Showing papers in "Trees-structure and Function in 2008"

Genetic associations, variability and diversity in seed characters, growth, reproductive phenology and yield in Jatropha curcas (L.) accessions

Abstract: A thorough and extensive wild germplasm exploration survey was undertaken and 32 high yielding candidate plus trees (CPTs) of Jatropha curcas from different locations from a latitudinal and longitudinal spread between 12°41′ and 22°′E longitude and 77° and 84°40′N latitude covering 11 locations in an area spread of 150,000 km2 was collected for evaluating genetic association, and variability in seed and growth characters. Significant trait differences were observed in all the seed characters viz., seed morphology and oil content as were observed in growth characters viz., plant height, and female to male flower ratio and seed yield in the progeny trial. Broad sense heritability was high in general and exceeded 80% for all the seed traits studied. Female to male flower ratio showed near to 100% heritability followed by yield (83.61) and plant height (87.73). The path analysis revealed that female to male flower ratio had highest positive direct relationship with seed yield (0.789), followed by number of branches (0.612) and number of days from fruiting to maturity (0.431). Negative indirect effects were seen in number of days from flowering to fruiting which indirectly and negatively influenced yield through plant height and number of branches. Hierarchical clustering by Ward’s minimum variance cluster analysis showed phylogeographic patterns of genetic diversity. K-means clustering revealed that trees from different geographic regions were grouped together in a cluster and as were trees from the same geographical area placed in different clusters suggesting that geographical diversity did not go hand in hand with genetic diversity. In addition clustering identified promising accession with favourable traits for future establishment of elite seedling seed orchard and clonal seed orchard for varietal and hybridization programmes.

Growth response to climate and drought in Pinus nigra Arn. trees of different crown classes

Abstract: Tree-ring chronologies were examined to investigate the influence of climate on radial growth of Pinus nigra in southeastern Spain. We addressed whether drought differentially affected the ring-widths of dominant and suppressed trees and if our results supported the hypothesis that, in a Mediterranean climate, suppressed conifer trees suffer greater growth reductions than dominant trees. Climate-growth relationships were analyzed using response and correlation functions, whereas the effect of drought on trees growth was approached by superposed epoch analysis in 10 dry years. A cool, wet autumn and spring, and/or mild winter enhanced radial growth. Latewood was the most sensitive ring section in both kinds of trees and it was primarily influenced by current year precipitations. Earlywood was mostly influenced by climatic conditions previous to the growing season. In general, May was the most influential month. Pinus nigra was shown to be very drought sensitive tree in the study area. Tree-rings in suppressed trees showed lower growth reductions caused by drought than those of dominant trees. However, dominant trees recovered normal growth faster. Dominant trees showed a more plastic response, and suppression appeared to reduce the effect of climate on tree radial growth. Some possible causes for these effects are discussed. Our results support the essential role of the balance between light and moisture limitations for plant development during droughts and show that it is not appropriate to generalize about the way in which suppression affects climate-growth relationship in conifers.

Tree-ring variation, wood formation and phenology of beech (Fagus sylvatica) from a representative site in Slovenia, SE Central Europe

Abstract: Long-term variation in tree-ring widths (1873–2006) and intra-annual dynamics of cambial activity and tree-ring formation in 2006 were studied in mature beech (Fagus sylvatica L.) trees at a typical forest site near Ljubljana (46°N, 14°40′E, 400 m a.s.l.) and related to leaf phenology and climate data. Tree-ring widths were negatively affected by minimum March and maximum August temperatures and favoured by May and July precipitation. Precipitation of the previous August and temperature of the previous November also had a positive effect. Leaf unfolding was affected by March and April temperatures, occurring later if they were low. Leaf yellowing was positively affected by minimum July temperatures and negatively by September precipitation. In 2006, leaf unfolding occurred on 16 April and was immediately followed by reactivation of cambium at breast height of the trees. One week later, the cambium obtained its maximum width (around 11 cell layers) and the rate of division increased until the end of May/beginning of June. By the end of June, 75% of the tree-ring was formed. Cambial cell divisions stopped from the end of July to mid-August. The average time of cambial activity was 100 days. Leaf yellowing occurred at the end of October, i.e. nearly 2 months after the cessation of cambial cell division. We discuss the usefulness of a combination of long-term (tree-ring width and phenology) and short-term (wood formation at a cellular level) data to understand better the environmental signals registered by a tree during growth.

Carbon allocation in fruit trees: from theory to modelling

Abstract: Carbon allocation within a plant depends on complex rules linking source organs (mainly shoots) and sink organs (mainly roots and fruits). The complexity of these rules comes from both regulations and interactions between various plant processes involving carbon. This paper presents these regulations and interactions, and analyses how agricultural management can influence them. Ecophysiological models of carbon production and allocation are good tools for such analyses. The fundamental bases of these models are first presented, focusing on their underlying processes and concepts. Different approaches are used for modelling carbon economy. They are classified as empirical, teleonomic, driven by source–sink relationships, or based on transport and chemical/biochemical conversion concepts. These four approaches are presented with a particular emphasis on the regulations and interactions between organs and between processes. The role of plant architecture in carbon partitioning is also discussed and the interest of coupling plant architecture models with carbon allocation models is highlighted. As an illustration of carbon allocation models, a model developed for peach trees, describing carbon transfer within the plant, and based on source–sink and Munch transport theory is presented and used for analyzing the link between roots, shoots and reproductive compartments. On this basis, the consequences of fruit load or plant pruning on fruit and vegetative growth can be evaluated.

