The Utilization of Carbohydrate and Nitrogen Reserves by Taxus During Its Spring Growth Period

The spring growth and the utilization of carbohydrate and nitrogen reserves in this growth was studied in Taxus media cv. Hicksii plants 0, 2, 4 and 6 weeks after the plants started growing in the spring. The effect of nitrogen applied the previous season on the storage and utilization of the carbohydrate and nitrogen reserves during spring growth was determined. The plants were separated into buds (all new growth), stems, needles (those produced the previous season) and roots and analyzed for changes in total nitrogen, basic and non-basic amino acids, total available carbohydrate, sugars, hemicelluloses, organic acids and chlorophyll. The bulk of the soluble nitrogen reserves were stored as arginine in the stems and old needles. With the onset of spring growth, arginine nitrogen was converted to other amino acids which accumulated in the new growth (buds). The roots, stems and needles of plants grown under high nitrogen levels always contained more total nitrogen than those grown under low nitrogen levels. The bulk of the carbohydrate reserves were stored as hemicelluloses. The plants grown under high nitrogen levels utilized the bulk of the carbohydrate reserves from the roots and smaller amounts from the stems and old needles, while plants grown under low nitrogen levels used only the reserves in the roots. In the low nitrogen plants, carbohydrates accumulated in the needles and stems. Both the carbohydrate and nitrogen reserves were important in the dry weight increase due to spring growth. However, the nitrogen reserves were the limiting factor and the high nitrogen plants grew twice as much, produced more chlorophyll, and utilized more nitrogen and carbohydrate reserve in spring growth than low nitrogen plants. The additional chlorophyll allowed the production of more carbohydrates and these additional carbohydrates were used in increased growth rates, while in the low nitrogen plants the carbohydrate produced was less and accumulated within the plant.     

The Utilization of Carbohydrate and Nitrogen Reserves in the Spring Growth of Lilac

The spring flush of growth and the utilization of reserve materials in this growth was studied in lilac plants 0, 2, 4 and 6 weeks after bud break. The influence of nitrogen applied the previous season on the storage and utilization of carbohydrate and nitrogen reserves was determined. The plants were separated into buds, stems and roots and analyzed for changes in total available carbohydrates, sugars, hemi-celluloses, total nitrogen, basic and non-basic amino acids and organic acids. The bulk of the carbohydrate reserves occurred as soluble sugars in the roots, although the reserves of sugars and hemicellulose in the stem was important during the first two weeks after bud break. The bulk of the nitrogen reserves were stored as non-basic amino acids in the stems and roots. However, the roots of plants grown under high nitrogen levels contained twice us much total nitrogen as roots grown under low nitrogen. This additional nitrogen which was stored in the roots of high nitrogen plants was released as arginine. The dry weight of buds increased 3–10 fold during the initial two week period and during the next four weeks doubled again. This bud growth was correlated with the stored nitrogen reserves. The high nitrogen plants grew twice as much and utilized more of the reserve carbohydrates in spring growth than low nitrogen plants. Carbohydrates were synthesized in this new growth and the high nitrogen plants utilized this carbohydrate for additional growth while low nitrogen plants transported it to the stems and roots.     

Free amino acids and total nitrogen during shoot development in Scots pine seedlings

The concentration of free amino acids and total nitrogen was studied in needles, stems and roots of seedlings of Pinus sylvestris L. for five weeks during the second growth period ("summer"). In one group of seedlings the source/sink relation was disturbed through removal of the terminal buds. The seedlings were cultivated in artificial year-cycles in a climate chamber.
Total nitrogen increased in needles and sterns of intact seedlings in the beginning of the "summer" and decreased during shoot growth. In seedlings, from which the buds had been removed, nitrogen remained at high levels in the primary needles and accumulated in steins and roots. The results are consistent with utilization of nitrogen in older needles and in the stem during shoot elongation.
The pool of free amino acids increased in the beginning of the "summer" and decreased after bud break in primary needles, stems and roots. Arginine and glutamine, in the roots also asparagine, were the dominating amino acids (amides included). Together, these compounds (plus glutamate and aspartate) contributed about 90% of the nitrogen in the amino acid pool in all organs. In primary needles and in the stem, arginine predominated at the end of hardening (75–85% of the amino acid nitrogen). Free amino acids contributed at most ca 10% of the total nitrogen in primary needles, where the ratio of free amino acid nitrogen: total nitrogen was highest at the end of dormancy and in the early "summer". Free amino acids accumulated after bud removal in primary needles and especially in stems and roots. Glutamine became relatively more dominant than arginine in the different organs.
The observations are consistent with the role of arginine and glutamine for storage and transport of nitrogen in conifers. Because of the low concentrations of amino acid nitrogen in the primary needles, arginine is not considered a major nitrogen reserve in needles of Scots pine seedlings.     

