Showing papers in "Trees-structure and Function in 2006"

Potential risks for European beech (Fagus sylvatica L.) in a changing climate

Abstract: Over large areas of Europe, coniferous monocultures are being transformed into mixed forests by the re-introduction of broadleaf tree species belonging to the potential natural vegetation. One important species of interest in this changing forest policy is European beech (Fagus sylvatica). However, at present, this forest management directive has ignored potential adverse effects of global climate change on wide-spread re-introduction of beech to these areas. Average global surface temperatures have risen by approx. 0.8°C in the period between 1861 and 2005 and are expected to continue to increase until the end of this century by 1.5–5.8°C above the 1990 value. To estimate the climate change in the southern part of central Europe in future, we reviewed calculations from regional climate models. Temperature increase for the southern part of central Europe is projected to be up to 2°C within the next 40 years. In contrast, the annual precipitation will most likely remain constant over the same time period, but will experience significant changes in seasonal patterns. Rising intensities of individual precipitation events may result in increasing number and intensities of flooding events and reduced precipitation during the growing season in a higher frequency of summer droughts. Growth and competitive ability of European beech will not, necessarily, respond to increasing CO2 concentrations but may be strongly impacted by intensive drought that occurs during the growing season. Seedlings as well as adult trees may suffer from xylem embolism, restricted nutrient uptake capacity and reduced growth under limited water availability. However, it remains uncertain to what extent other environmental factors (e.g. soil properties, competitive interactions) may modify the drought response of beech, thus either enhancing susceptibility or increasing drought tolerance and resilience potential. Water-logged soils, predicted during the spring for several regions due to higher than average precipitation, could negatively impact nutrient uptake and growth of beech. Whereas other dominant species as, e.g. oak are well adapted to that environmental stress, beech is known to be sensitive to water-logging and flooding. Thus, the competitive capacity of beech might—depending on the other environmental conditions—be reduced under the expected future climate conditions. Silvicultural practices must be aware today of the potential risks which a changing climate may impose on sustainable forest development.

Modeling xylem and phloem water flows in trees according to cohesion theory and Münch hypothesis

Abstract: Water and solute flows in the coupled system of xylem and phloem were modeled together with predictions for xylem and whole stem diameter changes. With the model we could produce water circulation between xylem and phloem as presented by the Munch hypothesis. Viscosity was modeled as an explicit function of solute concentration and this was found to vary the resistance of the phloem sap flow by many orders of magnitude in the possible physiological range of sap concentrations. Also, the sensitivity of the predicted phloem translocation to changes in the boundary conditions and parameters such as sugar loading, transpiration, and hydraulic conductivity were studied. The system was found to be quite sensitive to the sugar-loading rate, as too high sugar concentration, (approximately 7 MPa) would cause phloem translocation to be irreversibly hindered and soon totally blocked due to accumulation of sugar at the top of the phloem and the consequent rise in the viscosity of the phloem sap. Too low sugar loading rate, on the other hand, would not induce a sufficient axial water pressure gradient. The model also revealed the existence of Munch “counter flow”, i.e., xylem water flow in the absence of transpiration resulting from water circulation between the xylem and phloem. Modeled diameter changes of the stem were found to be compatible with actual stem diameter measurements from earlier studies. The diurnal diameter variation of the whole stem was approximately 0.1 mm of which the xylem constituted approximately one-third.

Leaf plasticity in response to light of three evergreen species of the Mediterranean maquis

Abstract: Morphological, anatomical, biochemical and physiological traits of sun and shade leaves of adult Quercus ilex, Phillyrea latifolia and Pistacia lentiscus shrub species co-occurring in the Mediterranean maquis at Castelporziano (Latium) were studied. Fully expanded sun leaves had 47% (mean of the three species) greater leaf mass area (LMA) and 31% lower specific leaf area (SLA) than shade leaves. Palisade parenchyma thickness contributed on an average 42% to the total leaf thickness, spongy layer 43%, upper epidermal cells 5%, and upper cuticle thickness 3%. Stomatal size was greater in sun (25.5 μm) than in shade leaves (23.6 μm). Total chlorophyll content per fresh mass was 71% greater in shade than in sun leaves, and nitrogen content was the highest in sun (13.7 mg g−1) than in shade leaves (11.8 mg g−1). Difference of net photosynthetic rates (P N) between sun and shade leaves was 97% (mean of the three species). The plasticity index (sensu Valladares et al., New Phytol 148:79–91, 2000a) was the highest for physiological leaf traits (0.86) than for morphological, anatomical and biochemical ones. Q. ilex had the highest plasticity index of morphological, anatomical and physiological leaf traits (0.37, 0.28 and 0.71, respectively) that might explain its wider ecological distribution. The higher leaf plasticity of Q. ilex might be advantageous in response to varying environmental conditions, including global change.