Climate–growth relationships of the dominant tree species from semi-arid savanna woodland in Ethiopia

Abstract: Long-term climate–growth relationships, were examined in tree rings of four co-occurring tree species from semi-arid Acacia savanna woodlands in Ethiopia. The main purpose of the study was to prove the presence of annual tree rings, evaluate the relationship between radial growth and climate parameters, and evaluate the association of El Nino and drought years in Ethiopia. The results showed that all species studied form distinct growth boundaries, though differences in distinctiveness were revealed among the species. Tree rings of the evergreen Balanites aegyptiaca were separated by vessels surrounding a thin parenchyma band and the growth boundary of the deciduous acacias was characterized by thin parenchyma bands. The mean annual diameter increment ranged from 3.6 to 5.0 mm. Acacia senegal and Acacia seyal showed more enhanced growth than Acacia tortilis and B. aegyptiaca. High positive correlations were found between the tree-ring width chronologies and precipitation data, and all species showed similar response to external climate forcing, which supports the formation of one tree-ring per year. Strong declines in tree-ring width correlated remarkably well with past El Nino Southern Oscillation (ENSO) events and drought/famine periods in Ethiopia. Spectral analysis of the master tree-ring chronology indicated occurrences of periodic drought events, which fall within the spectral peak equivalent to 2–8 years. Our results proved the strong linkage between tree-ring chronologies and climate, which sheds light on the potential of dendrochronological studies developing in Ethiopia. The outcome of this study has important implications for paleoclimatic reconstructions and in restoration of degraded lands.

Climate-related variability in carbon and oxygen stable isotopes among populations of Aleppo pine grown in common-garden tests

Abstract: The Aleppo pine (Pinus halepensis Mill) is found in the Mediterranean under a broad range of moisture and thermal conditions Differences in severity and duration of water stress among native habitats may act as selective forces shaping the populations’ genetic make-up in terms of contrasting drought strategies We hypothesised that these strategies should translate into intraspecific variation in carbon isotope composition (δ13C, surrogate of intrinsic water-use efficiency, WUEi) of wood holocellulose, and such variation might be linked to changes in oxygen isotope composition (δ18O, proxy of stomatal conductance) and to some climatic features at origin Thus, we evaluated δ13C, δ18O, growth and survival for 25 Aleppo pine populations covering its geographic range and grown in two common-garden tests We found intraspecific variability for δ13C and growth, with high-WUEi populations (which showed 18O-enriched holocellulose) having low growth These results suggest stomatal regulation as common control for δ13C and productivity We also detected sizeable relationships between δ13C and climate factors related to the magnitude and timing of drought such as the ratio of summer to annual rainfall The main climate variable associated with δ18O was minimum temperature, but only in the coldest trial, suggesting differences in growth rhythms among sources Overall, slow growing populations from highly-seasonal dry areas of the western Mediterranean exhibited a conservative water-use, as opposed to fast growing sources from the northernmost distribution range The particular behaviour of the Mediterranean Aleppo pine as compared with other conifers demonstrates different selective roles of climate variables in determining intraspecific fitness

Variation in mesophyll anatomy and photosynthetic capacity during leaf development in a deciduous mesophyte fruit tree (Prunus persica) and an evergreen sclerophyllous Mediterranean shrub (Olea europaea)

Abstract: The relative importance that biomechanical and biochemical leaf traits have on photosynthetic capacity would depend on a complex interaction of internal architecture and physiological differences. Changes in photosynthetic capacity on a leaf area basis and anatomical properties during leaf development were studied in a deciduous tree, Prunus persica, and an evergreen shrub, Olea europaea. Photosynthetic capacity increased as leaves approached full expansion. Internal CO2 transfer conductance (g i) correlated with photosynthetic capacity, although, differences between species were only partially explained through structural and anatomical traits of leaves. Expanding leaves preserved a close functional balance in the allocation of resources of photosynthetic component processes. Stomata developed more rapidly in olive than in peach. Mesophyll thickness doubled from initial through final stages of development when it was twice as thick in olive as in peach. The surface area of mesophyll cells exposed to intercellular air spaces per unit leaf area tended to decrease with increasing leaf expansion, whereas, the fraction of mesophyll volume occupied by the intercellular air spaces increased strongly. In the sclerophyllous olive, structural protection of mesophyll cells had priority over efficiency of photochemical mechanisms with respect to the broad-leaved peach. The photosynthetic capacity of these woody plants during leaf development relied greatly on mesophyll properties, more than on leaf mass per area ratio (LMA) or nitrogen (N) allocation. Age-dependent changes in diffusion conductance and photosynthetic capacity affected photosynthetic relationships of peach versus olive foliage, evergreen leaves maturing functionally and structurally a bit earlier than deciduous leaves in the course of adaptation for xeromorphy.

