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1.
To examine physiological responses to thinning, fertilization, and crown position, we measured net photosynthesis (P(n)), transpiration (E), vapor pressure difference (VPD), stomatal conductance (g(s)), and xylem pressure potential (Psi(1)) between 0930 and 1130 h under ambient conditions in the upper and lower crowns of a 13-year-old loblolly pine (Pinus taeda L.) plantation six years (1994) after the treatments were applied. Photosynthetic photon flux density (PPFD) and air temperature (T(a)) within the canopy were also recorded. Needle P(n) of thinned trees was significantly enhanced by 22-54% in the lower crown, because canopy PPFD increased by 28-52%. Lower crown foliage of thinned plots also had higher E and g(s) than foliage of unthinned plots, but thinning had no effect on needle Psi(1) and predawn xylem pressure potential (0430-0530 h; Psi(pd)). Tree water status did not limit P(n), E and g(s) during the late-morning measurements. Fertilization significantly decreased within-canopy PPFD and T(a). Needle Psi(1) was increased in fertilized stands, whereas P(n), E and g(s) were not significantly altered. Upper crown foliage had significantly greater PPFD, P(n), VPD, g(s), E, and more negative Psi(1) than lower crown foliage. In both crown positions, needle P(n) was closely related to g(s), PPFD and T(a) (R(2) = 0.77 for the upper crown and 0.82 for the lower crown). We conclude that (1) silvicultural manipulation causes microclimate changes within the crowns of large trees, and (2) needle physiology adjusts to the within-crown environmental conditions.  相似文献   

2.
The research site, Wingst Compartment 123B, is a 68-year-old Norway spruce (Picea abies (Karst.)) stand located in the coastal area of northern Germany. This area receives high atmospheric inputs of ammonium and also has relatively high ozone concentrations (0.061 mg m−3).Ten trees were categorized as healthy to slightly damaged (3–29% needle loss) or severely damaged (49–71% needle loss). Apparent net photosynthetic rates were measured on detached branches at light saturation (1000 μE m−2 s−1). Needles were analyzed for chlorophyll, N, C, Ca, Mg, K, Zn, Mn and Fe.When compared to the healthy-to-slightly-damaged trees, the severely damaged trees tended to have higher rates of net apparent photosynthesis in the 1 and 2-year-old needles and similar rates in the current-year needles. All three needle ages from the severely damaged trees had higher average stomatal conductances to water vapor (gs. Although the damaged trees had significantly less total chlorophyll in all needle ages sampled, there was no statistically significant difference in the chlorophyll a:b ratio between the healthy and severely damaged trees.Nitrogen contents of the current-year needles were slightly lower in the severely damaged trees. Carbon and calcium levels did not significantly differ between the damage classes, although the average Ca content of all younger needles was generally under the recommended sufficiency levels. The current-year needles of the severely damaged trees had significantly less magnesium (0.42–0.46 mg Mg g−1) than those of the healthy trees, and all trees had Mg values in the deficiency range (< 0.7 mg g−1). The severely damaged trees also had lower average potassium levels in the older needles.The annual volume increment per unit crown surface area declined with increasing crown damage. Trees with a 50% needle loss showed a 62% loss of volume increment.Soil investigations revealed conditions of high soil acidity and poor nutrient capacity. The low pH values (pH < 3.8) in 64% of all samples indicated a high risk of acid toxicity for plant roots in the investigated area.The significance of these results relative to the current ideas concerning forest decline is discussed.  相似文献   

3.
The photosynthetic response to pruning was measured in two Eucalyptus regnans stands, aged 2 and 3 years, located in areas of high productivity on the coast of the province of Arauco, Chile. Variables such as rates of CO2 assimilation and stomatal conductance were measured in three ages of foliage on trees with different pruning severity treatments, which corresponded to the removal of 0 % (control), 30, 50 and 70 % of live crown length. The 2-year-old stand measurements were performed at the time of pruning and 6, 10, 14 and 18 weeks later, and the 3-year stand, 5, 9, 18 and 28 weeks after pruning. In both trials, significant differences were found between the foliage ages for all instances of measurement showing the mature foliage the highest values up to 30 % higher than old foliage. There were also significant differences between pruning severity treatments in both trials in which, in general, the highest values of CO2 assimilation were observed among the highest pruning severity treatments with values up to 40 % higher than the unpruned trees.  相似文献   