Inter-annual and seasonal variability of radial growth, wood density and carbon isotope ratios in tree rings of beech (Fagus sylvatica) growing in Germany and Italy

Abstract: We investigated the variability of tree-ring width, wood density and 13C/12C in beech tree rings (Fagus sylvatica L.), and analyzed the influence of climatic variables and carbohydrate storage on these parameters. Wood cores were taken from dominant beech trees in three stands in Germany and Italy. We used densitometry to obtain density profiles of tree rings and laser-ablation-combustion-GC-IRMS to estimate carbon isotope composition (δ 13C) of wood. The sensitivity of ring width, wood density and δ 13C to climatic variables differed; with tree-ring width responding to environmental conditions (temperature or precipitation) during the first half of a growing season and maximum density correlated with temperatures in the second part of a growing season (July–September). δ 13C variations indicate re-allocation and storage processes and effects of drought during the main growing season. About 20% of inter-annual variation of tree-ring width was explained by the tree-ring width of the previous year. This was confirmed by δ 13C of wood which showed a contribution of stored carbohydrates to growth in spring and a storage effect that competes with growth in autumn. Only mid-season δ 13C of wood was related to concurrent assimilation and climate. The comparison of seasonal changes in tree-ring maximum wood density and isotope composition revealed that an increasing seasonal water deficit changes the relationship between density and 13C composition from a negative relation in years with optimal moisture to a positive relationship in years with strong water deficit. The climate signal, however, is over-ridden by effects of stand density and crown structure (e.g., by forest management). There was an unexpected high variability in mid season δ 13C values of wood between individual trees (−31 to −24‰) which was attributed to competition between dominant trees as indicated by crown area, and microclimatological variations within the canopy. Maximum wood density showed less variation (930–990 g cm−3). The relationship between seasonal changes in tree-ring structure and 13C composition can be used to study carbon storage and re-allocation, which is important for improving models of tree-ring growth and carbon isotope fractionation. About 20–30% of the tree-ring is affected by storage processes. The effects of storage on tree-ring width and the effects of forest structure put an additional uncertainty on using tree rings of broad leaved trees for climate reconstruction.

Changes in leaf morphology and anatomy with tree age and height in the broadleaved evergreen species, Eucalyptus regnans F. Muell

Abstract: Relatively little is known about changes in leaf attributes over the lifespan of woody plants. Knowledge of such changes may be useful in interpreting physiological changes with age. This study investigated changes in leaf morphology and anatomy with tree age and height in the broadleaved evergreen species, Eucalyptus regnans. Fully expanded leaves were sampled from the upper canopy of tree ages ranging from 6 to 240 years, and tree heights ranging from about 10–80 m. There were significant changes in leaf form with increasing tree age and height. Leaf size and specific leaf area (SLA; leaf area/leaf mass) decreased, leaf thickness increased, and leaves became narrower relative to their length, with increasing tree age and height. Cuticle thickness and leaf waxiness, including wax occlusion of the stomatal antechamber, increased with increasing age and height. By comparison, there were no clear trends in stomatal frequency or stomatal length with tree age, although there were curvilinear relationships between an index of total stomatal pore area per leaf lamina and both tree age and tree height. The results support the hypothesis that leaves of E. regnans become more xeromorphic with tree age and height. The results are discussed in relation to their significance for changes in water relations in the canopy with age.

Growth/climate response shift in a long subalpine spruce chronology

Abstract: A new Norway spruce (Picea abies (L.) Karst.) tree-ring width chronology based on living and historic wood spanning the AD 1108–2003 period is developed. This composite record combines 208 high elevation samples from 3 Swiss subalpine valleys, i.e., Lotschental, Goms, and Engadine. To retain potential high- to low-frequency information in this dataset, individual spline detrending and the regional curve standardization are applied. For comparison, 22 high elevation and 6 low-elevation instrumental station records covering the greater Alpine area are used. Previous year August–September precipitation and current year May–July temperatures control spruce ring width back to ∼1930. Decreasing (increasing) moving correlations with monthly mean temperatures (precipitation) indicate instable growth/climate response during the 1760–2002 period. Crucial June–August temperatures before ∼1900 shift towards May-July temperature plus August precipitation sensitivity after ∼1900. Numerous of comparable subalpine spruce chronologies confirm increased late-summer drought stress, coincidently with the recent warming trend. Comparison with regional-, and large-scale millennial-long temperature reconstructions reveal significant similarities prior to ∼1900 (1300–1900 mean r=0.51); however, this study does not fully capture the commonly reported 20th century warming (1900–1980 mean r=−0.17). Due to instable growth/climate response of the new spruce chronology, further dendroclimatic reconstruction is not performed.

Gas diffusion through wood: implications for oxygen supply

Abstract: Living tissue in tree stems has to be supplied with oxygen, which can be transported upwards with the transpiration stream; but in times of zero sapflow, the only source is the oxygen stored or diffusing radially through bark and xylem. We measured radial and axial diffusion of oxygen against nitrogen gas in wood of coniferous (Picea abies (L.) Karst. and Taxus baccata L.), ring-porous (Quercus robur L. and Fraxinus excelsior L.) and diffuse-porous (Fagus sylvatica L. and Carpinus betulus L.) trees at different water and gas contents in the laboratory. The diffusion coefficient (D) in radial direction was mostly between 10−11 and 10−7 m2 s−1 and was strongly related to the gas content. At 40% gas volume, D increased 5–13-fold in Picea, Taxus and Quercus, 36-fold in Fraxinus, and about 1000-fold in Carpinus and Fagus relative to D at 15% gas volume. In the axial direction, diffusion was 1 or 2 orders of magnitude faster. Between-species differences in diffusion velocities can largely be explained by wood structure. In general, D was lowest in conifers, highest in diffuse-porous and intermediate in ring-porous hardwoods, where the large vessels were mostly blocked by tyloses. Model calculations showed that at very high water content, radial diffusion can be too low to ensure the supply of respiring sapwood with sufficient oxygen and an important function of gas in living stems appears to be the supply of oxygen through storage and diffusion.