Seasonal changes in photoprotective mechanisms of leaves from shaded and unshaded field-grown coffee (Coffea arabica L.) trees

Abstract: Coffee is native to shady environments, but often grows and yields better without shade. Thus, it may be reasoned that coffee leaves should display enough plasticity to acclimate themselves to contrasting light environments. However, little is known about mechanisms associated with such plasticity in coffee. This work aimed, therefore, to explore differences in leaf photoprotective mechanisms. Plants were grown in the field and received either 48 or 100% natural light. Evaluations were made using outer leaves from the sun-facing sides of the coffee hedgerow in Vicosa (Brazil) in August and October, when growth and photosynthetic rates are expected to be minimal and maximal, respectively, and in December, when temporary depressions in those variables are common. Regardless of light treatments, coffee leaves showed: (1) very low photosynthetic rates (generally below 2.5 μmol m−2 s−1), (2) chronic photoinhibition in August (dry, cool season) that was accompanied by strong loss of pigment concentration, and (3) discrete, dynamic photoinhibition in October and December (rainy, warm season). Compared with shaded leaves, sunlit leaves generally exhibited lower pigment concentration, lower quantum yield of electron transport, steeper inclinations and similar electron transport rate. Total ascorbate pool tended to be larger in sunlit than in shaded leaves (but with similar redox state), whereas activities of key antioxidant enzymes, as well as malondialdehyde accumulation and electrolyte leakage, were similar between those leaf types. As a whole, the photosynthetic apparatus of the coffee tree showed a low phenotypic plasticity to varying irradiance.

Wood anatomy and hydraulic architecture of stems and twigs of some Mediterranean trees and shrubs along a mesic-xeric gradient

Abstract: Woody species populating the major Mediterranean ecosystems in the world are characterized by different levels of adaptation to the seasonal Mediterranean climate conditions. Many species of these ecosystems show wood features that allow high efficiency of transport when water is available, while maintaining hydraulic safety during drought periods. This study focuses on the anatomy of juvenile and mature wood of some species representative of continuous sequences of Mediterranean vegetation formations according to gradients of water availability, from xeric to relatively mesic: Cistus monspeliensis L., Rhamnus alaternus L., Myrtus communis L., Pistacia lentiscus L., Olea europaea L., Quercus ilex L., Fraxinus ornus L. and Ostrya carpinifolia L. Twigwood collected in Southern Italy was anatomically compared with the stemwood of the same species represented in the reference slide collection of the National Herbarium of the Netherlands (Lw). The “hydraulic distance” between the wood of main stems and twigs was estimated on the basis of suites of anatomical features related to water efficiency/safety. Although some attributes (i.e. porosity and type of imperforate tracheary elements) were similar in young twigs and older rings, other traits (i.e. vessel frequency and size) evidenced the different hydraulic properties of twig and stemwood. The difference between juvenile and mature structures was large in the species of the mesic end of the gradient while it was relatively small in those more xeric. This tendency is in agreement with the habit gradient from medium-sized trees to small evergreen/drought deciduous shrubs according to decreasing water availability in Mediterranean vegetation types.

Long-term changes in tree-ring–climate relationships at Mt. Patscherkofel (Tyrol, Austria) since the mid-1980s

Abstract: Although growth limitation of trees at Alpine and high-latitude timberlines by prevailing summer temperature is well established, the loss of thermal response of radial tree growth during last decades has repeatedly been addressed. We examined long-term variability of climate–growth relationships in ring width chronologies of Stone pine (Pinus cembra L.) by means of moving response functions (MRF). The study area is situated in the timberline ecotone (ca. 2,000–2,200 m a.s.l.) on Mt. Patscherkofel (Tyrol, Austria). Five site chronologies were developed within the ecotone with constant sample depth (≥19 trees) throughout most of the time period analysed. MRF calculated for the period 1866–1999 and 1901–1999 for ca. 200- and ca. 100-year-old stands, respectively, revealed that mean July temperature is the major and long-term stable driving force of Pinus cembra radial growth within the timberline ecotone. However, since the mid-1980s, radial growth in timberline and tree line chronologies strikingly diverges from the July temperature trend. This is probably a result of extreme climate events (e.g. low winter precipitation, late frost) and/or increasing drought stress on cambial activity. The latter assumption is supported by a <10% increase in annual increments of ca. 50-year-old trees at the timberline and at the tree line in 2003 compared with 2002, when extraordinary hot and dry conditions prevailed during summer. Furthermore, especially during the second half of the twentieth century, influence of climate variables on radial growth show abrupt fluctuations, which might also be a consequence of climate warming on tree physiology.

Seasonal development of secondary xylem and phloem in Schizolobium parahyba (Vell.) Blake (Leguminosae : Caesalpinioideae)

Abstract: The cambial activity and periodicity of secondary xylem and phloem formation have been less studied in tropical tree species than in temperate ones. This paper describes the relationship between seasonal cambial activity, xylem and phloem development, and phenology in Schizolobium parahyba, a fast growing semideciduous seasonal forest tree from southeastern Brazil. From 2002 to 2003, wood samples were collected periodically and phenology and climate were recorded monthly in the same period. S. parahyba forms annual growth increments in wood, delimited by narrow initial parenchyma bands. The reduction of the cambial activity to a minimum correlates to the dry season and leaf fall. The higher cambial activity correlates to the wet season and the presence of mature leaves. In phloem, a larger conductive region was observed in the wet season, when the trees were in full foliage. The secondary phloem did not exhibit any incremental zone marker; however, we found that the axial parenchyma tends to form irregular bands.

