Mature Needles Research Articles

A small-scale RNA isolation protocol useful for high-throughput extractions from recalcitrant plants

Many plants indigenous to South Africa are rich in secondary and oxidizing compounds such as pigments, complex polysaccharides and polyphenols. This makes isolation of high quality RNA for analysis of gene expression difficult. Here we describe a cost-effective isolation protocol suitable for RNA extraction from recalcitrant plant species. This method uses small amounts of tissue, so is useful when material is limited, and is easy to process large numbers of samples at once. We have used the method successfully with mature leaves of Protea hybrid ‘Sylvia’, and species P. repens, Leucospermum hybrid ‘Succession’, resurrection plants Xerophyta humilis and Craterostigma pumilum, and mature needles of Pine (Pinus radiata). RNA was analyzed spectrophotometrically and was found to be of high purity with low levels of contaminating compounds. Electrophoretic analyses on denaturing formaldehyde agarose gels and an Agilent 2100 Bioanalyzer confirmed the presence of RNA of high integrity. This is the first description of plant RNA integrity number (RIN) values for these plants using the algorithm designed for analyses of plant RNA containing multiple ribosomal bands. The RNA could successfully be used for reverse transcription and gene amplification.

Concentração e retranslocação de nutrientes em acículas de <i>Pinus taeda </i>L.

Objetivou-se avaliar a concentração e retranslocação de nutrientes em acículas de Pinus taeda L.. O estudo foi realizado em dois povoamentos, um implantado em área de campo nativo e outro em área de segunda rotação, com mesma espécie e mesma idade (7,5 anos) no município de Cambará do Sul, RS. As acículas foram coletadas nas plantas nos quatro pontos ortogonais (sul, norte, leste e oeste), amostrando-se acículas jovens, maduras e senescentes. O material foi seco em estufa, moído e analisado quimicamente (macro e micronutrientes). As concentrações de N, P, K, B, Cu e Zn diminuíram, de Ca, Fe e Mn aumentaram e o Mg e S mantiveram-se constantes com o aumento da idade das acículas. A taxa de retranslocação (acícula senescente-nova) foi superior a 50% para a maioria dos nutrientes, com exceção ao Mn e Fe, que apresentaram efeito cumulativo e o Ca, usado como elemento referência pela sua baixa mobilidade.

A case of severe frost damage prior to budbreak in young conifers in Northeastern Ontario: Consequence of climate change?

In spring 2007, young planted and natural conifers suffered extensive needle and bud injury near Hearst and Kapuskasing in northeastern Ontario. Damage was observed on all species of conifers up to 20 years old and 8 m in height. Taller trees, especially those in the overstory, and young understory trees protected by a closed canopy had less damage. The damage was caused by earlier than normal loss of cold hardiness followed by late spring frosts according to damage observations, weather station data, and calculated thermal time requirements for budbreak and cold hardiness of conifers. During May 19 to 21, 2007, minimum temperatures were recorded between -8°C and -9°C, and before this period, temperatures were warm enough to induce early dehardening and loss of trees' cold hardiness. According to the historical weather data for Kapuskasing, estimated budbreak time has become earlier since 1918 and freezing temperatures during budbreak and shoot elongation (between growing degree days 100 and June 15) have become more frequent since 1980. If the trend towards earlier budbreak is due to climate change, then the type of frost damage we observed in northeastern Ontario in 2007 could become more common. We discuss implications of such events and suggest research needed to understand the risk of frost damage with climatic warming and to reduce damage. Key words: conifer frost damage, mature needle and bud (or needle/bud) mortality, early dehardening and budbreak (or dehardening/budbreak), climatic warming

Effect of bud burst forcing on transcript expression of selected genes in needles of Norway spruce during autumn

