Movement of Nutrients in Radiata Pine Needles in Relation to the Growth of Shoots

The pattern of needle growth and the movement of mineral nutrients(nitrogen, phosphorus, potassium and calcium) in needles ofradiata pine (Pinus radiata D. Don) were studied from needleinitiation to 2 years of age. During this period, very prominentcyclic patterns of nutrient accumulation, retranslocation andreplenishment were observed for nitrogen, phosphorus and potassium,which highlighted the potential role of needles as a nutrientreserve for growth. Significant retranslocation occurred from very young needlesabout 3 months after initiation. The phases of retranslocationcoincided with new flushes of shoot growth, and the growth ofnew shoots on a branch resulted in nutrient withdrawal frompre-existing needles, regardless of needle age and season. Suchwithdrawal occurred even in fertilized and irrigated trees onhigh quality sites and under environmental conditions conducivefor nutrient uptake. At all times, except for the short periodafter initiation when needles were actively growing, the nutrientsin the needle were readily available for retranslocation. Contraryto the general view, retranslocation of nutrients was not necessarilyrelated to senescence and ageing of needles. Because new shoots are the primary ‘sinks’ for retranslocatednutrients, an ongoing competition between different parts ofa branch for internal nutrients can be envisaged, preferencebeing for the youngest shoot in the hierarchy. The relevanceof these results to our understanding of ‘optimum nutrition’of pine trees is discussed. Pinus radiata D. Don, radiata pine, mineral nutrition, retranslocation, phosphorus, nitrogen, shoot growth     

Growth and Nutrient Retranslocation in Needles of Radiata Pine in Relation to Nitrogen Supply

The effects of N application on tree growth and the retranslocationof N, P, and K from young needles to new growth were examinedin young radiata pine (Pinus radiata D. Don) trees. Nitrogen fertilization increased the number and size of needles,rates of shoot production, stem volume growth and tree biomass.Foliar N and P contents (µg per needle) fluctuated ina cyclic fashion with prominent phases of accumulation, retranslocationand replenishment. The patterns of these fluctuations in controland N-fertilized trees were similar, although the fluxes ofN, P and K in and out of needles were increased by N fertilization.Greater translocation (g per tree) of N and K from needles ofN fertilized trees occurred because fertilization increasedthe needle weight and the proportion of N and K retranslocatedfrom individual needles. Nitrogen fertilization increased theretranslocation of P largely as a result of higher needle mass.Trees supplied with more than adequate amounts of P in the soilretranslocated up to 58 per cent of the initial pool of P fromyoung needles. The periods of high retranslocation coincidedwith periods of high concentrations of soil mineral N and withshoot production. Conversely, the periods of rapid replenishmentof N and P into the needles coincided with the time of slowshoot growth and low concentration of soil mineral N. The growthrate of trees, rather than the availability of nutrients inthe soil was the main factor controlling retranslocation. For radiata pine, retranslocation from needles is not a mechanismspecific for coping with low soil fertility. It seems to bea mechanism which enhances the nutrient supply to apical growingpoints, especially during periods of flushing. Pinus radiata, nitrogen supply, shoot growth, nutrient fluctuations and retranslocation, nutrient use and adaptation     

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.     

Uncoupling of chlorophyll and nutrients in lakes – possible reasons,expected consequences

Total phosphorus and total nitrogen explained a low percentage of summer chlorophyll variability in epilimnia of the Great Masurian Lakes. Division of the whole data set into two subgroups of lakes improved approximation of the chlorophyll nutrient relationship but revealed also functional differences between the lakes distinguished in that way. Chlorophyll in eutrophic lakes correlated well with nitrogen and phosphorus, that in mesotrophic lakes (those with summer chlorophyll <=22 mg m^–3 as calculated in the model) was related to none of the nutrients. Higher summer chlorophyll content in epilimnetic waters was accompanied by higher chl:PP and chl:PN ratios. Algal adaptation to poor light conditions in eutrophic lakes is postulated as a possible reason for that difference.Chlorophyll – nutrient relationships varied with the trophic status of lakes. Epilimnetic chlorophyll strictly followed phosphorus changes in eutrophic lakes but did not do so in mesotrophic ones. Detailed comparison of selected meso- and eutrophic lakes showed marked differences in the seasonal changes of chlorophyll and nutrient concentrations and in sedimentation rates, especially in spring. Nutrient limitation rather than zooplankton grazing is suggested as a possible mechanism of controlling algal abundance and the sequence of spring events in a eutrophic lake. It is hypothesised that phosphorus turnover in eutrophic lakes is dominated by seasonal vertical fluxes, while in mesotrophic lakes it is more conservative with consumption and regeneration restricted mostly to metalimnion. Possible consequences of such conclusion are discussed in the paper.     

