Translocation of amino acids in the xylem of apple (Malus domestica Borkh.) trees in spring as a consequence of both N remobilization and root uptake

Nitrogen is remobilized from storage for the growth of Malus domestica leaves each spring. Seasonal patterns of N translocation in the xylem sap as a consequence of remobilization were determined in 2-year-old 'Golden delicious' trees grafted on M9 rootstocks. The trees were grown in sand culture and (15)NH(4)(15)NO(3) at 10.4 atom% abundance supplied during August-September. The following year no further N was supplied and destructive harvests were taken during bud burst and leaf growth to determine the patterns of N remobilization together with the isolation of xylem sap for an analysis of their amino acid profiles and (15)N enrichments by GC-MS. The concentration of amino acids in the xylem sap rose following bud burst, peaked at full bloom and then fell again during petal fall and fruit set. The peak in amino acid concentration corresponded with the period when the rate of N remobilization was the fastest. The majority of labelled N was recovered in Asn, Gln + Glu and Asp demonstrating that they were being translocated as a consequence of remobilization. In a second experiment, 8-year-old trees growing in an orchard were fertilized with N either in the autumn or spring. Xylem sap samples were collected in the spring and early summer and, by comparison with the amino acid profiles recovered in trees from both treatments, Asn was identified as the main compound translocated as a consequence of both remobilization and root uptake of N, although there was evidence that root uptake of N occurred later. The data are discussed in relation to quantifying the internal cycling of N in trees.     

Variations in the amino acid composition of xylem sap of Betula pendula Roth. trees due to remobilization of stored N in the spring

Seasonal patterns of N translocation in the xylem sap of Betula pendula were studied, to determine whether specific amino acids were recovered in spring as a consequence of N remobilization. Seedlings were grown in sand culture and provided with ¹⁵NH₄¹⁵NO₃ (at 2·2 atom percent excess) for one growing season. The following winter dormant trees were transplanted into fresh sand and given N at natural abundance thereafter. Destructive harvests were taken during bud burst and leaf growth to determine the pattern of ¹⁵N remobilization and N uptake, along with isolation of xylem sap for analysis of their amino acid profiles and ¹⁵N enrichment by GC-MS. ¹⁵N remobilization occurred immediately following bud burst, while N derived from root uptake did not appear in the leaves until 12 d after bud burst. During N remobilization there was a 10-fold increase in the concentration of N in the xylem sap, due predominantly to increases in citrulline and glutamine. The ¹⁵N enrichment of these two amino acids demonstrated the increase in their concentration in the xylem sap following bud burst was due to N remobilization. These results are discussed in relation to measuring N remobilization and storage capacity of trees in the field.     

Determining the role of N remobilization for growth of apple (Malus domestica Borkh) trees by measuring xylem-sap N flux

The contribution of N remobilization to the seasonal growth of field-grown Malus domestica (apple) trees was measured using two different techniques. 'Fuji' trees grafted on M.9 apple rootstocks were planted in the field and fertilized and irrigated for two growing seasons. During the second year, the trees received 15N-labelled fertilizer and destructive harvests were taken during the spring and summer to determine the pattern of N remobilization and uptake. At the same time, patterns of N translocation in the xylem were measured by sampling saps at each harvest and analysing them for their constituent amino acids and amides. Total water flux through the trunk xylem was also measured throughout the sampling period using the heat balance technique. The flux of amino compounds in the xylem was then calculated to see if this approach could quantify remobilization. Most of the N for leaf growth was provided by remobilization, which lasted for some 40 d following bud-burst. The labelled N was not taken up until 14 d after remobilization had started. The predominant amino compounds recovered in the xylem were Asn, Asp, Arg, and Gln, whose concentration peaked during remobilization, except for Arg whose concentration was highest at bud-break and declined thereafter. The amount of N translocated in the xylem as Asn, Asp and Gln correlated well with the amount of N remobilized (as measured by the recovery of unlabelled N in the new above-ground growth). The data suggest that Arg is translocated predominantly as a consequence of root uptake and they are discussed in relation to measuring N remobilization in field-grown trees.     

