Showing papers in "Trees-structure and Function in 2012"

Size-dependent responses to summer drought in Scots pine, Norway spruce and common oak

Abstract: In this study, we provide a detailed analysis of tree growth and water status in relation to climate of three major species of forest trees in lower regions of Bavaria, Southern Germany: Scots pine (Pinus sylvestris), Norway spruce (Picea abies) and common oak (Quercus robur). Tree-ring chronologies and latewood δ13C were used to derive measures for drought reaction across trees of different dimensions: growth reduction associated with drought years, long-term growth/climate relations and stomatal control on photosynthesis. For Scots pine, growth/climate relations indicated a stronger limitation of radial growth by high summer temperatures and low summer precipitation in smaller trees in contrast to larger trees. This is corroborated by a stronger stomatal control on photosynthesis for smaller pine trees under average conditions. In dry years, however, larger pine trees exhibited stronger growth reductions. For Norway spruce, a significantly stronger correlation of tree-ring width with summer temperatures and summer precipitation was found for larger trees. Additionally, for Norway spruce there is evidence for a change in competition mode from size-asymmetric competition under conditions with sufficient soil water supply to a more size-symmetric competition under dry conditions. Smaller oak trees showed a weaker stomatal control on photosynthesis under both dry and average conditions, which is also reflected by a significantly faster recovery of tree-ring growth after extreme drought events in smaller oak trees. The observed patterns are discussed in the context of the limitation-caused matter partitioning hypothesis and possible species-specific ontogenetic modifications.

Temperature variation among mangrove latitudinal range limits worldwide

Abstract: Mangroves are mainly tropical tree species that occur on either side of the equator and because temperature decreases with increasing latitude, the latitudinal limits of mangroves are expected to be mainly controlled by temperature-related drivers. Here, we hypothesized that the mangrove genera (Avicennia and Rhizophora) have the same limiting temperature at all of their upper latitudinal limits at the global scale. We first derived six parameters from monthly mean sea surface temperature (SST) and air temperature (AT). Furthermore, we investigated whether the variation in these temperature parameters is related (i) to the position of the limit, (ii) to specific temperature requirements of congeneric species and/or (iii) to aridity. All temperature-based parameters derived from AT and SST are highly variable among the upper latitudinal limits of Avicennia and Rhizophora. Hence, we found no common isotherms to characterize the limits of the two mangrove genera, which contradict previous studies. The high temperature variation among limits can be due to partial range filling towards the latitudinal limits. This is supported by the higher warmest month temperatures at the latitudinal limits of the northern hemisphere as compared to the southern hemisphere. However, temperature parameters at limits, with no or less than 250 km of available poleward coast, are not different from other limits, and adult tree height at the limits is not correlated with the temperature-based variables. Mean air temperature is warmer at limits with an arid climate, suggesting mechanisms of compensation towards higher temperatures when Avicennia and Rhizophora have to cope with both aridity and low temperature.

Physiological impacts of magnesium-deficiency in Citrus seedlings: photosynthesis, antioxidant system and carbohydrates

Abstract: Magnesium (Mg)-deficiency affects productivity and quality in agriculture, yet at a physiological level it is not well understood. Citrus grandis and Citrus sinensis seedlings were irrigated for 12 weeks with 0, 50, 500 or 2,000 μM MgSO4. Thereafter, Mg-deficiency-induced changes in photosynthesis, antioxidant system and carbohydrates were investigated. Mg-deficiency affected CO2 assimilation more in C. grandis leaves than in C. sinensis ones, but Mg-deficiency-induced accumulation of sugars was not higher in the former except for sucrose. Mg-deficiency-induced photoinhibitory impairment occurring on the whole photosynthetic electron transport chain was more severe in C. grandis leaves than in C. sinensis ones. Mg-deficient leaves had higher or similar activities of antioxidant enzymes and contents of antioxidant metabolites except for catalase (CAT) activity and reduced glutathione (GSH) content. However, Mg-deficiency increased leaf malondialdehyde (MDA) content. In conclusion, the greater decrease in CO2 assimilation in Mg-deficient C. grandis leaves may be caused by the greater decrease in the photosynthetic electron transport capacity. Mg-deficiency-induced up-regulation in leaf antioxidant system does not provide enough protection to Mg-deficient leaves against the oxidative damage.

Defoliation increases risk of carbon starvation in root systems of mature aspen

Abstract: Large trees are noted to decline and die over several years after defoliation or extended periods of drought. The underlying mechanisms of this decline are thought to be driven by moisture limitations to photosynthesis, but alternative considerations also suggest carbon storage limitations as a driver. This research assesses the non-structural carbohydrate reserves in crowns and roots tissues during and after defoliation by insects in trembling aspen. We monitored the non-structural carbon reserves of nine tall mature aspen forest stands over 8 years, including two defoliation events. We report on the carbohydrate dynamics in root and crown tissues during and after defoliation. Following defoliation, branch reserves recovered to levels of undefoliated control trees within the same season, while roots took up to 2 years to recover. We argue that in large trees, tissues closest to the foliage are the first sinks to access C in the phloem stream, while roots, which are more distal and separated by a long bole, will only receive adequate supplies of C when the other more proximate sinks are sated. These results support the hypothesis that in times of limited carbon assimilation, root tissues in mature trees experience the longest reduction in carbon reserves, which likely plays a critical role in tree decline and mortality.