湖南省冷水江市大嵊山大气污染与马尾松衰亡

 作者对湖南省冷水江市大嵊山大气污染与马尾松衰亡进行了研究,研究结果表明大气综合污染指数在3个研究点上分别为1.00(对照)、1.76和2.23。而以林分密度、林分非衰亡率、针叶长度、针叶干重、马尾松平均高、平均胸径等因子计算出的林分外貌综合得分从173.9下降到143.5和132.5。在一年四季,马尾松针叶中叶绿素含量也是清洁区显著高于污染区,而叶绿素a／b值则是污染区的高,峰值较正常的提前。马尾松在受到大气污染作用后,针叶中营养元素含量呈下降趋势,尤其是氮。根据树干解析发现大气污染对马尾松高生长和胸径生长都具有抑制作用,但并不表现出同步效应,对高生长的抑制有一个滞后现象,时间在2～3年。另外,大气污染对马尾松的结果影响很大,污染区的马尾松单株拥有球果数仅为清洁的25％,用灰色系统理论对马尾松材积与相关影响因子进行关联度分析发现,材积与综合污染指数的倒数有很好的关联性,关联度达到了0.773。     

Seasonal ionic fluctuations and annual growth rates in stands of Pinus silvestris L. and Picea abies Karst. (L.)

Seasonal variations in potassium, calcium, nitrogen, phosphorus, and magnesium contents of needles from two different stands of Pinus silvestris L. and Picea abies (L.) Karst. were determined monthly during a period of two years, and the growth rates once a year during five years. The stands were growing on sand or on clay. The supposed transport of potassium to the shoot during autumn could not be demonstrated. The nutrient status of pine and spruce growing on sand and clay was very similar, except for calcium and magnesium. There were only small differences in ion contents between pine and spruce, except for calcium. On soils with low water-holding capacity, the available water in dry years is the limiting factor affecting the growth rate of spruce but not of pine. It is concluded that the nutrient status of the leaves, the growth rates and the available water in the soil are factors that should have an important part in any discussion of fertilization of coniferous forests.     

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.     

长白山阔叶红松林不同演替阶段林下红松幼苗能量与养分季节动态

为了解林下红松幼苗生长和养分存储季节动态,以长白山原始阔叶红松林(原始林)和次生杨桦林(次生林)林下2年生红松幼苗为对象,研究林下光合有效辐射(PAR)、幼苗生物量、非结构性碳水化合物(NSC)、全氮(N)和全磷(P)等指标的季节变化,分析两林分林下光照的季节动态及其差异对红松幼苗生长和养分积累的影响。结果表明: 原始林和次生林林下月PAR累积量季节变化都呈“双峰”型,夏季为郁闭期,两林分林下光线弱。春季和秋季为阔叶树无叶期,林下光照条件变好,且次生林林下光照明显好于原始林;原始林和次生林红松幼苗的生物量、NSC、全N和全P浓度的季节动态与林下光照的季节变化基本一致,在春季和秋季表现为显著增加,在夏季呈下降趋势。春季幼苗的淀粉浓度增加,夏季淀粉和可溶性糖浓度均逐渐降低,到8月达到最低值,秋季可溶性糖浓度显著升高。春季和秋季次生林林下幼苗的生物量和NSC浓度整体上均显著高于原始林,而夏季两林分差异不显著。因此,春季和秋季的林下光照条件差异是影响原始林和次生林中红松幼苗养分积累和生长更新差异的主要原因。     