Effects of aluminium and pH on growth and potassium uptake by three ectomycorrhizal fungi in liquid culture

Clonal plants of white clover (Trifolium repens L.) were grown in a controlled environment with either low or high rates of applied nitrate-N (providing, notionally, insufficient or sufficient N for unrestricted growth), or in the absence of applied N. Plants receiving no nitrate-N were inoculated with Rhizobia and fixed their own N₂. All plants were maintained with a maximum of three fully unfolded leaves per apex (lenient defoliation) until day 68 when half of the plants were severely defoliated. The export and translocation of carbohydrates from the first fully unfolded main stolon leaf was measured three days later using ¹⁴C.Reduced carbon translocation to stolon tissue and roots, and increased translocation to young branches, occurred following severe defoliation in all three nitrogen treatments. However, N-deficient plants showed large reductions in total export of carbohydrates (44 vs. 17% of ¹⁴C assimilated for lenient vs. severe defoliation) whereas N-sufficient plants (either receiving nitrate-N or fixing their own N₂) showed small increases in total export (means of 54% vs. 62% in the respective defoliation treatments). Furthermore, carbohydrate translocation to old branches ceased altogether in severely defoliated, N-deficient plants, but increased in severely defoliated, N-sufficient plants, illustrating that plant responses to multiple-factor stresses may differ greatly from those seen as the result of single-factor stresses. Interactions between nitrogen nutrition and defoliation in total carbohydrate export, and in carbohydrate supply to old branches, could have serious negative effects on the short-term C economy and physiological integration, and hence on the adaptability, of clonal plants growing with a mineral deficiency in the presence of grazing animals.     

Seasonal Changes in Respiration, Photosynthesis, and Translocation of the 14C Labelled Products of Photosynthesis in Young Pinus strobus L. Plants

Three-year-old Pinus strobus plants, grown under conditionsof either high or low light intensities, were brought from thenursery to the laboratory every three to four weeks from themiddle of April 1961 until January 1962. Translocation, measuredas the amount of ¹⁴C recovered from the roots at the end ofseven hours of illumination following exposure of the shootto ¹⁴CO₂, was found to be high in the spring, dropping to negligibleamounts during June and July, increasing again in the autumnand declining after October. Seasonal variation in root respirationwas found to parallel that of translocation. Rates of apparentphotosynthesis were low during the spring, rising to a maximumduring September, and then declining over the winter. The respiration,photosynthesis, and translocation of the low-light grown plantsfollowed a similar pattern to those grown in high-light, exceptthat in general rates were of a lower order. In the high-light grown plants more than 90 per cent of theabsorbed carbon was present in the ethanol-soluble form, ofwhich sugars formed at least 90 per cent. This was even morepronounced in the case of low-light grown plants. The main sugarwas always sucrose. The raffinose content was found to decreaseduring the warmer months. The new needles, during their period of maximum growth, fixedcarbon dioxide photosynthetically at a rate comparable to thatof the old needles. The new stems also possessed a relativelyhigh carbon dioxide fixing ability. Shoot growth, as measured by the increase in length of the newleader stem and new needles, showed the typical patterns forpine species.     

Effect of Carbohydrate Demand on the Remobilization of Starch in Stolons and Roots of White Clover (Trifolium repens L.) after Defoliation

White clover plants were grown from stolon tips in growth cabinetsand then defoliated. Thereafter, changes in the contents ofnon-structural carbohydrates such as starch, sucrose, glucose,fructose, maltose, and pinitol in stolons and roots were monitored.Initial contents of carbohydrate reserves, photosynthetic supplyof new carbohydrates and carbohydrate demand after defoliationwere varied by growing the plants at various CO₂ partial pressures,by varying the extent of defoliation and by removing eitherroots or stolon tips at the time of defoliation. Remobilization of carbohydrate reserves in stolons increasedproportionally to their initial contents and was greater whenplants had been severely defoliated, suggesting that carbohydrateswere remobilized according to availability and demand. Starchwas the predominant reserve carbohydrate. Starch degradationwas associated with decreased contents of sucrose, glucose andfructose in young stolon parts and roots but not in old stolonparts suggesting that starch degradation was not strictly controlledby the contents of these sugars. A decrease in the demand forcarbohydrates by removal of roots did not decrease starch degradationbut increased the contents of sucrose, glucose, and fructose.Removal of stolon tips decreased starch degradation and contentsof sucrose, glucose, and fructose. The results suggest thatstarch degradation was controlled by a factor other than sucrose,glucose, and fructose which was exported from stolon tips, e.g.gibberellin. Key words: White clover, storage carbohydrates, remobilization, regrowth     