4.
Physiological parameters were measured under natural light conditions and needle orientation from towers and walkways erected in the canopy of a loblolly pine (Pinus taeda L.) plantation. Four silvicultural treatments were randomly assigned to the twelve plots in the fall of 1988. Plots were thinned to a density of 731 trees per hectare or left unthinned, at a density of 2990 trees per hectare. The plots were left unfertilized or fertilized with 744 kg/ha of diammonium triple superphosphate was applied. During the fifth growing season (1993) following thinning and fertilization, needle level physiology was not different with respect to the thinning treatment for fertilized or unfertilized plots. In contrast, upper crown levels within the fertilized and unfertilized plots had significantly higher light levels and photosynthetic rates than lower crown foliage. Light levels were greater in the thinned, fertilized plots than in the unthinned, fertilized plots. In contrast, no effect of thinning on canopy light levels was found in the unfertilized plots. Within crown variation in photosynthesis was strongly dependent on canopy light levels. A strong interaction of canopy level with thinning was apparent for net photosynthesis. Loblolly pine, being a shade intolerant species, showed only small physiological differences between needles from different parts of the crown. Because of the variability found in this study, more extensive sampling is needed to correctly describe the physiology of a forest canopy with adequate precision.  相似文献   

5.
Young trees were harvested to explore non-destructive methodologies to estimate live branch dry weights in young fast-growing Eucalyptus species under different spacing and fertilizer treatments. Branch growth can vary with silvicultural management such as spacing, fertilizing and thinning, and over relatively short periods in response to environmental conditions. Many published regressions based on standard measurements of height and diameter are site, age and treatment specific. The aim of this study was to improve our capacity to predict woody crown dry weight, based on stem measurements, and to minimize (or eliminate) treatment effects on the resulting model. In young trees, branches are temporary support structures for foliage and are often discarded as the base of the green crown rises. As temporary structures they represent an investment of biomass and nutrient elements, and are subject to selection pressures to maximize the return on investment by the tree. Trees were harvested from existing plantation experiments located in south-eastern Queensland for E. grandis W. Hill ex Maiden (ranging from 0.28 to 15.85 m in height, to 5 years old) and south-western Australia for E. globulus Labill. (0.10–34.4 m in height, to 10.2 years) in order to examine the impact of spacing, nitrogen and phosphorus fertilization on early growth. Relationships to estimate crown woody biomass from non-destructive measurements were developed, and these relationships tended to have different slopes and intercepts for trees with predominantly juvenile foliage and those with intermediate or adult foliage. Dry weight of whole-crown live branch wood (Wbranch) was related to heights and/or diameter at breast height (DBH), but the regressions parameters were different, depending on treatment. The relationships became more generic (i.e. less dependent on treatment effects) between Wbranch and stem sectional area at the height of the base of the green crown (SACB), consistent with the pipe model theory (R2 > 0.91 for the two species for trees with intermediate/adult leaves). However, Wbranch was more closely related again to the stem volume above the base of the green crown and treatment effects were not significant (VCon,gc, R2 > 0.93). Branches exit the stem below the green crown, and for E. grandis the best relationship was on stem volume above the lowest live branch (VCon,llb, R2 0.94). Limited sampling from four other species with similar or contrasting crown characteristics indicated that the relationship could be applied quite generally. Individual E. grandis branch woody dry weight was closely related to the conical volume of the main (first order) branch (Vcon,br, R2 0.98). The whole crown equivalent, branch woody dry weight plus stem dry weight above the lowest live branch, was also closely related to the stem volume within the woody crown (VCon,llb, R2 0.97–0.99). While the slope of this relationship was still significantly different between trees with juvenile and intermediate/adult foliage, it had a similar form, suggesting that trees with juvenile foliage allocated a different proportion of their woody biomass within the crown to branches than older trees.  相似文献   

