苹果叶片再生体系建立研究

以乔纳金苹果试管苗叶片为外植体诱导不定芽再生，在培养基中添加不同浓度TDZ与NAA或IAA配合，使用琼脂或Polygel作为固化剂。结果表明，较适宜的叶片再生不定芽的培养基为TDZ 2．0mg／L和NAA 1．0mg／L，或TDZ 2．0mg／L与IAA 4．0mg／L。较适宜的组培固化剂为5．0g／L的Polygel。在不同的组培固化剂中，卡那霉素均能抑制不定芽的发生数量，但琼脂和Polygel效果不同。     

Remobilization and uptake of N by newly planted apple (Malus domestica) trees in response to irrigation method and timing of N application

Environmentally sound management of N in apple orchards requires that N supply meets demand. In 1997, newly planted apple trees (Malus domestica Borkh. var. Golden Delicious on M.9 rootstock) received daily applications of N for six weeks as Ca(15NO3)(2) through a drip irrigation system at a concentration of 112 mg l(-1) at 2-8, 5-11 or 8-14 weeks after planting. Irrigation water was applied either to meet estimated evaporative demand or at a fixed rate. In 1997, trees were harvested at 5, 8, 11 and 14 weeks after planting; and in 1998 at 3 weeks after full bloom. The amount of fertilizer N recovered was similar in trees in both irrigation treatments, but efficiency of fertilizer use was greater for trees receiving demand-controlled irrigation than fixed-rate irrigation. This was attributed to lower N inputs, greater retention time in the root zone and less N leaching in the demand-controlled irrigation treatments compared with fixed-rate irrigation treatments. Less fertilizer N was recovered by trees receiving an early application of N than a later application of N and this was related to the timing of N supply with respect to tree demand. Demand for root-supplied N was low until 11 weeks after planting, because early shoot and root growth was supported by N remobilized from woody tissue, which involved 55% of the total tree N content at planting. Rapid development of roots > 1 mm in diameter occurred between 11 and 14 weeks after planting, after remobilization ended, and was greater for trees receiving an early application of N than for trees receiving a later application of N. Late-season tree N demand was supplied by native soil N, and uptake and background soil solution N concentrations were higher for trees receiving demand-supplied irrigation compared with fixed-rate irrigation. Total annual N uptake by roots was unaffected by treatments and averaged 6-8 g tree(-1). Nitrogen applications in 1997 affected growth and N partitioning in 1998. Trees receiving early applications of N had more flowers, spur leaves and bourse shoots than trees receiving later applications of N. Consequently, more N was remobilized into fruits in trees receiving early applications of N compared with fruits in trees receiving later applications of N. Demand for N in the young apple trees was low. Early season demand was met by remobilization from woody tissues and the timing of demand for root-supplied N probably depends on whether flowering occurs. Method of N delivery affected the efficiency of N use. We conclude that N demand can be met at soil solution N concentrations of around 20 mg l(-1).     

Root-zone temperatures affect phenology of bud break, flower cluster development, shoot extension growth and gas exchange of 'Braeburn' (Malus domestica) apple trees

We investigated the effects of root-zone temperature on bud break, flowering, shoot growth and gas exchange of potted mature apple (Malus domestica (Borkh.)) trees with undisturbed roots. Soil respiration was also determined. Potted 'Braeburn' apple trees on M.9 rootstock were grown for 70 days in a constant day/night temperature regime (25/18 degrees C) and one of three constant root-zone temperatures (7, 15 and 25 degrees C). Both the proportion and timing of bud break were significantly enhanced as root-zone temperature increased. Rate of floral cluster opening was also markedly increased with increasing root-zone temperature. Shoot length increased but shoot girth growth declined as root-zone temperatures increased. Soil respiration and leaf photosynthesis generally increased as root-zone temperatures increased. Results indicate that apple trees growing in regions where root zone temperatures are < or = 15 degrees C have delayed bud break and up to 20% fewer clusters than apple trees exposed to root zone temperatures of > or = 15 degrees C. The effect of root-zone temperature on shoot performance may be mediated through the mobilization of root reserves, although the role of phytohormones cannot be discounted. Variation in leaf photosynthesis across the temperature treatments was inadequately explained by stomatal conductance. Given that root growth increases with increasing temperature, changes in sink activity induced by the root-zone temperature treatments provide a possible explanation for the non-stomatal effect on photosynthesis. Irrespective of underlying mechanisms, root-zone temperatures influence bud break and flowering in apple trees.     

