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1.
? Previously, a large intra-specific diversity and a tight genetic control have been shown for Δ13C (carbon isotope discrimination) in a pedunculate oak (Quercus robur L.) family, which is an estimator for intrinsic water use efficiency (W i), a complex trait defined as the ratio of net CO2 assimilation rate (A) to stomatal conductance for water vapour (g s ). ? In the present study, twelve genotypes with extreme phenotypic values of Δ13C were selected within this family to (i) asses the stability of genotype differences across contrasting environments and for different measures W i; (ii) quantify the relationship between Δ13C and Wi within this family; (iii) identify which leaf traits drive the diversity in W i observed in this family. ? Genetic variability of Δ13C and W i was largely independent from different temporal integration scales and their correlation was found to be strong (R 2 = 88% for leaf sugars) within this family. ? Weak correlations between measures of W i with estimators of photosynthetic capacity, suggest a minor role of the latter in the diversity of W i. ? However, the tight correlation between g s and Δ13C as well as W i, and the related genotypic variation in stomatal density, suggest that the genotypic diversity in W i within this pedunculate oak family might be due to differences in g s . 相似文献
2.
? Quercus ilex L., the dominant species in Mediterranean forests and one with a great capacity for resprouting after disturbances, is threatened by the expected increase in fire frequency and drought associated with climate change. ? The aim of this study was to determine the contribution of photosynthesis limitants, especially mesophyll conductance (g mes) during this species’ resprouting and under summer drought. ? Resprouts showed 5.3-fold increased g mes and 3.8-fold increased stomatal conductance (g s) at mid-day with respect to leaves of undisturbed individuals. With increased drought, structural changes (decreased density and increased thickness) in resprouts contributed to the observed higher photosynthesis and increased g mes. However, g mes only partially depended on leaf structure, and was also under physiological control. Resprouts also showed lower non-stomatal limitations (around 50% higher carboxylation velocity (V c,max) and capacity for ribulose-1,5-bisphosphate regeneration (J max)). A significant contribution of g mes to leaf carbon isotope discrimination values was observed. ? g mes exhibits a dominant role in photosynthesis limitation in Q. ilex and is regulated by factors other than morphology. During resprouting after disturbances, greater capacity to withstand drought, as evidenced by higher g mes, g s and lower non-stomatal limitants, enables increased photosynthesis and rapid growth. 相似文献
3.
? The effect of two weeds (grasses and broom, Cytisus scoparius) competition on the growth and functional traits of European beech saplings (Fagus sylvatica) was investigated in an experimental plantation in the French Massif central. ? We hypothesized that grasses would have a much more harmful effect than broom on beech growth through strong competition for soil water and nitrogen. ? A randomized block design was used with three separate blocks, each possessing three types of vegetation; grasses (mainly Agrostis capillaris, Holcus mollis and H. lanatus), broom, and bare soil as a control. ? Two years after plantation beech sapling growth was significantly greater in bare soil than with competition from grasses, and was intermediate on broom. Growth was positively correlated with beech leaf nitrogen content (Nm) and xylem water potential (Ψx). N and Ψx were dependent, with nitrogen uptake probably decreasing with increasing drought. There was no clear correlation between growth and light transmitted 10 cm below the apex of the saplings. ? Beech leaf mass on an area basis (LMA) was correlated with the three resource variables (water, nitrogen and light) and with growth, confirming that LMA is a sensitive functional trait integrating the degree of stress experienced by the saplings. ? The results suggest that broom is less competitive than grasses and, if properly managed on a sufficiently well-watered site, can generate satisfactory conditions for beech establishment and growth. 相似文献
4.
? Transplant shock, implicated by depressed seedling physiological status associated with moisture stress immediately following planting, limits early plantation establishment. Large root volume (Rv) has potential to alleviate transplant shock because of higher root growth potential and greater access to soil water. ? We investigated impacts of drought and transplant Rv on photosynthetic assimilation (A), transpiration (E), stomatal conductance (g s ), predawn leaf xylem water potential (ΨL), and growth of northern red oak (Quercus rubra L.) seedlings to explain mechanisms associated with susceptibility to transplant shock. One year-old barerooot seedlings were graded into four Rv categories and either well watered or subjected to drought consisting of low, medium, or high moisture stress by discontinuing irrigation at 22-day intervals for 3 months. Thereafter, all treatments were re-watered to examine recovery. ? Transplant shock was signified by reduced A, E, g s, and ΨL, which generally increased with increasing moisture stress and Rv. Physiological status improved during recovery, though stress was still evident in seedlings exposed to medium or high moisture stress and in larger Rv seedlings. Growth declined with increasing moisture stress but was generally similar among Rv treatments, likely reflecting greater A at the whole plant level and/or reliance upon stored reserves in large Rv seedlings. ? The most effective drought avoidance mechanisms were root growth, stomatal regulation, reduced leaf area, and higher growth allocation to roots relative to shoots. Our results suggest that large initial Rv does not enhance drought avoidance during the first season after transplant in northern red oak seedlings. 相似文献
5.