Temporal shifts in leaf phenology of beech ( Fagus sylvatica ) depend on elevation

Abstract: We analyzed the leaf phenology of European beech (Fagus sylvatica) and its variation due to spatial and temporal climatic variability, using a modified data set of the phenological network in Slovenia. We used first leaf unfolding (LU) and general leaf colouring (LC) time series of 47 sites (altitudes from 55 to 1,050 m a.s.l.) and corresponding climate series (52 of precipitation and 38 of temperature) for the period 1955–2007, collected by the Environmental Agency of the Republic of Slovenia. Across the network in average, LU occurred from 14 April until 13 May, and LC from 3 October until 29 October. LU was delayed by 2.6 days and LC was promoted by 1.9 days when the altitude increased by 100 m. Year-to-year variation of LU was significantly correlated with March and April temperatures. March temperatures had a greater effect at lower elevations and April ones at higher elevations. LC was related to August and September temperatures, and occurred later if the temperatures were higher. Recently, March and April temperatures showed an increasing trend and LU occurred 1.52 days earlier per decade at 1,000 m a.s.l. but no significant shifts were observed at lower altitudes. August temperatures were also increasing but the trends of LC were not significant and were not clearly related to altitude. Our detailed sub-regional data from a relatively small area with high geographic variability showed that changes in climate affect phenological response, mainly leaf unfolding, to a greater degree at higher altitudes than at lower ones.

Growth patterns in relation to drought-induced mortality at two Scots pine (Pinus sylvestris L.) sites in NE Iberian Peninsula

Abstract: Drought-related tree mortality has become a widespread phenomenon. Scots pine (Pinus sylvestris L.) is a boreal species with high ecological amplitude that reaches its southwestern limit in the Iberian Peninsula. Thus, Iberian Scots pine populations are particularly good models to study the effects of the increase in aridity predicted by climate change models. A total of 78 living and 39 dead Scots pines trees were sampled at two sites located in the NE of the Iberian Peninsula, where recent mortality events have been recorded. Annual tree rings were used to (1) date dead trees; (2) investigate if there was an association between the occurrence of tree death and severe drought periods characterized by exceptionally low ratios of summer precipitation to potential evapotranspiration (P/PET); and (3) to compare the growth patterns of trees that died with those of surviving ones. Mixed models were used to describe the relationships between tree growth (in terms of basal area increment, BAI, and the percentage of latewood, LW%) and climate variables. Our results showed a direct association between Scots pine mortality and severe drought periods characterized by low summer water availability. At the two sites, the growth patterns of dead trees were clearly distinguishable from those of the trees that survived. In particular, the BAI of dead trees was more sensitive to climate dryness (low P/PETsummer, high temperatures) and started to decline below the values of surviving neighbors 15–40 years before the time of death, implying a slow process of growth decline preceding mortality.

The effects of spacing on growth, morphology and biomass production and allocation in two hybrid poplar clones growing in the boreal region of Canada

Abstract: Intra-clonal competition was studied in young hybrid poplar plantations to assess the effects of spacing on growth, biomass production and allocation, and morphological characteristics of above- and below-ground tree parts. Three spacings were used as whole-plots (1 × 1 m, 3 × 3 m and 5 × 5 m), with two hybrid poplar clones as subplots (BT747, Populus balsamifera L. × P. trichocarpa Torr. & Gray; MB915, P. maximowiczii A. Henry × P. balsamifera L.) in a split-plot design. After six growing seasons, diameter at breast height (dbh) increased by about 120% from the 1 × 1 m to the 5 × 5 m spacing for clone MB915, while there was no significant change in dbh for the other clone. The effect of spacing on height growth was opposite for the clones; it increased by about 175% from the narrowest to the widest spacing for clone MB915, while it decreased by about 27% for clone BT747. Estimates of above-ground biomass production after six growing seasons were significantly reduced with increasing spacing, with 29.6, 4.9 and 3.2 MgDM ha−1 on average from the narrowest to the widest spacing. Branch traits and the vertical distribution of leaf area were the most affected by spacing for both clones, while live crown ratio and percentage of syllepsis did not change. Spacing also affected proportions of biomass allocated to stem, leaves, and branches, but allocation to roots did not change.

Instability of climate signal in tree-ring width in Mediterranean mountains: a multi-species analysis

Abstract: Temporal instability of climate signal in tree-ring width of the five dominant species (Pinus nigra, P. sylvestris, P. uncinata, Abies alba, Fagus sylvatica) growing under Mediterranean mountainous climate was studied over the last century (1910–2004). To disentangle the tree–climate–site complex, the effects of both soil water availability (SWA) (dry, mesic and humid sites) and altitude (from 430 to 1,690 m) were investigated on the response patterns. Responses to climate were analysed using bootstrapped correlation coefficients from 17 ring-width chronologies built from 293 trees sampled in 64 stands in South-Eastern France. Temporal analyses were performed considering forty-six 50-years intervals (from 1910–1959 to 1955–2004). May–June drought was the primary limiting factor. For P. sylvestris, summer precipitation also played a key role. F. sylvatica was the less responding species with no clear common pattern. Low SWA led to an increasing correlation with precipitation in May for P. nigra and A. alba. Precipitation from May to August prevailed on the driest conditions for P. sylvestris. Correlation analyses suggested that warm autumn or winter enhanced growth, except for F. sylvatica. For P. nigra, the importance of April temperature increased with increasing altitude. Temporal analyses revealed a stability of sensitivity for the highest contexts (P. uncinata and F. sylvatica). At lower altitudes, the correlation with minimum temperature in April increased while temperature more often exceeded the threshold of 0°C over the last decades. For precipitation, a decrease in the strength of correlation was observed without close relationships with local xericity.