Spatial variations in xylem sap flux density in evergreen oak trees with radial-porous wood: comparisons with anatomical observations

Abstract: To estimate whole-tree water use when employing sap flow measurements, integration of the sap flux density (F d) over the sapwood area is needed. Accordingly, it is necessary to obtain information on the characteristics of stem water transportation such as spatial variations in F d and the active xylem area in the stem cross-section. Although evergreen oak trees with radial-porous wood represent a major component of secondary forests in western Japan, detailed information on their stem water transportation characteristics remains unclear. In the present study, we used the heat dissipation method (Granier method) to conduct measurements of azimuthal and radial variations in the F d of Quercus glauca Thunb. ex Murray, a representative evergreen broad-leaved tree in western Japan. Further, by analyzing the anatomy of the xylem structure, we examined why F d varies spatially in the stem cross-section. By using a dye solution injected into a radial hole bored into the tree trunk, we confirmed that the entire stem is hydroactive. We also compared the spatial variations in F d and water conductivity per xylem area (K s) which were estimated by using the observed vessel diameters and their density over the stem cross-section and Hagen–Poiseuille’s law. Azimuthal and radial variations in F d reached about 60 and 50% of the maximum values, respectively, and could be explained by spatial variation in K s. As a result, we obtained statistical parameters describing the spatial variation in F d in Q. glauca and determined that whole-tree water use estimated from measurements in one direction had at most ±20% potential errors for studied trees.

Dynamic analysis of olive trees in intensive orchards under forced vibration

Abstract: The mechanical harvesting of fruit for oil production in an intensive olive tree orchard is generally accomplished by applying vibration to the tree’s trunk. This vibration is consequently transmitted to the branches, causing the fruit to detach. Although this practice is commonly used, the effects on tree behavior under forced vibration are not firmly established. Dynamic analysis was performed on 17 olive trees (Olea europaea L.) growing in an intensively-managed orchard using modal testing techniques. Modal parameter identification was focused inside the range excitation frequency used by the most commonly available trunk shakers on the market. The olive trees featuring a low morphological variability and modal parameters were obtained for a representative olive tree. The first two modes of vibration of the main tree frame were identified with damping ratios of 26.9 and 17.1% and natural frequencies of 20.2 and 37.7 Hz, respectively. A third mode of vibration of less importance was found at a higher frequency. Therefore, many local modes of vibration were detected near these natural frequencies, primarily located on secondary branches. During the testing, the olive trees behaved like a damped harmonic oscillator with predominantly mass damping in these modes.

Carbon assimilation by tree stems: potential involvement of phosphoenolpyruvate carboxylase

Abstract: In woody species, the photosynthesis of stems, especially young branches, occurs by refixing part of the internal respiratory CO2. The present study aims to improve the physiological characterization of stem photosynthesis by examining enzymatic characteristics. During an entire growing season, three enzymatic activities that are linked to C3 and C4 metabolism were investigated in relation to the CO2 efflux and chlorophyll content of current year stems of European beech and were compared to the corresponding characteristics of leaves. High activities of phosphoenolpyruvate carboxylase (PEPC) and NADP malic enzyme were detected in stems (up to 13 times and 30 times higher in stems than in leaves, respectively), whereas Rubisco activity remained low in comparison with leaves. Stem maximal Rubisco and PEPC activities occurred at the beginning of the season when the total chlorophyll content and the CO2 assimilation rate were also maximal. Stems were characterized by a PEPC:Rubisco ratio that was equal to 2.5 [an intermediate value between that of C3-plants (about 0.1) and that of C4-plants (about 10)], whereas it was equal to 0.1 in leaves. Eight other tree species were also measured and the PEPC:Rubisco ratio was, on average, equal to 3.6. The potential role of PEPC in stem carbon assimilation is discussed in relation to its known involvement in the anaplerotic function of C3 plants and in the carbon metabolism of the C4 pathway.

Age-dependent tree-ring growth responses to climate in Qilian juniper (Sabina przewalskii Kom.)

Abstract: Qilian juniper (Sabina przewalskii kom.) is one of the dominant tree species on Qinghai-Tibetan Plateau and has been used in dendroclimatological studies. Here we designed a test to examine whether or not the climate- growth responses in tree rings of Qilian Juniper vary with the change in tree's age. A total number of 135 increment cores were sampled from Qilian Juniper trees at five sites, in which 112 cores were selected and grouped into five 100-year age classes for analysis of age-dependent cli- mate-growth relationships. Chronology statistics, response functions and ANOVA F-test were used to test the con- sistency of five age-class mean chronologies (AGCs). The results showed that mean sensitivity (MS) and standard deviation (SD) did not change significantly with age. Response function analysis indicated that (a) climate accounts for a high amount of variance in tree-ring widths; (b) tree-ring growth has significant positive correlation with mean monthly air temperature of previous October and November, and with total monthly precipitation of current January and June, while has significant negative correlation with mean monthly air temperature of current May; and (c) AGC-2, AGC-3 and AGC-4 have stronger response to climate change than AGC-1 and AGC-5. The ANOVA F-test showed that generally there are significant differences between the first age class and other four age classes, but among the four classes in which trees are older than 200 years, the differences are usually insignificant. Overall the long-lived Qilian Juniper is still an ideal tree species for dendroclimatic reconstruction.