? We investigated the effects of flooding for three weeks on physiological responses and uptake of NH 4 + and NO 3 ? by black spruce (Picea mariana (Mill.) BSP.) and tamarack (Larix laricina (Du Roi) K. Koch) seedlings fertilized with labeled (15NH4)2SO4 or K15NO3 in a growth chamber experiment. ? Flooding reduced photosynthesis (A), transpiration (E), water use efficiency (WUE), and current uptake of NH 4 + and NO 3 ? in both species. ? Under flooding, there were no significant differences between the two species in uptake of either NH 4 + or NO 3 ? at the whole-plant level but black spruce had higher translocation of NH 4 + to the shoots than did tamarack. ? Under non-flooded conditions, black spruce seedlings exhibited higher uptake of both NH 4 + and NO 3 ? than did tamarack and demonstrated preferential uptake of NH 4 + (19. 7 mg g?1dw) over NO 3 ? (12.3 mg g?1dw after three weeks). In contrast, non-flooded tamarack seedlings had equal uptake of NH 4 + (4.96 mg g?1dw) and NO 3 ? (4.97 mg g?1dw). ? We hypothesize that the ability of tamarack to equally exploit both 15NH 4 + and 15NO 3 ? would confer an advantage over black spruce, when faced with limitations in the availability of different forms of soil nitrogen. 相似文献
6.
? The aim of this work was to examine the anatomy and functioning of secondary xylem in stems in relation to the decline of European ash (Fraxinus excelsior L.). ? We tested the hypothesis that declining trees show changes in the structure of wood, which result in impaired water transport. ? Anatomical analyses were carried out on wood samples (comprising all annual rings formed during the 30 years life of the analysed trees) collected at breast height from the main stem of healthy, weakened and dead ash trees. The width of annual wood increments, the diameter and density of earlywood vessels were measured and the theoretical hydraulic conductivity index through the secondary xylem calculated by application of Hagen-Poisseuille’s formula. ? Anatomical characteristics changed both with the age of trees and in response to unfavorable factors. The largest vessels were observed in healthy trees, which implied that they had the highest hydraulic conductivity index, whereas trees considered to be in decline produce smaller vessels and hence had reduced conductivity. 相似文献
7.
? Assessment of forest sustainability requires reliable soil quality indicators. The present study evaluated the use of several potential such indicators in forests in the Basque Country under different types of management, involving: (i) species change and (ii) heavily mechanised forest operations. ? Five adjacent forest stands were selected for study: (i) two unmanaged forests (Quercus robur, Fagus sylvatica) and one (40-year-old) Pinus radiata plantation, to investigate the effect of species change; and (ii) a chronosequence of mechanised radiata pine plantations (3 and 16 years old), to investigate heavy mechanisation. ? Several physical, chemical and biological parameters were analysed in the mineral soil. Species change could not be assessed with chemical parameters, but parameters related to organic matter indicated the disturbance caused by heavy mechanisation. The Least Limiting Water Range was a good indicator of soil physical degradation induced by heavy mechanisation. Biological parameters proved sensitive indicators: (i) the fungal phospholipid fatty acid biomarker 18:2ω6 for species change; and (ii) the ratio of Gram-positive/Gram-negative bacteria for heavy mechanisation. Nevertheless, these parameters are complementary, and monitoring programmes should include physical, chemical and biological parameters. ? Further studies are required to assess natural boundaries of variation in soil quality indicators, and their resistance and resilience. 相似文献
8.