Expression of selected genes in needles of Norway spruce (Picea abies [L.] Karst) was investigated by following their transcription levels during late autumn. Transcription was assessed in mature needles which likely serve as sensor of environmental cues that enable trees in the temperate and boreal regions to change between stages of growth, frost tolerance and bud dormancy. Samples were collected from grafts kept under outdoor conditions and after bud burst forcing in greenhouse at 20 degrees C (12 h darkness) for one week. Transcription was assayed with real-time RT-PCR. During the sampling period, chilling requirement was partially fulfilled, and time to bud burst after forcing was decreased. Of the 27 transcripts studied, expression of 16 was significantly affected either by forcing, sampling time, or interaction between them. PaSAP, PaACP, PaSGS3, PaWRKY, PaDIR9, PaCCCH and dehydrin genes responded drastically to forcing temperatures at all sampling points, showing no correlation with readiness for bud burst. Expression patterns of some vernalization pathway gene homologs PaVIN3, and also of PaMDC, PaLOV1 and PaDAL3 had a clear opposite trends between forcing and outdoor conditions, which could imply their role in chilling accumulation and bud burst regulation/cold acclimation. These genes could constitute putative candidates for further detailed study, whose regulation in needles may be involved in preparation towards bud burst and chilling accumulation sensing.

Isotopic studies of leaf water. Part 2: Between-age isotopic variations in pine needles

We studied between-age oxygen and hydrogen isotopic variations of two pine species, red pine ( Pinus resinosa Ait) and white pine ( Pinus strobus L.), with particular attention paid to variations associated with needle maturity. The 2D model by Shu et al. (this volume) was applied to simulate oxygen isotopic ratios of the pine needles; calculated results were compared with data collected from trees in the Hanover, NH area. The calculations indicate that the mechanism most responsible for age-dependent isotopic variations is the variation in transpiration rate along the needle. Because stomata mature progressively from needle tip to needle base, young needles transpire most of their water near the tip. Mature needles, on the other hand, transpire water more evenly along their lengths. We cannot successfully simulate hydrogen isotopic variations, and it remains to be investigated what mechanism or physical process is not included in the model that affects hydrogen isotopic compositions in leaf water.

Effects of clear-cutting and soil preparation on natural 15N abundance in the soil and needles of two boreal conifer tree species†

This study presents the impacts of clear-cutting and site preparation on soil and needle 15N-fractionation of Scots pine (Pinus sylvestris, L.) and Norway spruce (Picea abies (L.), Karst). Three microsites on different methods of site preparation were used: (i) mound (broken O/E/B horizons piled upside down over undisturbed humus), (ii) deep (exposed C-horizon) and (iii) shallow (exposed E/B horizon). We found significant differences between species, between closed forest and clear-cuts as well as between different site preparations. For instance, in the context of interspecific variations, the mean needle nitrogen concentrations of both seedlings (1.15,±0.10 %) and mature (1.09,±0.07 %) pine trees were significantly higher compared to corresponding needle concentrations of seedlings (0.88,±0.06 %) and mature trees (0.79,±0.02 %) of spruce. Similarly, we observed significantly more 15N-enriched needles of mature spruces (−4.0,±0.20 ‰) as well as of seedlings (−5.0,±0.11 ‰) relative to that of mature pine needles (−5.6,±0.10 ‰) and seedlings (−6.0,±0.31 ‰). These variations were assumed to be caused by the variation in mycorrhizal associations between the species. We assume that the proportion of mycorrhizal N-uptake of pines might have been larger than that of spruce. Regarding the clear-cut effects on N and 15N of both tree species, we observed that, in the mature natural stand, needle N concentrations of both pine (1.09,±0.07 %) and spruce (0.79,±0.02 %) tree species did not change significantly after clear-cutting (pine: 1.01,±0.06 %; spruce: 0.74,±0.04 % ). However, clear-cutting resulted in the significant increase in needle 15N natural abundance of both pine (−2.70,±0.06 ‰) and spruce (−2.09,±0.05 ‰) in comparison to that of natural stand (pine:−5.60,±0.10 ‰; spruce:−4.00,±0.20 ‰), which is assumed to be due to the increased level of nitrification and leaching of nitrate after clear-cutting. In the context of site preparation methods, soil and needle N were observed to be more 15N-enriched in deep and shallow treatment sites compared to that of closed forest site and untreated clear-cut site, which indicated that the main source of N uptake seems to be mainly directly from the soil of the corresponding horizons of mineral soil with higher δ15N. †Revised version of a paper presented at the VIII Isotope Workshop of the European Society for Isotope Research (ESIR), 25–30 June 2005, Leipzig-Halle, Germany