Do warmer growing seasons ameliorate the recovery of mountain birches after winter moth outbreak?

Subarctic mountain birch (Betula pubescens ssp. czerepanovii) forests in northern Fennoscandia have shown a slight recovery from recent severe defoliation by the winter moth (Operophtera brumata). This development in trees is hypothesized to be a result of ameliorated growing conditions through increased summer temperatures. We examined if accumulated thermal sum affects the ability of mountain birches to tolerate foliage losses. We quantified the number of leaf-bearing short shoots, the emergence of inflorescences and the seasonal height growth of long shoots in both intact and defoliated trees. We also determined the concentrations of carbon and nitrogen in leaves and carbohydrates in roots. Our results show that defoliation constrained the growth of long shoots, as well as the emergence of inflorescences regardless of thermal sum accumulation. However, the number of leaf-bearing short shoots did not differ between intact and defoliated trees. In the both tree groups, the amounts of emerging leaves increased as a response to thermal sum accumulation. Also the leaf carbon concentration increased in defoliated trees at higher thermal sums, whereas it decreased in intact controls. Generally, the mean carbohydrate concentrations were greater in roots of defoliated than intact trees. However, with increased thermal sums, root carbohydrates increased in intact trees but remained the same in defoliated trees. We conclude that thermal sum accumulation does not greatly promote the recovery of mountain birches. Although the damaged trees produced more leaves at warmer growing sites, this did not increase their height growth or carbohydrate gain in roots.     

The Influence of Removing Tubers on Dry-matter Production and Net Assimilation Rate of Potato Plants

To study the effect of removing tubers on growth and net assimilationrate (E) of potato, plants were grown in pots partly filledwith soil with the shoot growing through a polythene cover.Tubers developed in the space between the cover and the soilsurface. Removing tubers immediately they began to form had little effecton E at the beginning of the experiment but later greatly reducedit. Shading reduced E more at the beginning of the experimentthan later. Removing tubers decreased total dry weight, butmuch of the material that would have moved to tubers accumulatedin leaves and stems. In intact plants the loss of weight byshading was mainly from the tubers; in plants without tubersit was mainly from stems and leaves. Removing tubers increasedleaves on lateral stems. Increasing the amount of nitrogen supplieddiminished the effect on E of removing tubers, presumably becausethe extra allowed other sinks for carbohydrate to develop. Thegrowth of some buds of the potato plant is so strongly inhibitedthat they cannot grow and act as sinks for excess carbohydratewhen tubers are removed. Such internal inhibition of growthmay sometimes suffice to influence the magnitude of E of normalplants. Removing tubers usually increased sugar and starch contentand protein N content of stems and leaves.     

Changes of carbon and nitrogen metabolites in white spruce (Picea glauca [Moench] Voss) of contrasted growth phenotypes

The present study documents the changes occurring at the biochemical level in white spruce trees (Picea glauca [Moench] Voss) with contrasted growth phenotypes during the summer period. Full-siblings of tall versus small spruces were grown under controlled conditions at constant day/night temperatures (24/15°C) and exposed to a decreasing photoperiod (15.7–12.2 h) simulating natural photoperiod reduction during the summer in eastern Canada. Growth parameters (stem height and tree biomass) were determined and non structural carbohydrates, soluble proteins and amino acids were quantified in current-year needles and stem, oldest stem and roots from mid-July until the end of September 2006. Sucrose was the main soluble sugar found in all organs, but its concentrations did not significantly change during the summer. In contrast, starch concentrations rapidly declined by the end of the experiment, especially in needles and stems. Both sucrose and starch did not generally differ between growth phenotypes. Total soluble protein significantly accumulated by mid-August (14.4 h of photoperiod) in small trees. Arginine and glutamine were the most abundant amino acids found in spruce organs, and their concentrations strongly increased at 14.4 h of photoperiod, especially in small trees. Our results highlight marked differences in nitrogen metabolism in late summer between contrasted growth phenotypes, especially for arginine, an amino acid typically associated with growth arrest and nitrogen reserve in perennial species. They also reveal that old stems and roots are important storage organs of organic reserves.     