6.
Leaf area is a key driver of growth models and leaf weight is important for studying carbon and nutrient cycling in forestry. Both can change over relatively short intervals in young plantations in response to silvicultural treatments and climatic conditions. Relationships to estimate leaf dry weight and leaf area of young Eucalyptus grandis W. Hill ex Maiden and Eucalyptus globulus (Labill.) were developed from harvested trees ranging from 0.28 to 15.85 m and 0.12 to 34.4 m in height respectively. Trees were harvested from existing experiments in south-eastern Queensland and south-west Western Australia in order to assess the effects of spacing and application of nitrogen and phosphorus fertilizer on early plantation growth. A range of tree measurements were taken to determine the most efficient way to monitor the performance of young plantation eucalyptus. Leaf weight (Wleaf, kg) and leaf area (m2) were related to stem cross sectional area at the height of the base of the green crown (SACB), but the slope and intercept of the relationship differed for trees with predominantly juvenile foliage and those with predominantly intermediate or adult foliage. Specific leaf area (m2 kg?2) changed as the trees aged and leaf area was more closely related to the size of the support structure, represented by the stem volume within the green crown, approximated by the volume of a cone above the base of the green crown (VC,gc). Significantly, the relationships also applied to individual branches, that is, leaf weight was related to sectional area near the base of the branch (SAb) and leaf area to the volume of the main (first order) branch (VC,br). Most of the published work has been directed at trees of commercial size or to small trees in pot experiments, much less to small trees in the establishment phase of growth of interest to experimenters and managers looking at early intervention. This study provides a mechanism to directly assess canopies of intermediate size trees which are of interest for assessing treatment effects or early intervention for managers.  相似文献   

7.
Proe MF  Mead DJ  Byrne D 《Tree physiology》2000,20(10):653-661
Stem injection of (15)N-labeled ammonium sulfate was used to determine effects of pruning on canopy nitrogen dynamics in open-grown Pinus radiata D. Don in New Zealand. Trees were planted in July 1990 and the isotope introduced in December 1994. Tree crowns were divided into three zones: base section, from which branches of pruned trees were removed; mid section, between the pruned zone and the height of the trees at the start of the year in which they were pruned; and top section, which grew predominantly after the isotope was applied. Pruning removed 32% of the green crown length, representing 75% of foliage biomass. Needles were sampled from each region of the crown until July 1996. Branch growth was used to predict foliage biomass for each sampling occasion. Approximately 45% of the applied isotope was recovered from needles sampled in December 1994 (1 week after application and immediately before pruning), two-thirds of which occurred in needles in the base section. Thereafter, changes in isotope content of needles in the base section of unpruned trees largely reflected foliage biomass fluctuations and dilution of the isotope by continued uptake from the unlabeled soil nitrogen pool. Recovery of isotope in needles from the mid-crown section increased by 58 and 86% from December 1994 to July 1995 in control and pruned trees, respectively. Within this crown section, there was evidence of isotope translocation from old to new needles, with both isotope dilution and efflux observed in the needle cohorts that had been present at the time the isotope was applied. Therefore, isotope dynamics did not reflect the dynamics of the total nitrogen pool in the mid-crown section. By July 1996, a small proportion of the applied isotope was recovered from the new foliage formed in the top section of the crown. Within the top section, isotope dynamics closely matched total nitrogen fluxes. Pruning the lower crown did not affect nitrogen dynamics elsewhere in the crown for the following 18 months.  相似文献   

8.
Second-generation Pinus radiata D. Don trees, propagated from cuttings of 4-year-old trees previously grown at ambient (36 Pa) and elevated (65 Pa) CO2 partial pressure (Ca) were grown under the same conditions in open-top chambers for a further year. As cuttings of the original trees, these second-generation trees were physiologically the same age as the first-generation trees with the only difference between the two being size. This allowed us to test the effects of tree size independently of age or duration of exposure. Total non-structural carbohydrate concentration, area-based nitrogen concentration, leaf mass per unit area and chlorophyll concentration measured in three foliage age cohorts were unaffected by either age or Ca. There were no signs of photosynthetic down-regulation in trees grown at elevated Ca. When measured at the growth Ca, photosynthetic rate in young needles during summer, autumn and spring was 34, 43 and 38% higher, respectively, in trees grown at elevated Ca than in trees grown at ambient Ca. In older needles, the corresponding photosythetic rate increases were 26, 47 and 49%. Water-use efficiency, determined by stable carbon isotope analysis, was 49% higher in foliage in the elevated Ca treatment than in foliage in the ambient Ca treatment. This increase was entirely due to photosynthetic enhancement, because stomatal conductance did not differ between treatments. We conclude that down-regulation of photosynthesis at elevated Ca is related to tree size rather than tree age or duration of exposure, and that enhanced photosynthetic rates can be maintained while sink strength is high enough to use the excess photosynthates.elevated CO2, needle age, photosynthetic down-regulation, photosynthetic enhancement, sink strength, water-use efficiency.  相似文献   