The bi-directional exchange of oxygenated VOCs between a loblolly pine (<I>Pinus taeda</I>) plantation and the atmosphere

Abstract. Using new in-situ field observations of the most abundant oxygenated VOCs (methanol, acetaldehyde, acetone, C3/C4 carbonyls, MVK+MAC and acetic acid) we were able to constrain emission and deposition patterns above and within a loblolly pine (Pinus taeda) plantation with a sweetgum (Liquidambar styraciflua) understory. During the day canopy scale measurements showed significant emission of methanol and acetone, while methyl vinyl ketone and methacrolein, acetaldehyde and acetic acid were mainly deposited during the day. All oxygenated compounds exhibited strong losses during the night that could not be explained by conventional dry deposition parameterizations. Accompanying leaf level measurements indicated substantial methanol and acetone emissions from loblolly pine. The exchange of acetaldehyde was more complex. Laboratory measurements made on loblolly pine needles indicated that acetaldehyde may be either emitted or taken up depending on ambient concentrations, with the compensation point increasing exponentially with temperature, and that mature needles tended to emit more acetaldehyde than younger needles. Canopy scale measurements suggested mostly deposition. Short-term (approx. 2 h) ozone fumigation in the laboratory had no detectable impact on post-exposure emissions of methanol and acetone, but decreased the exchange rates of acetaldehyde. The emission of a variety of oxygenated compounds (e.g. carbonyls and alcohols) was triggered or significantly enhanced during laboratory ozone fumigation experiments. These results suggest that higher ambient ozone levels in the future might enhance the biogenic contribution of some oxygenated compounds. Those with sufficiently low vapor pressures may potentially influence secondary organic aerosol growth. Compounds recently hypothesized to be primarily produced in the canopy atmosphere via ozone plus terpenoid-type reactions can also originate from the oxidation reaction of ozone with leaf surfaces and inside the leaf. This needs to be taken into account when scaling up very reactive biogenic compounds.

High Irradiance Induced Changes of Photosystem 2 in Young and Mature Needles of Cypress (Cupressus sempervirens L.)

Photoinhibition of photosynthesis was studied in young and mature detached sun needles of cypress under high irradiance (HI) of about 1 900 μmol m-2 s-1. The degree of photoinhibition was determined by means of the ratio of variable to maximum chlorophyll (Chl) fluorescence (Fv/Fm) and electron transport measurements. Compared with the mature needles, the young needles, containing about half the amount of Chl a+b per unit area, exhibited a higher proportion of total carotenoids (Car) as xanthophyll cycle pigments and had an increased ratio of Car/Chl a+b. The potential efficiency of photosystem (PS) 2, Fv/Fm, markedly declined in HI-treated young needles without significant increase of F0 level. In contrast, the Fv/Fm ratio declined with significant increase of F0 level in mature needles. In isolated thylakoids, the rate of whole chain and PS2 activity markedly decreased in young HI-needles in comparison with mature needles. A smaller inhibition of PS1 activity was observed in both needles. In the subsequent dark incubation, fast recovery was found in both needle Types that reached maximum PS2 efficiencies similar to those observed in non-photoinhibited needles. The artificial exogenous electron donors DPC, NH2OH, and Mn2+ failed to restore the HI-induced loss of PS2 activity in mature needles, while DPC and NH2OH significantly restored it in young needles. Hence, HI-inactivation was on the donor side of PS2 in young needles and on the acceptor side of PS2 in mature needles. Quantification of the PS2 reaction centre proteins D1 and 33 kDa protein of water splitting complex following HI-exposure of needles showed pronounced differences between young and mature needles. The large loss of PS2 activity in HI-needles was due to the marked loss of D1 protein of the PS2 reaction centre in mature needles and of the 33 kDa protein in young needles.