Seasonal change in specific needle weight ofPinus thunbergii

To evaluate the reserve dynamics in pine needles, an index of specific needle weight (SNW; dry weight per unit length of needles) was provided. Developed needles ofPinus thunbergii did not show any additional elongation in their second year. Thus the seasonal change in SNW of developed needles was proved to indicate the dynamics of reserves in needles. SNW showed distinct seasonal change. It increased from autumn to carly spring, followed by a decrease by mid summer. This pattern of change was similar to the change in specific leaf weight (SLW) of evergreen broad leaves in temperate regions. It was concluded that the change in SNW indicated clearly the dynamics of reserves in needles, showing the accumulation in non-growth seasons and the consumption in subsequent growth seasons. The decrease in SNW during the growth season was 10–15% of the maximum found in early spring.     

Fractionated extraction and speciation of macronutrients from Scots pine and Norway spruce needles of different ages

Summary The relationship between proteins and the macroelements potassium, magnesium, calcium, sulphur and phosphorus was studied in homogenates of needles of different ages from Scots pine (Pinus sylvestris L.) and Norway spruce [Picea abies (L.) Karst.]. Complete extractions by acid digestion, protein extractions by a buffer-detergent and non-protein extractions by a buffer alone showed that most of the potassium and magnesium of the needles was soluble independent of the proteins. Only a minor part (50–60 ppm, dry weight) of the magnesium could be referred to the chlorophyll content of the needles. Both potassium and magnesium appeared independent of the protein gel filtration. This was also valid for the minor fraction of the total calcium content, which was extractable in a buffer. Heterogeneous calcium deposits are also suggested by extraction using a chelator (EGTA). Part of the buffer-soluble sulphur and phosphorus compounds occurred independently of solubilized proteins, and had complex distribution patterns after gel filtration, even outside the high molecular separation range. It is suggested that further analyses along the present lines, compared with conventional analyses on total extracts, may extend the usefulness of mineral nutrient analyses in plants.     

山东省台上金矿区赤松林叶绿素含量的季节动态

在1991年春、夏、秋三个季节对山东省招远市台上金矿区赤松林叶绿素含量的变化进行了测定,并与背景区作比较,对金矿区和背景区赤松针叶中的Au、Ag、Cu、Pb元素含量也进行了比较。金矿区和背景区Au、Ag、Cu、Pb元素含量有明显差异,金矿区高于背景区数倍,这对赤松的生长有一定影响,与叶绿素含量有一定的正相关;无论金矿区还是背景区,赤松一年生叶和二年生叶的叶绿素总量变化规律大体一致,都是春季较低,随气温上升而开始增加,至夏末达到最大值,然后从秋季开始下降,金矿区叶绿素总量低于背景区,一年生叶略高于二年生叶;当叶绿素总量变化时,叶绿素a/b的比率稍有波动,但几乎保持不变,金矿区和背景区也无差异。     

Increases in Phosphorus Requirements for CO(2)-Enriched Pine Species

Pinus radiata D. Don (half-sib families 20010 and 20062) and Pinus caribaea var hondurensis (an open-pollinated family) were grown for 49 weeks at seven levels of phosphorus and at CO₂ concentrations of either 340 or 660 microliters per liter, to establish if the phosphorus requirements differed between the CO₂ concentrations and if mycorrhizal associations were affected. When soil phosphorus availability was low, phosphorus uptake was increased by elevated CO₂. This may have been related to changes in mycorrhizal competition. When the phosphorus concentration in the youngest fully expanded needles was above 600 milligrams per kilogram the shoot weight of all pine families was greater at high CO₂ due to increases in rates of photosynthesis. More dry weight was partitioned to the stems of P. radiata family 20010 and P. caribaea. At foliar phosphorus concentrations above 1000 milligrams per kilogram (P. radiata) and 700 milligrams per kilogram (P. caribaea), growth did not increase at 340 microliters of CO₂ per liter. Soluble sugar levels in the same needles mirrored the growth response, but the starch concentration declined with increasing phosphorus. At 660 microliters of CO₂ per liter, shoot weight and soluble sugar concentrations were still increasing up to a foliar P concentration of 1800 milligrams per kilogram for P. radiata and 1600 milligrams per kilogram for P. caribaea. The starch concentrations did not decline. These results indicate that higher foliar phosphorus concentrations are required to realize the maximum growth potential of pines at elevated CO₂.     