Fast replenishment of initial carbon stores after defoliation by the pine processionary moth and its relationship to the re-growth ability of trees

Abstract: Defoliation by herbivores may alter the source:sink balance of trees leading to transient decreases in carbon (C) stores. When C stores are replenished concurrently with re-growth both processes may compete, store formation proceeding at the expenses of growth. However, the interactions between both processes are not fully understood. We investigated the effects of defoliation by the pine processionary moth (PPM, Thaumetopoea pityocampa Dennis and Schiff.) on the non-structural carbohydrate (NSC) and nitrogen (N) stores and the growth of Pinus nigra Arnold trees. Short-term effects were evaluated immediately after a PPM outbreak and at the end of the first growing season in trees suffering a range of defoliation damage. Long-term effects were explored by a 17-year-long PPM defoliation experiment, with 11 years of repeated defoliation treatments followed by 6 years of recovery. Defoliation by PPM was followed by transient NSC decreases, but trees were able to exceed initial NSC pools and compensate growth in just one growing season. Such recovery was linked to increased foliage N. Repeated severe defoliations decreased growth and survival of trees in the long-term, but trees increased starch allocation to stems. Defoliation led to an accumulation of C storage compounds in P. nigra trees irrespective of their ability to re-grow. In trees included in the short-term experiment, the accumulation of stores proceeded concurrently with re-growth. However, the repeated severe defoliations included in our long-term experiment impaired the growth of trees, surplus C being accumulated as stores. These results indicate that, growth declines in pines defoliated by PPM are not due to C (source) limitation but may respond to the reduced sink strength of growing meristems due to defoliation, and thus, a decrease in C allocation to growth.

Climatic impacts and drought control of radial growth and seasonal wood formation in Pinus halepensis

Abstract: Short- and long-term growth responses to drought and climatic influences still remain poorly understood. In this study, we investigated the impact of climatic drivers (temperature, precipitation) and drought, using the Standardized Precipitation Index (SPI) calculated at different time scales (1–48 months), on earlywood (EW) and latewood (LW) widths in Pinus halepensis. Nine forests subjected to dry summer conditions were sampled in Mediterranean semi-arid areas from north-eastern Spain. In addition, we explored the seasonal dynamics of cambial activity and wood formation in relation to short-term climate variability. We found two peaks of tracheid cell production corresponding to EW (May–June) and LW (mid-July–August) growth phases, associated with a sharp decrease in enlarging cells in early July in response to low water availability. In the period of analysis (1970–2005), EW growth was positively correlated with precipitation in previous December and current January, April, May and June, while it was negatively correlated with temperature in June and July. LW was correlated positively with minimum temperatures in January. Probably this was an indirect relationship as a consequence of increased EW width at higher January temperatures. Drought affected more negatively EW than LW formation as evidenced the higher SPI-EW correlation (r = 0.72) than the SPI-LW one (r = 0.54). The strongest EW response to drought was observed in July, whereas the highest LW response to drought occurred in September; and this seasonal pattern matched the phases of lowest EW and LW tracheid production. Under a future reduction of winter and spring precipitation, the studied forests may show a decrease in tracheid cell production, causing a decline of radial growth, a reduction in hydraulic conductivity and, indirectly, a hampered carbon uptake in such semi-arid woodlands.

Relationships between endophyte diversity and leaf optical properties

Abstract: A single tropical plant species can harbour hundreds of endophyte species within its tissues. Beyond this, little is known about the relationship between endophyte colonization, leaf traits and spectral properties of leaves. We explore these relationships in Coccoloba cereifera, a plant well known for its symbiotic properties. Endophyte richness in C. cereifera was statistically correlated with leaf traits such as water content, the ratio of fresh weight/dry weight and polyphenol/leaf specific weight. Endophyte diversity was also related to spectral vegetation indices of chlorophyll content. The associations among endophyte diversity, leaf traits and spectral reflectance pose new questions and present new opportunities to better understand plant–fungal symbioses and related leaf optical properties.

Climate effects on productivity and resource-use efficiency of Norway spruce (Picea abies [L.] Karst.) and European beech (Fagus sylvatica [L.]) in stands with different spatial mixing patterns

Abstract: Species mixing is widely held to stabilize productivity, increase resilience and contribute to risk minimization in forest stands in need of special as a result of longevity. However, research on the effects of mixing on productivity and resource consumption so far yielded fairly incoherent results rather than general findings. We focused on the effects of the spatial mixing pattern and the annual climate conditions on the mixing effect, which to date have seldom been considered as modifiers of mixing effects. Nine years of intensive survey of four pure stands of Norway spruce (Picea abies [L.] Karst.) and European beech (Fagus sylvatica [L.]) and two mixed plots with different mixing pattern showed: (1) mixing hardly changed annual net primary productivity at stand level when Norway spruce and European beech are cultivated group-wise but increased by 37 % on account of a higher efficiency of water and light use in individual tree-wise mixture. (2) Favourable climatic conditions increased the superiority of mixed versus pure stands productivity, while, in particular, water stress cancelled the benefit of mixing considerably. (3) An interaction between the spatial pattern and variable climatic conditions was revealed. Both improved light and water use were found in favourable years in close inter-specific intermingling. However, in unfavourable years the spatial pattern played a less pronounced role in terms of productivity.