Defoliation-induced responses in peroxidases, phenolics, and polyamines in scots pine (Pinus sylvestris L.) needles.

Effects of artificial defoliation on defensive needle chemistry in Scots pine (Pitus sylvestris L.) were evaluated with particular emphasis on peroxidases, phenolic compounds, soluble sugars, polyamines, and foliar nitrogen levels. The study was carried out on a nutrient-poor Scots pine stand with 8- to 25-year-old trees. Defoliation treatment consisted of repeated defoliation in two successive years with respective control trees. Defoliation was done before needle flushing by removing all mature needles. Guaiacol peroxidase activity increased in the needles after the first defoliation. The difference between treatments diminished towards autumn, and disappeared before the second defoliation in the next summer. After the second defoliation, the activities showed a similar trend. Apparently, peroxidases are involved in inducible chemical changes and recovery reactions that occur in the intact needles shortly after defoliation. After the second defoliation, total nitrogen concentration in the current year needles was about 20% lower, and free putrescine (a polyamine) concentration was 40% lower in the defoliated trees than in control needles. These changes indicate a loss of nitrogen due to defoliation. Specific phenolic compounds such as quercitrin, (+)-catechin, and two catechin derivatives increased in current year needles in response to defoliation. Accumulation of starch and sucrose in the current year needles of repeatedly defoliated trees may imply decreased assimilate transport. The results are indicative that changes in needle phytochemistry in response to defoliation accompany changes in needle nitrogen metabolism.

Interactions between growth, herbivory and long-term foliar dynamics of Scots pine

It is generally thought that carbon-limited conifers with low priority stem growth investment will suffer significantly reduced wood formation following defoliation by insects, as long as resource sinks (apical buds and young needles) are unaffected compared to sources (mature needles). We examined the long-term consequences of periodic defoliation by a moth (Bupalus piniaria L.) on the growth of Scots pine (Pinus sylvestris L.), by retrospectively determining annual rates of needle retention using the needle trace method, and comparing these rates with patterns of radial growth obtained by tree-ring analysis. Cumulative moth densities in the current and previous year had the strongest negative influence on subsequent tree growth. Radial and volume increments were reduced substantially (by up to 50%) for 2–3 years after peaks in the moth population. In turn, tree growth was positively correlated with needle retention, with better growth promoting better retention in the following two seasons. This dominant relationship masked the more subtle impact of B. piniaria on needle retention. However, when each needle cohort was examined separately, it was possible to detect the immediate effects of B. piniaria on the loss of the youngest (0 to 1-year-old) needle cohort. Needle budgeting differed for trees in two study compartments, where the rate of tree growth was evidently different. In the compartment where trees grew more slowly they retained a greater number of needle sets over time by shedding fewer of the older needles, but they responded more quickly to the negative effects of the defoliator by losing needles more rapidly in years when the defoliator was abundant.

Performance of pine looper Bupalus piniarius larvae under population build‐up conditions

AbstractIn the first year of an outbreak, Bupalus piniarius larvae, encounter intense crowding. In the later stages of larval development, they are forced to feed on the non‐preferred current‐year needles of Scots pine or even on alternative hosts. It was hypothesized that larval feeding on a non‐preferred resource (current‐year needles) will negatively affect B. piniarius performance. It was also hypothesized that larval mutual interference (crowding without competition for food) will have negative additive effects. These hypotheses were tested in laboratory and field experiments. Fourth instar larvae were reared singly and under crowded conditions in cohorts of ten. Larvae in both situations were reared on control branches (containing both mature and current‐year shoots) and branches containing only current‐year shoots. Crowded larvae were reared also on Norway spruce, an alternative host. Crowding and feeding on a non‐preferred resource had opposite effects on B. piniarius larval performance. Crowding in the late larval instars enhanced larval performance while absence of the preferred resource had negative effects. Larval growth rate was higher and development time was shorter for larvae exposed to crowded conditions than for solitary larvae. There was, however, no difference between the groups in final pupal weights or survival. Survival was 25% lower for larvae feeding on non‐preferred current‐year needles and pupal weights 9% lower, compared with results for larvae feeding on mature needles. Larvae feeding on Norway spruce suffered greatly extended development time, 82% lower survival, and resulted in 60% lighter pupae compared with conspecifics on Scots pine. It was concluded that not only quantity but also quality of the available food resource is critical for B. piniarius development.