Nitrogen storage and its interaction with carbohydrates of young apple trees in response to nitrogen supply

Bench-grafted 'Fuji/M.26' apple (Malus domestica Borkh.) trees received a constant nitrogen (N) supply (10.7 mM) from bud break to the end of June, and were then fertigated with 0, 5, 10, 15 or 20 mM N in a modified Hoagland's solution for 2 months during the summer. In mid-October, half of the trees fertigated at each N concentration were sprayed twice with 3% urea, whereas the remaining trees served as controls. All trees were harvested after natural leaf fall and were stored at 2 degrees C. Five trees from each of the N treatment combinations were destructively sampled during dormancy to determine the composition of N and total nonstructural carbohydrates (TNC). As the N supply from fertigation increased, amounts of N in both free amino acids and proteins increased, whereas C/N ratios decreased. Foliar urea applications in the fall significantly increased amounts of N in both free amino acids and proteins, but decreased their C/N ratios. Arginine, the most abundant amino acid in both free amino acids and in proteins, accounted for an increasing proportion of N in free amino acids and proteins with increasing N supply from fertigation or foliar urea application. The ratio of protein N to free amino acid N decreased from about 27.1 to 3.2 as N supply from fertigation increased from 0 to 20 mM, and decreased further to 3.0 in response to foliar urea applications in the fall. Concentrations of glucose, fructose, sucrose and TNC decreased as the N supply from fertigation increased, whereas concentrations of sorbitol and starch remained relatively unchanged. Foliar urea applications decreased the concentration of each TNC component and the TNC concentration in each N fertigation treatment. A negative linear relationship was found between carbon in TNC and N in proteins and free amino acids. The sum of carbon in TNC, proteins and free amino acids remained constant in response to N supply from fertigation. However, foliar urea applications decreased the sum of carbon in proteins, free amino acids and TNC because about 21% of the decrease in TNC carbon was not recovered in free amino acids or proteins. Young apple trees store N and carbon dynamically in response to N supply. As N supply increases, an increasing proportion of N is found in the form of free amino acids, which have a low carbon cost, although proteins remain the main form of N storage. Furthermore, part of the carbon from TNC is incorporated into amino acids and proteins, decreasing the carbon stored as TNC and increasing the carbon stored as amino acids and proteins.     

Freezing pattern and frost killing temperature of apple (Malus domestica) wood under controlled conditions and in nature

The freezing pattern and frost killing temperatures of apple (Malus domestica Borkh.) xylem were determined by differential thermal analysis and infrared differential thermal analysis (IDTA). Results from detached or attached twigs in controlled freezing experiments and during natural field freezing of trees were compared. Non-lethal freezing of apoplastic water in apple xylem as monitored during natural winter frosts in the field occurred at -1.9?±?0.4 °C and did not change seasonally. The pattern of whole tree freezing was variable and specific to the environmental conditions. On detached twigs high-temperature freezing exotherms (HTEs) occurred 2.8 K below the temperature observed under natural frosts in the field with a seasonal mean of -4.7?±?0.5 °C. Microporous apple xylem showed freezing without a specific pattern within a few seconds in IDTA images during HTEs, which is in contrast to macroporous xylem where a 2D freezing pattern mirrors anatomical structures. The pith tissue always remained unfrozen. Increasing twig length increased ice nucleation temperature; for increased twig diameter the effect was not significant. In attached twigs frozen in field portable freezing chambers, HTEs were recorded at a similar mean temperature (-4.6?±?1.0 °C) to those for detached twigs. Upon lethal intracellular freezing of apple xylem parenchyma cells (XPCs) low-temperature freezing exotherms (LTEs) can be recorded. Low-temperature freezing exotherms determined on detached twigs varied significantly between a winter minimum of -36.9 °C and a summer maximum -12.7 °C. Within the temperature range wherein LTEs were recorded by IDTA in summer (-12.7?±?0.5 to -20.3?±?1.1 °C) various tiny clearly separated discontinuous freezing events could be detected similar to that in other species with contrasting XPC anatomy. These freezing events appeared to be initially located in the primary and only later in the secondary xylem. During the LTE no freezing events in the bark and central pith tissue were recorded. Attached twigs were exposed to various freezing temperatures at which LTEs occur. Even if 60% of XPCs were frost-damaged twigs were able to recuperate and showed full re-growth indicating a high regeneration capacity even after severe frost damage to XPCs.     