Sap flux density measurements based on the heat field deformation method

Abstract: Accurate measurements of whole tree water use are needed in many scientific disciplines such as hydrology, ecophysiology, ecology, forestry, agronomy and climatology. Several techniques based on heat dissipation have been developed for this purpose. One of the latest developed techniques is the heat field deformation (HFD) method, which relies on continuous heating and the combination of a symmetrical and an asymmetrical temperature measurement. However, thus far the development of this method has not been fully described in the scientific literature. An understanding of its underlying principles is nevertheless essential to fully exploit the potential of this method as well as to better understand the results. This paper therefore structures the existing, but dispersed, data on the HFD method and explains its evolution from an initial ratio of temperature differences proportional to vapor pressure deficit to a fully operational and practically applicable sap flux density measurement system. It stresses the importance of HFD as a method that is capable of measuring low, high and reverse flows without necessitating zero flow conditions and on several sapwood depths to establish a radial profile. The combination of these features has not been included yet in other heat-based sap flow measurement systems, making the HFD method unique of its kind.

A Simple Calibration Improved the Accuracy of the Thermal Dissipation Technique for Sap Flow Measurements in Juvenile Trees of Six Species

Abstract: The thermal dissipation technique is widely used to estimate transpiration of individual trees and forest stands, but there are conflicting reports regarding its accuracy. We compared the rate of water uptake by stems of six tree species in potometers with sap flow (F S) estimates derived from thermal dissipation sensors to evaluate the accuracy of the technique. To include the full range of xylem anatomies (i.e., diffuse-porous, ring-porous, and tracheid), we used saplings of sweetgum (Liquidambar styraciflua), eastern cottonwood (Populus deltoides), white oak (Quercus alba), American elm (Ulmus americana), shortleaf pine (Pinus echinata), and loblolly pine (Pinus taeda). In almost all instances, estimated F S deviated substantially from actual F S, with the discrepancy in cumulative F S ranging from 9 to 55%. The thermal dissipation technique generally underestimated F S. There were a number of potential causes of these errors, including species characteristics and probe construction and installation. Species with the same xylem anatomy generally did not show similar relationships between estimated and actual F S, and the largest errors were in species with diffuse-porous (Populus deltoides, 34%) and tracheid (Pinus taeda, 55%) xylem anatomies, rather than ring-porous species Quercus alba (9%) and Ulmus americana (15%) as we had predicted. New species-specific α and β parameter values only modestly improved the accuracy of F S estimates. However, the relationship between the estimated and actual F S was linear in all cases and a simple calibration based on the slope of this relationship reduced the error to 1–4% in five of the species, and to 8% in Liquidambar styraciflua. Our calibration approach compensated simultaneously for variation in species characteristics and sensor construction and use. We conclude that species-specific calibrations can substantially increase the accuracy of the thermal dissipation technique.

Vf scab resistance of Malus

Abstract: The apple production in temperate regions with spring rains, the Scab caused by the fungus Venturia inaequalis is the most important constraint. To produce spotless apples and avoid damage that develops during storage, growers apply fungicide on a regular or weather-determined basis. All major apple cultivars are highly susceptible to this disease. To limit the need for fungicide applications, apple breeders are currently introgressing disease resistance from wild Malus accessions into commercial lines. The first attempts to do this were made 100 years ago. As apples are self-incompatible, pseudo-backcrossing is used to eliminate unwanted traits from wild Malus and select new cultivars that are attractive to both producers and consumers. This process, from the first cross of a commercial cultivar with a wild, disease-resistant Malus, is extremely long due to apple’s long juvenile phase, the need for more than seven backcross steps and the high heterozygosity of this genus. Therefore, most of today’s scab-resistant cultivars rely on a single introduction of scab resistance from Malus floribunda 821, referred to as Vf. In this paper, we trace the history of Vf from its initial identification through its use in breeding and commercial production. We sum up the literature describing how and where Vf resistance has been overcome by new pathotypes of V. inaequalis. Finally, we describe the current knowledge of the genes behind Vf resistance, its mode of action and the use of Vf genes in gene technology.

Tree shape plasticity in relation to crown exposure

Abstract: Trees outside closed forest stands differ in the relation between stem diameter, height and crown volume from trees that grew with neighbours close by. Whether this plasticity in tree shape varies between species in relation to their light requirement is unknown. We purposefully sampled 528 trees ranging 5–100 cm diameter at breast height growing in a range of light conditions. Across ten broad-leaved species observed in Sumatra or Kalimantan, a generic relationship was found between light exposure of the crown and a light-dependent a l parameter that modifies the height–diameter allometric equation (H = a l D b ) from those for closed stands. In our results, vertical stretching is well predicted by light availability. In fully open conditions, trees are on average 31% shorter for the same diameter than under (partial) shade. Most of the stretching response occurs in all species as soon as some degree of lateral shading occurs. The response, however, varies by species (8–44% reduction) in a way apparently unrelated to species’ successional status. Crown volume varied less than stem height in its relationship with stem diameter across all light conditions tested. The scaling of crown volume with stem diameter, however, differed markedly between tree species.