Reduced realised fecundity in the pine looper Bupalus piniarius caused by host plant defoliation

Summary1. Whether the potential fecundity of herbivorous insects is realised or not may depend on female behaviour, which in turn may be influenced by host plant acceptability. Female Bupalus piniarius were observed to discriminate against needles growing out the year following defoliation (current‐year needles) of its host plant Pinus sylvestris.2. It was hypothesised that the discriminatory behaviour was due to current‐year needles being less secure as a substrate. Field and laboratory experiments were designed to test this hypothesis and to estimate the discrepancy between potential and realised fecundity when females were offered defoliated branches.3. In a laboratory oviposition experiment, B. piniarius females were exposed to branches bearing either current‐year needles only or both mature and current‐year needles. Daily oviposition rate, egg batch size, longevity, and mature eggs and fat retained at death were recorded for each female. In field experiments, the rate at which eggs dropped from expanding needles and the capacity of neonate larvae hatching from the dropped eggs to colonise a tree were assessed.4. Significantly fewer eggs were laid when females were exposed to defoliated branches.5. Twenty‐six and 16% of the eggs laid on current‐year needles dropped from the needles in 1998 and 1999 respectively, whereas no eggs dropped from mature needles in 1998 and only one egg (< 1%) dropped in 1999.6. A very small proportion of larvae hatching on the forest floor (simulated egg drop) was able to recolonise host trees.7. These results emphasise the importance of oviposition behaviour on realised fecundity when analysing insect population dynamics. In the case of B. piniarius, egg placement, although a minor detail during the normal course of events, became of key importance when defoliation deprived females of their preferred egg attachment site.

Effects of nutrient supply on photosynthetic acclimation and photoinhibition of one‐year‐old foliage of Picea abies

The present study examined the effect of nutrient supply on acclimation potential and photoinhibitory susceptibility in one‐year‐old foliage of shade‐grown Norway spruce (Picea abies Karst.) seedlings transferred to high‐light, as compared to seedlings grown in shade or in high‐light. After the transfer, the photosynthetic response to intercellular CO2 and chlorophyll fluorescence parameters were measured, and the allocation of leaf N within the photosynthetic apparatus was estimated. The effects of light and nutrient supply markedly differed. Light availability positively affected both photosynthetic capacity on an area basis (but not on a mass basis) and leaf N allocation to ribulose‐1,5‐biphosphate carboxylase/oxygenase (Rubisco), thereby increasing photosynthetic capacity per unit nitrogen. By contrast, nutrient supply in high‐light affected photosynthetic capacity both on an area and a mass basis, but did not affect the allocation of N within the photosynthetic apparatus. Fluorescence parameters indicated that shade‐grown seedlings transferred to high‐light with low‐nutrient supply, underwent prolonged photoinhibition. By contrast, transferred seedlings with high‐nutrient supply were able to avoid photoinhibition, increasing their photosynthetic capacity on an area basis. On the whole, nutrient shortage was found to prevent the acclimation response and to increase the photoinhibitory susceptibility to changing light conditions in P. abies mature needles.

Influence of nutrient supply on shade-sun acclimation of Picea abies seedlings: effects on foliar morphology, photosynthetic performance and growth.