Photoprotective responses of Mediterranean and Atlantic trees to the extreme heat-wave of summer 2003 in Southwestern Europe

Abstract: Summer 2003 was extremely hot in Europe. High light in combination with heat and drought exacerbates the generation of photo-oxidative stress. Under these conditions photoprotective responses can be critical for plant survival. Photoprotection was analysed in 2003 in several Mediterranean and Atlantic woody species. These data were compared with previous summers (1998, 1999 and 2001) to evaluate the potential acclimation for each species. A pattern of changes consisting on a decrease in chlorophyll, ascorbate and Fv/Fm and an increase in tocopherol, xanthophyll cycle pigments (VAZ) and de-epoxidation index was regularly observed. Acclimation potential was measured by the use of the plasticity index for each parameter. Mediterranean species were more plastic than Atlantic ones. The latter were unable to increase antioxidant pools to the same extent or to down-regulate the efficiency of light energy conversion. These results indicate that most Mediterranean species are able to perform an efficient acclimation to heat stress, whilst Atlantic species will be more affected by climate warming.

Differences in patterns of cell death between ray parenchyma cells and ray tracheids in the conifers Pinus densiflora and Pinus rigida

Abstract: Differences in patterns of cell death between ray parenchyma cells and ray tracheids in the conifers Pinus densiflora and Pinus rigida were clarified. Differentiation and cell death of ray tracheids occurred successively and both were related to the distance from the cambium. In this respect, they resembled those of longitudinal tracheids. Thus, the cell death of short-lived ray tracheids could be characterized as time-dependent programmed cell death. In contrast, ray parenchyma cells survived for several years or more, and no successive cell death occurred, even within a single radial line of cells in a ray. Thus, the features of death of the ray parenchyma cells were different from those of ray tracheids. Cell death occurred early in ray parenchyma cells that were in contact with ray tracheids. The initiation of secondary wall thickening occurred earlier in ray parenchyma cells that were in contact with ray tracheids in Pinus densiflora than in others. In addition, localized thickening of secondary walls occurred only in ray parenchyma cells that were in contact with ray tracheids in Pinus rigida. Moreover, no polyphenols were evident in such cells in either species. Therefore, ray parenchyma cells that were in contact with ray tracheids appeared not to play a role in the formation of heartwood extractives. Our observations indicate that short-lived ray tracheids might affect the pattern of differentiation and, thus, the functions of neighboring long-lived ray parenchyma cells in conifers.

Growth patterns of Nothofagus pumilio trees along altitudinal gradients in Tierra del Fuego, Argentina

Abstract: The influence of ecological factors resulting from altitude on growth characteristics of Nothofagus pumilio was analyzed. N. pumilio forests grow in the southern Andes from near sea level to 600 m.a.s.l. Eight study sites were selected in the southwestern area of Tierra del Fuego, on north- and south-facing slopes, and distributed along an altitudinal gradient (200–600 m.a.s.l.). Growth cycles throughout time were identified. The correlation between climate and tree growth was determined. Tree diameter and height decreased whereas stand density increased towards tree-line. South-facing slopes showed higher values in common growth variability, probably because of stronger climatic controlling factors. Climate-growth correlation models revealed long-term temperature influences on growth variability, and showed variations among the different plots. Differences were detected in the spectral power component of the chronologies throughout the altitudinal profile. The series had a significant spectral peak at frequencies around 7 years, possibly related to mast seeding cycles. This signal became weaker as the altitude increased probably due to lower seed production. These results suggest a strong altitudinal component in growth variability of N. pumilio in Tierra del Fuego.

Tropical moist Polylepis stands at the treeline in East Bolivia: the effect of elevation on stand microclimate, above- and below-ground structure, and regeneration

Abstract: We studied Polylepis forests along an elevational transect between 3,650 and 4,050 m a.s.l. at the treeline of the moist eastern cordillera in Bolivia to examine changes in above- and below-ground stand structure, leaf and root morphology, and regeneration in relation to stand microclimate. Field measurements and model predictions indicated relatively cold growth conditions of the Polylepis forests. Tree height, stem diameter, and basal area of the stands decreased markedly while stem density increased with elevation. Leaf morphology differed between the two occurring Polylepis species, and trees at the treeline had smaller leaves with higher specific leaf area. In contrast, fine root biomass increased from 37 g m−2 at the lowermost stand to 234 g m−2 at the treeline. Trees of the uppermost stand had higher specific root surface area and a much higher number of root tips per unit dry mass. Thus, root surface area and total number of root tips per unit ground area increased conspicuously from the lowermost stand to the treeline. Density of young growth inside the forest increased towards the treeline, while density in the open grassland decreased with elevation. Young growth originated from sexual reproduction at the lower forest but was comprised exclusively of root suckers at the treeline stand. We conclude that both the marked change in carbon allocation towards the root system, as well as the changes in root morphology with elevation indicate an adaptation to reduced nutrient supply under cold conditions of these Polylepis stands at the treeline in E Bolivia.