Seasonal differences in green leaf breakdown and nutrient content of deciduous and evergreen tree species and grass in a granitic headwater stream

Litter processing was examined in autumn–winter and spring–summer in a second order stream in Galicia (NW Spain). We compared decay rate and nutrient dynamics of green leaves of several deciduous (riparian: Alnus glutinosa, Betula alba and Populus×canadensis; terrestrial: Castanea sativa, Quercus robur), and evergreen tree species (terrestrial: Pinus radiata and Eucalyptus nitens), in addition to ray-grass (Lolium perenne). In the autumn–winter period, the decay rates (–k) ranged between 0.0086 degree-days^–1 for poplar, and 0.0019 degree-days^–1 for birch leaves. Alder showed the most rapid breakdown in spring–summer (0.0124 degree-days^–1), and pine the slowest (0.0016 degree-days^–1). Deciduous species exhibited general higher processing rates than evergreen species and ray-grass. The initial nitrogen and phosphorus contents were higher in riparian species leaves and ray-grass, being higher in spring (2.28±0.14% and 0.24±0.04% of nitrogen and phosphorus, respectively) than in autumn (1.88±0.36% of nitrogen and 0.18±0.03% of phosphorus). A significant correlation coefficient was found only between mean nitrogen leaf packs contents during incubation and decay rates (r=0.61; p=0.012).In deciduous species, processing was faster during the spring–summer than in the autumn–winter period, which may be attributed to the greater nutritional value and less consistency of the leaves during this season. Within evergreen species, pine had a significantly faster processing rate in autumn, attributed in this study to greater physical fragmentation of the needles. Ray-grass and eucalyptus did not exhibit any seasonal differences in processing rate.During the spring–summer period, litterfall inputs are quantitatively less important than during the autumn–winter, but due to high retention and fast breakdown during the spring–summer, green inputs should contribute substantially to nutrient incorporation and cycling in benthic communities.     

Ribulose bisphosphate carboxylase, protein and nitrogen in Scots pine seedlings cultivated at different nutrient levels

Seedlings of Scots pine (Pinus sylvestris L.) of a northern provenance were cultivated in nutrient solution for 10 weeks in a climate chamber. The nutrient solution (renewed by solution exchange) contained 2.5, 10 or 50 mg N I^?1. All other essential elements were added in optimal proportion to the nitrogen. Seedlings cultivated at 10 and 50 mg N I^?1 were similar with respect to all characteristics studied. Seedlings cultivated at 2.5 mg N I^?1 showed a lower growth rate, especially for the shoot, and an altered morphology, with high root:shoot ratios and long, slender roots. The nitrogen concentrations in shoot and needles as well as in whole seedlings were not significantly affected by the nitrogen supply, while the nitrogen concentrations in the roots were somewhat lower at 2.5 mg N I^?1. Ribulose bisphosphate carboxylase (EC 4.1.1.39) activity and the concentrations of carboxylase, total and soluble protein and of chlorophyll in the needles were consistently much lower for seedlings cultivated at 2.5 mg N I^?1, than for seedlings grown at higher nutrient levels. A close correlation was observed between activity and concentration of the carboxylase (r=0.95). Carboxylase activity and protein were more sensitive to a low nutrient supply than was chlorophyll. The data show how activity and concentration of ribulose bisphosphate carboxylase and the concentrations of soluble and total protein and of chlorophyll in needles of pine seedlings can be negatively affected by the nutrient supply, also when the nitrogen concentrations in the needles are close to those observed at optimal nutrient supply. It is suggested that pine seedlings store assimilated non-protein nitrogen in the needles when protein synthesis is under restraint. The nitrogen concentration in needles and seedlings could not be used as a measure of the physiological state of the seedlings.     