Norway spruce seedlings (Picea abies Karst.) were grown in low light for one year, under conditions of adequate and limiting nutrition, then transferred to high light. Three months after transfer we measured photosynthesis, leaf nitrogen concentration, leaf chlorophyll concentration and leaf mass per area (LMA) of current-year and 1-year-old shoots; silhouette area ratio (SAR, the ratio of shoot silhouette area to projected needle area) was also measured in current-year shoots. At the foliage level, the effects of light and nutrient treatments differed markedly. Light availability during foliage expansion primarily affected LMA and SAR (morphological acclimation at the needle and shoot level, respectively). By contrast, nutrient supply in high light affected photosynthetic capacity per unit of leaf tissue (physiological acclimation at the cellular level) but did not affect LMA and SAR. The capacity for shade-sun acclimation in foliage formed before transfer to high light differed greatly from that of foliage formed following the transfer. The morphological inflexibility of mature needles (measured by LMA) limited their shade-sun acclimation potential. In contrast, at high nutrient supply, shoots that developed just after the change in photosynthetic photon flux density largely acclimated, both morphologically and physiologically, to the new light environment. The acclimation response of both current- and 1-year-old shoots was prevented by nutrient limitation. Analysis of growth at the whole-plant level largely confirmed the conclusions drawn at the shoot level. We conclude that nutrient shortage subsequent to the opening of a canopy gap may strongly limit the acclimation response of Norway spruce seedlings. Successful acclimation was largely related to the plant's ability to produce sun foliage and adjust whole-plant biomass allocation rapidly.

Effects of previous defoliation on pine looper larval performance

Summary1 During outbreaks of the pine looper, Bupalus piniarius, its host, Pinus sylvestris, is severely defoliated. The larvae of this geometrid normally feed on mature needles. However, because trees are totally defoliated during outbreaks, the next generation is forced to feed on current‐year needles.2 Bupalus piniarius larvae feeding on previously defoliated trees may show lower performance either because of induced resistance or because larvae have to feed on needles not normally fed upon (current instead of mature).3 These hypotheses were tested in an experiment where larvae were reared on (i) shoots naturally defoliated the previous year, and thus, bearing only current‐year needles, (ii) non‐defoliated shoots where larvae had access only to current‐year needles, and (iii) control shoots with access to both current and mature needles.4 There was no support for the induction hypothesis. Survival was lower on naturally defoliated shoots than on control shoots (81.3 vs. 90.9%), but survival was lower also on non‐defoliated shoots where larvae had access only to current‐year needles (78.8%). Data on larval feeding distribution showed a strong preference for mature needles.5 Needle nitrogen concentration of current‐year needles was 38% higher on defoliated trees than on non‐defoliated trees.6 It is concluded that defoliation affected larval performance primarily through the removal of the preferred type of needles and not because of an induced resistance. Effects of increased concentrations of allelochemicals in defoliated shoots, if present, were probably cancelled out by increased nitrogen concentrations.

Differential expression of genes encoding the light-dependent and light-independent enzymes for protochlorophyllide reduction during development in loblolly pine.

The expression patterns of the two distinct subfamilies of genes (designated porA and porB) encoding the light-dependent NADPH:protochlorophyllide oxidoreductases (PORs) in loblolly pine (Pinus taeda L.) were examined. Transcripts arising from both gene subfamilies were shown to be present at high levels in the cotyledons of dark-grown pine seedlings and to a lesser extent in their stems. Exposure of dark-grown seedlings to light resulted in increased levels of both porA and porB transcripts, as well as increased levels of mRNAs encoding other photosynthesis-related gene products, suggesting that they are under a common mode of regulation. Relative levels of the porA and porB transcripts were similar in seedling cotyledons and primary needles of two-month-old pine trees, whereas only porB transcripts were present at a significant level in mature secondary needles of two-year-old trees. Immunoblot analysis showed that the 37 kDa PORA protein was most abundant in dark-grown tissues, decreased dramatically upon exposure to light, but could still be detected at low levels in light-grown seedlings. In comparison, levels of the 38 kDa PORB protein were not significantly changed upon transfer of dark-grown tissues to light. While both PORA and PORB were detected in cotyledons and primary needles, only PORB could be detected in mature needles. Transcripts derived from the three plastid genes, chlL, chlN, and chlB, encoding subunits of the light-independent protochlorophyllide reductase were detected in the cotyledons and stems of dark-grown seedlings, and in mature needles. The highest levels of chlL, chlN, and chlB transcripts were detected within the top one-third of the stem and decreased gradually towards the stem/root transition zone. Correspondingly, the highest levels of light-independent chlorophyll formation took place near the top of the hypocotyl. A similar pattern of expression was observed for other photosynthesis-related gene products, including porA and porB. Our results suggest that many aspects of the light-dependent, tissue-specific and developmental regulation of POR expression first described in angiosperms were already established in the less evolutionarily advanced gymnosperms. However, unlike angiosperms, light is not the dominant regulatory factor controlling porA expression in these species.

