Translocation of nitrogen in the xylem of field-grown cherry and poplar trees during remobilization

Studies of small trees growing in pots have established that individual amino acids or amides are translocated in the xylem sap of a range of tree species following bud burst, as a consequence of nitrogen (N) remobilization from storage. This paper reports the first study of N translocation in the xylem of large, deciduous, field-grown trees during N remobilization in the spring. We applied 15N fertilizer to the soil around 10-year-old Prunus avium L. and Populus trichocharpa Torr. & Gray ex Hook var. Hastata (Dode) A. Henry x Populus balsamifera L. var. Michauxii (Dode) Farwell trees before bud burst to label N taken up by the roots. Recovery of unlabeled N in xylem sap and leaves was used to demonstrate that P. avium remobilizes N in both glutamine (Gln) and asparagine (Asn). Sap concentrations of both amides rose sharply after bud burst, peaking 14 days after bud burst for Gln, and remaining high some 45 days for Asn. There was no 15N enrichment of either amide until 21 days after bud burst. In the Populus trees, nearly all the N was translocated in the sap as Gln, the concentration of which peaked and then declined before the amide was enriched with 15N, 40 days after bud burst. Xylem sap of clonal P. avium trees was sampled at different positions in the crown to assess if the amino acid and amide composition of the sap varied within the crown. Sap was sampled during remobilization (when the concentration of Gln was maximal), at the end of remobilization and at the end of the experiment (68 days after bud burst). Although the date of sampling had a highly significant effect on sap composition, the effect of position of sampling was marginal. The results are discussed in relation to N translocation in adult trees and the possibility of measuring N remobilization by calculating the flux of N translocation in the xylem.     

Storage of foliar-absorbed nitrogen and remobilization for spring growth in young nectarine (Prunus persica var. nectarina) trees

The effectiveness of spraying foliage with urea to provide nitrogen (N) to augment the seasonal internal cycling of N in young nectarine trees (Prunus persica (L.) Batsch var. nectarina (Ait. f. Maxim.), cv. Stark Red Gold) was studied. One-year-old trees were grown with contrasting N supplies during the summer and foliage was sprayed with a 2% urea solution labeled with (15)N just before leaf senescence started. After leaf abscission had finished, the trees were repotted in sand and given no further N. Remobilization of both labeled and unlabeled N for leaf growth the following spring was quantified. Leaves absorbed between 58 and 69% of the (15)N intercepted by the canopy irrespective of tree N status. During leaf senescence, the majority of (15)N was withdrawn from the leaves into the shoot and roots. Remobilization of (15)N the following spring was also unaffected by tree N status. About 38-46% of (15)N in the trees was recovered in the new growth. More unlabeled N (derived from root uptake) was remobilized for leaf growth in the spring than was withdrawn from leaves during canopy senescence the previous autumn. Therefore, soil-applied N augmented N storage pools directly, and contributed more to N remobilization the following spring than did foliar-absorbed (15)N.     

Relationships between light, leaf nitrogen and nitrogen remobilization in the crowns of mature evergreen Quercus glauca trees

We estimated the amount of nitrogen (N) remobilized from 1-year-old leaves at various positions in the crowns of mature Quercus glauca Thunb. ex Murray trees and related this to the production of new shoots. Leaf N concentration on an area basis (Na) and total N (Nt= Na x lamina area of all leaves on a shoot) were related to photosynthetic photon flux (PPF) on the leaves of current-year and 1-year-old shoots. When new shoots (S02 shoots; flushed in 2002) flushed, only a portion of the leaves on the previous year's shoots (S01 shoots; flushed in 2001) were shed. After the S02 shoots flushed, S01 shoots were defined as 1-year-old shoots (S01* shoots). Both Na and Nt were positively correlated with PPF for S01 shoots, but not for S01* shoots. The fraction of remobilized N (% of the maximum Na in S01 leaves) from remaining leaves was 5-35%, with the fraction size being positively correlated with the number of S02 shoots on an S01* shoot (new shoot number). However, the mean fraction of remobilized N from fallen leaves was 45% and was unrelated to new shoot number. The total amount of N remobilized from both fallen and remaining leaves was 1-20 mg per S01* shoot. Total remobilized N was positively correlated with new shoot number. There was a statistically significant positive relationship between the light-saturated net photosynthetic rate on a leaf area basis (Amax) and Na for both S01* and S02 leaves. However, when we compared leaves with similar Na, Amax of S01* leaves was only half that of S02 leaves, indicating that 1-year-old leaves had lower instantaneous N-use efficiency (Amax per unit Na) than current-year leaves. Ratios of chlorophyll a:b and Rubisco:chlorophyll were lower in S01* leaves than in S02 leaves, indicating that 1-year-old leaves were acclimatized to lower light environments. Thus, in Q. glauca, the N allocation theory (i.e., that N is distributed according to local PPF) applied only to the current-year shoots. Although the amount of foliar N in 1-year-old shoots was not strongly affected by the PPF on 1-year-old leaves, it was affected by interactions with current-year shoots.     

