The phenolics and a hydrolysable tannin polyphenol oxidase of Medinilla magnifica

The production of viable meristem cultures of Medinilla magnifica has proved to be very difficult. This may be due, in part, to a pronounced ‘browning’ response of the tissues on cutting. For this reason the phenolic compounds and the hydrolysable-tannin polyphenol oxidase from Medinilla were studied. The distribution of the compounds was: simple phenols 19% , flavonoids 5% , hydrolysable tannins 69% , condensed tannins 7%. Amongst the simple phenols and phenolic acids, the following were identified: phloroglucinol, p-hydroxybenzoic acid, vanillic acid, protocatechuic acid, gallic acid (both in free and bound form the most abundant simple phenol), syringic acid, trans-p-coumaric acid, trans-ferulic acid and trans-caffeic acid. No kaempferol or quercetin or their derivatives were detected but condensed tannins are present. Methods for the extraction, fractionation and quantitative determination of phloroglucinol and the phenolic acids, as well as correction factors for losses during the extraction, alkali treatment and derivatization, are presented in a supplementary publication. With regard to the hydrolysable tannin polyphenol oxidase activity of Medinilla stems, the enzyme(s) is rather specific since at neither of its two pH optima (6 and 7) could a classical polyphenol oxidase activity be detected. The enzyme was strongly inhibited by 2-mercaptoethanol. Preliminary experiments have further shown that in addition to the hydrolysable tannins of the tissue, the ferrous ions of the medium, and oxygen together with the hydrolysable tannin polyphenol oxidase could play a role in the browning response. Ways to overcome this difficulty have been suggested.     

Optimization of photosynthesis,growth, and biochemical composition of the microalga <Emphasis Type="Italic">Rhodomonas salina</Emphasis>—an established diet for live feed copepods in aquaculture

The cryptophyte Rhodomonas salina is widely used as feed for copepod cultures. However, culturing conditions to obtain high-quality algae have not yet been efficiently optimized. Therefore, we aimed to develop a cultivation protocol for R. salina to optimize its nutritional value and provide technical recommendations for later large-scale production in algal photobioreactors. We studied photosynthesis, growth, pigments, fatty acid (FA) and free amino acid (FAA) composition of R. salina cultured at different irradiances (10–300 μmol photons m^?2 s^?1) and nutrient availability (deficiency and excess). The optimal range of irradiance for photosynthesis and growth was 60–100 μmol photons m^?2 s^?1. The content of chlorophylls a and c decreased with increasing irradiance while phycoerythrin peaked at irradiances of 40–100 μmol photons m^?2 s^?1. The total FA content was maximal at optimal irradiances for growth, especially under nutrient deficiency. However, highly unsaturated fatty acids, desired components for copepods, were higher under nutrient excess. The total FAA content was highest at limiting irradiances (10–40 μmol photons m^?2 s^?1) but a better composition with a higher fraction of essential amino acids was obtained at saturated irradiances (60–140 μmol photons m^?2 s^?1). These results demonstrate that quality and quantity of FA and FAA of R. salina can be optimized by manipulating the irradiance and nutrient conditions. We suggest that R. salina should be cultivated in a range of irradiance 60–100 μmol photons m^?2 s^?1 and nutrient excess to obtain algae with high production and a balanced biochemical composition as feed for copepods.     

Tannins as gibberellin antagonists

Fourteen chemically defined hydrolyzable tannins and six impure mixtures of either condensed or hydrolyzable tannins were found to inhibit the gibberellin-induced growth of light-grown dwarf pea seedlings. The highest ratio of tannins to gibberellic acid tested (1000: 1 by weight) inhibited from 80 to 95% of the induced growth for all tannins tested except for two monogalloyl glucose tannins which inhibited only 50% of the induced growth. The lowest ratio tested (10: 1) inhibited the induced growth by less than 25% except for the case of terchebin where 50% inhibition was found. The inhibition of gibberellin-induced growth was found to be completely reversed by increasing the amount of gibberellin in three cases tested. Tannins alone did not inhibit endogenous growth of either dwarf or nondwarf pea seedlings. Eight compounds related to tannins, including coumarin, trans-cinnamic acid, and a number of phenolic compounds were also tested as gibberellin antagonists. Most of these compounds showed some inhibition of gibberellin-induced growth, but less than that of the tannins. At the highest ratio (1000: 1) the greatest inhibition was 55%; at the lowest ratio (10: 1) no more than 17% was observed. These compounds did not inhibit endogenous growth, and the inhibition of gibberellin-induced growth could be reversed by increasing the amount of gibberellin in two cases tested.     