Sources of N for leaf growth in a high-density apple (Malus domestica) orchard irrigated with ammonium nitrate solution

Elstar apple trees (Malus domestica Borkh.) on M.9 rootstock received either 5 or 35 g N tree(-1) year(-1) during the first two growing seasons after planting, applied as Ca(NO(3))(2) on a daily basis for nine weeks through a drip irrigation system. During the third growing season (1994), all trees were treated with 20 g N tree(-1) year(-1) as (15)NH(4) (15)NO(3) with applications starting on April 22 and continuing for 10 weeks. Soil solution nitrate-N and ammonium-N were monitored weekly with suction lysimeters located 30 cm beneath the drip emitters. Spur and shoot leaves were sampled intensively from full bloom to the end of rapid shoot growth. During the period of nitrogen application, soil solution nitrate-N and ammonium-N were relatively constant, at about 24 and 1.0 mg l(-1) respectively. Growth of the spur leaves was completed by one week after full bloom (May 12), whereas biomass of the shoot leaves increased until mid-June. Nitrogen for growth of the spur leaves was supplied mainly from remobilization, which was dependent on previous N supply. Accumulation of fertilizer N in spur leaves was independent of previous N treatments and continued until the end of the monitoring period (June 24), but contributed only 13% to total spur leaf N. Nitrogen for shoot leaf growth was independent of previous N treatments and was initially supplied primarily by remobilization, but by the end of extension growth, fertilizer N contributed 48% to total shoot leaf N. Linear increases in leaf N uptake throughout the period of rapid shoot growth and the large contribution of fertilizer N to total shoot leaf N were attributed to the constant supply of N available in the root zone through daily N fertilization.     

Growth of young apple trees in relation to reserve nitrogen and carbohydrates

Bench-grafted Fuji/M.26 apple (Malus domestica Borkh.) trees were fertilized with a nutrient solution (fertigation) containing 0, 2.5, 5, 7.5, 10, 15 or 20 mM nitrogen (N) in a modified Hoagland's solution from June 30 to September 1. In mid-October, half of the trees in each N treatment were sprayed twice with 3% urea, 1 week apart. The remaining trees served as controls. All trees were harvested after leaf fall and stored at 2 degrees C over winter. One group of trees from each treatment was destructively sampled before bud break to determine amounts of reserve N and total nonstructural carbohydrates (TNC); the remaining trees were transplanted to N-free medium in the spring. These trees were supplied with Hoagland's solution with or without 10 mM N (from 15N-depleted NH4NO3) for 60 days, starting from bud break. With increasing N supply from fertigation, tree N concentration increased, whereas TNC concentration decreased. Foliar urea applications increased tree N concentration and decreased TNC concentration in each N fertigation treatment. There was a negative linear relationship between tree N concentration and TNC concentration. Irrespective of whether N was provided the following spring, trees with high N reserves but low carbohydrate reserves produced a larger total leaf area at the end of the regrowth period than trees with low N reserves but high carbohydrate reserves. The pooled data on reserve N used for new growth showed that, regardless of the spring N supply, there was a linear relationship between total N accumulated in the tree during the previous season and the amount of reserve N remobilized for new shoot and leaf growth. About 50% of tree N content was remobilized to support new shoot and leaf growth over the range of tree N status examined. We conclude that the initial growth of young apple trees in the spring is determined mainly by reserve N, not reserve carbohydrates. The amount of reserve N remobilized for new growth in spring was proportional to tree N status and was unaffected by current N supply.     