Context In the context of a probable increase in intensity and frequency of extreme summer drought events, a better understanding of the key processes involved in water relations is needed to improve the theoretical foundations of predictive process-based models. Aims This paper aims to analyse how temperate deciduous trees cope with water shortage. Methods The exceptional summer drought of 2003 in Europe provided an opportunity to monitor stomatal conductance and twig water potential in European beech ( Fagus sylvatica L.) at predawn and midday and to analyse variations with respect to leaf height within the canopy. By comparing our field measurements of twig water potential to values found in the literature, we confirmed the strong impact of soil water shortage on crown water relations. Results This paper shows that (1) the vertical gradient of stomatal conductance within the crown disappeared under extreme soil water depletion; (2) at maximum drought intensity, predawn twig water potential ( ψ pd) reached ?2.3 MPa at a height of 14 m in the crown and ?2.0 MPa at a height of 10 m. The significant differences in ψ pd between the two measurement heights in the canopy may be due to night transpiration; (3) there was a close relationship between predawn twig water potential and relative extractable soil water; (4) as drought conditions intensified, there was a close relationship between canopy radiation interception and predawn water potential, as estimated daily from relative extractable soil water. 相似文献
9.
? In mixed-species forest stands, large losses in tree species diversity often occur during the regeneration phase. In a former coppice-with-standards, we investigated whether the limiting stage in the recruitment process of advance regeneration is the immediate seedling response to canopy release. Experimental canopy gaps were opened and the survival and growth of advance seedlings (Fagus sylvatica, Acer pseudoplatanus, Acer campestre, Acer platanoides) growing in the gaps or under closed canopy were monitored for three years. ? All species responded positively and rapidly to canopy release. Survival was not affected by gap opening. Diameter increment after gap opening was similar across species, and height increment was greater for Acer platanoides and for Acer pseudoplatanus. Post-release diameter and height growth were mainly determined by pre-release seedling size. Competition from neighbouring seedlings did not affect growth in the three years following canopy opening. ? In the recruitment process of F. sylvatica and Acer sp. advance regeneration, the recovery from canopy release did not appear as a limiting step that would filter against some species. Pre-release size was the main factor accounting for post-release growth and is probably a major determinant of long-term seedling dominance. 相似文献
10.
? Microsatellite markers were used to describe the genetic structure and variability of early, intermediate and late phenological forms of European beech (Fagus sylvatica L.). Two hundred and seventy individuals from three populations located in southern Poland were divided into three forms according to the phenological criterion — bud burst, and analyzed for allelic variation at five highly polymorphic microsatellite loci. ? Population differentiation was moderate and differed significantly among phenological forms. Average values of F ST and R ST decreased across phenological forms and amounted to F ST values of 0.135, 0.110 and 0.108 and R ST values of 0.365, 0.231 and 0.098 for early, intermediate and late forms of beech, respectively. ? Analysis of Molecular Variance (AMOVA) revealed different genetic structures characteristic of respective phenological forms of beech. The amount of within-population variability increased with the delay of the beginning of vegetation and amounted to 64%, 77% and 90% of total variability, depending on phenological form. A similar trend was found in average pairwise genetic distance between individuals belonging to a given phenological form (11.78, 11.85 and 12.22, from early to late forms). ? Our results demonstrate the importance of late spring frosts as a factor influencing the genetic structure of beech, and as a cause of the decrease in genetic variability as well as the increase in population differentiation proportional to the degree of phenological earliness. 相似文献
11.
? Several techniques were used to investigate the threshold minimum temperature inducing severe frost damage during winter in Scots pine (Pinus sylvestris L.) needles and stems from southern provenances in the Iberian Peninsula. ? Chlorophyll (Chl) fluorescence, electrolyte leakage (EL), visual scoring (VS), and the normalized difference vegetation index (NDVI) were compared. ? Chl fluorescence, and in particular the maximum potential photosystem II (PSII) efficiency — estimated through the dark-acclimated FV/FM ratio-, was found to be a simple, non-destructive indicator of freezing tolerance in needles, as expected. ? Moreover, the existence of a Chl-containing tissue, the cortical bark chlorenchyma, allowed us the use of Chl fluorescence as a new non-destructive indicator of frost damage in live tissues of Pinus sylvestris L. stems. ? Freezing tolerance values of southern provenances are compared with those found by other authors in the northern distribution limit of the species. 相似文献
12.
? In this study, longitudinal specific modulus of elasticity along the grain (specific MOEL = MOEL/ρ) as well as radial and tangential shear moduli (G LR and (G LT ) of Populus Deltoides wood were examined in free flexural vibration in a free-free bar method, where end-cracks produced manually in LT plane along and parallel to annual rings in four different sizes. ? The effects of four different crack sizes (0, 6, 12, and 18 cm) on elastic parameters of the bars were examined for their vibration properties based on Timoshenko bar equations, in order to find a procedure to make a confident choice of a clear specimen among the cracked ones, considering three initial modes of vibration. ? Based on research findings, a significant correlation existed between radial and tangential shear moduli of the clear bars as G LR was approximately 15 percents higher than (G LT . After making the shortest crack sizes, however, this correlation entirely faded. Statistically for 6 cm crack, decreases in specific MOE L for measurement on the tangential impact were not significant though they were for longer cracks. ? It was also revealed that in specimen under the study if longitudinal specific modulus of elasticity from both LR and LT flexural vibrations were almost equal and G LR was slightly larger than (G LT , the user could be confident enough to consider the specimen without severe longitudinal cracks. 相似文献
13.
