable non-invasive method for testing the sensitivity of diameter variation to cold temperature. Variation in rate and duration of daily stem shrinkage in response to low air temperature in winter appeared to occur independently of the effects of water deficit suffered by plants the previous summer. Key words: Cold acclimation, low temperature, poplar, stem shrinkage.
Introduction Instantaneous and seasonal responses to environmental stimuli are often used as selection criteria in breeding programmes (Dillen et al., 2007). Low temperature is one of the most important environmental factors limiting growth (Boyer, 1982), affecting the development and distribution of plants. In temperate zones, many plant species have the ability to cold acclimate, i.e. exposure to low non-freezing temperature will increase tolerance to freezing stress both in the short term as in annual herbaceous plants and seasonally as in over-wintering herbaceous and woody plants. Low winter temperatures
induce cold acclimation (Rodrigo, 2000), which is characterized by growth cessation, bud dormancy, leaf senescence, and abscission (Heide and Prestrud, 2005). Frost is identified when the environmental temperature falls below 0 C (Tsarouhas, 2002), which causes freezing of plant tissues, inducing injury by intracellular and/or extracellular ice formation and loss of plant productivity (Ashworth, 1986). Li et al. (2004) demonstrated that there were differences in the rates and degrees of cold acclimation between northern and southern ecotypes of Betula pendula in Nordic countries. Differences in cold acclimation between genotypes
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3656 | Cocozza et al. mathematical functions, such as derivatives, can be used to perform a sensitivity analysis (Baldocchi, 1994). In addition, under several conditions, quantitative solutions are fast and unbiased in comparison with qualitative methods (Norman, 1982; Baldocchi, 1994). In this study, winter cold acclimation was evaluated by stem shrinkage analysis on two poplar clones, ‘I-214’ (Populus3canadensis) and ‘Dvina’ (Populus deltoides), grown in field conditions. These two poplar clones revealed significant differences under limited water availability during the previous summer; ‘I-214’ reduced and ‘Dvina’ ceased stem growth (Giovannelli et al., 2007). After irrigation resumed, ‘Dvina’ showed a higher capacity to restore stem growth than ‘I-214’. However, regardless of the irrigation regime, rainfed or irrigated, clone ‘Dvina’ displayed a higher stem radial increment than clone ‘I-214’ (Facciotto and Zambruno, 2004). The composite origin of stem diameter variations derives from an irreversible component due to radial growth and a reversible component due to changes in the water balance of stem tissues (Daudet et al., 2005). Phloem and cambium can change size as a result of diurnal cycles of hydration, whereas mature xylem can contract and expand due to elastic deformation involving internal tensions with little water loss (Irvine and Grace, 1997). Yet thermal expansion and contraction of woody tissues add to genetically determined tree water status, making changes in diameter of plant stems difficult to interpret. It was hypothesized that differences between poplar genotypes in stem growth and drought acclimation elicited by shifting water availability during summer are translated into clone-specific stem diameter changes after freeze– thawing cycles in winter. A high-resolution description of daily stem shrinkage related to air temperature oscillation was derived from cold sensitivity analysis of woody tissue revealed by point dendrometers. Temperature is a major controller of seasonality in plants, and a large body of literature exists relating the effects of temperature to development and phenology. The two basic components of seasonality are timing and synchrony. The specific aim of the study was to apply an analytical solution to seasonal synchronization of temperature-excited oscillations in stem diameter changes, thus determining the influence of thermal cycles on elastic shrinkage. Another objective was to assess the thermal threshold inducing clone-specific stem radial variation.
Materials and methods Study site and experimental plantation The experimental plot was at the CRA-ISP (Istituto di Sperimentazione per la Pioppicoltura), in Casale Monferrato (AL), Piemonte, Italy (4507#52##N, 830#17##E, 106 m a.s.l.). The site has a temperate climate with equinoctial rainfall distribution. The long-term (1926–2005) average annual temperature is 12.1 C, with total rainfall of 765 mm
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have been reported for other temperate forest trees in Mediterranean environments (Scarascia-Mugnozza et al., 1989; Almeida et al., 1994). Plants can adopt two main strategies to survive low temperatures: freezing avoidance or freezing tolerance (Sakai and Larcher, 1987). Freezing avoidance is mainly obtained by supercooling of water contained within plant tissues; this mechanism is, however, limited to specific organs, such as seeds or buds in winter (Sakai and Larcher, 1987). Freezing avoidance also occurs by preventing ice formation (von Fircks, 1994) and producing antifreeze compounds (Renaut et al., 2005; Morin et al., 2007). The acquisition of freezing tolerance is, therefore, the most common mechanism developed by plants to endure freezing stress. However, freezing-induced plant death can be caused by mechanical injury from ice crystal formation (Zamecnik and Janacek, 1992; Griffith and Antikainen, 1996), water loss either directly or indirectly through permeability changes in the cell membrane, and changes in protein conformation and content (Antikainen and Griffith, 1997). Most frost-sensitive plants have no significant mechanisms of freezing tolerance and must avoid ice formation to avoid frost injury (Lindow, 1983). The freezing process begins with ice crystal formation inside plant tissues, within intra- or intercellular spaces (Levitt, 1980), after supercooling to –2 C or –3 C (Christersson and Sandstedt, 1978). Intracellular ice crystal formation is supposed to be always lethal, probably due to mechanical destruction of membranes resulting from the rapid growth of ice crystals in the protoplast (Fahy, 1995). Frost damage in plants is observed when plants are actively growing, caused by intracellular ice crystal formation inducing cell dehydration and turgor loss in shoots (Christersson, 1971). However, ice crystals in natural conditions occur as extracellular formation, which takes place in intercellular spaces when water moves from inside cells to the intercellular spaces where it freezes (Christersson, 1971). When the living bark of trees shrinks at freezing temperature, water moves out of cells and the internal osmotic concentration increases, and this mechanism prevents intracellular freezing (Loris et al., 1999). In winter, stem radial changes, frost shrinkage, and thaw expansion are caused by turgor adjustments in elastic bark cells, in the same way as diurnal stem fluctuations occur in summer (Zweifel and Ha¨sler, 2000). In winter, stem radial fluctuations of deciduous species are entirely temperature induced, even in Mediterranean climates, being larger than in summer and lacking shrinkage–swelling cycles during the morning–night pattern. Trees of temperate zones undergo cyclic changes of freezing tolerance each year. Empirical links between stem shrinkage and low temperature could be used to model wood anatomy as a function of environmental signals and physiological processes. This approach, however, is not always ideal because iterative solutions of non-linear biological systems can behave chaotically if parameters exceed certain values (May, 1976). An analytical solution for coupling stem diameter variation and air temperature values would be preferred, because
Stem diameter variation in poplars | 3657
Irrigation treatment and climatic analysis All tanks received only natural rainfall until DOY 173. At this time, plant growth was similar: height 29566 cm and 304610 cm, basal area 360653 cm2 and 417630 cm2, and total leaf area 1.5660.1 m2 and 1.6260.17 m2 for ‘I-214’ and ‘Dvina’, respectively (the length and the width of each leaf lamina were measured and used to estimate leaf area after allometric calibration). From DOY 174 onwards, two different irrigation regimes were applied: (i) an intensive irrigation regime in which the soil water content was maintained close to field capacity by flushing the tanks with 70 mm of water every week; and (ii) natural rainfall and late intensive irrigation, in which irrigation, scheduled as in the intensive irrigation regime, only started on DOY 224. The timing of the start of irrigation was based on threshold values of soil water content (