Association of red coloration with senescence of sugar maple leaves in autumn

Abstract: We evaluated the association of red coloration with senescence in sugar maple (Acer saccharum Marsh.) leaves by assessing differences in leaf retention strength and the progression of the abscission layer through the vascular bundle of green, yellow, and red leaves of 14 mature open-grown trees in October 2002. Computer image analysis confirmed visual categorization of leaves as predominantly green, yellow or red, and chemical quantification of leaf pigment concentrations verified that leaf color reflected underlying differences in leaf biochemistry. Significantly lower chlorophyll concentrations within red and yellow leaves indicated that senescence was more advanced in leaves from these color categories relative to green leaves. Among leaf types, only red leaves contained high concentrations of anthocyanins. There were significant differences in leaf retention capacity among color categories, with the petioles of green leaves being the most firmly attached to twigs, followed by red and then yellow leaves.

DNA methylation in different origin clonal offspring from a mature Sequoiadendron giganteum genotype

Abstract: A meristem-issued rejuvenated line was obtained in 1986 from a 100-year-old Sequoiadendron giganteum tree and has been since then micropropagated in tissue culture conditions maintaining its juvenile-like characteristics. By contrast, grafts and rooted microcuttings from the same genotype planted in outdoor conditions for several years exhibited mature foliage traits and the grafts started to produce cones, which are obvious indicators of physiological aging. These three different clonal lines were compared with regard to global DNA methylation assessed by HPLC. The in vitro rejuvenated line showed a much higher level of DNA methylation (23% as average value) than the two other outdoor origins from the same clone which displayed similar degrees of global methylation (average values of 13.4% for the grafts and 13.8% for the cuttings). Overall these DNA global methylation values obtained for the first time in S. giganteum are consistent with the level of methylation reported for many plants using the same HPLC protocols. The fact that shoots exhibiting a juvenile-like leaf morphology can be characterized by higher DNA methylation than mature-like ones is discussed in relation to physiological aging, referring to other studies on the same topic.

X-ray microdiffraction reveals the orientation of cellulose microfibrils and the size of cellulose crystallites in single Norway spruce tracheids

Abstract: The microfibril angle (MFA) distribution and the size of cellulose crystallites in isolated double cell walls of Norway spruce (Picea abies [L.] Karst.) tracheids were determined by synchrotron X-ray microdiffraction using the reflections 200 and 004. Samples were 25 μm thick longitudinal sections of earlywood from annual rings 6–18 of several stems. The asymmetric MFA distributions extended from −20° to 90°. The mean MFA of tangential cell walls decreased from an average of 24° into 19° from the pith to the bark. The mode of the MFA distribution was about 10° smaller than the mean MFA. The standard deviation of the MFA distribution varied between 18° and 25°. The mean MFA and the mode of the MFA distribution were larger in radial than in tangential cell walls. MFA distributions of mature wood samples exhibited a separate small peak at around 90°. The average width and length of cellulose crystallites varied between 28.9–30.9 A and 192–284 A, respectively. Both increased slightly as a function of annual ring number from the pith up to the 15th annual ring. An irrigation–fertilisation treatment of some of the stems resulted in longer cellulose crystallites compared to the untreated stems.

Ensuring a representative sample of earlywood vessels for dendroecological studies: an example from two ring-porous species

Abstract: The analysis of time series of wood cell anatomical features (such as the earlywood vessels of ring-porous trees) is a successful approach to understand the effect of environmental factors on tree growth and thus constitutes a valuable source of information about past environmental conditions. However, despite the rising interest in analyzing wood anatomical time series, little or no attention has been paid to establish an adequate sample of cells in order to minimize the risk of missing a valuable environmental signal. In order to contribute to such methodological bases, this paper is aimed at (1) identifying a representative sample of earlywood vessels within a tree, which encode the same climatic information, and (2) assessing if it is preferable to obtain the sample of vessels along one or two radii. Four individuals of sessile oak (Quercus petraea (Mattuschka) Liebl.) and sweet chestnut (Castanea sativa Mill.) were harvested and all their earlywood vessel lumina were measured along two 40-mm wide radial strips. Measured vessels were selected stepwise while increasing the tangential width of the wood section from 1 to 40 mm, analyzing at each step (1) the common signal of chronologies and (2) the correlation to the main climatic variables controlling growth. Additionally, both radii in each tree were analyzed together and separately. The results showed that a total tangential width of 10 mm was enough to stabilize the climatic signal with improvement when distributed along two different radii, but a slightly larger tangential width was required to reach an optimal common signal. We suggest that, at least for the case of these two species growing at this specific climatic context, two 5-mm increment cores ensure a representative vessel selection.