Prospects and limitations of microbial pesticides for control of bacterial and fungal pomefruit tree diseases.

Abstract: The tree constitutes an ecosystem in which microorganisms play an essential role in its functionality. Interactions that microorganisms establish with plants may be beneficial or detrimental and are of extreme importance in the exploitation of trees in agriculture as crop production systems. Fruit trees, especially pomefruit trees including apple, pear and several ornamentals are of great economic importance but its production is affected by several diseases. Fungal and bacterial fruit tree diseases are mainly controlled with chemical fungicides and bactericides, but health and environmental concerns about the use of chemical pesticides have result in strong regulatory actions and have stimulated the development of beneficial microorganisms as microbial pesticides. Up to now, several microorganisms have been registered in different countries and in the EU as biocontrol agents (BCA) covering mainly fire blight, soil-borne fungal diseases and postharvest fruit fungal rot. The key aspects in the success of this technology for disease control are related to biosafety and environmental impact of biocontrol agents, the traceability and fate in the environment and food chain, the improvement by physiological, genetic engineering or the use of mixtures or formulations as well as the industrial production and development of delivery systems for treatment application to trees.

Structural evaluations of zygotic embryos and seedlings of the macaw palm (Acrocomia aculeata, Arecaceae) during in vitro germination

Abstract: Acrocomia aculeata is an oil producing tropical palm tree with exceptional potential for producing biofuel. As the propagation of this species is often difficult because of its pronounced seed dormancy, the present work examined the morphology and the anatomy of zygotic embryos and seedlings during in vitro germination. Embryos were put in MS media supplemented with organic compounds and cultivated in the dark at 30°C for 20 days. The dry weights, lengths, and diameters of the cotyledonary petioles, haustoria, roots, ligules, and leaf sheaths of embryos obtained from mature seeds and seedlings removed from culture were measured every 2 days; anatomical and histochemical evaluations were performed on embryos and seedlings removed from culture after 2, 5, 8, 10, 12, and 15 days. Elongation of the embryo axis was observed to initiate after 2 days. Elongation of the cotyledonary petiole was observed starting on the fifth day; this is a morphological indication of germination that is associated with the formation of starch and raphides as well as the differentiation of tracheary elements. The growth of the cotyledon is due to increases in cell volumes as well as the development of a meristematic band peripheral to the haustorium. In spite of the fact that the radicle is less differentiated than the plumule, radicular development is precocious and the root emerges first, indicating the absence of morphological dormancy. Atrophy of the haustorium and the accumulation of phenolic compounds in subepidermal cell layers occur due to culturing conditions.

Variation in wood density and anatomy in a widespread mangrove species

Abstract: Wood density is an important plant trait that influences a range of ecological processes, including resistance to damage and growth rates. Wood density is highly dependent on anatomical characteristics associated with the conductive tissue of trees (xylem and phloem) and the fibre matrix in which they occur. Here, we investigated variation in the wood density of the widespread mangrove species Avicennia marina in the Exmouth Gulf in Western Australia and in the Firth of Thames in New Zealand. We assessed how variation in xylem vessel size, fibre wall thickness and proportion of phloem within the wood contributed to variation in wood density and how these characteristics were linked to growth rates. We found the wood density of A. marina to be higher in Western Australia than in New Zealand and to be higher in taller seaward fringing trees than in scrub trees growing high in the intertidal. At the cellular level, high wood density was associated with large xylem vessels and thick fibre walls. Additionally, wood density increased with decreasing proportions of phloem per growth layer of wood. Tree growth rates were positively correlated with xylem vessel size and wood density. We conclude that A. marina can have large xylem vessel sizes and high growth rates while still maintaining high wood density because of the abundance and thickness of fibres in which vessels are found.

Do the phenology and functional stem attributes of woody species allow for the identification of functional groups in the semiarid region of Brazil

Abstract: The phenology of tree species in environments that are subject to strong climatic seasonality is mainly determined by water availability, which may vary as a function of wood density. The relationship among phenology, water potential, wood density and the capacity of water storage in the stem were determined for woody species of caatinga vegetation (dry forest) in the semiarid region of NE Brazil. Leaf flush and fall, flowering and fruiting events were recorded over a 31-month period, and the water potential was measured over a two-year period. These data were related to precipitation, water availability in the soil and photoperiod. Seven deciduous species exhibited low wood density (DLWD, <0.5 g cm−3), high capacity of water storage in the stem (until 250 % of the dry weight) and high water potential during the year, as opposed to 15 deciduous species that showed high wood density (DHWD, ≥0.5 g cm−3). Leaf flush, flowering and the fruiting of DHWD species were related to precipitation, whereas these phenological events occurred at the end of the dry season and/or the beginning of the rainy season for DLWD species and were related to the photoperiod. The two evergreen species showed variations of water potential that were intermediate between those of DHWD and DLWD deciduous species, leaf flush during the dry season and flowering at the end of dry season. These results suggest the existence of three functional groups: evergreen species, DHWD deciduous species and DLWD deciduous species.