Seasonal dynamics of shoot nutrients in Schoenus ferrugineus (Cyperaceae)

Seasonal patterns of biomass and standing stock (g m⁻²) of nitrogen, phosphorus, potassium and calcium were documented in Schoenus ferrugineus L. from an annually mowed calcareous fen in southern Germany. The peak standing crop of nitrogen, phosphorus and potassium occurred in mid-July. Prior to the end of the growing season, 44% of total potassium, 34% of total phosphorus and 28% of total nitrogen were retranslocated out of the shoots, based on differential nutrient losses between covered and uncovered plots. There is no evidence that any calcium was retranslocated, but 24% of peak calcium and 13% of potassium was leached from standing dead shoots. More than half of the peak phosphorus was found in the overwintering green shootbases. In the light of the low availability of nutrients in the soil, retranslocation of phosphorus in particular is essential, if adequate internal nutrient levels are to be maintained, despite various proposed uptake mechanisms.     

Seasonal patterns of nutrient deposition in a Quercus douglasii woodland in central California

The monthly deposition of total nitrogen, phosphorus, potassium, calcium and magnesium via canopy throughfall, and various components of the litterfall was measured for 31 months under mature Quercus douglasii and in the bulk precipitation in the surrounding open grassland. Seasonal patterns of nutrient concentration in leaf litter, throughfall, and precipitation were also measured. Total annual subcanopy deposition exceeded open precipitation deposition by approximately 45–60x for nitrogen, 5–15x for phosphorus, 30–35x for potassium, 25–35x for calcium, and 5–10x for magnesium. Total annual subcanopy deposition was low in comparison to other oak woodland sites reported in the literature. Throughfall and leaf litter were the primary sources of nutrients and thus determined the seasonal peaks of nutrient deposition. The first autumn rains and leaf fall were associated with one peak in nutrient deposition, and throughfall during early spring leaf emergence was associated with a second peak in potassium, magnesium and phosphorus. Non-leaf plant litter (excluding acorns) provided approximately 15–35% of most nutrients, with twigs and bark depositing over 12% of the annual calcium flux in 1987–1988, and flower litter depositing over 8% of the annual nitrogen flux in 1986–1987. Acorns had high concentrations of phosphorus and nitrogen and during the mast season of 1987–1988 they contained a large proportion of the total subcanopy annual flux of these elements. With acorns excluded, total annual nutrient deposition was similar between years, but timing of nutrient deposition differed. Late summer leaf fall associated with drought, variation in precipitation, and variation in deposition of non-leaf parts were associated with seasonal differences in nutrient deposition between years.     

Food reserves of Scots pine (Pinus sylvestris L.)

Summary The amounts of starch, soluble sugars, triacylglycerols, diacylglycerols and free fatty acids were studied in Scots pine (Pinus sylvestris L.) during an annual cycle in current-year needles and in 1-, 2- and 3-year-old needles collected shortly after bud break. Determination of the compounds was performed using specific enzymatic assays, capillary gas chromatography and thin layer chromatography. Newly emerging needles contained relatively large amounts of starch, but only trace amounts of fat. During autumn and winter, fat content rose, while starch content decreased; amounts of both these reserve materials were very high the next spring shortly before bud break and decreased again during shoot elongation. Concentration of intermediates in triacylglycerol biosynthesis (diacylglycerols and free fatty acids), were low in summer and high in winter. The same pattern was observed for fructose and glucose (the predominant soluble sugars), galactose/arabinose and raffinose/melibiose. In contrast, sucrose concentrations were highest in spring and in autumn. Mature needles of different ages collected in May showed significant differences only in their triacylglycerol and starch content. Concentration changes of reserve materials are discussed in relation to season, mobilization and translocation processes, dormancy, frost resistance and the possibility of carbohydrate-fat interconversions.     