Extraordinary drought of 2003 overrules ozone impact on adult beech trees (Fagus sylvatica)

Abstract: The extraordinary drought during the summer of 2003 in Central Europe allowed to examine responses of adult beech trees (Fagus sylvatica) to co-occurring stress by soil moisture deficit and elevated O3 levels under forest conditions in southern Germany. The study comprised tree exposure to the ambient O3 regime at the site and to a twice-ambient O3 regime as released into the canopy through a free-air O3 fumigation system. Annual courses of photosynthesis (Amax), stomatal conductance (gs), electron transport rate (ETR) and chlorophyll levels were compared between 2003 and 2004, the latter year representing the humid long-term climate at the site. ETR, Amax and gs were lowered during 2003 by drought rather than ozone, whereas chlorophyll levels did not differ between the years. Radial stem increment was reduced in 2003 by drought but fully recovered during the subsequent, humid year. Comparison of AOT40, an O3 exposure-based risk index of O3 stress, and cumulative ozone uptake (COU) yielded a linear relationship throughout humid growth conditions, but a changing slope during 2003. Our findings support the hypothesis that drought protects plants from O3 injury by stomatal closure, which restricts O3 influx into leaves and decouples COU from high external ozone levels. High AOT40 erroneously suggested high O3 risk under drought. Enhanced ozone levels did not aggravate drought effects in leaves and stem.

Stem and leaf water potentials, gas exchange, sap flow, and trunk diameter fluctuations for detecting water stress in lemon trees

Abstract: The sensitivity of continuous (on a whole-day basis) and discretely (at midday) measured indicators of the plant water status in adult lemon trees in response to a cycle of water deprivation and recovery, and the feasibility of obtaining baselines for tree water status indicators was investigated in 30-year-old Fino lemon trees (Citrus limon (L.) Burm. fil.) grafted on sour orange (C. aurantium L.) rootstocks. Control plants (T0) were irrigated daily above their crop water requirements in order to obtain non-limiting soil water conditions, while T1 plants were subjected to water stress by withholding irrigation for 50 days, after which time irrigation was restored and plant recovery was studied for 16 days. In T0 plants the water relations and the plant symptoms confirmed that they had not suffered waterlogging. In contrast, T1 plants showed a substantial degree of water stress, which developed very slowly. Maximum daily trunk shrinkage (MDS) increased in response to water stress during the first 15 days of the experiment, but when the stem water potential (Ψstem) fell below −1.8 MPa, the MDS signal intensity decreased. However, Ψstem and sap flow (SF) signal intensities progressively increased during the water stress period. The results showed that MDS is a very suitable plant-based indicator for precise irrigation scheduling in adult lemon trees. Reference or baseline relationships for MDS, Ψstem, and SF measurements as a function of several parameters related to the evaporative demand of the atmosphere were obtained. This fact open up the possibility of considering a plant-based indicator measurement at a given time relative to the expected value under non-limiting water conditions, which can be calculated from the reference relationships.

Interannual growth response of Norway spruce to climate along an altitudinal gradient in the Tatra Mountains, Poland

Abstract: Ring-width chronologies of Picea abies (L.) Karst. from ten sites in the Tatra Mountains, Poland, were developed to explore growth/climate responses in stands along an altitudinal gradient ranging from 839 to 1468 m a.s.l. There were positive relationships between current-year radial growth and mean monthly temperatures in March, April, June and July, but with increasing elevation, the strength of this correlation declined for March–April and increased for June–July temperatures. The mean monthly temperature in October of the previous year positively influenced radial growth of trees at all sites. Lower mean temperatures in January negatively affected growth of trees at the high-elevation sites. Trees at the low-elevation sites responded positively to a warm early spring, whereas trees at the high-elevation sites showed positive growth responses to higher summer temperatures. Growth of trees at the high-elevation sites was better explained by the temperature regime than was growth at the lower-elevation sites. Therefore, it is likely that these sites may be particularly sensitive to potential effects of temperature change.

Radial-growth and wood-anatomical changes in overaged Quercus pyrenaica coppice stands: functional responses in a new Mediterranean landscape

Abstract: Recent land-use changes in intensively managed forests such as Mediterranean coppice stands might profoundly alter their structure and function. We assessed how the abandonment of traditional management practices in coppice stands, which consisted of short cutting-cycles (10–15 years), has caused overaging (stems are usually much older than when they were coppiced) and altered their wood anatomy and hydraulic architecture. We studied the recent changes of wood anatomy, radial growth, and hydraulic architecture in two stands of Quercus pyrenaica, a transitional Mediterranean oak with ring-porous wood forming coppice stands in W–NW Spain. We selected a xeric and a mesic site because of their contrasting climates and disturbance histories. The xeric site experienced an intense defoliation after the severe 1993–1994 summer drought. The mesic site was thinned in late 1994. We studied the temporal variability in width, vessel number and diameter, and predicted the hydraulic conductivities (Kh) of earlywood and latewood. In the mesic site, we estimated the vulnerability to xylem cavitation of earlywood vessels. Overaging caused a steep decline in latewood production at a cambial age of 14 years., which was close to the customary cutting cycle of Q. pyrenaica. The diameter distribution of vessels was bimodal, and latewood vessels only accounted for 4% of the Kh. Overaging, acting as a predisposing factor in the decline episode, was observed at the xeric site, where most trees did not produce latewood in 1993–1995. At the mesic site, thinned trees formed wider tree-rings, more latewood and multiseriate tree-rings than overaged trees. The growth enhancement remained 8 years after thinning. Most of the hydraulic conductivity in earlywood was lost in a narrow range of potentials, between −2.5 and −3.5 MPa. We have shown how hydraulic conductivity and radial growth are closely related in Q. pyrenaica and how aging modulates this relationship.