? Alterations in plant chemistry underpin a suite of physiological adaptations to arid conditions. Qualitative and quantitative differences in leaf chemistry are found in the genus Eucalyptus correlating with physiological adaptation to aridity. ? Here we investigate seasonal water relations of three field grown eucalypt species grown at a common site known to differ in their ability to accumulate the cyclic sugar alcohol, quercitol. ? We show that quercitol contributes significantly to osmotic relations in field grown trees of Eucalyptus melliodora but is present only in trace amounts in E. rubida and E. obliqua. ? Measured concentrations of quercitol account for the difference in osmotic potentials between species and can be interpreted as a mechanism for adaptation to low water availability. 相似文献
14.
? The effects of drought, enhanced UV-B radiation and their combination on plant growth and physiological traits were investigated in a greenhouse experiment in two populations of Populus cathayana Rehder originating from high and low altitude in south-west China. ? In both populations, drought significantly decreased biomass accumulation and gas exchange parameters, including net CO2 assimilation rate (A), stomatal conductance (g s ), transpiration rate (E) and photosynthetic nitrogen use efficiency (PNUE). However, instantaneous water use efficiency (WUE i ), transpiration efficiency (WUE T ), carbon isotope composition (δ13C) and nitrogen (N) content, as well as the accumulation of soluble protein, UV-absorbing compounds and abscisic acid (ABA) significantly increased in response to drought. On the other hand, cuttings from both populations, when kept under enhanced UV-B radiation, showed very similar changes, as under drought, in all above-mentioned parameters. ? Compared with the low altitude population, the high altitude population was more tolerant to drought and enhanced UV-B, as indicated by the higher level of biomass accumulation, gas exchange, water-use efficiency, ABA concentration and UV-absorbing compounds. ? After one growing season of exposure to different UV-B levels and watering regimes, the decrease in biomass accumulation and gas exchange, induced by drought, was more pronounced under the combination of UV-B and drought. Significant interactions between drought and UV-B were observed in WUE i , WUET, δ13C, soluble protein, UV-absorbing compounds, ABA and in the leaf and stem N, as well as in the leaf and stem C:N ratio. ? Our results showed that UV-B acts as an important signal allowing P. cathayana seedlings to respond to drought and that the combination of drought and UV-B may cause synergistically detrimental effects on plant growth. 相似文献
15.
? Sample size is a critical issue for genetic diversity studies and conservation programs. However, sample size evaluation requires previous knowledge of allele frequencies estimated with precision and this is not often the case. ? Here, we evaluated sample size requirements for accurate genetic diversity in adult trees and family arrays in a 12 ha plot of Fraxinus excelsior L. (Oleaceae) in a community forest in central France. Data consisted of 579 adult trees and 480 offspring from 24 families genotyped at four nuclear microsatellites. ? Mean square errors (MSE) estimates performed on Monte Carlo simulations of resampled data indicated that several adult individuals (> 300) are necessary for accurate measures of allele richness. However, expected heterozygosity requires smaller samples (< 30). Seeds captured about 90% of adult allelic diversity requiring a sampling effort roughly 50% larger than that of adult trees (480 seeds vs. 300 adults) suggesting that seed sampling is heavily penalized for allele counts. Nevertheless, gene diversity of seeds was essentially identical to that of the adult population. ? Extrapolation of these results to other ash tree populations appears feasible because of similar levels of diversity reported in the literature but it is not granted for species with significant selfing or high genetic structure. 相似文献
16.
?The study aimed at clarifying basic life traits (fecundity, mortality and development) of Monochamus galloprovincialis, the vector of Bursaphelenchus xylophilus, the causative agent of the Pine Wilt Disease, in Portugal. ? Mating and oviposition experiments were conducted on P. sylvestris logs under laboratory conditions during two years. Larval development was followed outdoors. ? Fecundity was high, with 138.2 eggs per female. ? For the first time, the number of larval instars (4) in M. galloprovincialis was recognized and instars were described. ? Informations are provided on the shape and size of the larval galleries. Boring of galleries in sapwood and heartwood started at the third instar. All instars could overwinter but adults emerged simultaneously resulting in a univoltine life cycle for the majority of the individuals. ? An obligatory diapause in the forth instar was assumed. However, 8.1% of the insects had a two year development. ? Important differences in mortality were noted between the two experimental years, which could be explained by differences on the size of the breeding logs. ? There is a high biological proximity between M. galloprovincialis populations in France and those in Portugal and Northern Europe. However, a higher fecundity and longevity was observed in France, as well as a higher percentage of insects with a two year development, compared with portuguese populations. 相似文献
17.