Cryopreservation of dormant orthodox seeds of forest trees: mazzard cherry (Prunus avium L.)

? The sensitivity of dormant seeds of mazzard cherry (Prunus avium L.) of Polish provenances to extreme desiccation and/or the ultra-low temperature of liquid nitrogen, LN (?196 °C), was investigated to identify the optimum seed water content (w.c.) at this temperature.

? Germination and seedling emergence tests in this study showed that there is no critical seed w.c. for deeply desiccated seeds (stone w.c. 1.6%), although such desiccated seeds were sensitive to the temperature of LN in the seedling emergence test. For seeds frozen in LN, the highest germinability was observed at w.c. of 9.0–16.9%, but seedling emergence was then significantly lower than in nonfrozen seeds. The 2-year of storage in LN of seeds desiccated to 7.8% w.c. did not decrease germinability after thawing, in comparison with 2-year of storage at ?3 °C. Storage in LN showed that if seeds were stored after breaking of their dormancy, germinability after storage was lower because of the necessity of seed desiccation to the lower level (～ 8%) of w.c. after stratification (before storage). Secondary dormancy was induced in seeds desiccated after stratification.

? The results of this study demonstrate the potential for long-term cryopreservation of mazzard cherry seeds in forest gene banks.

     

大连地区甜樱桃增产技术

大连地区大面积栽培甜樱桃过程中,普遍存在树势衰弱,病害较重,单株产量低的问题。针对现状,结合甜樱桃的生物学特性和当地生境特点,运用综合性的技术措施,不断增加甜樱桃的产量,促进甜樱桃产业的可持续发展。     

欧洲大樱桃试管快繁技术研究

取欧洲大樱桃茎段作外植体，探讨了其快速繁殖技术，筛选出最佳增殖、生根培养基，找出了影响试管苗移栽成活率的因素。试管苗增殖系数达到10左右，生根率达92.5%，生根率达92.5%，移栽成活率达95％以上。     

欧洲甜樱桃研究进展及开发利用前景

在汲取国内外相关研究成果及学术观点的基础上,详细阐述了欧洲甜樱桃的生物学和生态学特性、起源及地理分布,探讨了果实所含营养成分及其营养和医疗保健价值;分析了存量资源的保存现状、优良品种及砧木选育的研究进展;指出了资源开发利用过程中存在的不足,展望了欧洲甜樱桃系列产品综合开发和创新利用的广阔前景。旨在实现欧洲甜樱桃无公害、标准化栽培及资源的可持续利用,为推动功能性饮品、保健品及药品的产业化发展,提供理论依据和科技支撑。     

Effects of timing of nitrogen fertilization on shoot development in peach (Prunus persica) trees

Shoot development was studied for two consecutive years in peach trees fertilized with N either in the previous fall or in the middle of the growing season. During the first year, two additional treatments were studied: no N supply and nitrate supplied in the irrigation water throughout the growing season. The number of shoots that developed depended on nitrogen availability in the period following bud break. During shoot development, leaf emergence occurred in one, two, or three stages, which ended at about 500 to 600 degree days, 1,000 to 1,200 degree days, and 1,500 to 2,000 degree days after bloom, respectively. The proportion of shoots exhibiting a second or third developmental stage depended on nitrogen availability at the beginning of that stage. Increasing nitrogen availability during a developmental stage prolonged the stage and increased the number of leaves produced.     

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.     