The effects of clipping and fertilization on nitrogen nutrition and allocation by mycorrhizal and nonmycorrhizal Panicum coloratum L., a C4 grass

Summary Mycorrhizal and nonmycorrhizal plants of Panicum coloratum L. were grown in a factorial treatment design under two nitrogen levels and two clipping heights with an unclipped control. The nitrogen concentration in different plant components was determined following 9 weeks of growth under experimental conditions. Mycorrhizal infection increased green leaf and sheath nitrogen concentration by a relatively small, but significant percentage and had no effect on nitrogen allocation to the various plant components. Clipping increased leaf nitrogen concentration but inhibited growth to the extent that, when compared with the unclipped controls, less nitrogen remained in residual plant biomass with up to half of the total nitrogen allocated to offtake (the material removed by clipping). Plants receiving the higher nitrogen fertilization had higher tissue concentration of N and more N allocated to above-ground living tissues. Mycorrhizal infection interacted with clipping height and also with N availability significantly. Infection was unable to ameliorate the negative effects of the most severe clipping regime and of the low nitrogen availability on leaf and sheath N content. This is possibly due to mycorrhizal demand for carbohydrates competing with the carbohydrate requirement of roots for nitrogen uptake.     

Effect of nitrogen nutrition on the carbohydrate repression of photosynthesis in leaves of Phaseolus vulgaris L.

When carbohydrates accumulate in leaves, photosynthesis is repressed. Limited nitrogen nutrition is thought to enhance this repressing effect. However, the interaction between carbohydrate and nitrogen limitation in leaf photosynthesis has not been examined intensively. In this study, we grew Phaseolus vulgaris L. plants at three different nitrogen levels, and examined the effects of sucrose feeding to the roots on the nitrogen content, carbohydrate content and photosynthetic properties of the primary leaves. Nitrogen content and photosynthetic rate were lower and the carbohydrate content was greater in plants grown with limited nitrogen than in well-fertilized plants. Sucrose feeding to the plants increased carbohydrate content and decreased photosynthetic rate and nitrogen content. The increase in carbohydrate content and the decreases in nitrogen content and photosynthetic rate occurred at the same time, and the negative relationship between the carbohydrate content and photosynthetic rate did not differ among nitrogen nutrition levels. These results show that carbohydrate accumulation in the leaves leads to a decrease in photosynthetic rate. At low nitrogen nutrition levels, carbohydrates accumulated markedly, which accelerated this effect. It appears that the nitrogen nutrition level influences leaf photosynthesis through changing the carbohydrate level rather than through modifying sensitivity of the leaf to the carbohydrate level.     

Photosynthesis and assimilate partitioning between carbohydrates and isoprenoid products in vegetatively active and dormant guayule: physiological and environmental constraints on rubber accumulation in a semiarid shrub

The stems and roots of the semiarid shrub guayule, Parthenium argentatum, contain a significant amount of natural rubber. Rubber accumulates in guayule when plants are vegetatively and reproductively dormant, complicating the relationship between growth/reproduction and product synthesis. To evaluate the factors regulating the partitioning of carbon to rubber, carbon assimilation and partitioning were measured in guayule plants that were grown under simulated summer‐ and winter‐like conditions and under winter‐like conditions with CO₂ enrichment. These conditions were used to induce vegetatively active and dormant states and to increase the source strength of vegetatively dormant plants, respectively. Rates of CO₂ assimilation, measured under growth temperatures and CO₂, were similar for plants grown under summer‐ and winter‐like conditions, but were higher with elevated CO₂. After 5 months, plants grown under summer‐like conditions had the greatest aboveground biomass, but the lowest levels of non‐structural carbohydrates and rubber. In contrast, the amount of resin in the stems was similar under all growth conditions. Emission of biogenic volatile compounds was more than three‐fold higher in plants grown under summer‐ compared with winter‐like conditions. Taken together, the results show that guayule plants maintain a high rate of photosynthesis and accumulate non‐structural carbohydrates and rubber in the vegetatively dormant state, but emit volatile compounds at a lower rate when compared with more vegetatively active plants. Enrichment with CO₂ in the vegetatively dormant state increased carbohydrate content but not the amount of rubber, suggesting that partitioning of assimilate to rubber is limited by sink strength in guayule.     