Climate sensitivity of radial growth in European beech (Fagus sylvatica L.) at different aspects in southwestern Germany

Abstract: The climate sensitivity of radial growth in European beech (Fagussylvatica L.) was analyzed within a narrow valley in the Swabian Alb (southwestern Germany). We collected stem disks from three aspects (NE, NW and SW) of trees belonging to different social classes. Common climatic factors limiting growth across the valley were identified using a principal component analysis (PCA). Further, we performed hierarchical cluster analysis (HCA), redundancy analysis (RDA) and bootstrapped correlation analysis to reveal differences in chronologies and climate-growth relationships between aspect and social class. Climatic variables considered in our analyses were monthly and seasonal data on temperature and precipitation, as well as a self-calibrating Palmer drought severity index (sc-PDSI). We identified drought in the period June–August as the most prominent factor limiting growth across the valley. Dominant and co-dominant trees at the NW and SW aspects were found to be particularly drought sensitive, whereas intermediate trees were less susceptible to drought. Underlying causes of established climate–growth relationships are discussed in the context of drought susceptibility, tree-size modulation and tree physiological processes.

Comparative study of diurnal and nocturnal sap flow of Quercus ilex and Phillyrea latifolia in a Mediterranean holm oak forest in Prades (Catalonia, NE Spain)

Abstract: Droughts are a cyclical disturbance in Mediterranean ecosystems and climate change models forecast an increase of their frequency and severity. Some experimental and observational studies have shown that co-occurring species may cope with drier conditions with different strategies and present different responses. Here, we investigate sap flow response to drought in order to explain the observed differential growth and mortality of Quercus ilex and Phillyrea latifolia at Prades Holm oak forest (NE Spain). We measured sap flow of these species and compared their diurnal, nocturnal and seasonal patterns and their relationship with environmental variables. Both species described qualitatively similar daily patterns, either during daylight or night. Sap flow rates were significantly higher in P. latifolia except in autumn and spring. P. latifolia was more sensitive to soil moisture. Nocturnal sap flow was detected in both species with no significant differences and hourly rates suffered a progressive increase from 3 a.m. to dawn in most sampled nights. Our results indicate a better adaptation of P. latifolia to this site as it can take better advantage of wet periods while maintaining higher sap flow rates during dry periods. Along with previous ecophysiological studies at the same location it may be inferred that at its drier distributional limit Q. ilex would be at disadvantage with respect to other species like P. latifolia, as the latter would cope better with increasing xeric conditions already occurring and further predicted for Mediterranean ecosystems. Our results also show nocturnal sap flow to be relevant in individual water losses in these two species as they can be up to 35–40 % of daily sap flow. Further research on the underlying mechanisms of this nocturnal sap flow is required since it may also enhance early morning CO2 fixation or nutrient supply to leaves.

Improving secondary embryogenesis in Quercus robur : application of temporary immersion for mass propagation

Abstract: The effects of the culture system used for embryo proliferation were investigated with the aim of improving multiplication rates and somatic embryo quality in two embryogenic lines of Quercus robur derived from mature trees (B-17 and Sainza). Embryo proliferation medium was defined following comparison of five different semi-solid media, and the highest multiplication rates (based on the total number of embryos and number of cotyledonary-shaped embryos) were achieved with medium supplemented with 0.44 μM benzyladenine for both lines. Embryo proliferation on semi-solid medium was compared with that obtained by a temporary immersion system (TIS), in which four cycles with immersion frequencies of 1 min every 6, 8, 12 or 24 h were tested. TIS promoted a significant increase in proliferated embryo biomass, with the growth index (GI) two and four times higher than in semi-solid medium in B-17 and Sainza genotypes, respectively. An immersion cycle of 1 min every 8 or 12 h produced approximately 700 somatic embryos (B-17) and 1,500 somatic embryos (Sainza) per RITA® bioreactor, with significant differences in the latter genotype with respect to gelled medium. TIS had also a significant effect on somatic embryo synchronization as it enabled a higher production of cotyledonary embryos (90%), which represents increases of 14% (B-17) and 20% (Sainza) with respect to gelled medium. For germination of embryos proliferated in TIS two maturation systems were applied: (1) culture in semi-solid medium containing 6% sorbitol or (2) culture by TIS (without sorbitol) at a frequency of 1 min immersion every 48 h. Germination ability was higher after maturation on sorbitol medium and plantlet conversion occurred in 48% (B-17) and 13% (Sainza) embryos. TIS produced large numbers of well-developed cotyledonary embryos, hence reduced the cost and labor.