Coupling sap flow velocity and amino acid concentrations as an alternative method to (15)N labeling for quantifying nitrogen remobilization by walnut trees

The temporal dynamics of N remobilization was studied in walnut (Juglans nigra x regia) trees growing in sand culture. Trees were fed with labeled N ((15)N) during 1999 and unlabeled N in 2000. Total N and (15)N contents in different tree compartments were measured during 80 d after bud burst and were used to estimate N remobilization for spring growth. The seasonal (and occasionally diurnal) dynamics of the concentration and (15)N enrichment of the major amino acids in xylem sap were determined concurrently. Sap flow velocity was also measured for sample trees. A new approach coupling amino acid concentrations to sap flow velocity for quantifying N remobilization was tested. A decrease of the labeled N contents of medium roots, tap roots, and trunk was observed concurrently to the increase in the labeled N content of new shoots. Remobilized N represented from previous year storage 54% of N recovered in new shoots. Arginine, citruline, gamma-amino butyric acid, glutamic acid, and aspartic acid always represented around 80% of total amino acid and amide N in xylem sap and exhibited specific seasonal trends and significant diurnal trends. N translocation was mainly insured by arginine during the first 15 d after bud burst, and then by glutamic acid and citruline. The pattern of N remobilization estimated by the new approach was consistent with that measured by the classical labeling technique. Implications for quantifying N remobilization for large, field-growing trees are discussed.     

Nitrogen transport in the xylem sap of Quercus ilex: the role of ornithine

The storage and remobilization of nitrogen in deciduous and evergreen species is a major source of N, supporting the seasonal growth of trees. In evergreens, in addition to wood and roots, older leaves are important reservoirs of N used in the growth of new foliage. Just before bud burst, when transpiration is inactive or low, and when uptake of nitrogen by the roots may be restricted due to low temperatures, levels of organic N in the xylem are high. Amino acids usually comprise the bulk of this organic N. Changes in amino acid concentrations in early spring are thought to result mainly from hydrolysis of N reserves, and not from current N uptake. The seasonal profiles of amino acids in the xylem sap of Quercus ilex, an evergreen Mediterranean tree, were investigated. The first amino acid detected in the xylem sap before spring was ornithine, which may result from the breakdown of arginine present in storage proteins. Arginine is one of the main amino acids present in storage proteins because each arginine molecule has four nitrogen atoms. When protein degradation increases the free arginine pool, the arginase activity is enhanced and, consequently, the conversion of arginine to ornithine. It seems that ornithine has an important role in N transport early in the growth season of Q. ilex.     

Nitrogen and Cation Nutrition of Three Ecologically Different Plant Species

Apple rootstocks M.7 were given a nitrogen application either in the spring or in the preceding autumn. At the time of the spring application some rootstocks were ringed. During the 50-day experimental period from bud-break, shoot growth and the amount of nitrogen incorporated into the new shoots were slightly reduced in the spring-treated trees and strongly reduced in the ringed trees of both treatments. Roots of unringed autumn-fertilized trees showed higher levels of total and amino nitrogen than those of similar trees in the spring treatment; to a lesser degree, the reverse held for xylem sap from the stem. Ringing increased the amino-nitrogen level in the roots, which suggests a reduced translocation rate. The nitrogen treatments led to marked differences in the percentage composition of the amino-nitrogen fraction of roots and xylem sap. The distribution of amino acids and amides in the roots and that in xylem sap of the same trees was divergent, but arginine and asparagine often were the most important constituents. Aspartic acid was rather abundant in xylem sap. Ringing did not affect the composition of the amino-nitrogen fraction in the roots quantitatively but increased the proportion of arginine in the sap. The possible relationship between the composition of xylem sap and soluble nitrogen in the roots is discussed. It is argued that especially in spring-fertilized trees appreciable amounts of nitrogen must be translocated via the phloem in addition to the transport in the xylem.     

Amino acid content in xylem sap of regrowing alfalfa (Medicago sativa L.): Relations with N uptake,N2 fixation and N remobilization