9.
Summary The aim of the present study was to investigate whether the resistance of beech foliage(Fagus sylvatica) against oxidative stress was affected by soil quality, nitrogen or CO2 fertilisation, or lachnid infestation(Phyllaphis fagi). For this purpose young beech trees were grown for four years in reconstructed calcareous or acidic forest soils in open top chambers under ambient or elevated CO2 concentrations with two levels of nitrogen fertilisation. At harvest lachnid colonisation was observed, preferentially on leaves from trees in calcareous soil and on leaves from trees fertilised with the high nitrogen level. General leaf characteristics such as pigment concentrations, dry mass, and leaf mass ber area were not affected by the soil type, nitrogen fertilisation or CO2 regime. Leaves colonised with lachnids displayed slightly increased leaf mass per area. When the stress resistance was challenged by exposure to paraquat — a herbicide inducing oxidative stress — leaves from trees grown on calcareous soil maintained significantly longer membrane integrity and, thus, were better protected against stress than leaves from trees on acidic soil. Other experimental variables had negligible or no effects on the resistance against oxidative stress.   相似文献   

10.
The impacts of elevated temperature and CO2 on young silver birch (Betula pendula Roth) saplings after 0, 25, 50 or 75% artificial defoliation were assessed by measuring plant height and dry mass of aboveground compartments and roots and various morphological and physiological variables. Defoliation either increased or decreased plant growth depending on the severity of damage and the climatic treatment. At 21 °C and 400 mg L?1 CO2, defoliated plants were not able to compensate for the lost foliage, but growth compensation and adaptation to the changed conditions were greater; growth of young defoliated silver birch saplings increased, which led to increased height and a tendency to enhance final aboveground and root biomass and leaf nitrogen and carbon content compared to the nondefoliated controls. Nevertheless, the short-term effect of the different climatic conditions did not result in a significant overgrowth of defoliated plants. A slight increase in temperature and CO2 were the most acceptable conditions for defoliated plants; however, a 4 °C increase with correspondingly higher CO2 was more stressful as shown by less growth in height and biomass allocation to leaves, stems and roots. The findings from the pilot experiment are more applicable to young birch trees, but stress on young trees may be reflected in future tree growth.  相似文献   

11.
To study the effects of elevated CO(2) on gas exchange, nonstructural carbohydrate and nutrient concentrations in current-year foliage of 30-year-old Norway spruce (Picea abies (L.) Karst.) trees, branches were enclosed in ventilated, transparent plastic bags and flushed with ambient air (mean 370 &mgr;mol CO(2) mol(-1); control) or ambient air + 340 &mgr;mol CO(2) mol(-1) (elevated CO(2)) during two growing seasons. One branch bag was installed on each of 24 selected trees from control and fertilized plots. To reduce the effect of variation among trees, results from each treated branch were compared with those from a control branch on the same whorl of the same tree. Elevated CO(2) increased rates of light-saturated photosynthesis on average by 55% when measured at the treatment CO(2) concentration. The increase was larger in shoots with high needle nitrogen concentrations than in shoots with low needle nitrogen concentrations. However, shoots grown in elevated CO(2) showed a decrease in photosynthetic capacity compared with shoots grown in ambient CO(2). When measured at the internal CO(2) concentration of 200 &mgr;mol CO(2) mol(-1), photosynthetic rates of branches in the elevated CO(2) treatments were reduced by 8 to 32%. The elevated CO(2) treatment caused a 9 to 20% reduction in carboxylation efficiency and an 18% increase in respiration rates. In response to elevated CO(2), starch, fructose and glucose concentrations in the needles increased on average 33%, whereas concentrations of potassium, nitrogen, phosphorus, magnesium and boron decreased. Needle nitrogen concentrations explained 50-60% of the variation in photosynthesis and CO(2) acclimation was greater at low nitrogen concentrations than at high nitrogen concentrations. We conclude that the enhanced photosynthetic rates found in shoots exposed to elevated CO(2) increased carbohydrate concentrations, which may have a negative feedback on the photosynthetic apparatus and stimulate cyanide-resistant respiration. We also infer that the decrease in nutrient concentrations of needles exposed to elevated CO(2) was the result of retranslocation of nutrients to other parts of the branch or tree.  相似文献   

12.
Total foliage dry mass and leaf area at the canopy hierarchical level of needle, shoot, branch and crown were measured in 48 trees harvested from a 14-year-old loblolly pine (Pinus taeda L.) plantation, six growing seasons after thinning and fertilization treatments.