Variability of the photosynthetic characteristics of mature needles within the crown of a 25-year-old Pinus pinaster

Photosynthetic characteristics of 1- and 2-year-old needles were determined in excised shoots of maritime pine (Pinus pinaster Ait.) with an open gas exchange system. We used the nonlinear least mean squares method to derive values for quantum yield of electron transport (alpha), maximum carboxylation velocity (V(cmax)), and maximum electron transport rate (J(max)), from photosynthetic response curves to light and CO(2). Crown height had no significant effect on any of the parameters; however, V(cmax) and J(max), as well as alpha were 43, 26 and 35% higher, respectively, in 1-year-old needles than in 2-year-old needles. The main effect of irradiance on needles was a small decline in leaf concentrations of nitrogen and phosphorus from the top to the bottom of the canopy. Only J(max) demonstrated a linear relationship with both nitrogen content (R(2) = 0.42) and irradiance at the shoot level. Because needle age accounted for most of the variability in photosynthesis, we incorporated needle age into the photosynthesis model of Farquhar et al. (1980). The modified model underestimated the daily assimilation rate of 1-year-old needles in the field, especially when assimilation rates were high.

Effects of elevated CO2‐grown loblolly pine needles on the growth, consumption, development, and pupal weight of red‐headed pine sawfly larvae reared within open‐topped chambers

Seedlings of loblolly pine, Pinus taeda, were grown in open‐topped chambers under four levels of CO2: two ambient and two elevated. Larvae of the red‐headed pine sawfly, Neodiprion lecontei, were reared from early instar to pupation, primarily on branches within chambers. Larval growth and mortality were assessed and leaf phytochemistry samples of immature and mature leaves collected weekly. Mature leaves grown under elevated CO2 had significant reductions in leaf nitrogen and increases in non‐structural carbohydrate contents, resulting in foliage being a poorer food source for larvae, i.e. higher carbohydrate:nitrogen ratio. Nutritional constituents of immature needles were unaffected by seedling CO2 treatment. Volatile mono‐ and sesquiterpenes were unrelated to plant CO2 treatments for either leaf age class. Larval consumption of immature needles significantly increased on seedlings grown under CO2 enrichment, while mature needle consumption was not different between the treatments. The average weight gain per larva significantly declined in late instar larvae consuming elevated CO2‐grown needles. In spite of this reduced growth, neither the days to pupation nor pupal weights were different among the CO2 treatments. This study suggests that enriched CO2‐induced alterations in pine needle phytochemistry can affect red‐headed pine sawfly performance. However, compensatory measures by larvae, such as choosing to consume more nutritious immature needles, apparently helps offset enriched CO2‐induced reductions in the leaf quality of mature needles.

Nutrient contents and concentrations in relation to growth of Picea abies and Fagus sylvatica along a European transect.