During vegetative regrowth of Medicago sativa L., soil N, symbiotically fixed N₂ and N reserves meet the nitrogen requirements for shoot regrowth. Experiments with nodulated or non-nodulated plants were carried out to investigate the changes in N flows originating from the different N sources and in xylem transport of amino acids during regrowth. Exogenous N uptake, N₂ fixation and endogenous N remobilization were estimated by ¹⁵N labelling and amino acids in xylem sap were analysed. Removal of shoots resulted in great declines of exogenous N flows derived either from N₂ or from NH₄NO₃ during the first week of regrowth, thereafter recovery increased linearly. Mineral N uptake as well as N₂ fixation occurred mainly between the 10th and 18th day after removal of shoots while exogenous N assimilation in intact plants remained at a steady level. Nitrogen remobilization rates in defoliated plants increased by at least three to five-fold, especially during the first 10 days following shoot removal. Compared to control plants, contents of amino acids in xylem sap, during the first 10 days of regrowth, were reduced by about 72% and 82% in NH₄NO₃ grown and in N₂ fixing plants, respectively. Asparagine was the main amino acid transported in xylem sap of both treated plants. Its relative contents during this period significantly decreased from 75% to 59% and from 67% to 36% respectively in non-nodulated plants and in nodulated ones. This decline was accompanied by compensatory increase in the relative contents of aspartate and glutamine.     

Short-term changes in xylem N compounds in Lolium perenne following defoliation

Previous studies have indicated that an increased asparagine to glutamine ratio (Asn : Gln) occurs in the xylem fluid of Lolium perenne 24 h after defoliation. However, the absolute changes in Asn and Gln leading to the increased Asn : Gln ratio are unknown. The present study tested the hypotheses that: (1) defoliation-induced changes in xylem amino acid composition occur in L perenne within the first 24 h following defoliation, irrespective of phasing with respect to the diurnal light/dark cycle; and (2) the increase in Asn : Gln ratio in the xylem fluid of L perenne following defoliation is due to an increase in Asn content. Plants of L perenne L. 'Aurora' were grown in flowing solution culture for 40 d. Plants were then either left intact, defoliated at the end of the light period or defoliated at the end of the dark period. 15N-labelled NO3- was supplied following defoliation to discriminate between the recovery of N absorbed prior to, and following, defoliation. Xylem samples were collected over the subsequent 24 h period with amino acids speciated by GC-MS. There was support for the first hypothesis: increased Asn : Gln ratios occurred within the first 24 h, irrespective of the phasing of defoliation with respect to light/dark cycles. The second hypothesis was not supported: the concentration of all amino acids in the xylem exudate declined after defoliation, and the increased Asn : Gln ratio was accounted for by a disproportionately large reduction in Gln levels. Low concentrations of amino acids in the xylem of defoliated plants precluded accurate discrimination of their nitrogen content into pre- and post-defoliation sources.     

Copper uptake and translocation in chicory (Cichorium intybus L. cv Grasslands Puna) and tomato (Lycopersicon esculentum Mill. cv Rondy) plants grown in NFT system. II. The role of nicotianamine and histidine in xylem sap copper transport

The effect of rooting media Cu concentration (0.05–20 mg Cu L^-1) on amino acid concentrations and copper speciation in the xylem sap of chicory and tomato plants was measured using 6 week old plants grown in a nutrient film technique system (NFT). Irrespective of the Cu concentration in the nutrient solutions, more than 99.68% and 99.74% of total Cu in tomato and chicory xylem sap was in a bound form. When exposed to high Cu concentrations in the rooting media, amino acid concentrations in the sap increased. Relative to other amino acids, the concentrations of glutamine (Gln), histidine (His), asparagine (Asn), valine (Val), nicotianamine (NA) and proline (Pro) in tomato xylem saps, and His, γ-aminobutyric acid (Gaba), glutamic acid (Glu), leucine (Leu), NA and phenylalanine (Phe) in chicory xylem saps showed the greatest increases. The data indicate that induced synthesis of some free amino acids as a specific and proportional response to Cu treatment. For a single complexation amino acid, the solution Cu²⁺concentration vs pH titration curve for NA at 0.06–0.07 mM was most similar, closely followed by His at 0.5–0.6 mM, to the solution Cu²⁺concentration behaviour in both tomato and chicory xylem sap. It is concluded that increased Cu concentrations in the rooting media induced selective synthesis of certain amino acid which include NA, His, Asn and Gln which have high stability constants with Cu. NA and His have the highest binding constants for Cu and the concentrations of NA and His in chicory and tomato xylem saps can account for all the bound Cu carried in the sap. This revised version was published online in June 2006 with corrections to the Cover Date.     