In the unthinned treatment, upper crown needles were heavier and had more leaf area than lower crown needles. Branch- and crown-level leaf area of the thinned trees increased 91 and 109%, respectively, and whole-crown foliage biomass doubled. The increased crown leaf area was a result of more live branches and foliated shoots and larger branch sizes in the thinned treatment. Branch leaf area increased with increasing crown depth from the top to the mid-crown and decreased towards the base of the crown. Thinning stimulated foliage growth chiefly in the lower crown. At the same crown depth in the lower crown, branch leaf area was greater in the thinned treatment than in the unthinned treatment. Maximum leaf area per branch was located nearly 3–4 m below the top of the crown in the unthinned treatment and 4–5 m in the thinned treatment. Leaf area of the thinned-treatment trees increased 70% in the upper crown and 130% in the lower crown. Fertilization enhanced needle size and leaf area in the upper crown, but had no effect on leaf area and other variables at the shoot, branch and crown level. We conclude that the thinning-induced increase in light penetration within the canopy leads to increased branch size and crown leaf area. However, the branch and crown attributes have little response to fertilization and its interaction with thinning.  相似文献   


13.
Saplings of Fagus sylvatica and Picea abies were grown under conditions of intra and interspecific competition in a 2-year phytotron study under combinations of ambient and elevated ozone (+O3 which is 2 × O3, but <150 nl l−1) as well as carbon dioxide concentrations (+CO2 which is amb. CO2 + 300 μl CO2 l−1) in a full factorial design. Saplings were analysed for various mineral nutrients in different plant organs as well as biomass production and crown development. The study was based on the assumption that nutritional parameters important for growth and competitiveness are affected by stress defence under limiting nutrient supply. The hypotheses tested were (1) that nutrient uptake-related parameters (a) as well as efficiencies in nutrient use for above-ground competition (b) of beech rather than spruce are impaired by the exposure to elevated O3 concentrations, (2) that the efficiency in nutrient uptake of spruce is enhanced by elevated CO2 concentrations in mixed culture, and (3) that the ability to occupy above-ground space at low nutrient cost is co-determinant for the competitive success in mixed culture. Clear nitrogen deficiencies were indicated for both species during the 2-year phytotron study, although foliar nitrogen-biomass relationships were not so close for spruce than for beech. O3 stress did not impair nutrient uptake-related parameters of beech; thus hypothesis (1a). was not supported. A negative effect of elevated O3 (under amb. CO2) on the N and P based efficiencies in above-ground space occupation (i.e. lower crown volume per unit of N or P invested in stems, limbs and foliage) of beech supported hypothesis (1b). It appeared that ozone stress triggered a nutrient demand for stress defence and tolerance at the expense of above-ground competition (trade-off). Crown volume of beech under O3 stress was stabilized in monoculture by increased nutrient uptake. In general, the +CO2-treatment was able to counteract the impacts of 2 × O3. Elevated CO2 caused lower N and S concentrations in current-year foliage of both tree species, slightly higher macronutrient amounts in the root biomass of spruce, but did not increase the efficiencies in nutrient uptake of spruce in mixed culture. Therefore hypothesis (2) was not supported. At the end of the experiment spruce turned out to be the stronger competitor in mixed culture as displayed by its higher total shoot biomass and crown volume. The amounts of macronutrients in the above-ground biomass of spruce individuals in mixed culture distinctly exceeded those of beech, which had been strongly reduced by interspecific competition. The superior competitiveness of spruce was related to higher N and P-based efficiencies in above-ground space occupation as suggested in hypothesis (3). This article belongs to the special issue “Growth and defence of Norway spruce and European beech in pure and mixed stands”.  相似文献   