Araucaria araucana tree-ring chronologies in Argentina: spatial growth variations and climate influences

Abstract: Seventeen tree-ring chronologies from the conifer Araucaria araucana (Molina) K. Koch have been analyzed across its range of distribution in Argentina. We studied the growth patterns and determined the main climatic factors influencing A. araucana radial growth. All the chronologies show a strong common signal observed by the high amount of variance explained by the first principal component (PC1) and the high mean correlation (r = 0.597) between the chronologies over the 1676–1974 interval. On this basis, we developed a regional chronology that is 866 years long (A.D. 1140–2006) and includes 621 tree-ring series. Based on the PC2 scores, chronologies were clearly separated by elevation in high- and low-elevation records. Regional tree growth is strongly negatively related to temperatures during summer and fall in the previous-growing season and spring in the current-growing season, respectively. A positive association of tree growth with precipitation is recorded during spring in the current growing season. These results suggest a close relationship between A. araucana tree growth and water availability on a regional scale. This observation is also consistent with a positive and significant correlation between our A. araucana regional record and a reconstruction of November–December rainfall for northern Patagonia inferred from the xeric Austrocedrus chilensis during the past 400 years. Negative correlations between A. araucana regional growth and the sea surface temperature in the Nino 3.4 region reflect the occurrence of above-mean summer temperatures in the region during positive tropical Pacific SST anomalies. The negative relationship with the Antarctic Oscillation (AAO) results from reduced precipitation in our study region during the positive phase of the AAO. The effect of elevation on water availability is consistent with significant correlations between ring-width variations at lower elevations and the Palmer Drought Severity Index during spring and summer in the current growing season. Our study emphasizes the high dendroclimatological potential of A. araucana chronologies for reconstructing past climate variations in northern Patagonia during the past millennium.

Nitrogen fertilization has differential effects on N allocation and lignin in two Populus species with contrasting ecology

Abstract: Black cottonwood (BC, Populus trichocarpa) and hybrid aspen (HA, P. tremula 9 tremuloides) differ in their ecology of being adapted to wet and drier conditions as riparian and early successional forest species, respec- tively. We tested the hypothesis that these ecological dif- ferences were reflected in higher nitrogen (N) use efficiency in HA than in BC and that HA would allocate more resources belowground than BC in the presence of high and low N availability. We expected that responses of wood properties to elevated N would be more pronounced in the species with higher wood formation in response to N supply. HA showed higher belowground biomass parti- tioning than BC in the presence of low (0.2 mM) and high (2 mM) N supply, but in contrast to our expectation whole- plant nitrogen use efficiency and the stem carbon-to- nitrogen balance were lower than in BC. In response to elevated N, HA exhibited stronger stimulation of biomass production than BC, especially of the stem, which showed significant increases in biomass and volume but decreases in density. Lignification, especially the production of guaiacyl (G)-compared to syringyl (S)-lignin, was delayed in HA compared with BC wood. Since G lignin leads to stronger crosslinking than S lignin, its delayed formation may have enabled stronger expansion and higher volume increment of HA than of BC stems. Our results suggest that BC, a poplar species adapted to fluctuating N supply, is less responsive to differences in N availability than aspen that occurs in low N environments.

Discrete versus continuous analysis of anatomical and δ13C variability in tree rings with intra-annual density fluctuations

Abstract: Intra-annual density fluctuations (IADFs) are anomalies of tree rings where wood density is abruptly altered after sudden changes in environmental conditions. Their characterisation can provide information about the relationship between environmental factors and eco-physiological processes during tree growth. This paper reports about the variability of anatomical traits and stable carbon isotopic composition along tree rings as resulting from the application of two different methodological approaches: (a) the separation of each ring into different regions (earlywood, latewood and IADF) and the comparison of anatomical and isotopic parameters measured in those specific sectors and (b) the analysis of such features in continuum along ring width. Moreover, different parameters of vessels (i.e. ecd—equivalent circle diameter, elongation, sphericity and convexity of vessel lumen) were considered to identify those more appropriate for the representation of intra-annual anatomical variations. The analysis was conducted on Arbutus unedo L. growing on the Elba Island (Italy); tree rings of this species form IADFs with features clearly responsive to the environmental conditions experienced during plant growth. Results showed that the first approach, although more suitable to obtain data for subsequent statistical comparisons and for the calculation of correlations with environmental parameters, suffers from elements of subjectivity due to the size and position of the selected tree-ring regions. The in continuum method allows a clearer identification of the variation of tree-ring properties along ring width. Regarding anatomical parameters, shape indexes were not suitable indicators of intra-annual variability. The overall analysis suggested that using both methodologies in synergy helps to gain complete information and avoid misleading interpretations of IADFs in tree rings.

Photosynthetic limitations in coffee plants are chiefly governed by diffusive factors

Abstract: It has long been held that the regulation of photosynthesis in source leaves may be controlled by carbohydrates. The mechanisms that govern the diurnal fluctuation of photosynthesis and the potential role of feedback regulation by carbohydrates during photosynthesis in coffee (Coffea arabica) leaves were investigated in three independent and complementary experiments. An integrative approach using gas exchange measurements in addition to carbon isotope labelling and steady-state carbohydrate and amino acid analysis was performed. Canonical correlation analysis was also performed. In field-grown plants under naturally fluctuating environmental conditions (Experiment I), the overall pattern of gas exchange was characterised by both low stomatal conductance (g s) and net carbon assimilation rate (A) in the afternoon; no apparent signs of photoinhibition were observed. Under conditions of low air evaporative demand (Experiment II), only slight decreases (~20%) in A were observed at the end of the day, which were associated with a reduction (~35%) in g s. For both conditions, any increase in carbohydrate and amino acid pools over the course of the day was small. In leaves from girdled branches (Experiment III), a remarkable decrease in A and particularly in g s was observed, as were increases in starch but not in hexoses and sucrose pools. Furthermore, the rate of 14CO2 uptake (assessed under saturating CO2 conditions) and the partitioning of recently fixed 14C were not affected by girdling. It is proposed that the diurnal oscillations in A and the differences in A in leaves from girdled and non-girdled branches were merely a consequence of diffusive limitations rather than from photochemical constraints or direct metabolite-mediated down-regulation of photosynthesis.