? This review considers potential effects of atmospheric change and climate warming within the timberline ecotone of the Central European Alps. After focusing on the impacts of ozone (O3) and rising atmospheric CO2 concentration, effects of climate warming on the carbon and water balance of timberline trees and forests will be outlined towards conclusions about changes in tree growth and treeline dynamics. ? Presently, ambient ground-level O3 concentrations do not exert crucial stress on adult conifers at the timberline of the Central European Alps. In response to elevated atmospheric CO2 Larix decidua showed growth increase, whereas no such response was found in Pinus uncinata. Overall climate warming appears as the factor responsible for the observed growth stimulation of timberline trees. ? Increased seedling re-establishment in the Central European Alps however, resulted from invasion into potential habitats rather than upward migration due to climate change, although seedlings will only reach tree size upon successful coupling with the atmosphere and thus loosing the beneficial microclimate of low stature vegetation. ? In conclusion, future climate extremes are more likely than the gradual temperature increase to control treeline dynamics in the Central European Alps. 相似文献
18.
? The density and identity of tree neighbourhood is a key factor to explain tree mortality in forests, especially during the stem exclusion phase. ? To understand this process, we built a logistic model for mortality in a spatially explicit context, including tree and neighbourhood predictors. Additionally, we used this model to build mortality risk frequency distributions. Finally, we tested this model against a random mortality model to predict the spatial pattern of the forest. ? Annual mortality rate was high for pedunculate oak (Quercus robur, 6.99%), moderate for birch (Betula celtiberica, 2.19%) and Pyrenean oak (Q. pyrenaica, 1.58%) and low for beech (Fagus sylvatica, 0.26%). Mortality risk models for pedunculate oak and birch included stem diameter, tree height, canopy position and neighbourhood. Mortality was affected by the specific nature of the neighbourhood showing a clear competitive hierarchy: beech > pedunculate oak > birch. Models based on random mortality and logistic regression model were able to predict the spatial pattern of survivors although logistic regression predictions were more accurate. ? Our study highlights how simple models such as the random mortality one may obscure much more complex spatial interactions. 相似文献
19.
? Wood colour of Tectona grandis produced from fast-growth plantations is highly variable and the causes of this variation are relatively unknown. ? With the purpose of understanding the colour variation, different fast-growth plantations were sampled with different growth rates, tree ages, and sites. ? Wood colour was measured with a CIELab system, where three variables are estimated: coordinate L* for lightness, coordinate a* defines redness and coordinate b* defines yellowness. ? Results showed only a negative correlation between L* and a*. L* and a* were negatively and positively respectively correlated with pith distance in heartwood, but not for b*. No correlations were found between L* and b* in sapwood and plantation characteristics, while a* was positively correlated with age and height of tree and growth rate. In heartwood, tree age and diameter at breast height were correlated with all colour parameters, but tree height and plantation density were correlated with a* and b*. Cluster site had correlation with L*. Multiple correlation analysis showed that the heartwood is increasing darker (L*) and redder (a*) when the trees are older and bigger. Correlation coefficient shown that sapwood and heartwood with lighter colour (L*) is less resistance to fungal attack, but redness colour (a*) increasing decay resistance. 相似文献
20.
? The aim of this study is to assess the impact of drought on insect-tree relationships. Survival and feeding performances of leaf-beetles, Chrysomela populi put in cages with leaves of host-plants submitted to different levels of water stress were compared. ? Ninety 1-year-old poplar (Populus × euramericana) cuttings were grown in a greenhouse, and distributed into 3 groups submitted to different water treatments during six weeks. Adult C. populi were then encaged for four days with these cuttings, together with the five terminal leaves of a twig. Beetle survival and consumed leaf areas were then determined. ? Predawn leaf water potential values indicated that the drought treatments induced different levels of plant water stress. Plant height growth and total leaf numbers were reduced by plant stress. Beetle survival and leaf areas eaten were also reduced proportionally to plant water deficit. ? In conclusion, this experiment suggests that drought has a negative impact on C. populi survival and feeding. 相似文献
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