Carbohydrate sources and sinks in woody plants

Each perennial woody plant is a highly integrated system of competing carbohydrate sinks (utilization sites). Internal competition for carbohydrates is shown by changes in rates of carbohydrate movement from sources to sinks and reversals in direction of carbohydrate transport as the relative sink strengths of various organs change. Most carbohydrates are produced in foliage leaves but some are synthesized in cotyledons, hypocotyls, buds, twigs, stems, flowers, fruits, and strobili. Although the bulk of the carbohydrate pool moves to sinks through the phloem, some carbohydrates are obtained by sinks from the xylem sap. Sugars are actively accumulated in the phloem and move passively to sinks along a concentration gradient. The dry weight of a mature woody plant represents only a small proportion of the photosynthate it produced. This discrepancy results not only from consumption of plant tissues by herbivores and shedding of plant parts, but also from depletion of carbohydrates by respiration, leaching, exudation, secretion, translocation to other plants through root grafts and mycorrhizae and losses to parasites. Large spatial and temporal variations occur in the use of reserve- and currently produced carbohydrates in metabolism and growth of shoots, stems, roots, and reproductive structures. A portion of the carbohydrate pool is diverted for production of chemicals involved in defense against fungi, herbivores, and competing plants. Woody plants accumulate carbohydrates during periods of excess production and deplete carbohydrates when the rate of utilization exceeds the rate of production. Stored carbohydrates play an important role in metabolism, growth, defense, cold hardiness, and postponement or prevention of plant mortality.     

Coping with herbivory: Photosynthetic capacity and resource allocation in two semiarid Agropyron bunchgrasses

Summary Agropyron desertorum, a grazing-tolerant bunchgrass introduced to the western U.S. from Eurasia, and Agropyron spicatum, a grazing-sensitive bunchgrass native to North America, were examined in the field for photosynthetic capacity, growth, resource allocation, and tiller dynamics. These observations allowed identification of physiological characteristics that may contribute to grazing tolerance in semiarid environments. A uniform matrix of sagebrush, Artemisia tridentata, provided an ecologically relevant competitive environment for both bunch-grass species. Physiological activity, growth, and allocation were also followed during recovery from a severe defoliation treatment and were correlated with tiller dynamics.Potential photosynthetic carbon uptake of both species was dominated by stems and leaf sheaths during June, when maximum uptake rates occurred. For both species, water use efficiency of stems and sheaths was similar to that of leaf blades, but nitrogen investment per photosynthetic surface area was less than in blades. In addition, soluble carbohydrates in stems and sheaths of both species constituted the major labile carbon pools in control plants. Contrary to current theory, these findings suggest that culms from which leaf blades have been removed should be of considerable value to defoliated bunchgrasses, and in the case of partial defoliation could provide important supplies of organic nutrients for regrowth. These interpretations, based on total pool sizes, differ markedly from previous interpretations based on carbohydrate concentrations alone, which suggested that crowns contain large carbohydrate reserves. In this study, crowns of both species contained a minor component of the total plant carbohydrate pool.Following defoliation, A. desertorum plants rapidly reestablished a canopy with 3 to 5 times the photosynthetic surface of A. spicatum plants. This difference was primarily due to the greater number of quickly growing new tillers produced following defoliation. Agropyron spicatum produced few new tillers following defoliation despite adequate moisture, and carbohydrate pools that were equivalent to those in A. desertorum.Leaf blades of regrowing tillers had higher photosynthetic capacity than blades on unclipped plants of both species, but the relative increase, considered on a unit mass, area, or nitrogen basis, was greater for A. desertorum than for A. spicatum. Agropyron desertorum also had lower investment of nitrogen and biomass per unit area of photosynthetic tissues, more tillers and leaves per bunch, and shorter lived stems, all of which can contribute to greater tolerance of partial defoliation.Greater flexibility of resource allocation following defoliation was demonstrated by A. desertorum for both nitrogen and carbohydrates. Relatively more allocation to the shoot system and curtailed root growth in A. desertorum resulted in more rapid approach to the preclipping balance between the root and shoot systems, whereas root growth in A. spicatum continued unabated following defoliation. Nitrogen required for regrowth in both species was apparently supplied by uptake rather than reserve depletion. Carbohydrate pools in the shoot system of both species remained very low following severe defoliation and were approximately equivalent to carbon fixed in one day by photosynthesis of the whole canopy.Dedicated to Drs. Michael Evenari and Konrad Springer     