Changes in phytochemical content and pharmacological activities of three <Emphasis Type="Italic">Chlorella</Emphasis> strains grown in different nitrogen conditions

The phytochemical content and biological activity of three Chlorella strains cultured in low (35 mg L^?1) or high (700 mg L^?1) nitrogen (N) and harvested on days 5 and 10 were evaluated. High N resulted in a higher biomass in Chlorella MACC 438 and MACC 452 while MACC 555 produced a higher biomass in low N. MACC 555 (low N/day 5) had the highest phenolic content, and MACC 438 in low N/day 5 and high N/day 5 accumulated the highest flavonoids and condensed tannins, respectively. Iridoids were most abundant in MACC 452 on low N/day 10. Harvest time had the greatest effect on the phytochemical content with phenolics, flavonoids, and condensed tannins decreasing over time and iridoids increasing in low N and decreasing in high N conditions. Extracts were more active in β-carotene-linoleic acid model compared to 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging assay. Most extracts had good antimicrobial activity. Extracts became less potent over time in the antioxidant, acetylcholinesterase inhibitory (AChE), and antimicrobial assays when growing in low N and more potent in the antioxidant and AChE assays when grown in high N. Thus, phytochemical content and biological activities of the three Chlorella strains were affected by N levels, harvest time, and strain.     

Changes in composition of phenolic compounds and antioxidant properties of <Emphasis Type="Italic">Vitis amurensis</Emphasis> seeds germinated under osmotic stress

The research focused on the changes of phenolic compounds as well as their antiradical activity and reducing power isolated from Amur grape (Vitis amurensis) seeds during germination under optimal conditions and under osmotic stress. The seeds were found to contain tannins, (+) catechin, (−) epicatechin, and gallic acid (in free, ester- and glycoside-bound forms). Extracts from the seeds were also shown to contain two other phenolic acids: caffeic and p-coumaric acids, in very low levels. During a 3-day seed germination test under osmotic stress (−0.5 MPa), the content of total phenolics, tannins and phenolic acids declined as compared to the control. However, seed germination under stress conditions led to a significant increase in the amount of catechins. Because catechin is the one of the units in condensed tannins, its dynamic increase during seed germination may be involved in metabolism of tannins under osmotic stress. It is also likely that the synthesis of catechins is greater under stress conditions and these compounds may be engaged in the process of acclimatization of grapevines to stress conditions. The content of total phenolic compounds in seed extracts is positively correlated with their antioxidant properties. The extracts from seeds germinated under optimal conditions exhibited strong antiradical properties against the DPPH (2,2-diphenyl-1-picrylhydrazyl) radical as well as reducing power. As regards the extracts from grape seeds germinated under osmotic stress, this capability was much weaker. The research demonstrated that antioxidants could interfere with the oxidation process induced by various stresses by acting as oxygen scavengers, therefore the tolerance to drought stress might be correlated with an increase in the antioxidant potential.     

Effects of irradiance during growth on tolerance of geranium to sub- and supra-optimal boron supply