Comparative ecophysiological effects of drought on seedlings of the Mediterranean water-saver Pinus halepensis and water-spenders Quercus coccifera and Quercus ilex

Abstract: Ecophysiological and structural traits of seedlings of the water-saver Pinus halepensis and the water-spenders Quercus coccifera and Q. ilex were studied in response to water stress under greenhouse conditions. Water deficit reduced stomatal conductance (g s) and, as a consequence, both net CO2 assimilation (A) and transpiration rate (E) were also reduced. Water stress also emphasized midday down-regulation of the photochemical efficiency (dynamic photoinhibition) reducing quantum yield of noncyclic electron transport (ΦPSII), photochemical quenching (qP) and photochemical efficiency of the open reaction centres of PSII ( $$F_{\rm v} ^\prime /F_{\rm m} ^\prime$$ ) and involved an increase of thermal dissipation of excess energy. However, water stress not only induced dynamic photoinhibition but also brought a reduction in F v/F m (chronic photoinhibition). Despite the water-saving strategy of P. halepensis that limited net CO2 assimilation, this species showed a higher photochemical efficiency and lower photoinhibition than Quercus species. This was not the result of a different photochemical quenching but was linked to a higher value of $$F_{\rm v} ^\prime /F_{\rm m} ^\prime$$ , indicating a less severe photo-inactivation of PSII. Water stress resulted in a loss of pigment content and in an increase of the carotenoids/chlorophyll ratio, antioxidant capacity and the biomass rate allocated to roots as opposed to that assigned to leaves. P. halepensis showed a lower photoinhibition and antioxidant activity than Quercus species due to its lower pigment content and higher proportion of carotenoids allowing P. halepensis to use, in a more effective way, the lesser excess energy absorbed.

Plant morphology and root hydraulics are altered by nutrient deficiency in Pistacia lentiscus (L.)

Abstract: The plants in arid and semiarid areas are often limited by water and nutrients. Morpho-functional adjustments to improve nutrient capture may have important implications on plant water balance, and on plant capacity to withstand drought. Several studies have shown that N and P deficiencies may decrease plant hydraulic conductance. Surprisingly, studies on the implications of nutrient limitations on water use in xerophytes are scarce. We have evaluated the effects of strong reductions in nitrogen and phosphorus availability on morphological traits and hydraulic conductance in seedlings of a common Mediterranean shrub, Pistacia lentiscus L.. Nitrogen deficiency resulted in a decrease in aboveground biomass accumulation, but it did not affect belowground biomass accumulation or root morphology. Phosphorus-deficient plants showed a decrease in leaf area, but no changes in aboveground biomass. Root length, root surface area, and specific root length were higher in phosphorus-deficient plants than in control plants. Nitrogen and phosphorus deficiency reduced both root hydraulic conductance and root hydraulic conductance scaled by total root surface area. On the other hand, nutrient limitations did not significantly affect root conductance per unit of foliar surface area. Thus, adaptation to low nutrient availability did not affect seedling capacity for maintaining water supply to leaves. The implications for drought resistance and survival during seedling establishment in semi-arid environments are discussed.

Vertical canopy gradients in δ13C correspond with leaf nitrogen content in a mixed-species conifer forest

Abstract: Stable carbon isotope composition varies markedly between sun and shade leaves, with sun leaves being invariably more enriched (i.e., they contain more13C). Several hypotheses have emerged to explain this pattern, but controversy remains as to which mechanism is most general. We measured vertical gradients in stable carbon isotope composition (δ13C) in more than 200 trees of nine conifer species growing in mixed-species forests in the Northern Rocky Mountains, USA. For all species except western larch, δ13C decreased from top to bottom of the canopy. We found that δ13C was strongly correlated with nitrogen per unit leaf area (N area), which is a measure of photosynthetic capacity. Usually weaker correlations were found between δ13C and leaf mass per area, nitrogen per unit leaf mass, height from the ground, or depth in the canopy, and these correlations were more variable between trees than for N area. Gradients of δ13C (per meter canopy depth) were steeper in small trees than in tall trees, indicating that a recent explanation of δ13C gradients in terms of drought stress of upper canopy leaves is unlikely to apply in our study area. The strong relationship between N area and δ13C here reported is consistent with the general finding that leaves or species with higher photosynthetic capacity tend to maintain lower CO2 concentrations inside leaves. We conclude that photosynthetic capacity is a strong determinant of δ13C in vertical canopy profiles, and must be accounted for when interpreting δ13C values in conifer forests.