Nutrient Relations of Groundsel (Senecio vulgaris) Infected by Rust (Puccinia lagenophorae) at a Range of Nutrient Concentrations I. Concentrations, Contents and Distribution of N, P and K

Groundsel (Senecio vulgaris L.), healthy or infected with therust fungus Puccinia lagenophorae was grown in sand and fedwith a complete nutrient medium diluted to give a range of concentrations.Analysis of bulked, dried tissues of the plant showed that undernutrient-rich conditions rust infection resulted in increasedconcentrations of total (Kjeldahl) nitrogen and potassium buthad little effect on phosphorus concentration. Thus, despitereduced dry weight growth, total plant nitrogen contents wereno less in rusted than control plants. Although total contentsof phosphorus and potassium were reduced by rust, effects wereprobably related to loss of these nutrients in fungal spores. Interactions between rust infection and nutrient supply weresignificant but differed between nutrients: rust caused increasednitrogen concentrations only under nutrient-rich conditionsbut increased phosphorus concentrations only when nutrient supplywas limited. Increased concentrations were not confined to infectedtissues. Mechanisms underlying rust-nutrient interactions appearto be complex and to depend inter alia on the partitioning andrecycling of the particular nutrient within the plant. Rust-inducedincreases in potassium concentration occurred under both highand low nutrient conditions but were confined to infected tissues.Potassium accumulation in nutrient deficient conditions wasprobably due to increased transpirational flux into infectedtissues, but under nutrient-rich conditions reduced potassiumexport appeared to assume greater significance. The possible implications of the changed nutrient relationsfor the wider interactions of rust-infected plants in naturalvegetation are discussed. Senecio vulgaris, Puccinia lagenophorae, rust infection, nutrient deficiency, nutrient content, nutrient concentration, nutrient distribution     

Relationships between phenology and the remobilization of nitrogen, phosphorus and potassium in branches of eight Mediterranean evergreens

Few studies have examined the effects of plant growth on nutrient remobilization in phenologically contrasting species. Here we evaluated the consequences of above-ground seasonality of growth and leaf shedding on the remobilization of nutrients from branches in eight evergreen Mediterranean phanaerophytes that differ widely in phenology. Vegetative growth, flower bud formation, flowering, fruiting, leaf shedding, and the variations in nitrogen (N), phosphorus (P) and potassium (K) pools in branches throughout the year were monitored in each species. Nitrogen and P remobilization occurred in summer, after vegetative growth and synchronously with leaf shedding. Despite the time-lag between growth and remobilization, the branches that invested more nutrients in vegetative growth also remobilized more nutrients from their old organs. Potassium remobilization peaked in the climatically harshest periods, and appears to be related to osmotic requirements. We conclude that N and P remobilization occurs mainly associated with leaf senescence, which might be triggered by factors such as the replenishment of nutrient reserves in woody organs, the hormonal relations between new and old leaves, or the constraints that summer drought poses on the amount of leaf area per branch in summer.     

Seasonal Fluctuations of Ascorbate-Related Enzymes: Acute and Delayed Effects of Late Frost in Spring on Antioxidative Systems in Needles of Norway Spruce (Picea abies L.)

Seasonal changes of ascorbate peroxidase and monodehydroascorbateradical reductase activities were studied in foliar tissuesof Norway spruce (Picea abies L.). In mature needles, APX activitiesdid not show seasonal fluctuations and were similar to thosefound in resting buds. Monodehydroascorbate radical reductaseactivity was higher in needles than in buds and higher in winterthan in summer. Maximum activities of both enzymes were foundbefore bud break and minimum activities in newly formed needles.When spruce seedlings were exposed to an artifical frost eventof –5°C for one night in spring, ascorbate peroxidaseactivity declined in young needles before the onset of visibleinjury but corresponding to a sudden upsurge in lipid peroxidation.After one week, some shoots showed severe symptoms of injury,some were slightly injured and others did not show any visibleinjury. In lethally injured needles, antioxidative protection(ascorbate peroxidase, monodehydroascorbate radical reductase,glutathione reductase, glutathione, ascorbate, superoxide dismutase)had collapsed. Surviving needles showed a coordinated increasein all components of the antioxidative system suggesting anefficient induction of defense systems. However, enhanced protectionwas observed only transiently. In fall, needles that had beenexposed to frost in spring contained significantly less antioxidantsthan unstressed needles indicating that unseasonal frost causedmemory effects. (Received September 16, 1995; Accepted May 28, 1996)