In our previous study on geranium, we showed that increases in growth irradiance from sub-optimal to near-optimal could delay boron deficiency effects on photosynthesis. In this study, we further investigated the effects of growth irradiance on tolerance to B stress by growing geranium (Pelargonium × hortorum cv. Maverick White) under sub- to supra-optimal B concentrations (4.5, 45, and 450 μM) and under three irradiances of 100, 300, or 500 μmol m^?2 s^?1 PAR for 30 d. In general, at low and medium irradiances, sub- and supra-optimal B availability decreased root and shoot dry masses, but at high irradiance, the B stress was prevented. Net photosynthetic rate decreased by the supra-optimal B concentration at the high irradiance only suggesting B-related photoinhibition. Tissue B content and root specific B uptake only modestly decreased by the low B treatment, but increased greatly by the high B availability, and the higher irradiance decreased the tissue B content and the root B uptake only at the low and medium B supplies. Interestingly, the increases in irradiance decreased the content and uptake of all other nutrients, except Fe uptake. Effects of the B stress on the content of other nutrients were variable, but the B stress often exacerbated decreases in nutrient content with the increasing irradiance which would be especially important under nutrient-limiting conditions. Hence, in this study, the B stress effects on growth were mitigated by the increases in growth irradiance, which offset negative effects on physiology, and the protective effects of irradiance were likely caused by its positive effects on plant carbon/energy status rather than on tissue B content or B uptake.     

Shoot development of Norway spruce (Picea abies) involves changes in piperidine alkaloids and condensed tannins

Key Message

Secondary chemistry of P. abies peaks early in shoot development. Condensed tannins accumulate already in late buds while piperidine alkaloid biosynthesis take place in early stage shoots.

Abstract

Plants protect new vegetative parts with defensive secondary metabolite compounds. We investigated how concentrations of piperidine alkaloids and condensed tannins change during bud burst and shoot growth in adult Picea abies. We detected 12 individual piperidine compounds, of which epipinidinone and 1,2-dehydropinidinone and two tentatively identified 1,6-imines are reported for the first time in P. abies. In addition three piperidine alkaloid compounds remain partly identified. We found that concentrations of both total piperidine alkaloids and condensed tannins were highest immediately after bud burst. While concentrations of condensed tannins started to increase during bud opening, the dilution effect decreased concentrations in the developing needles of mature branches. By contrast, the decrease of total alkaloid concentrations in mature shoots was not due to the dilution effect, but was connected to the disappearance of precursor components of biosynthesis. The concentrations of major alkaloid components remain stable from dormant buds to mature needles and twigs, underlining their importance for P. abies, although their real ecological significance is yet to be solved. Based on the structural features and timing of appearance of individual compounds, we also propose a hypothetical biosynthesis route for trans-substituted coniferous piperidine alkaloids.     

Resource allocation in different parts of juvenile mountain birch plants: effect of nitrogen supply on seedling phenolics and growth

The composition and concentrations of phenolic compounds were studied in the first true leaves, cotyledons, stems and roots of 2.5-week-old seedlings of mountain birch ( Betula pubescens ssp. czerepanovii ). The differences in secondary compounds among these plant parts were both qualitative and quantitative. In all parts, condensed tannins accounted for more than 50% of the phenolics. In the first true leaves and cotyledons, chlorogenic acid was the most abundant of the HPLC phenolics. The main components in stems were (+)-catechins and rhododendrins whereas in roots, the main components were ellagitannins. The seedlings were grown at three levels of nitrogen supply (very low-N, low-N, moderate-N), and the effect of nitrogen on concentrations of phenolic compounds was studied in all plant parts. The dry weight of all plant parts, except the roots, increased with increased nitrogen. In all parts, the concentration of condensed tannins was higher at lower levels of nitrogen than at moderate-N. The concentrations of total HPLC phenolics and also those of the compound groups of HPLC phenolics were, however, affected only in the first true leaves and roots. The concentrations in the first true leaves were generally higher in seedlings grown at very low-N and low-N than in seedlings grown at moderate-N. The concentrations in roots were highest at low-N. Not all compounds responded to nitrogen supply in the same manner. The changes in concentrations cannot be exclusively interpreted as changes in the accumulation of phenolic compounds, due to dilution caused by the increase in biomass in better nitrogen availability. There were differences in carbon allocation between condensed tannins and HPLC phenolics in seedlings grown at different nitrogen levels.     