Seasonal variation of nitrogenous compounds in the xylem sap of Citrus

Samples of tracheal sap of Citrus sinensis (L.) Osbeck cv. Washington Navel were taken from field trees throughout the year and the nitrogen composition of the sap was determined. The nitrogenous fraction of the sap was composed mainly of free amino acids (92–97% of total nitrogen) and nitrates throughout the year. Proline was the most abundant amino acid during almost the entire cycle, and its concentration was especially high during the autumn and winter period. Nevertheless, a significant part (40–60%) of the total organic nitrogen was transported as arginine. Total nitrogen as well as amino acids and nitrates were maximal at spring flush. At spring flush and summer flush there was also a diversification of α-amino nitrogen among different amino acids. During the spring flush, nitrates, asparagine and γ-aminobutyric acid in the xylem sap seemed to have a radicular origin, whereas glutamic acid and arginine were released from the surrounding parenchyma. The results suggest a metabolic transformation in the wood parenchyma of nitrogenous compounds coming from the roots (including reduction of nitrates) and a turnover of different nitrogen metabolites between the xylem and surrounding cells.     

Mobilisation of nutrients and transport via the xylem sap in a shrub (Ligustrum ovalifolium) during spring growth: N and C compounds and interactions

In open-field soilless culture there can be great deal of leaching, particularly in rainy springs. Ligneous plants have the capacity to store large quantities of nutrients in perennial organs. Knowledge of the plant's internal nutrient mobilisation during spring to supply growing organs could lead to reduction of fertiliser application. To quantify the fraction of storage mobilisation available for growth of new organs during spring, Ligustrum ovalifolium shrubs were grown for 2 years with or without fertilisation in the second spring. Nitrogen (N) absorption and N and carbon (C) mobilisation from storage were followed during spring growth via the sap quality. A mathematical combination of the sap composition with flow velocity provided the transported quantities of N and C. Nitrogen and C mobilisation towards new shoots took place during all the spring growth from bud break onwards. In unfertilised plants, C was mobilised primarily as sugars (stachyose, mannose and sucrose) and starch. In fertilised plants, the same sugars were transported in the xylem sap, but at lower concentrations. Stachyose concentration was lower in fertilised than in unfertilised plants and decreased during spring growth. Nitrogen was transported in the xylem sap mainly as amino acids in both fertilisation treatments. Glutamine was the predominant form at bud break and during shoot elongation. In fertilised plants, arginine became predominant after shoot elongation, and was related to low C availability. The interactions of N with C are discussed; specifically, insufficient availability of N limits the use of C, more of which is directed to aerial organs by sap flow.     

Seasonal variation of amino acids in the xylem sap of “Populus x canadensis” and its relation to protein body mobilization

Summary The seasonal changes in the pattern of 21 amino acids occurring in the xylem vessels of Populus twigs have been studied in connection to the mobilization of protein bodies in ray parenchyma cells at the electron microscopic level. Hydrolysis of protein bodies in spring and movement of amino acids into vessels are found to be closely linked. Comprising more than 75% of total amino acid content, glutamine (Gln) is by far the dominant N-constituent of the sap. Gln reaches up to 11 mol ml^-1 in the spring sap while other amino acids only show 1/20 to 1/100 of this amount. From the measured Gln accumulation rates in the vessels in nature and in the vessels of isolated shoots, a minimum flux rate for Gln of 5.6 pmol cm^-2 min^-1 is calculated for the ray contact cell/vessel interface. Furthermore, because Gln constitutes 75% of the amino acid content of the sap but only 1.3% of the amino acids in the 32 kDa storage protein of the ray cells in the wood (Clausen and Apel 1991), it becomes evident that most amino acids originating from protein body mobilization do not enter the vessels but are used for Gln synthesis preceding Gln release into the vessels.     

Detection and characterization of nitrogen circulation through the sieve tubes and xylem vessels of rice plants

Nitrogen movement through the xylem vessels and sieve tubes in rice plants was studied using xylem and phloem sap analysis in combination with stable and radioactive nitrogen isotope techniques.More than 90% of nitrogen was translocated in the sieve tubes of rice plants as amino acids. When 15N (99.6 atom%) was applied as a nitrate to the root, 15N first appeared in phloem sap of the leaf sheath within 10 minutes and increased to 37 atom% excess 5 hours after the experiment had started. In long-term experiments, 63% of nitrogen in the phloem sap of the leaf sheath and 15% in that of the uppermost internode came from nitrogen absorbed within the last 24 hours and 50 hours, respectively.To obtain information about the more rapid circulation of nitrogen in the plant, radioactive 13N was used as a tracer. A positron-emitting tracer imaging system was used to show that 13N was transferred to the leaf sheath within 8 minutes of its application to the roots. Analysis of the xylem sap of the leaf sheath showed that when the nitrate was applied to the roots, most of the nitrogen in the xylem was transported as a nitrate.These data showed that phloem and xylem sap analysis together with the stable and radioactive nitrogen techniques provide a good method for the detection of nitrogen cycles in plants.     