Nitrogen mobilization, nitrogen uptake and growth of cuttings obtained from poplar stock plants grown in different N regimes and sprayed with urea in autumn

Nitrogen mobilization, nitrogen uptake and growth of cuttings obtained from poplar stock plants fertigated with different nitrogen (N) treatments and sprayed with urea in autumn were studied. Stock plants propagated from poplar cuttings were trained to a single shoot and fertigated with 0, 5, 10, 15 or 20 mmol l(-1) N during the first growing season. In October, a subset of stock plants from each N fertigation treatment was sprayed twice with either 3% urea or water, and overwintered outside. In March, total tree biomass and total N concentration and content of stems were estimated for stock plants in each treatment, and cuttings were taken from the middle of each stock plant and stored in plastic bags at 2 degrees C. In mid-April, cuttings were planted in 7.5-l pots containing N-free medium and grown outdoors with a weekly fertigation with nutrient solution containing 0 or 10 mmol l(-1) 15NH4 15NO3. In mid-July, cuttings were harvested, and new shoot (new stems and leaves), shank (old cutting stem) and roots were analyzed for new biomass growth and total N and 15N content. Growth of stock plants was positively related to N supply in the previous growing season. Foliar urea application in autumn had no effect on subsequent stock plant growth even though urea sprays increased both N concentration and content in stem tissues. Biomass growth of cuttings obtained from stock plants was closely related to their N content when the cuttings were grown in an N-free medium regardless of previous treatments applied to the stock plants. When N was supplied in the growth medium, the strength of the relationship between regrowth and N content of cuttings was significantly reduced. Cuttings from stock plants treated with foliar urea and grown in a N-free medium remobilized between 75 and 82% of their total N for new growth, whereas cuttings from plants receiving no urea spray remobilized only between 60 and 69% of their total N for new growth. Current N fertilization of the cuttings reduced the percentage of N remobilized. We conclude that new growth of poplar cuttings in spring was more dependent on currently applied N than on reserve N, and urea N applied as a spray in autumn was more easily remobilized than N taken up by roots during the previous season.     

初春气象条件对苹果开花期的影响分析

通过分析苹果开花期年际变化特征及气象条件对苹果花期的影响,证明初春温度是影响苹果开花期早晚的主要气象因子。3月至4月上旬≥0℃积温每增加或减少10℃,开花期提早或推迟1 d;3月下旬至4月上旬平均最高气温每偏高或偏低0.5℃,开花期提早或推迟1 d;根据初春气象条件,准确预报苹果开花期,为做好果园田间管理,有效防御霜冻灾害提供科学依据。     

库尔勒香梨树体生长与15N的吸收及分配动态

为给库尔勒香梨园合理施肥及氮肥利用率的提高提供参考,以6年生库尔勒香梨为研究对象,采用15N同位素示踪技术,研究萌芽前期至果实成熟期库尔勒香梨树体生长和氮素吸收、分配动态。结果表明:库尔勒香梨树体基径随着生育期的推移逐渐增大,于果实成熟期达到最大(8.71cm);库尔勒香梨叶片的叶面积指数、叶绿素SPAD值和叶片光合速率均随着香梨年生育期的推进呈现先增大后减小的趋势,均在第2个快速膨大期达到最大,分别为2.40、42.03和12.50μmol/(m^2·s);在年生育末期,库尔勒香梨单株树体的生物量为19958g,氮素积累量为199.44g,各器官中以当年新生器官果实的生物量和氮素积累量为最高,分别占整株树体生物量和氮素积累量的33.33%和25.08%。不同生育期15N在树体内的运转随生长中心的变化而变化。盛花期15N在1年生枝中的分配势最强,新梢旺长期和第2个快速膨大期15N在叶片中的分配势最强,果实成熟期15N在果实中的分配势最强。在果实成熟期库尔勒香梨树体当季15N肥料利用率为17.35%。     

Long-term photosynthetic acclimation to increased atmospheric CO(2) concentration in young birch (Betula pendula) trees