Differences in nitrogen economy of temperate trees

Twenty-four temperate tree species were classified into three groups based on cluster analysis of relative growth rate, nitrogen concentration, nitrogen-production efficiency, nitrogen-distribution ratio and nitrogen-use efficiency as follows: Group I (Asteridae and Rosidae), Group II (Dilleniidae and Hamamelidae) and Group III (Coniferopsidae). Relative growth rate (RGR) was high in Group II, moderate in Group I and low in Group III. The regression coefficient for the relationship between RGR and leaf nitrogen concentration was higher in Group II than in Group I, and no relationship was observed in Group III. Parameter analysis of RGR indicated that RGR per unit leaf nitrogen was important for all three groups, but that the allocation of nitrogen to leaves was particularly important in Groups I and II. The ratio of dark respiratory rate (R) to net photosynthetic rate (A) was higher in Group I than in Group II. Neither A nor R was measured in the Group III species. A linear relationship was observed between leaf nitrogen concentration and A in Group II, but this relationship was not evident in Group I.     

Seasonal variation in xylem pressure of walnut trees: root and stem pressures

Measurements of air and soil temperatures and xylem pressure were made on 17-year-old orchard trees and on 5-year-old potted trees of walnut (Juglans regia L.). Cooling chambers were used to determine the relationships between temperature and sugar concentration ([glucose] + [fructose] + [sucrose], GFS) and seasonal changes in xylem pressure development. Pressure transducers were attached to twigs of intact plants, root stumps and excised shoots while the potted trees were subjected to various temperature regimes in autumn, winter and spring. Osmolarity and GFS of the xylem sap (apoplast) were measured before and after cooling or warming treatments. In autumn and spring, xylem pressures of up to 160 kPa were closely correlated with soil temperature but were not correlated with GFS in xylem sap. High root pressures were associated with uptake of mineral nutrients from soil, especially nitrate. In autumn and spring, xylem pressures were detected in root stumps as well as in intact plants, but not in excised stems. In contrast, in winter, 83% of the xylem sap osmolarity in both excised stems and intact plants could be accounted for by GFS, and both GFS and osmolarity were inversely proportional to temperature. Plants kept at 1.5 degrees C developed positive xylem pressures up to 35 kPa, xylem sap osmolarities up to 260 mosmol l(-1) and GFS concentrations up to 70 g l(-1). Autumn and spring xylem pressures, which appeared to be of root origin, were about 55% of the theoretical pressures predicted by osmolarity of the xylem sap. In contrast, winter pressures appeared to be of stem origin and were only 7% of the theoretical pressures, perhaps because of a lower stem water content during winter.     

齐齐哈尔市城区2010年春树木枯死原因分析

通过调查分析,确定了垂榆等树种死亡的主要原因是冻害所致,提出了预防及补救措施。     

Organic and inorganic sulfur transport in the xylem sap and the sulfur budget of Picea abies trees

Temporal changes in inorganic and organic sulfur compounds (sulfate, glutathione, cysteine, methionine) were analyzed in xylem sap of 40-year-old Norway spruce (Picea abies (L.) Karst.) trees growing on acidic soils at a healthy and a declining stand in the Fichtelgebirge (North Bavaria, Germany). Studies were carried out (1) to quantify glutathione (GSH) transport in the xylem of spruce, (2) to study the significance of reduced sulfur versus sulfate (SO(4) (2-)) transport in the xylem, and (3) to compare total sulfur (S) transport in the xylem with the amount of foliar uptake of SO(2) in an air-polluted environment. Glutathione was the main reduced S compound in the xylem ranging in concentration from 0.5 to 5 &mgr;mol l(-1). Concentrations of inorganic SO(4) (2-) in the xylem sap were up to 50 times higher than those of GSH ranging from 60 to 230 &mgr;mol l(-1). During the growing season, concentrations of all S compounds in the xylem were highest in May (up to 246 &mgr;mol l(-1)) and decreased during summer and fall (up to 21 &mgr;mol l(-1)). On average, SO(4) (2-) concentrations in xylem sap were 30% higher at the declining site compared with the healthy site. Diurnal changes in organic S compounds were significant for GSH and cysteine with high concentrations during the night and low concentrations during the day. Diurnal changes in inorganic concentrations were not significant. Xylem sap concentrations of SO(4) (2-) and cysteine were twice as high and GSH concentrations were tenfold higher in surface roots than in branches. At both sites, transport of organic S was low (up to 3% of total S) compared to transport of SO(4) (2-). Annual transport of total S in the xylem (SO(4) (2-) was the main component) ranged from 60 to 197 mmol tree(-1) year(-1) at the healthy site and from 123 to 239 mmol tree(-1) year(-1) at the declining site. Although gaseous uptake of SO(2) was estimated to be similar at both sites (38 mmol tree(-1) year(-1); Horn et al. 1989), the ratio between annual gaseous uptake of SO(2) and transport of S in the xylem was 1:4 and 1:5 at the healthy and declining sites, respectively.     