Total nitrogen and free amino acids in Morus alba stems from autumn through spring

During leaf senescence and abscission, total nitrogen in leaves of mulberry ( Morus alba L. ev. Shin-ichinose) declined substantially whereas total nitrogen in buds, bark and stem wood increased markedly, suggesting translocation of nitrogen from senescent leaves in the autumn. After leaf abscission the winter buds and stems remained almost unchanged with respect to fresh and dry weight and total nitrogen until bud break in spring. In burst buds these parameters then increased drastically during the new growth while they decreased markedly in stems. Free arginine in the stem bark accumulated in parallel with the accumulation of total nitrogen in buds and stems in the autumn. Accumulation of proline in the wood, bark and buds also started in October but continued even after leaf-fall, increasing until mid-January (wood), mid-February (bark) and the new growth (buds). Prior to and in the early stage of bud break, proline in bark and wood decreased significantly and arginine in stem bark decreased slightly. Simultaneously, proline and arginine in the dormancy-releasing buds and asparagine, aspartic acid and glutamic acid in the buds and stems increased appreciably, suggesting that this increase in free amino acids was mainly derived from free amino acids (proline and arginine) stored in stems. The resulting marked decrease in total nitrogen and the drastic increase in asparagine in the stems and sprouting buds/new shoots were primarily due to a breakdown of protein stored in stems.     

Performance of the green spruce aphid, Elatobium abietinum (Walker) on previously defoliated Sitka spruce

Abstract 1 The green spruce aphid, Elatobium abietinum, is an important defoliator of Sitka spruce in the U.K. However, it is usual for years in which high E. abietinum populations occur to be followed by a year with low aphid densities. The possibility that the performance of E. abietinum is reduced on previously infested Sitka spruce, and that this is the cause of year‐to‐year fluctuations in population density, was investigated by comparing population development and the growth rate of individual aphids on experimentally defoliated trees. 2 Separate experiments were performed to determine whether aphid performance was reduced either in the autumn immediately after defoliation in the spring, or was reduced in the spring of the next year. Different rates of initial defoliation on trees used to test aphid performance were created by artificially infesting the trees with aphids in the spring before the experiments, and varying the time of infestation. 3 Population development and the mean relative growth rate (MRGR) of individual aphids on previously defoliated and undefoliated Sitka spruce did not differ significantly in the spring of the next year. No differences were observed in the nutrient content of the 1‐year‐old needles of previously defoliated or undefoliated trees at this time. 4 In the autumn and winter immediately after spring defoliation, aphid MRGR was significantly higher on trees that had been heavily defoliated earlier in the season compared with trees that had been lightly defoliated. However, the difference in MRGR decreased over the winter period. Nitrogen, phosphorous and potassium concentrations were 9.4–12.2% higher, at the beginning of the autumn, in the current year needles of heavily defoliated trees than in the current year needles of lightly defoliated trees. 5 The experiments indicate that high populations of E. abietinum in the spring do not induce any defensive mechanisms in Sitka spruce that adversely affect subsequent generations of the aphid. By contrast, the results suggest that high spring densities of the aphid improve the nutritional quality of the current year's foliage for autumn generations.     

Carbon and nitrogen partitioning in the biennial monocarp Arctium tomentosum Mill

Summary Growth and nitrogen partitioning were investigated in the biennial monocarp Arctium tomentosum in the field, in plants growing at natural light conditions, in plants in which approximately half the leaf area was removed and in plants growing under 20% of incident irradiation. Growth quantities were derived from splined cubic polynomial exponential functions fitted to dry matter, leaf area and nitrogen data.Main emphasis was made to understanding of the significance of carbohydrate and nitrogen storage of a large tuber during a 2-years' life cycle, especially the effect of storage on biomass and seed yield in the second season. Biomass partitioning favours growth of leaves in the first year rosette stage. Roots store carbohydrates at a constant rate and increase storage of carbohydrates and nitrogen when the leaves decay at the end of the first season. In the second season the reallocation of carbohydrates from storage is relatively small, but reallocation of nitrogen is very large. Carbohydrate storage just primes the growth of the first leaves in the early growing season, nitrogen storage contributes 20% to the total nitrogen requirement during the 2nd season. The efficiency of carbohydrate storage for conversion into new biomass is about 40%. Nitrogen is reallocated 3 times in the second year, namely from the tuber to rosette leaves and further to flower stem leaves and eventually into seeds. The harvest index for nitrogen is 0.73, whereas for biomass it is only 0.19.     