To study the long-term response of photosynthesis to elevated atmospheric CO(2) concentration in silver birch (Betula pendula Roth.), 18 trees were grown in the field in open-top chambers supplied with 350 or 700 &mgr;mol mol(-1) CO(2) for four consecutive growing seasons. Maximum photosynthetic rates, stomatal conductance and CO(2) response curves were measured over the fourth growing season with a portable photosynthesis system. The photosynthesis model developed by Farquhar et al. (1980) was fitted to the CO(2) response curves. Chlorophyll, soluble proteins, total nonstructural carbohydrates, nitrogen and Rubisco activity were determined monthly. Elevated CO(2) concentration stimulated photosynthesis by 33% on average over the fourth growing season. However, comparison of maximum photosynthetic rates at the same CO(2) concentration (350 or 700 &mgr;mol mol(-1)) revealed that the photosynthetic capacity of trees grown in an elevated CO(2) concentration was reduced. Analysis of the response curves showed that acclimation to elevated CO(2) concentration involved decreases in carboxylation efficiency and RuBP regeneration capacity. No clear evidence for a redistribution of nitrogen within the leaf was observed. Down-regulation of photosynthesis increased as the growing season progressed and appeared to be related to the source-sink balance of the trees. Analysis of the main leaf components revealed that the reduction in photosynthetic capacity was accompanied by an accumulation of starch in leaves (100%), which was probably responsible for the reduction in Rubisco activity (27%) and to a lesser extent for reductions in other photosynthetic components: chlorophyll (10%), soluble protein (9%), and N concentrations (12%) expressed on an area basis. Despite a 21% reduction in stomatal conductance in response to the elevated CO(2) treatment, stomatal limitation was significantly less in the elevated, than in the ambient, CO(2) treatment. Thus, after four growing seasons exposed to an elevated CO(2) concentration in the field, the trees maintained increased photosynthetic rates, although their photosynthetic capacity was reduced compared with trees grown in ambient CO(2).     

Nitrogen contribution of five leguminous trees and shrubs to alley cropped maize in Ibadan, Nigeria

There are abundant local legume trees and shrubs potentially suitable for alley cropping systems in the sub-Saharan Africa, which are yet to be studied. The nitrogen contribution of two years old Albizia lebbeck and S. corymbosato yield of maize grown in alley cropping was compared to that of Senna siamea, Gliricidia sepium and Leucaena leucocephala in four seasons at Ibadan. Maize shoot biomass and maize grain yield in A. lebbeck alley compared favourably with that in G. sepium and L. leucocephala. Maize biomass and grain yield in S. corymbosa alleys were the lowest. Within A. lebbeck, L. leucocpehala, and G. sepium alleys there were no significant differences in the maize yield in the alleys that received 0, 40 or 80 kg N/ha. Application of more than 40 kg N/ha in S. corymbosa alleys was not necessary as there was no significant increase in maize yield at the higher level of nitrogen. Maize yield and N uptake in A. lebbeck alleys were not significantly different from yield and N uptake in G. sepium, and L. leucocephala at the same fertilizer level. There was a significant correlation between hedgerow tree biomass and maize grain yield. At the end of twelve weeks after pruning application, the organic residues of the pruning applied in the alleys ranged from 5% in G. sepium and 44% in A. lebbeck in the first year compared with the original pruning applied which showed that the slow rate of A. lebbeck decomposition could have a beneficial effect on the soil. The maize N recovery from applied N fertilizer was low (10–22%). Percentage N recovery from the prunings was low in the non-N fixing trees (12–22%), while the recovery was high (49–59%) in A. lebbeck as well as in the other nitrogen fixing tree prunings. Thus A. lebbeck, apart from enhancing maize growth and grain yield like in L. leucocephala and G. sepium, had an added advantage because it remained longer as mulching material on the soil because of its slow rate of decomposition. It was able to survive pruning frequencies with no die-back. This indicates that A. lebbeck is a good potential candidate for alley cropping system in West Africa. S. corymbosa performed poorly compared with the other legume trees. Though it responded to N fertilizer showing a positive interaction between the hedgerow and fertilizer application, it had a high die back rate following pruning periods and termite attack.This revised version was published online in November 2005 with corrections to the Cover Date.     