Mineral nutrition of Norway spruce (Picea abies (L.) Karst.) and beech (Fagus sylvatica L.) was investigated along a transect extending from northern Sweden to central Italy. Nitrogen (N) concentrations of needles and leaves in stands growing on acid soils did not differ significantly between central Italy and southern Sweden (1.0 +/- 0.1 mmol N g(-1) for needles and 1.9 +/- 0.14 mmol N g(-1) for leaves). In both species, foliar N concentrations were highest in Germany (1.2 mmol N g(-1) for needles and 2.0 mmol N g(-1) for leaves) and decreased by 50% toward northern Sweden (0.5 mmol N g(-1)). Both species showed constant S/N and P/N ratios along the transect. Calcium, K and Mg concentrations generally reflected local soil conditions; however, Mg concentrations reached deficiency values in Germany. Leaf area per unit dry weight varied significantly along the transect with lowest values for Norway spruce recorded in northern Sweden and Italy (3.4 m(2) kg(-1)) and a maximum in central Europe (4.7 m(2) kg(-1)). A similar pattern was observed for beech. Despite the low variation in foliar N concentrations on the large geographic scale, local and regional variations in N concentrations equalled or exceeded the variation along the entire continental transect. Furthermore, nutrient contents (i.e., nutrient concentration x dry weight per needle or leaf) showed a greater variation than nutrient concentrations along the transect. Nitrogen contents of Norway spruce needles reached minimum values in northern Sweden (2.4 micro mol N needle(-1)) and maximum values in Denmark (5.0 micro mol N needle(-1)). The N content of beech leaves was highest in Denmark (242 micro mol N leaf(-1)). At the German site, foliar N content rather than N concentration reflected the seasonal dynamics of foliar growth and N storage of the two species. During foliage expansion, there was an initial rapid increase in N content and a decrease in N concentration. This pattern lasted for about 2 weeks after bud break and was followed by 6 weeks during which dry weight and N content of the foliage increased, resulting in a further decrease in N concentration. During summer, dry weight and N content of mature needles of Norway spruce increased further to reach a maximum in autumn, whereas N concentration remained constant. In spring, reallocation of N from 1- and 2-year-old needles was 1.5 and 1.0 micro mol N needle(-1), respectively. This remobilized N was a major source of N for the development of new needles, which had an N content of 1.5 micro mol N needle(-1) after bud break. The seasonal remobilization of N from old foliage decreased with increasing needle age. Needle N content and dry weight decreased progressively with age (1 micro mol N needle(-1) between age classes 2 and 5), whereas N concentrations remained constant. For Norway spruce, annual stemwood production was correlated with needle N content but not with foliar N concentration or with the total amount of N in the canopy. Interspecific and geographical differences in plant nutrition are discussed on the basis of competitive demands for C and N between growth of foliage and wood.

Effects of Elevated Co 2 , Soil Nutrient Levels, and Foliage Age on the Performance of Two Generations of Neodiprion lecontei (Hymenoptera: Diprionidae) Feeding on Loblolly Pine

We investigated how changes in loblolly pine needle phytochemistry caused by elevated CO{sub 2}, leaf age, and soil nutrient levels affected the performance of 2 individual generations of the multivoltine folivorous insect pest Neodiprion lecontei. In 2 feeding trials, mature needles produced in the previous (spring) and current (fall) year from seedlings grown in open-topped chambers under 4 CO{sub 2} and 2 soil nutrient levels were fed to 2 separate generations of red beaded pine sawfly larvae. Strong seasonal differences (i.e., spring versus fall) in leaf nutritional and defensive constituents resulted in significant between-generation differences in the growth, consumption, and growth efficiency of sawfly larvae. Enriched CO{sub 2}-grown needles bad higher levels of starch and starch/nitrogen ratios in older, overwintering spring needles, which were lower in leaf nitrogen and monoterpenes than younger, current year needles (fall). Overall, larval growth was higher and consumption lower on the fall needles, presumably because of higher levels of leaf nitrogen compared with the spring needles. The plant CO{sub 2} concentration significantly contributed to the larval consumption responses between seasons (significant CO{sub 2} X season interaction), demonstrating that the 2 sawfly generations were affected differently by CO{sub 2}-induced phytochemical alterations in spring versus fall needles.more » The data presented here suggests that when investigating multivoltine folivorous insect responses to elevated CO{sub 2}-grown tree seedlings in which multiple leaf flushes within a growing season expose insects to an array of leaf phytochemical changes, >1 insect generation should be investigated. 54 refs., 3 figs., 1 tab.« less