Photosynthetic responses of birch and alder saplings grown in a free air CO2 enrichment system in northern Japan

Abstract: Though birch and alder are the common pioneer tree species which dominate in northeast Asia, little is known about the effects of the predicted increase in atmospheric CO2 concentrations ([CO2]) upon their photosynthesis in field conditions. To investigate this, we grew 2-year-old saplings of three Betulaceae species (Betula platyphylla var. japonica Hara, Betula maximowicziana Regel, and Alnus hirsuta Turcz) for 2 years in a free air CO2 enrichment system in northern Japan. Since the effect of high [CO2] is known to depend on soil conditions, we evaluated the responses in two soils which are widely distributed in northern Japan: infertile and immature volcanic ash (VA) soil, and fertile brown forest (BF) soil. For B. platyphylla, photosynthetic down-regulation occurred in both soils, but for B. maximowicziana, down-regulation occurred only in VA soil. The explanation is reduced nitrogen and Rubisco content in the leaf. For A. hirsuta, down-regulation occurred only in BF soil because of the accumulation of starch in foliage, which restricts CO2 diffusion inside the chloroplast. The higher photosynthetic rate of A. hirsuta in infertile VA soil could be due to the sink for photosynthates in the N2-fixing symbiont. These three species are all able to down-regulate at high [CO2]. However, it is possible that A. hirsuta would dominate in VA soil and B. maximowicziana in BF soil in the early stages of forest succession in a CO2-enhanced world.

Responses of nonstructural carbohydrates to shoot removal and soil moisture treatments in Salix nigra

Abstract: Aboveground disturbances are common in dynamic riparian environments, and Salix nigra is well adapted with a vigorous resprouting response. Soil moisture stresses are also common, and S. nigra is flood tolerant and drought sensitive. The objective of this study was to quantify nonstructural carbohydrate (NSC) reserves in S. nigra following shoot removal and soil moisture treatments. NSC reserves provide energy for regeneration of shoot tissue until new functional leaves are developed. Three soil moisture treatments: well-watered (W), periodic flooding (F) and drought (D); and three shoot removal treatments: no shoots removed (R0), partial shoot removal (R1), and complete shoot removal (R2) were applied. Plants were harvested when new shoot development was observed (day 13). Statistical significance in the 3 × 3-factorial design was determined in two-factor ANOVA at P < 0.05. Both roots and cuttings were important reservoirs for NSC during resprouting response, with decreases in root (31%) and cutting (14%) biomass in R2 compared to R0. Rapid recovery of photosynthetic surface area (from 15 to 37% of R0) was found in R1. A clear pattern of starch mobilization was found in roots in R0, R1 and R2, with lowest root starch concentration in W, F higher than W, and D higher than F. Shoot starch concentration was lower in F and D compared to W in R0, however, in R1 shoot starch was reduced in W compared to F and D, possibly indicating reduced rates of translocation during soil moisture stress. Evidence of osmotic adjustment was found in roots and shoots with higher total ethanol-soluble carbohydrates (TESC) during soil moisture stress in F and D treatments. Total plant NSC pool was greater in F and D treatments compared to W, and progressively reduced from R0 to R1 to R2. Results indicated negative effects of drought, and to a lesser extent periodic flooding on resprouting response in S. nigra, with implications for reduced survival when exposed to combined stresses of aboveground disturbance and soil moisture.

Root architecture and allocation patterns of eight native tropical species with different successional status used in open-grown mixed plantations in Panama

Abstract: We investigated biomass allocation and root architecture of eight tropical species with different successional status, as classified from the literature, along a size gradient up to 5 m. We focused on belowground development, which has received less attention than aboveground traits. A discriminant analysis based upon a combination of allocational and architectural traits clearly distinguished functional types and classified species according to successional status at a 100% success rate. For a given plant diameter, the pioneer species presented similar root biomass compared to the non-pioneer ones but higher cumulative root length and a higher number of root apices. A detailed study on the root system of a sub-sample of three species showed that the most late-successional species (Tabebuia rosea) had longer root internodes and a higher proportion of root biomass allocated to the taproot compared to the other two species (Hura crepitans and Luehea seemannii). Most pioneer species showed a higher leaf area ratio due to a higher specific leaf area (SLA). We conclude that the functional differences between pioneer and non-pioneer tree species found in natural forests were maintained in open-grown plantation conditions.

Effects of elevated CO 2 and temperature on secondary compounds in the needles of Scots pine (Pinus sylvestris L.)

Abstract: The aim of this study was to evaluate the long-term effects of elevated CO2 concentration (doubling of ambient CO2 concentration) and temperature (2–6°C elevation) on the concentration and content of secondary compounds in the needles of Scots pine (Pinus sylvestris L.) saplings grown in closed-top environmental chambers. The chamber treatments included (1) ambient temperature and CO2, (2) ambient temperature and elevated CO2, (3) elevated temperature and ambient CO2, and (4) elevated temperature and elevated CO2. The needle sampling and analyses of monoterpenes, HPLC-phenolics and condensed tannins in current- and 1-year-old needles were made in two consecutive years. The results showed that the effects of elevation of CO2 and temperature were greatest on the monoterpene concentration in the needles while the concentration of HPLC-phenolics remained almost unaffected by the changed growing conditions. Most of the observed decrease in monoterpene concentration was caused by the CO2 enrichment while the effect of elevated temperature alone was not as significant. The accumulation of condensed tannins tended to increase due to the elevation of CO2 alone compensating the reduced carbon allocation to monoterpenes. Overall, the responses of the concentrations of secondary compounds to the elevation of CO2 and temperature are variable and depend strongly on the properties and characteristics of each compound as well as on the interrelation between the production of these compounds and the primary production of trees.