Quantitative analysis of polyphenols and antioxidant activity in four Daphne L. species

The content of biologically active phenolic compounds (total polyphenols, tannins, flavonoids, and phenolic acids) were determined using spectrophotometry in four wild Croatian species of Daphne L. in the family Thymelaeaceae (Daphne alpina, D. cneorum, D. laureola, and D. mezereum). The concentration of total flavonoids (TF) was highest in the leaves of these Daphne species (0.12?C0.51% dry herb weight, DW) whereas the content of other phenolic compounds analyzed were highest in the roots, including total polyphenols (TP; 2.71?C19.03% DW), tannins (T; 1.14?C7.39% DW), and total phenolic acids (TPA; 0.12?C0.87% DW). D. alpina contained the highest amount of polyphenols, with the exception of flavonoids, where maximum concentrations were found in D. laureola. We also examined the antioxidant activity of leaf, stem, and root extracts. All extracts analyzed demonstrated high free radical scavenging activity with the highest concentration in the leaf extracts of D. alpina. Leaf extracts of D. cneorum showed the highest antioxidant activity in a ??-carotene bleaching assay.     

Quantitative changes in secondary metabolites of dark-leaved willow (Salix myrsinifolia) exposed to enhanced ultraviolet-B radiation

This is a study of the impact of increased ultraviolet-B (UV-B) radiation on the secondary chemistry of Salix myrsinifolia (dark-leaved willow). For nearly two decades, the loss of stratospheric ozone above the high latitudes of the Northern Hemisphere has increased UV-B radiation (280–320 nm) over the long-term mean. Willows (Salicaceae) are widely distributed in these northern regions. To determine the effects of increased UV-B radiation on willows, the plantlets of three clones of S. myrsinifolia were grown under ambient (3.6 kJ m⁻² day⁻¹) or enhanced (7.18 kJ m⁻² day⁻¹) UV-B irradiance. After the 2-week indoor experiment, the concentrations of UV-B-screening phenolics (flavonoids and phenolic acids) and low-UV-B-screening phenolics (salicylates and condensed tannins) in fresh leaves were investigated and the biomass of leaves, stems and roots was determined. As expected, the total amount of flavonoids in willow leaves clearly increased when plantlets were exposed to higher UV-B irradiation. However, the degree of increase of individual compounds varied: luteolin-7-glucoside, monomethyl-monocoumaryl-luteolin-7-glucoside and one myricetin derivative increased significantly, while the apigenin-7-glucuronide increased only slightly. The enhanced UV-B also increased the amount of p -hydroxycinnamic acid derivative. The UV-B effects on other phenolic acids and tannins were minor. In contrast to the other phenolics, the amounts of two salicylates, salicin and saligenin, decreased under enhanced UV-B irradiation. Our results indicate that the concentrations of both UV-B-screening and low-UV-B-screening phenolic compounds in leaves of S. myrsinifolia may vary in response to elevated UV-B radiation. However, while the UV-B protective flavonoids and phenolic acids accumulate during UV-B exposure, the concentrations of certain salicylates decrease.     

Effects of artificial grassland establishment on soil nutrients and carbon properties in a black-soil-type degraded grassland

Despite a growing knowledge of nutrient limitation for mangrove species and how mangroves adapt to low nutrients, there is scant information about the relative importance of N:P ratio and leaf phenolics variability in determining nutrient conservation. In this study, we evaluated possible nutrient conservation strategies of a mangrove Rhizophora stylosa under nutrient limitation. 1. The leaf nutrient concentrations of R. stylosa changed with season, with the highest N concentration in winter and the highest P concentration in spring for both mature and senescent leaves. Leaf N and P concentrations decreased significantly during leaf senescence. Based on N:P ratios R. stylosa forest was N-limited. Accordingly, the nitrogen resorption efficiency (NRE) was significantly higher than phosphorus resorption efficiency (PRE) for the R. stylosa leaves during leaf senescence. The NRE and PRE both reached the highest in the autumn. Average N and P concentrations in the senescent leaves were 0.15% and 0.06% for R. stylosa, respectively, indicating a complete resorption of N and an incomplete resorption of P. There was a significant negative correlation between nitrogen resorption proficiency (NRP) and NRE, meanwhile phosphorus resorption proficiency (PRP) and PRE correlation was also highly significantly. 2. R. stylosa leaves contained relatively high tannin level. Total phenolics, extractable condensed tannins and total condensed tannins contents increased during leaf senescence, and changed between seasons. The lowest concentrations of total phenolics, extractable condensed tannins and total condensed tannins occurred in summer, total phenolics concentrations were inversely related to nitrogen or phosphorus concentrations. 3. Our results confirmed that resorption efficiency during leaf senescence depends on the type of nutrient limitation, and NRE was much higher than PRE under N-limited conditions. R. stylosa forest developed several nutrient conservation strategies in the intertidal coastline surroundings, including high nitrogen resorption efficiency, low nutrient losses and high tannins level.     