Biomass functions applicable to Scots pine

Abstract: This study describes parameterization of biomass functions applicable to Scots pine (Pinus sylvestris, L.) in the conditions of Central Europe. Fifty-two sample trees from seven sites in different regions of the Czech Republic were used for destructive measurements. The observed aboveground biomass (B AB) and its individual components were examined by different types of non-linear regression models using one to five independent variables including stem diameter (D), tree height (H), tree age (A), crown length (C) and altitude (Z). The best single-equation approximation of B AB was a three-parameter model using D, H and Z, which was also best suited for bark. Including altitude into classical multiplicative exponential function with three independent variables (DHZ) and four parameters yielded the best model for stem over or under bark. Age was important for assessment of dead branches within DHA model, whereas living branches were best approximated using four variables including C (DHAC model). The most complex model (DHACZ) worked best for needle biomass. The comparison of B AB assessment by single regression equation and from sum of individual components showed a negligible difference for full-grown trees, whereas the additive assessment yielded considerably higher B AB for small or young trees. This corresponds to the assessed confidence intervals for individual trees that were larger for smaller trees. The paper also discusses the issue of commonly used linearization of biomass equations and application of linear regression, and provides comparative examples with nonlinear approach used here. The paper presents the parameter sets for the tested equations for B AB and individual biomass components.

Why does photosynthesis decrease with needle age in Pinus pinaster

Abstract: Rates of photosynthesis vary with foliage age and typically decline from full-leaf expansion until senescence occurs. This age-related decline in photosynthesis is especially important in species that retain foliage for several years, yet it is not known whether the internal conductance to CO2 movement (g i) plays any role. More generally, g i has been measured in only a few conifers and has never been measured in leaves or needles older than 1 year. The effect of ageing on g i was investigated in Pinus pinaster, a species that retains needle for 4 or more years. Measurements were made in autumn when trees were not water limited and after leaf expansion was complete. Rates of net photosynthesis decreased with needle age, from 8 μmol m−2 s−1 in fully expanded current-year needles to 4.4 μmol m−2 s−1 in 3-year-old needles. The relative limitation due to internal conductance (0.24–0.35 out of 1) was in all cases larger than that due to stomatal conductance (0.13–0.19 out of 1). Internal conductance and stomatal conductance approximately scaled with rates of photosynthesis. Hence, there was no difference among year-classes in the relative limitations posed by internal and stomatal conductance or evidence that they cause the age-related decline in photosynthesis. There was little evidence that the age-related decline in photosynthesis was due to decreases in contents of N or Rubisco. The decrease in rates of photosynthesis from current-year to older needles was instead related to a twofold decrease in rates of photosynthesis per unit nitrogen and V cmax/Rubisco (i.e., in vivo specific activity).

Genotypic variation in drought response of silver birch (Betula pendula Roth): leaf and root morphology and carbon partitioning

Abstract: This study investigates the drought response of four genotypes of Betula pendula with a focus on leaf and root morphological traits, leaf phenology and carbon partitioning between shoot and root. Potted one-year-old clonal plants of four genotypes from regions with low to high annual rainfall (550–1270 mm year−1) were subjected to drought periods of 12–14 weeks in two subsequent years. Well-watered control plants of the four genotypes differed significantly with respect to total leaf area per plant (LA) and specific leaf area (SLA), whereas differences in total fine root surface area (RA), root specific area (SRA), and the fine root:leaf mass ratio (FR:LM) were not significant. Highest LA and SLA were found in the clone originating from the driest environment. In complementary physiological investigations this clone was found to have the highest water use as well which was interpreted as competitive superiority in terms of water consumption. Drought resulted in an increase in SLA in all genotypes, and a decrease in LA. Leaf area reduction was more pronounced in the genotypes from high than in those from low rainfall origin. The ratio of total root to leaf surfaces remained more or less constant after drought application despite an increase in FR:LM. This is explained by a decrease in SRA resulting from a reduced abundance of very small fine rootlets (diameter <0.2 mm) in the drought-treated plants. The loss in total root surface area due to a reduction in finest root mass was compensated for by a relative increase in total root dry mass per plant. Comparison of results from the first and second drought period indicated a marked influence of timing of drought, root system size, and putative root limitation on plant drought response. We conclude that leaf and root morphology, the total leaf and root surfaces, and the morphological response to drought in birch are to a large extent under genetic control.

Carbohydrate and ethylene levels related to fruitlet drop through abscission zone A in citrus

Abstract: Citrus fruits have two abscission zones (AZ), named A (in the pedicel) and C (in the calyx). Early fruitlet abscission takes place exclusively through AZ A, while at June drop it is progressively inactivated and AZ C begins to operate. In previous work, it has been demonstrated that carbohydrate and ethylene regulate fruit drop through abscission zone C. In this paper, we have analysed the effect of these two factors in developing fruitlets of Satsuma mandarins (Citrus unshiu [Mak.] Marc.) cv. Okitsu to elucidate their involvement on abscission through AZ A. The data indicated that ACC content and ethylene production of fruitlets paralleled abscission rates. Sucrose supplementation increased fruit set, although did not counteract the abscising effect induced by ACC. Branch girdling of terminal fruitlets carrying several leaves significatively reduced ethylene production and abscission rates, and increased sugar content. Pedicel girdling showed the opposite. Taken together, the results revealed that the carbohydrate content may be a biochemical signal involved in the mechanisms controlling abscission through AZ A. The evidence also showed parallelisms between ethylene and its activation. As the induction of higher ethylene levels after the period of AZ A activity, however, was not able to promote fruit drop, it is also concluded that solely ethylene is not sufficient to activate abscission.