Apical control of lateral bud development and shoot growth in mulberry (Morus alba)

Measurements of changes in the degree of dominance by upper laterals over lower ones in coppice shoots (1-year-old stems) of 12-year old low- pruned stumps of mulberry ( Morus alba L. cv. Shin-ichinose) were made by removal of upper stem sections (pruning) or of lateral buds (debudding.) before spring bud burst, as part of a study of the factors involved in dominance relationships between the developing buds and elongating shoots. Besides inhibition of lower laterals by the upper, leading shoots, there was evidence for mutual inhibition (competition) of neighboring laterals along the stem. Thus in stems in which every other bud, or 4 out of every 5 buds were removed, there was a delay in growth cessation of lower laterals and their greater elongation than in controls. Such competition was seen to exist even between the uppermost and sub-terminal laterals, since the former elongated more in the absence of the latter.
In contrast to high and middle pruned stems, the delay in sprouting of the buds in low-pruned stems resulted in limited elongation of the shoots from such buds. This inhibition was removed when all the stems on a stump were pruned to the same length, suggesting that it was associated with intact stems with actively growing laterals. Patterns of regrowth of the short shoots (lower laterals) after summer pruning (middle-pruned) depended on the extent of removal of other stems with vigorously growing, upper laterals. These results demonstrate that both acropetal and basipetal influences are important in bud and shoot dominance relationships.     

Metabolic changes associated with vernalization of wheat. I. Carbohydrate and nitrogen patterns

A spring wheat (Triticum aestivum) and an obligate winter wheat (Triticum compactum) variety were each grown for 5 weeks in controlled environments at 2° and 25°. The threshold for flower induction in the winter wheat was 4 to 5 weeks at 2°, whereas the spring wheat had no low temperature requirement for flowering. Changes in the levels of carbohydrate and nitrogen fractions in the wheat leaves were determined during their growth in the cold and warm environments. There was an enhanced accumulation of the 5 carbohydrate fractions in both wheat varieties grown at 2° compared to 25°. Highly significant differences in the levels of sucrose, oligosaccharides, and starch were found between the spring and winter varieties grown at 2°. The winter wheat seedlings grown at 2° accumulated much more of these carbohydrates than the corresponding spring wheat. The carbohydrate patterns in both varieties grown at 25° were nearly identical except for the final 2 weeks of growth.

The level of nitrogenous substances in the tissues grown at 2° was much higher than in the corresponding tissues grown at 25°. The only significant difference between the spring and winter varieties was in the soluble protein fraction. This fraction rose nearly 3-fold in the winter variety grown at 2°, whereas it remained nearly constant in the similarly grown spring wheat. Most of the changing chemical patterns observed in relation to the vernalization treatment appear to be metabolic alterations associated with low temperature rather than alterations directly related with the vernalization response.

     

Seasonal changes in the utilization and turnover of assimilation products in 8-year-old Scots pine (Pinus sylvestris L.) trees

Summary The present study aimed at a physiological understanding of the seasonal changes of the carbohydrate patterns and levels in the various tissues of 8-year-old Scots pine (Pinus sylvestris L.) trees growing under ambient climatic conditions in the botanical garden at Bayreuth. The photosynthates of selected twig sections were labelled by ¹⁴CO₂ fixation and after chase periods of 1 h up to 8 months, the distribution of radiocarbon in the whole trees was determined and the labelling of identified carbohydrates was compared with the levels of these compounds in the individual tissues. Bud break and sprouting in spring is exclusively supplied by the recent photosynthates of the previous year's needles. During summer assimilates of the old needles were utilized for secondary growth of the axial system while growth of the recent-year's shoots was supported by their own photosynthesis. In autumn, soluble carbohydrates were produced instead of starch, a major part of which in addition to recent photosynthates was utilized for root growth during the cold season. Another part of the autumnal storage material was incorporated into the cell walls of the latest xylem and phloem elements still in winter. A pronounced starch-oligosaccharide interconversion upon frost hardening, and its reversal in spring as has been described for deciduous trees, could not be observed. This was due to maintenance of photosynthetic capability even in the cold season and the replacement of consumed storage material especially in late winter and early spring by new photosynthates.