14.
Physiological mechanisms by which nitrogen (N) fertilization affects growth and development in temperate deciduous forest trees are not clearly understood, especially under intensive silvicultural systems. Grafted, Tippecanoe 1 cultivar black walnut (Juglans nigra L.) trees were grown in an intensively managed plantation in west-central Spain and subjected to six, fixed-nutrient-ratio complete fertilizer treatments (defined as 0, 25, 50, 75, 150, and 300 g N tree?1) delivered via daily fertigation. Leaf chemistry and morphology were evaluated from June to September, and gas exchange was measured in July. Specific leaf mass, leaflet nitrogen (N), and chlorophyll concentrations varied over the course of the growing season, yet consistently increased with increasing fertilization. Net photosynthesis at ambient (A net) and light-saturated (A max) conditions increased from the unfertilized control to lowest treatment (25 g N) but did not increase at higher fertilizer rates. Photosynthetic N and chlorophyll use efficiencies decreased with increasing fertilization, but photosynthetic phosphorus and water use efficiencies increased. Transpiration rates and dark respiration were not significantly affected by treatment. Overall, the lowest fertilizer treatment (25 g N) had the greatest photosynthetic efficiency. Interactions between N and other nutrients with increasing fertilizer application suggested potential for nutrient imbalances at high fertilization rates. Our results provide a physiological justification for the use of low-to-moderate fertilization as an efficient strategy to promote black walnut plantation establishment under intensive cultural systems.  相似文献   

15.
The impacts of thinning, fertilization and crown position on seasonal growth of current-year shoots and foliage were studied in a 13-year-old loblolly pine (Pinus taeda L.) plantation in the sixth post-treatment year (1994). Length of new flushes, and their needle length, leaf area, and oven-dry weight were measured in the upper and lower crown from March through November. Total shoot length was the cumulative length of all flushes on a given shoot and total leaf area per shoot was the sum of leaf areas of the flushes.

By the end of June, first-flush foliage reached 70% of the November needle length (14.3 cm) and 65% of the final leaf area (15.0 cm2). Cumulative shoot length of first- and second-flush shoots achieved 95% of the annual length (30.3 cm), whereas total leaf area per shoot was 55% of the final value (75.3 dm2). Fertilization consistently stimulated fascicle needle length, dry weight, and leaf area in the upper crown. Mean leaf area of upper-crown shoots was increased by 64% six years after fertilization. A significant thinning effect was found to decrease mean leaf area per shoot in the crown. For most of the growing season, the thinned-fertilized trees produced substantially more leaf area per shoot throughout the crown than the thinned-nonfertilized trees. These thinned-fertilized trees also had greater needle length and dry weight, longer first flush shoots, and more leaf area per flush than trees in the thinned-nonfertilized plots. Needle length and leaf area of first flush shoots between April and July were linearly related to previous-month canopy air temperature (Ta). Total shoot length strongly depended on vertical light gradient (PPFD) within the canopy, whereas shoot leaf area was a function of both PPFD and Ta. Thus, trees produced larger and heavier fascicles, more and longer flush shoots, and more leaf area per shoot in the upper crown than the lower crown. We conclude that thinning, fertilization, and crown position regulate annual leaf area production of current-year shoots largely by affecting the expansion of first flush shoots and their foliage during the first half of the growing season.  相似文献   


16.
We conducted a 1-year greenhouse experiment to assess the impact of nutrient manipulations on seedling growth, biomass partitioning, and leaf gas exchange between two fast growing Pinus taeda clones that differed in growth efficiency. After 1 year we observed significant treatment and treatment by clone effects on growth, biomass partitioning, and gas exchange parameters. Fertilization increased total seedling biomass 18% primarily through an increase in foliage and coarse-roots. Clones did not differ in total seedling biomass, however, clone 85 produced more stem than clone 93 leading to 37% greater stem:leaf, while clone 93 maintained more branch biomass. The logging residue treatment increased stem:leaf by 30%, but had no effect on total biomass or partitioning. Differences in leaf morphology resulted in significantly greater canopy leaf area in clone 93 than clone 85. Increased foliar N concentration from fertilization had only minor effects on specific photosynthesis under saturating light (ASat), but lowered stomatal conductance (gs), transpiration (E), and internal to external CO2 concentration ratio (Ci/Ca) as well as improved water use efficiency (WUE) independently of genotype. When gas exchange data was scaled to the canopy level both genotypes achieved similar canopy level CO2 assimilation rates, but our data suggests they did this by different means. Although we did see a small effect of nutrient limitations in total canopy photosynthesis under saturating light (ACanopy), ASat, and total leaf area (TLA), our foliar N concentration ([N]) indicated that our level of logging residue incorporation did not cause [N] to decrease below sufficiency limits. From a practical standpoint, a better understanding of strategies for capturing and partition C may lead to better selection of clonal material, thereby, optimizing productivity.  相似文献   