Effects of a nutrient pulse supply on nutrient status of the Mediterranean trees Quercus ilex subsp. ballota and Pinus halepensis on different soils and under different competitive pressure

Abstract: Nutrient availability is a key factor in Mediterranean ecosystems that affects the primary productivity and the community structure. The great variability of its natural availability is now increasing due to frequent fires, pollution events and changes in rainfall regime associated to climate change. Quercus ilex ssp. ballota and Pinus halepensis are the most abundant tree species in the NW Mediterranean basin. They frequently compete in the early and middle successional stages. We investigated the effects of N and P pulse supplies on nutrient uptake capacity in these two species in an after-fire field area and in nursery conditions on different soil types and competing conditions. In the field, N fertilisation had weak effects on nutrient concentration and mineralomass likely as a consequence of this nutrient not being limiting in this field site whereas P fertilisation increased the P mineralomass and the Mg, S, Fe, K and Ca concentrations and mineralomass in the different biomass fractions of both species 1 and 3 years after fertilisation application. In the nursery experiments, P fertilisation increased the mineralomass and concentrations of P, Mg, S, Fe, K and Ca in all biomass fractions including the roots in both species and in different soils and competition conditions. The increment of nutrient mineralomass was due to both the increase of growth and of nutrient concentrations. Both species were able to absorb significant amounts of the P applied by fertilisation (between 5 and 20%) in short time (18 months). Competing vegetation decreased the positive effects of P fertilisation, and in many cases the negative effect of competing vegetation on nutrient mineralomass was stronger when P availability was increased by fertilisation. Q. ilex subsp ballota showed a greater competitive ability for P than the more pioneer species Pinus halepensis in the field but not in the nursery conditions. Pinus halepensis had greater nutrient mineralomass in calcareous than in siliceous soils. Q. ilex subsp. ballota had a higher root biomass allocation and root nutrient allocation than P. halepensis, but both species showed a high capacity to increase their nutrient uptake when its availability increased by fertilisation, thus assuring a great nutrient reserve for future growth periods and contributing to retain nutrients in the ecosystem.

Assessing photosynthetic efficiency in an experimental mangrove canopy using remote sensing and chlorophyll fluorescence

Abstract: This study examined the ability of the photochemical reflectance index (PRI) to track changes in effective quantum yield (Δ F/F m ′), non-photochemical quenching (NPQ), and the xanthophyll cycle de-epoxidation (DPS) in an experimental mangrove canopy. PRI was correlated with (Δ F/F m ′) and NPQ over the 4-week measurement period and over the diurnal cycle. The normalised difference vegetation index (NDVI) was not correlated with any aspect of photochemical efficiency measured using chlorophyll fluorescence or xanthophyll pigments. This study demonstrated that photochemical adjustments were responsible for controlling the flow of energy through the photosynthetic apparatus in this mangrove forest canopy rather than canopy structural or chlorophyll adjustments.

Biosafety in Populus spp. and other forest trees : from non-native species to taxa derived from traditional breeding and genetic engineering

Abstract: Forest trees are fundamental components of our environment, mainly due to their long lifetime and important role in forest ecology. In the past, some non-native tree species and taxa from traditional breeding have induced severe environmental impacts such as biological invasion, changes in the ‘gene pool’, and spread of diseases in forestry. Genetically modified trees obtained in different research groups worldwide are particularly confronted with increased concerns regarding biosafety issues. In the light of current biosafety research worldwide, various threats facing forests and natural tree populations are evaluated in this review: biological invasions, horizontal gene transfer, vertical gene transfer and effects on other organisms. Results available from groups working in biosafety research and risk avoidance using forest trees, with emphasis on transgenic trees, are reviewed. Independent biosafety research as well as the establishment of biosafety research programs for forest trees financed by national and international authorities is now more important than ever before. Biosafety problems detected in the past clearly show the importance of a prior case-by-case evaluation of non-native species, new taxa and also genetically modified trees according to the precautionary principle before their release to avoid risks to the environment and human health.

Growth cost and ontogenetic expression patterns of defence in cyanogenic Eucalyptus spp.

Abstract: Plant defences can incur allocation costs and such costs incurred early in ontogeny may result in opportunity costs with effects evident later in life. A unified understanding of the growth cost of defence requires the identification of plants with varying ontogenetic trajectories of preferably resource demanding defences and an appropriate measurement of the growth cost of these defences. To develop such tools, we first compared nitrogen-based chemical defence (cyanogenic glycosides) in juvenile and adult foliage of three species of Eucalyptus (Myrtaceae). We found marked differences between the species, with two having much lower concentrations of foliar cyanogenic glycosides in seedlings compared to adults. We next used seedlings of two species to measure the resource (nitrogen) and growth cost of deploying cyanogenic glycosides. We found evidence that for every 1.0 nitrogen invested in cyanogenic glycosides, 1.49 additional nitrogens were effectively added to the leaves. We also found that deployment of cyanogenic glycosides was associated with a reduction in net assimilation rate (NAR) at constant leaf nitrogen. We did not, however, detect an overall growth cost associated with cyanogenic glycoside deployment because the rise in leaf nitrogen associated with this deployment apparently counteracted the reduction in NAR.