Cork oak (Quercus suber L.) seedlings acclimate to elevated CO2 and water stress: photosynthesis, growth, wood anatomy and hydraulic conductivity

Abstract: Leaf gas-exchange, leaf and shoot anatomy, wood density and hydraulic conductivity were investigated in seedlings of Quercus suber L. grown for 15 months either at elevated (700 μmol mol−1) or normal (350 μmol mol−1) ambient atmospheric CO2 concentrations. Plants were grown in greenhouses in a controlled environment: relative humidity 50% (±5), temperature similar to external temperature and natural light conditions. Plants were supplied with nutrients and two water regimes (WW, well watered; WS, water stress). After 6 months exposure to CO2 enrichment an increase in photosynthetic rate, a decrease in stomatal conductance and a decrease in carbon isotope discrimination (Δ13C) were observed, along with enhanced growth and an increase in the number of branches and branch diameter. Over the same period, the shoot weight ratio increased, the root weight ratio decreased and the leaf weight ratio was unaffected. The specific leaf area increased due to an increase in total leaf thickness, mainly due to the palisade parenchyma and starch. However, after 9 and 15 months of elevated CO2 exposure, the above-mentioned physiological and morphological parameters appeared to be unaffected. Elevated CO2 did not promote changes in vessel lumen diameter, vessel frequency or wood density in stems grown in greenhouse conditions. As a consequence, xylem hydraulic efficiency remained unchanged. Likewise, xylem vulnerability to embolism was not modified by elevated CO2. In summary, elevated CO2 had no positive effect on the ecophysiological parameters or growth of water stressed plants.

The physiological and nutritional responses to an excess of boron by Verna lemon trees that were grafted on four contrasting rootstocks

Abstract: Citrus species are sensitive to an excess of boron (B). Currently, this toxicity is becoming a serious problem in the soils of arid and semi-arid environments throughout the world, where high concentrations of B may occur due to the agricultural use of wastewater. Citrus rootstocks can greatly influence the tolerance of citrus trees to different abiotic stresses. However, little is known about how the rootstock influences the tolerance of these trees to an excess of B. In this study, the effects of the nutrient solution’s B concentration (0.25, 2, 4.5 or 7 mg l−1) on the growth and other physiological, nutritional and biochemical parameters of Verna lemon trees that were grafted on four contrasting rootstocks [Carrizo citrange (CC), Cleopatra mandarin (CL), Citrus macrophylla (CM) and sour orange (SO)] were investigated. The plants were grown in a greenhouse in pots containing a universal substrate media and were watered daily with a Hoagland nutrient solution containing different concentrations of B. The results showed that the plant growth was progressively inhibited with an increasing concentration of B in the nutrient solution. However, the shoot was more sensitive to the B toxicity than were the roots. In addition, the growth inhibition was reduced in trees that were grafted on CL and CM when compared with those that were grafted on CC and SO. The concentration of B in the leaves, stems and roots also increased with an increase in the concentration of external B in the following order: leaves > roots > stem. The rootstock also had an influence on the B concentration in the different plant tissues. In the leaves, the B concentration was lowest in the plants that were grafted on the SO rootstock followed by the plants that were grafted on either the CM or CL rootstock and highest in the plants that were grafted on the CC rootstock. The net assimilation of CO2 ( $$ A_{{{\text{CO}}_{2} }} $$ ) and the stomatal conductance (g s) leaf gas exchange parameters were reduced with an excess of B in the leaves, and this reduction was less pronounced for trees on CM and CL. The intercellular CO2 concentration (C i) and the chlorophyll fluorescence indicated that the reduction of $$ A_{{{\text{CO}}_{2} }} $$ that was found with an excess of B was mainly due to non-stomatal factors. The mineral nutrition and organic solute data are also shown in this study. All of the data indicate that the tolerance to an excess of B is not related to the concentration of B that has accumulated in the leaves, which indicates that a combination of rootstock-dependent physiological, biochemical and anatomical responses determine the tolerance to an excess of B in citrus plants.

European pome fruit genetic resources evaluated for disease resistance

Abstract: Pome fruit genetic resources collections constitute a highly valuable resource not only for fruit breeding but also for direct use by nurseries, growers, and home gardeners. In order to use these resources efficiently and sustainably, reliable evaluation data on fruit and tree characteristics must be generated. Here we focus on pome fruit genetic resources evaluated phenotypically and genotypically for susceptibility to apple scab (Venturiainaequalis), powdery mildew (Podosphaeraleucotricha), fire blight (Erwiniaamylovora), pear rust (Gymnosporangiumsabinae) and storage diseases (e.g., Penicilliumexpansum). Examples are presented of several ongoing projects throughout Europe, with the aim to evaluate fruit genetic resources for disease susceptibility and potential use in breeding and for commercial use. The COST action 864 has fostered international cooperation in the evaluation of pome fruit genetic resources, and some of these evaluations therefore involve research groups from several of the participating countries.