Water storage capacitance and xylem tension in isolated branches of temperate and tropical trees

Trees of tropical semi-deciduous forests range from "drought-avoiding" stem-succulent species with low-density wood (< 0.5 g cm(-3)), which maintain high stem water potentials (psi(STEM) > -0.7 MPa) throughout the year, to "drought-tolerant" deciduous hardwood species (wood density > 0.75 g cm(-3)), which dehydrate strongly during seasonal drought (psi(STEM) < -6 MPa). In stem-succulent and other drought-avoiding species, xylem vessels are surrounded by extensive parenchyma providing intracellular water storage, whereas in deciduous species stem water storage is mainly extracellular. Thirteen tropical and two temperate tree species, representing different functional types, were studied. The contribution of stem water storage to these species' water use during water stress was determined by time-series analysis of dehydration and rehydration of excised leaf-bearing branches of these trees. During dehydration, stem water potential slowly declined 1-2 MPa in drought-avoiding species, but in deciduous species it rapidly fell 4-5 MPa, suggesting that water storage capacitance was related to xylem anatomy. After immersion of dehydrated, leafless branches in water, the decline in xylem tension and rate of water uptake during rehydration were linearly related, as predicted by application of Ohm's law to water flux. The decline of xylem tension during rehydration was biphasic, with a phase of rapid water uptake into extracellular spaces being followed by a prolonged phase of slow water uptake into living cells. The rate of water uptake during rehydration and the minima of leaf water potential observed in the field during the dry season were highly correlated with water storage capacitance, indicating that wood anatomy is a major determinant of drought adaptation.     

Microelectrode technique for in situ measurement of carbon dioxide concentrations in xylem sap of trees

We developed a new microelectrode technique for measuring CO2 concentration ([CO2]) in xylem sap of trees. This technique enabled us to make rapid and continuous measurements of xylem sap [CO2] in situ. In this report, we discuss the methodology and establish the feasibility of the technique. We also describe calibration procedures, temperature sensitivity, field use and other characteristics of the microelectrodes. An example of data collected in the field is provided. Microelectrode calibration was accomplished at constant temperature in air of known [CO2]. When sampling temperature differed from calibration temperature, correction was necessary. We developed an equation to correct for temperatures between 15 and 35 degrees C when calibration was conducted at 25 degrees C. Equations based on Henry's Law were used to convert measured gas phase [CO2] (%) to concentration of all products of CO2 dissolved in sap (mmol l(-1)). We inserted microelectrodes into stems of three tree species to measure diurnal changes in [CO2] in the xylem sap. A diurnal pattern with depression during the day and elevation at night was observed. Mean daily [CO2] ranged from 1.6 to 10.3 mmol l(-1). Microelectrodes were suitable for making diurnal measurements for up to 7 days without recalibration. We also used the microelectrodes to measure [CO2] of soil in situ. Soil [CO2] ranged from 1 to 4% (gas phase), with little diurnal variation.     

Variability with xylem depth in sap flow in trunks and branches of mature olive trees

Knowledge of sap flow variability in tree trunks is important for up-scaling transpiration from the measuring point to the whole-tree and stand levels. Natural variability in sap flow, both radial and circumferential, was studied in the trunks and branches of mature olive trees (Olea europea L., cv Coratina) by the heat field deformation method using multi-point sensors. Sapwood depth ranged from 22 to 55 mm with greater variability in trunks than in branches. Two asymmetric types of sap flow radial patterns were observed: Type 1, rising to a maximum near the mid-point of the sapwood; and Type 2, falling continuously from a maximum just below cambium to zero at the inner boundary of the sapwood. The Type 1 pattern was recorded more often in branches and smaller trees. Both types of sap flow radial patterns were observed in trunks of the sample trees. Sap flow radial patterns were rather stable during the day, but varied with soil water changes. A decrease in sap flow in the outermost xylem was related to water depletion in the topsoil. We hypothesized that the variations in sap flow radial pattern in a tree trunk reflects a vertical distribution of water uptake that varies with water availability in different soil layers.     