Fine root production and carbohydrate concentrations of mature longleaf pine (Pinus palustris P. mill.) as affected by season of prescribed fire and drought

Abstract: The historical range of longleaf pine (Pinus palustris P. Mill) has been greatly reduced, in part, by lack of fire. Recently, the application of fire has become an accepted practice for the restoration of longleaf pine to former parts of its natural range. This study was designed to evaluate the effects of season of prescribed fire on the root growth and nonstructural carbohydrate concentrations of longleaf pine, and identify the time of year when fire has the least negative effect on longleaf pine root processes. We found that root growth was generally less on July-burned plots than on either March- or May-burned plots and we attribute these responses to the effect of fire on interaction between root processes and the soil environment. Specifically, soil water and temperature conditions may have been less favorable for root growth on the July-burned plots compared to the March- and May-burned plots. With two years of information on the seasonal dynamics of foliage production, root growth, and root carbohydrates, we determined that at our study site, optimal prescribed fire would impact tree growth less in November through March compared to other times of the year. We also observed that severe drought during the 1998 growing season was associated with a 3-month delay in peak root growth, and prolonged drought in 1999 through 2000 coincided with a reduction in root starch storage. We conclude that season of prescribed fire potentially affects root processes, but that severe or prolonged drought may either interact with or override these effects.

The apoplastic antioxidant enzymatic system in the wood-forming tissues of trees

Abstract: The complete apoplastic enzymatic antioxidant system, composed by class I ascorbate peroxidases (class I APXs), class III ascorbate peroxidases (class III APXs), ascorbate oxidases (AAOs), and other class III peroxidases (PRX), of wood-forming tissues has been studied in Populus alba, Citrus aurantium, and Eucalyptus camaldulensis. The aim was to ascertain whether these enzymatic systems may regulate directly (in the case of APXs), or indirectly (in the case of AAOs), apoplastic H2O2 levels in lignifying tissues, whose capacity to produce and to accumulate H2O2 is demonstrated here. Although class I APXs are particularly found in the apoplastic fraction of P. alba (poplar), and class III APXs are particularly found in the apoplastic fraction of C. aurantium (bitter orange tree), the results showed that the universal presence of AAO in the extracellular cell wall matrix of these woody species provokes the partial or total dysfunction of apoplastic class I and class III APXs, and of the whole plethora of non-enzymatic redox shuttles in which ascorbic acid (ASC) is involved, by the competitive and effective removal of ASC. In fact, the redox state (ASC/ASC+DHA) in intercellular wash fluids (IWFs) of these woody species was zero, and thus strongly shifted towards DHA (dehydroascorbate), the oxidized product of ASC. This imbalance of the apoplastic antioxidant enzymatic system apparently results in the accumulation of H2O2 in the apoplast of secondary wood-forming tissues, as can be experimentally observed. Furthermore, it is hypothesized that since AAO uses O2 to remove ASC, it could regulate O2 availability in the lignifying xylem and, thorough this mechanism, AAO could also control the activity of NADPH oxidase (the enzyme responsible for H2O2 production in lignifying tissues) at substrate level, by controlling the tension of O2. That is, the presence of AAO in the extracellular cell wall matrix appears to be essential for finely tuning the oxidative performance of secondary wood-forming tissues.

Decay resistance of Togolese teak (Tectona grandis L.f) heartwood and relationship with colour

Abstract: Togolese teak (Tectona grandis L.f) is highly resistant to pathogen attack, but variability in natural durability exists between trees of different ages, plantations and geographical zones. Therefore, further information concerning this parameter of wood quality is necessary; however, traditional testing methods are difficult and time-consuming to carry out. We tested the possibility of using colorimetry to determine durability in heartwood samples taken from a wide range of trees. Twelve hundred samples from 31 trees were exposed to four fungi: Pycnoporus sanguineus, Antrodia sp., Gloephylum trabeum, and Coriolus versicolor. Wood samples were grouped into three classes (inner, intermediate and outer heartwood). The colour parameters of each sample were then determined using the CIELAB (L*, a*, b*) system and results correlated with the %mass loss of wood after fungal attack. Tests showed that Antrodia sp. and C. versicolor resulted in <20% mass loss, whereas all samples were rated as durable or highly durable with regard to P. sanguineus and G. trabeum. Inner heartwood was found to be the most resistant to pathogen attack and outer heartwood the least. Measurements of colour showed that heartwood was lightest nearest the pith and darkness and redness increased towards the outer heartwood. Regressions of lightness with %mass loss in the durability tests were always highly significant, whereas a* and b* were not always significantly regressed with %mass loss. Therefore, the use of colorimetry as a tool to estimate short-term natural durability both rapidly and cheaply could be considered in the case of plantation grown teak wood.

The architecture of Picea sitchensis structural root systems on horizontal and sloping terrain

Abstract: The coarse root systems of 24 Sitka spruce (Picea sitchensis (Bong.) Carr.) trees, from a 40-year-old plantation in west Scotland, were extracted, digitised in three dimensions, and root topology was recorded. Roots were from trees grown on a steep (ca. 30°) north-facing slope, and from an adjacent horizontal area with similar gleyed mineral soil. The prevailing wind was across-slope from the west. Analysis of below-ground parts of the trees in comparison with those above-ground revealed a positive linear relationship between coarse root volume and stem volume. Most non-directional characteristics of the root systems were similar between trees on the slope and on flat terrain. Allocation of root mass around trees was examined in relation to the slope and the prevailing wind direction. Trees on the horizontal area had more root mass in leeward sectors than other sectors, but trees on the slopes had more root mass in the windward sectors than other sectors. Centres of mass of the root systems from the horizontal part of the site were not significantly clustered in any direction, but root systems of trees on the slope had centres of mass significantly clustered across the slope in the windward direction. For trees on the slope, the mean direction of the largest sector without structural roots was 4° from north, i.e. downslope. The results are discussed in relation to soil characteristics and the biomechanical behaviour of trees on slopes.