Nitrogen remobilization in shoots of Paris polyphylla is altered by gibberellic acid application during senescence

Nitrogen remobilization during senescence has been studied in perennial herb Paris polyphylla. We analyzed changes in N content, amino acids, N-remobilization enzymes and effects of gibberellic acid (GA) during natural senescence. There was a gradual decrease in the contents of N, chlorophyll and soluble proteins and activities of glutamine synthetase (GS; EC 6.3.1.2) and glutamate dehydrogenase (GLDH; EC 1.4.1.2). Activity staining and Western blots showed that GS2 activity decreased, whereas GS1 activity was relatively stable over time. In contrast, the C/N ratio and total amino acid content increased. Among individual amino acids, the proportions of glutamine (Gln) and asparagine (Asn) increased, and proportions of arginine, aspartate and glycine decreased. Treatment with GA slowed the senescence and retarded decreases in the activities of GS and GLDH and the contents of N, chlorophyll and soluble proteins. Conversely, this treatment slowed increases in the C/N ratio, total free amino acid content, and proportions of Gln and Asn. We conclude that low N resorption efficiency during senescence of P. polyphylla results from a sharp decrease in N remobilization enzyme activity.     

Changes in the composition of xylem sap during development of the spadix of skunk cabbage (Symplocarpus foetidus)

The spadix of skunk cabbage, Symplocarpus foetidus, is thermogenic and maintains an internal temperature of around 20 degrees C even when the ambient air temperature drops below freezing. This homeothermic heat production is observed only during the stigma stage, and thereafter ceases at the male stage when pollen is shed. To clarify the regulatory mechanism by which the stigma stage-specific heat production occurs in the spadix, sugars, organic acids, and amino acids in xylem sap were analyzed and compared with those of post-thermogenic plants. Interestingly, no significant difference was observed in the total volume of xylem sap per fresh weight of the spadix between thermogenic (31.2+/-24.7 microl h(-1) g(-1)) and post-thermogenic (50.5+/-30.4 microl h(-1) g(-1)) plants. However, concentrations of sugars (sucrose, glucose, and fructose), organic acids (malate and succinate), and amino acids (Asp, Asn, Glu, Gln, Gly, and Ala) in xylem sap decreased remarkably in post-thermogenic plants. Our results indicate that the composition of the xylem sap differs during the development of the spadix of S. foetidus.     

Changes in the Composition of Xylem Sap during Development of the Spadix of Skunk Cabbage (Symplocarpus foetidus)

The spadix of skunk cabbage, Symplocarpus foetidus, is thermogenic and maintains an internal temperature of around 20 °C even when the ambient air temperature drops below freezing. This homeothermic heat production is observed only during the stigma stage, and thereafter ceases at the male stage when pollen is shed. To clarify the regulatory mechanism by which the stigma stage-specific heat production occurs in the spadix, sugars, organic acids, and amino acids in xylem sap were analyzed and compared with those of post-thermogenic plants. Interestingly, no significant difference was observed in the total volume of xylem sap per fresh weight of the spadix between thermogenic (31.2±24.7 μl h^?1g^?1) and post-thermogenic (50.5±30.4 μl h^?1g^?1) plants. However, concentrations of sugars (sucrose, glucose, and fructose), organic acids (malate and succinate), and amino acids (Asp, Asn, Glu, Gln, Gly, and Ala) in xylem sap decreased remarkably in post-thermogenic plants. Our results indicate that the composition of the xylem sap differs during the development of the spadix of S. foetidus.     