17.
We investigated the seasonal variation in the gas exchange of current and 1-year-old needles in the upper sun and lower shade crown of adult Pinus canariensis trees. In general, current year needles displayed lower gas exchange rates than the 1-year-old needles. In both needle age classes, gas exchange was significantly lower in the shade than in the sun crown. However irrespective of crown position and needle age, maximum daily net photosynthesis, transpiration, and stomatal conductance for water vapour were generally higher during the wet and cold winter as compared to the dry and hot summer. These higher gas exchange values obtained during the cold and wet season can mainly be explained by higher soil-water availability and lower evaporative demand as compared to the warm and dry seaon. In addition, we also observed a displacement in the temperature optimum of net photosynthesis towards lower temperatures during the cold and wet season as compared to the warm and dry season. The observed gas exchange characteristics indicate a conservative water saving strategy and thus allowing P. canariensis needles to maintain a positive carbon gain even at periods of high evaporative demand and low soil-water availability.  相似文献   

18.
We investigated mature dwarf Abies mariesii trees growing in conifer thicket–meadow parklands on a snowy subalpine plateau, where these dwarf trees are buried in the accumulated snow in winter. We focused on structural variation in the needles, shoots, and branchlets within different crown positions (leader crown vs lower crown) of the dwarf trees. In the leader crown, which appears above the snow surface earlier than the lower crown, current-year shoots and branchlets had greater total biomass, and foliage was more closely packed along the stem axis than in the lower crown, whereas current-year shoots in the leader crown had a lower needle mass ratio than in the lower crown. These results suggest that current-year shoots and branchlets in the leader crown have a specific structure that allows them to harvest more light, although construction and maintenance costs would be higher. In contrast, the structural characteristics of current-year shoots and branchlets in the lower crown efficiently concentrate incoming light by avoiding mutual shading within foliage, thus leading to increased biomass of photosynthetic needles within shoot and branchlet biomass. Such within-crown variability at various hierarchical levels from needles to branches in mature, but very dwarf, A. mariesii trees maintains the crown and allows survival within conifer clumps in areas of subalpine parklands that receive heavy snowfall.  相似文献   

19.
Several heavy wet snowfalls occurred during 2007-2009 across a broad-scale thinning and fertilization experiment to bring overstocked juvenile lodgepole pine (Pinus contorta var. latifolia) in the foothills of Alberta, Canada into an intensive management regime. We examined the bending and breakage of trees in relation to thinning and fertilization and used a multimodel information-theoretic approach to model stand and tree level predictors of snow damage. Fertilized stands suffered the greatest amount of snow damage, and this was most noteworthy when stands were also thinned; here 22% (17% broken stems) of trees were damaged compared to 8% (4% broken stems) in the thinned and unfertilized stands. At the stand level, needle weight and crown cover were reliable predictors of snow damage. At the tree level, separate models were developed for each combination of thinning and fertilization. All models used total tree volume; usually the smaller trees in the stands were more susceptible to damage but in the thinned and fertilized stands larger but slender trees with large asymmetrical crowns tended to be damaged. Also, trees with lower total stem volume were more susceptible to damage. Only in the thinned and fertilized stands were variables related to crown shape and asymmetry important predictors of snow damage. We conclude that snow damage is an important agent for self-thinning in unthinned stands and fertilization tends to exacerbate damage because of increase in foliage size. In areas with regular occurrence of heavy snow, we do not recommend fertilization at the same time as thinning, as the larger and more economically important trees in the stand are at risk.  相似文献   

20.
To predict the performance of coppice forests with Japanese oak (Quercus mongolica var. crispula) in future changing environment, we studied the growth, photosynthesis, and powdery mildew (Erysiphe alphitoides) infection of sprouts of Japanese oak under free-air CO2 enrichment. Elevated CO2 reduced powdery mildew infection in both leaves of the shoot emerged in spring (1st flush) and the lammas and proleptic shoots (2nd flush) of sprouts. We observed significant increase in the net photosynthetic rate at growth CO2 concentration (i.e., 370 and 500 μmol mol?1 for ambient and elevated CO2 treatments, respectively) in both 1st and 2nd flush leaves of sprouts grown under elevated CO2. On the other hand, no significant increase in net photosynthetic rate under elevated CO2 was found before cutting. The photosynthetic activity of 2nd flush leaves in the sprouts under ambient condition was greatly reduced by severe infection to powdery mildew. Growth of sprouts was enhanced in the elevated CO2 condition. We conclude the growth enhancement in Japanese oak sprouts under elevated CO2 in the present study was achieved not only by physiological response (i.e., photosynthetic stimulation) but also by disease interaction.  相似文献   

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