Winter stem xylem pressure in walnut trees: effects of carbohydrates, cooling and freezing

Pressure transducers were attached to twigs of orchard trees and potted trees of walnut (Juglans regia L.) to measure winter stem xylem pressures. Experimental potted trees were partially defoliated in the late summer and early autumn to lower the amount of stored carbohydrates. Potted trees were placed in cooling chambers and subjected to various temperature regimes, including freeze-thaw cycles. Xylem pressures were inversely proportional to the previous 48-h air temperature, but positively correlated with the osmolarity of the xylem sap. Defoliated trees had significantly lower concentrations of stored carbohydrates and significantly lower xylem sap osmolarities than controls. Plants kept at 1.5 degrees C developed xylem pressures up to 40 kPa, just 7% of the theoretical osmotic pressure of the xylem sap. However, exposure to low, nonfreezing temperatures followed by freeze-thaw cycles resulted in pressures over 210 kPa, which was 39% of the theoretical osmotic pressure. A simple osmotic model could account for the modest positive winter pressures at low, nonfreezing temperatures, but not for the synergistic effects of freeze-thaw cycles.     

Internal remobilization of carbohydrates, lipids, nitrogen and phosphorus in the Mediterranean evergreen oak Quercus ilex

Remobilization of internal resources is an important mechanism enabling plants to be partly independent of external nutrient availability. We assessed resource remobilization during the growing period in woody and foliar tissues of leafy branches of mature evergreen Mediterranean oak (Quercus ilex L.) at three field sites. We compared nonstructural carbohydrates, lipids, nitrogen and phosphorus pools in leaves and stems before bud burst (March) and at the end of the growing period (July). We also experimentally defoliated leafy branches to determine the storage function of old leaves. Changes in pools of carbon compounds in leaves and stems during spring and in response to defoliation indicated that foliar and woody tissues could provide carbon to support shoot growth. Independently of stem age, soluble sugar and lipid pools decreased significantly during spring. Changes in leaf pools between March and July involved all compounds measured except starch and were accompanied by a 5% decrease in mean leaf biomass. During the same period, 15% of the nitrogen and 25% of the phosphorus were removed from leaves. In contrast, woody tissues did not remobilize nitrogen or phosphorus. Our results support earlier hypotheses that leaves of evergreen species have a primary role in resource remobilization.     

Seasonal changes in the axial distribution of peroxidase activity in the xylem sap of beech (Fagus sylvatica L.) trees

Xylem sap was collected from trunk segments of adult beech (Fagus sylvatica L.) trees by water displacement. Peroxidase activity was analyzed in xylem saps collected in different phases of the yearly growth cycle and from different heights up the trunks (up to 14 m). The xylem saps contained two major peroxidase isozymes with acidic isoelectric points of 4.1 and 4.6, respectively. Mean peroxidase activity was low during the emergence of the new leaves and high in summer and in winter. In the cold season, peroxidase activity decreased from the stem base to the top, whereas significant gradients were not observed during the vegetative period.     

Transpiration sensitivity of urban trees in a semi-arid climate is constrained by xylem vulnerability to cavitation

Establishing quantitative links between plant hydraulic properties and the response of transpiration to environmental factors such as atmospheric vapor pressure deficit (D) is essential for improving our ability to understand plant water relations across a wide range of species and environmental conditions. We studied stomatal responses to D in irrigated trees in the urban landscape of Los Angeles, California. We found a strong linear relationship between the sensitivity of tree-level transpiration estimated from sap flux (m(T); slope of the relationship between tree transpiration and ln D) and transpiration at D=1 kPa (E(Tref)) that was similar to previous surveys of stomatal behavior in natural environments. In addition, m(T) was significantly related to vulnerability to cavitation of branches (P(50)). While m(T) did not appear to differ between ring- and diffuse-porous species, the relationship between m(T) and P(50) was distinct by wood anatomy. Therefore, our study confirms systematic differences in water relations in ring- versus diffuse-porous species, but these differences appear to be more strongly related to the relationship between stomatal sensitivity to D and vulnerability to cavitation rather than to stomatal sensitivity per se.