Induction of xylem sap methylglycine by a drought and rewatering treatment and its inhibitory effects on the growth and development of plant organs

In higher plants, the xylem vessels functionally connect the roots with the above-ground organs. The xylem sap transports various organic compounds, such as proteins and amino acids. We examined drought and rewatering-inducible changes in the amino acid composition of root xylem sap collected from Cucurbita maxima roots. The major free amino acids in C . maxima root xylem sap were methylglycine (MeGly; sarcosine) and glutamine (Gln), but MeGly was not detected in the xylem sap of cucumber. MeGly is an intermediate compound in the metabolism of trimethylglycine (TMG; betaine), but its physiological effects in plants are unknown. Drought and rewatering treatment resulted in an increase in the concentration of MeGly in root xylem sap to 2.5 m M . After flowering, the MeGly concentration in the xylem sap dropped significantly, whereas the concentration of Gln decreased only after fruit ripening. One milli molar MeGly inhibited the formation of adventitious roots and their elongation in C . maxima , but glycine, dimethylglycine, or TMG had no effect. Similar effects and the inhibition of stem elongation were observed in shoot cuttings of cucumber and Phaseolus angularis . These observations seem to imply a possible involvement of xylem sap MeGly in the physiological responses of C . maxima plants to drought stress.     

Extraction of tracheal sap from Citrus and analysis of its nitrogenous compounds

Tracheal sap was extracted from sections of stems (0.5 to 1.5 cm in diameter and 7.5 to 15.0 cm in length) of orange trees (Citrus sinensis (L.) Osbeck cv. Washington Navel) by using a combination of the vacuum and liquid displacement methods. The volume of sap obtained and its concentration of nitrogenous compounds were dependent on the volume of displacing liquid used for the extraction. Four ml of water-saturated 1-butanol extracted essentially all of the xylem fluid present in the stem sections without apparent production of artifacts. The time of sampling affected the nitrogen concentration of the tracheal sap, but not the content of xylem nitrogen per volume of stem material. The orientation of the stems in the tree and the diameter of the stems had an effect on their contents of xylem nitrogen, with southeastern orientation and thinner stems showing higher concentrations. We could not detect the presence of ammonium, nitrites or proteins in the tracheal sap of orange trees. Most of the nitrogen was present as amino acids and about 2% of the total in the form of nitrates. The qualitative composition of amino acids, as determined by TLC, was the same both in winter and spring tracheal sap. The main components of the sap were proline and arginine in winter, and these amino acids together with asparagine and aspartic acid in spring.     

A 15N Method to Quantify the Sources of Nitrogen for New Growth of Non-legumes, Examined using Kiwifruit

A new method is described for estimating the contributions ofnitrate-N, newly-reduced nitrate-N and remobilization of storednitrogen (N) for new growth of non-leguminous plants. Xylemsap is extracted from ¹⁵N-labelled and unlabelled plants. Nitrate-Nand amino-N in sap are separated using cation-exchange resinand analysed for ¹⁵N. Remobilization of stored N is estimatedusing [I-(¹⁵N enrichment of amino-N/¹⁵N enrichment of nitrate-N)]x amino-N. Newly-reduced nitrate-N is estimated by difference.Field-application of this method is described. Actinidia deliciosa, kiwifruit, nitrogen, ¹⁵N, remobilization, xylem sap, nitrate reduction     

Seasonal dynamics of major cations in xylem sap and needles of Norway spruce (Picea abies L. Karst.) in stands with different soil solution chemistry

Soil solution, xylem sap and needles of mature trees were sampled in three spruce stands over one vegetation period and analysed for major cations. Investigations of nutrient distribution between these three pools and evaluations of seasonal dynamics give the following results: The highest nutrient concentrations in the xylem sap occur at the time of bud break and become gradually lower during the vegetation period. The trees show similar trends of xylem sap concentrations with time for potassium, calcium and magnesium regardless of the nutritional status of the plots. No coupling of xylem sap to soil solution composition can be observed in spite of a high variability of soil solution chemistry in time. The major cations in the current needles exhibit a significantly different trend with time. No time-based correlations for nutrient contents could be found for the needles from the previous year.Despite mobilisation of storage pools in the deficient stand, trees are not able to increase the Ca and Mg contents in the needles up to the level of the other stands. Potassium could be retranslocated in sufficient extent for nutrition of current needles. Due to seasonal variability and dependence upon internal processes, such as retranslocation and mobilisation of nutrients, xylem sap does not seem to be a good tool for the estimation of the nutritional status of forest sites.It was concluded that only minor transport into new foliage via xylem sap will proceed after nutrient flush during the bud break and the nutrient content in the new biomass will be governed by dilution due to biomass growth or by nutrient transport by other means than xylem sap.