Antitranspirant functions of stem periderms and their influence on corticular photosynthesis under drought stress

Abstract: Transpiration and photosynthesis of current-year stems and adult leaves of different deciduous tree species were investigated to estimate their probable influence on carbon balance. Peridermal transpiration of young stems was found to be rather small as compared to the transpiration of leaves (stem/leaf like 1/5–1/20). A characteristic that was mainly attributable to the lower peridermal conductance to water and CO2, which made up only 8–28% of stomatal conductance. Water vapour conductance was significantly lower in stems, but also non-responsive to PAR, which led to a comparatively higher water use efficiency (WUE, ratio assimilation/transpiration). Thus, although corticular photosynthesis reached only 11–37% of leaf photosynthesis, it may be a means of improving the carbon balance of stems under limited water availability. The influence of drought stress on primary photosynthetic reactions was also studied. Under simulated drought conditions the drying time needed to provoke a 50% reduction (t 50) in dark- and light-adapted PSII efficiency (Fv/Fm, ΔF/Fm′) was up to ten times higher in stems than in leaves. Nevertheless, up to a relative water deficit (RWD) of around 40–50% dark-adapted PSII efficiency of leaves and stems was rather insensitive to dehydration, showing that the efficiency of open PS II reaction centres is not impaired. Thus, it may be concluded that in stems as well as in leaves the primary site of drought damage is at the level of dark enzyme reactions and not within PSII. However, enduring severe drought caused photoinhibitory damage to the photosynthetic apparatus of leaves and stems; thereby RWD50 values (= RWD needed to provoke a 50% reduction in Fv/Fm ad ΔF/Fm′) were comparably lower in stems as compared to leaves, indicating a possibly higher drought sensitivity of the cortex chlorenchyma.

Seedling growth variation in response to sand burial in four Artemisia species from different habitats in the semi-arid dune field

Abstract: We compared seedling growth of four Artemisia species dominated at different habitats to determine whether interspecific seedling growth variation of a same genus in tolerance to burial can be used to explain plant distribution in the sand dune field. Interdune lowland species, Artemisia gmelinii, stabilized dune species, A. frigida, semi-stabilized dune species, A. halodendron, and active dune species, A. wudanica were selected. Seedlings grown for 3 weeks were treated at five burial depths for three burial times in pot experiments. Species from the habitats with little burial had smaller survival rate, dry weight and stem elongation speed than those from the habitats with intensive burial when buried. Furthermore, when buried, the former tended to adjust biomass allocation between shoot and root and produce adventitious buds, while the latter tended to maintain a constant root:shoot ratio and produce adventitious roots. We conclude that (1) seedlings of species with a long evolutionary history of exposure to sand burial (from the active sand dune), show quicker stem growth when buried than do seedlings of species from the habitats with little or no sand burial; (2) seedlings of species which do not change root:shoot ratio might be more tolerant of sand burial than those do; (3) seedlings of species from the habitats with intensive sand burial is prone to produce adventitious roots and seedlings of species from the habitats with little or no sand burial tend to produce adventitious buds when buried.

Anatomic basis and insulation of serotinous cones in Pinus halepensis Mill

Abstract: Pinus halepensis Mill., a widespread, low elevation conifer common in Mediterranean Basin, shows a dual reproductive strategy: post-fire obligate seeder (from serotinous cones) and an early coloniser (from non-serotinous cones). Release of seeds encased in serotinous cones is induced either by fire (pyriscence, serotiny or bradychory) or by drying (xeriscence). Morphological differences in serotinous and non-serotinous cones in natural populations of P. halepensis in Southeastern Italy were analyzed. Relationships between tree size (diameter class) and serotiny were checked by counting and sampling serotinous and non-serotinous cones. The macro and microscopic characteristics that could affect cones’ opening were measured in sampled cones. Protection against high temperatures offered by wood scales was also evaluated by applying different temperatures and time exposures, and following the inner thermal raise. Results showed that non-serotinous cones had bigger resin ducts and more separate scales. Also it was highlighted that ovuliferous scales of serotinous cones were bigger and thicker. These scales had more lamellated (multilayered) sclereid cells, and were significantly thinner with a shorter lumen diameter. Continuous temperature-monitoring heat tests inside cones showed that temperatures close to the cone axis were rather low, so seed germination was not influenced. Results confirm that serotinous cones are more compact, rigid and consistent than non-serotinous cones. These characteristics explain the lower insulation, seed protection and the ease opening of non-serotinous cones as well. In conclusion, opening mechanism of pinecone scales under the effect of fire or dry conditions seem related to anatomic differences and it provides seeds with an efficient protection against heat.