Nitrogen availability, local light regime and leaf rank effects on the amount and sources of N allocated within the foliage of young walnut (Juglans nigra x regia) trees

Early season leaf growth depends largely on nitrogen (N) provided by remobilization from storage, and many studies have tested the effect of N availability to roots on the amount of N provided for new leaf development by remobilization. Although it is well known that the light regime experienced by a leaf influences the amount of N per unit leaf area (LA), the effect of the local light regime on the amount of N derived either directly from root uptake or from remobilization for early season leaf growth has never been tested at an intra- canopy scale. The objective of this study was to quantify the relative importance of (1) N availability to roots, (2) local light regime experienced by the foliage (at the shoot scale) and (3) leaf rank along the shoot, on the total amount of N allocated to leaves and on the proportions of N provided by remobilization and root uptake. To quantify the importance of N uptake and remobilization as sources of leaf N, potted hybrid walnut trees (Juglans nigra L. x regia L.) were grown outdoors in sand and fed with a labeled ((15)N) nutrient solution. By removing the apical bud, the trees were manipulated to produce only two shoots. The experimental design had two factors: (1) high (HN; 8 mol N m(-3)) and low (LN; 2 mol N m(-3)) N availability; and (2) high (HL; 90% of incident photosynthetically active photon flux (PPF)) and low (LL; 10% of incident PPF) light. Total leaf N per tree was unaffected by either N availability or irradiance. The HN treatment increased the amount of leaf N derived from root uptake at the whole-tree scale (typically around 8 and 2% in the HN and LN treatments, respectively). Nitrogen allocation within foliage of individual trees was controlled by the local light regime, which strongly affected individual leaf characteristics as leaf mass per unit LA and area- based amount of leaf (N(a)). Decreasing the light availability to a branch decreased the amount of N allocated to it, benefiting the less shaded branches. In contrast, shading of the lower branch did not affect the fraction of total leaf N remobilized for either the lower, shaded branch or the upper, unshaded branch. The relevance of these findings for tree growth modeling is discussed.     

The influence of severe shoot pruning on growth,carbon and nitrogen status in young peach trees (Prunus persica)

One-year-old peach trees (Prunus persica (L.) Batsch) were severely pruned in July by removing 60% of the shoots. Tree responses were analyzed in terms of architecture and nutritional status. Tree growth was recorded from July to September by nondestructive (leaf production, thickening and branching of the remaining secondary axes) and destructive measurements (biomass partitioning and concentrations of total nitrogen (N) and nonstructural carbohydrates (NC) in specific tissues). The dry weights of pruned trees were lower than those of control trees at the end of the growing season (i.e., 2.5 months after pruning), whereas shoot:root ratios were restored to the initial values. Tree response occurred in two stages. During the first 24 days following pruning, the growth components of the remaining secondary axes were similar to the control, and new secondary axes were produced. During the next 17 days, increases in both diameter and branching of secondary axes contributed to the maintenance of pruned tree growth rate (similar to that of control trees) and restoration of initial shoot:root ratios. No significant effect of pruning was observed on NC concentrations, whereas N concentrations increased in several organs of the pruned trees during the first growth period. The transient increase in internal N availability contributed to the initiation of new axes and the restoration of a more functional biomass partitioning between shoots and roots.     

Resistance against oxidative stress in leaves of young beech trees grown in model ecosystems with different soil qualities, elevated CO2, and lachnid infestation

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.      

Physiological responses of birch (Betula pendula) to ozone: a comparison between open-soil-grown trees exposed for six growing seasons and potted seedlings exposed for one season