Root and stem partitioning of Pinus taeda

Abstract: We measured root and stem mass at three sites (Piedmont (P), Coastal Plain (C), and Sandhills (S)) in the southeastern United States. Stand density, soil texture and drainage, genetic makeup and environmental conditions varied with site while differences in tree size at each site were induced with fertilizer additions. Across sites, root mass was about one half of stem mass when estimated on a per hectare basis. Stem mass per hectare explained 91% of the variation in root mass per hectare, while mean tree diameter at breast height (D), site, and site by measurement year were significant variables explaining an additional 6% of the variation in root mass per hectare. At the S site, the root:stem ratio decreased from 0.7 to 0.5 when mean tree D increased from 10 to 22 cm. At the P and C sites, where mean root:stem ratios were 0.40 and 0.47, respectively, no significant slope in the root:stem to mean tree D relationship was found over a more narrow range in mean tree D (12–15 and 12–18 cm, respectively). Roots were observed in the deepest layers measured (190, 190, and 290 cm for the P, C, and S sites, respectively); however, the asymptotically decreasing root mass per layer indicated the bulk of roots were measured. Root growth relative to stem growth would need to change with increased mean tree D to explain the results observed here. While these changes in growth rate among plant components may differ across sites, stem mass alone does a good job of estimating root mass across sites.

Dendrochronology of Norway spruce (Picea abies (L.) Karst.) from two range centres in lowland Poland

Abstract: In Europe, spruce grows in two main regions which meet in Poland, one to the north and east, the other to the south and west. The northeastern area ranges from the northern treeline extending from Norway to Siberia, to southern Sweden, north-eastern Poland and the southern Ural mountains. The southwestern spruce region reaches the mountainous areas of the Alps and the Balkans, the mountains and uplands of the Sudety Mountains, the Carpathians and neighbouring lowlands. Opinions about the distribution of Norway spruce have changed over the years, and its scarcity in the centre of Poland has been strongly debated. The favoured current theory is that Norway spruce once had a continuous distribution in Poland. It is assumed that the rare occurrence in the central Polish lowland is due to a combination of unfavourable soil conditions and previous management activity. The main aim of this work was to analyse climate–growth relationships of Norway spruce in eastern Poland and distinguish regions with similar increment patterns with regards to spruce range. Spruce growth in northern Polish sites is positively correlated with rainfall from May to July. Tree-ring widths in southern sites are more correlated with March temperature. Selected homogenous regions are the same as range types. Trees from the so-called “spruceless area” seem to have similar climate–growth relationships to trees from the southern region. This finding does not settle the question of the origin of the trees, but it does indicate that similar environmental conditions exist in these two areas and proves that the climate was not a limiting factor there.

Changes in Oregon white oak (Quercus garryana Dougl. ex Hook.) following release from overtopping conifers

Abstract: Oregon white oak or Garry oak (Quercus garryana Dougl. ex Hook.) is a shade-intolerant, deciduous species that has been overtopped by conifers during the past century in parts of its range due to an altered disturbance regime. We examined the response of suppressed Oregon white oak trees in western Washington, USA, to three levels of release from overtopping Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco). We treated individual oak trees with either full release from competition, partial (“half”) release from competition, or a stand-level thinning of Douglas-fir not directed toward release (control). Five years after treatment, oak trees had suffered no mortality or windthrow. Stem diameter growth was 194% greater in the full-release treatment relative to the control. Acorn production varied widely by year, but in years of higher production, acorn production was significantly greater in both release treatments than in the control. Frequency of epicormic branch formation was significantly increased for years 1 and 2 by the full release; the greatest response occurred between 2 and 6 m above ground level. The greatest number of epicormic branches formed on trees on which the majority of original limbs had died back prior to treatment. Trees with relatively less crown dieback at the time of treatment generally had greater stem growth and acorn production responses to release treatments. Our findings indicate that these released Oregon white oak trees are beginning to recover after an extended period of suppression.

Variation of specific leaf area and upscaling to leaf area index in mature Scots pine

Abstract: Reliable and objective estimations of specific leaf area (SLA) and leaf area index (LAI) are essential for accurate estimates of the canopy carbon gain of trees. The variation in SLA with needle age and position in the crown was investigated for a 73-year-old Scots pine (Pinus sylvestris L.) stand in the Belgian Campine region. Allometric equations describing the projected needle area of the entire crown were developed, and used to estimate stand needle area. SLA (cm2 g−1) as significantly influenced by the position in the crown and by needle age (current-year versus 1-year-old needles). SLA increased significantly from the top to the bottom of the crown, and was significantly higher near the interior of the crown as compared to the crown edge. SLA of current-year needles was significantly higher than that of 1-year-old needles. Allometric relationships of projected needle area with different tree characteristics showed that stem diameter at breast height (DBH), tree height and crown depth were reliable predictors of projected needle area at the tree level. The allometric relationships between DBH and projected needle area at the tree level were used to predict stand-level needle area and estimate LAI. The LAI was 1.06 (m2 m−2) for current-year needles and 0.47 for 1-year-old needles, yielding a total stand LAI of 1.53.