Physiological responses of 4-year-old potted saplings of an O3-tolerant clone of Betula pendula Roth to short-term ozone (O3) exposure (one growing season) were compared with those of 6-year-old open-soil-grown trees of the same clone fumigated with O3 for six growing seasons. In the 2001 growing season, both groups of plants were exposed to ambient (control) and 1.6x ambient (elevated) O3 concentration under similar microclimatic conditions in a free air O3 exposure facility. Growth, net photosynthesis, stomatal conductance, stomatal density, visible foliar injury, starch and nutrient concentrations, bud formation and differences in O3 responses between lower, middle and upper sections of the canopy were determined. The potted saplings were unaffected by elevated O3 concentration, whereas the open-soil-grown trees showed a 3-38% reduction in shoot growth, a 22% reduction in number of overwintering buds, a 26-65% decrease in autumnal net photosynthesis, 30% and 20-23% reductions in starch and nitrogen concentrations of senescing leaves, respectively, and disturbances in stomatal conductance. The greater O3 sensitivity of open-soil-grown trees compared with potted saplings was a result of senescence-related physiological factors. First, a lower net photosynthesis to stomatal conductance ratio in open-soil-grown trees at the end of the season promoted O3 uptake and decreased photosynthetic gain, leading to the onset of visible foliar injuries. Second, decreased carbohydrate reserves may have resulted in deleterious carry-over effects arising from the reduced formation of over-wintering buds. Finally, the leaf-level O3 load was higher for open-soil-grown trees than for potted saplings because of slower leaf senescence in the trees. Thus, O3 sensitivity in European white birch increases with increasing exposure time and tree size.     

TMV侵染对枯斑三生烟叶片中Ca2+分布的影响

以枯斑三生烟为材料,用细胞化学沉淀法测定了TMV侵染对烟草叶片细胞中Ca^2＋分布的影响,并探讨了Ca^2＋在植物抗病性中的作用。结果发现,枯斑三生烟健叶中的Ca^2＋主要分布于细胞间隙和液泡,接种TMV后,细胞间隙中的Ca^2＋逐渐向细胞内转移,在接种后48h,Ca^2＋主要分布于过敏性坏死细胞和近坏死区细胞,远坏死区细胞间隙缺Ca^2＋;以后由于枯斑停止发展,在接种后96h远坏死区细胞逐渐恢复钙稳态。     

Compressive strength of young Taiwania (Taiwania cryptomerioides) trees grown with different thinning and pruning treatments

Taiwania (Taiwania cryptomerioides Hay) is an important timber species in Taiwan. Growth in generally improved trees under intense silvicultural practice is so rapid that rotations or the practice of thinning trees may be as short as 20–30 years. Thus, the wood properties of young plantation trees need to be characterized to effectively use this resource. The effects of different thinning and pruning methods on the compressive strength parallel to grain of young Taiwania trees were explored. Average compressive strengths with various thinning treatments revealed the trend of no thinning > medium thinning > heavy thinning and in the pruning treatments showed the trend of medium pruning > no pruning > heavy pruning. However, most results showed no statistically significant differences among thinning and pruning treatments.     

Hydraulic conductance characteristics of peach (Prunus persica) trees on different rootstocks are related to biomass production and distribution

We investigated hydraulic conductance characteristics and associated dry matter production and distribution of peach trees grafted on different rootstocks growing in the field. A single scion genotype was grown on a low ('K146-43'), an intermediate ('Hiawatha') and a high ('Nemaguard') vigor rootstock. 'K146-43' and 'Hiawatha' rootstocks had 27 and 52% lower mean leaf-specific hydraulic conductances, respectively, than the more vigorous 'Nemaguard' rootstock. Tree growth rates and patterns of biomass distribution varied significantly among rootstocks. Mean dry mass relative growth rates of trees on 'K146-43' and 'Nemaguard' were 66 and 75%, respectively, of the rates of trees on 'Nemaguard', and the scion to rootstock dry mass ratios of trees on 'K146-43' and 'Hiawatha' were 63 and 82%, respectively, of the ratio of trees on 'Nemaguard'. Thus, differences in dry matter distribution between the scion and rootstock, which may be a compensatory response to the differences in leaf specific hydraulic conductance among rootstocks, appeared to be related to differences in growth rates. Correspondingly, there was a positive linear relationship between the scion to rootstock dry mass ratio and the rootstock to scion hydraulic conductance ratio when conductance was normalized for dry mass. This study confirms that rootstock effects on tree water relations and vegetative growth potential result, at least in part, from differences in tree hydraulic conductance associated with specific peach rootstocks.