Isolation and characterization of an anaerobic ruminal bacterium capable of degrading hydrolyzable tannins.

An anaerobic diplococcoid bacterium able to degrade hydrolyzable tannins was isolated from the ruminal fluid of a goat fed desmodium (Desmodium ovalifolium), a tropical legume which contains levels as high as 17% condensed tannins. This strain grew under anaerobic conditions in the presence of up to 30 g of tannic acid per liter and tolerated a range of phenolic monomers, including gallic, ferulic, and p-coumaric acids. The predominant fermentation product from tannic acid breakdown was pyrogallol, as detected by high-performance liquid chromatography and mass spectrometry. Tannic acid degradation was dependent on the presence of a sugar such as glucose, fructose, arabinose, sucrose, galactose, cellobiose, or soluble starch as an added carbon and energy source. The strain also demonstrated resistance to condensed tannins up to a level of 4 g/liter.     

Photosynthetic and Transpiration Rates of Soybean as Affected by Different Irradiances During Growth

The diurnal variation of net photosynthetic (PN) and transpiration (E) rates in soybean [Glycine max (L.) Merr. cv. Fukuyutaka] plants grown under 100, 50, or 25 % of full sun irradiance (I100, I50, I25 plants) were compared. In the morning, activities of the plants were measured at irradiances under which they grew. However, during the afternoon, all the plants were tested under full irradiance. The lower the growth irradiance, the lower PN, E, and mesophyll conductance values were found. Stomatal conductance was considerably lower in I25 plants only. Both the increase in specific leaf area (SLA) and the decrease in nitrogen content per leaf area unit contributed to the PN reduction of soybean plants grown under low irradiances. Though E of the plants grown under different irradiances differed less markedly than PN, the water use efficiency declined from I100 to I25.     

A critical analysis of techniques for measuring tannins in ecological studies

Summary A series of seventeen plant extracts rich in phenolic materials, including condensed and hydrolysable tannins, have been subjected to a series of chemical analyses in an attempt to gather ecologically significant information about their structure. Procedures investigated were (i) the Folin-Denis and Hagerman and Butler methods for quantifying total phenolics, (ii) the vanillin and proanthocyanidin methods for quantifying condensed tannins, (iii) the iodate and nitrous acid methods for hydrolysable tannins. It was found that the techniques for total phenolics correlated well, the Hagerman and Butler method giving higher estimates where solutions were particularly phenol rich. By contrast there was considerable discrepancy between the methods examined for condensed tannins. This is probably due primarily to the very different chemical reactions that form the basis of these procedures and also to the fact that the extract dependent products of the proanthocyanidin method vary in their A ₁ ¹ values. During the study of condensed tannins methods for estimating their contribution to total phenolics and for measuring their average polymer length were examined. In both cases different procedures produced very variable results. Available methods for hydrolysable tannins were found not to be generally applicable across all extracts thought to contain this type of tannin on the basis of chromatographic analysis. An attempt to produce a quantitative spectrophotometric assay for hydrolysable tannins based on changes in reactivity to ferric chloride due to hydrolysis is described. This proved to be of limited sensitivity but may have some merit for estimating levels in hydrolysable tannins in phenol-rich plant extracts that also contain condensed tannins. It is concluded that whilst the overall level of phenolics in extracts can be estimated with some confidence the information imparted by more specific assays is very dependent on the procedures employed, particularly when dealing with extracts from taxonomically highly diverse sources.     

Phenolic compounds in Norway spruce as affected by boron nutrition at the end of the growing season

The increase in concentrations of phenolic compounds in boron (B) deficiency has been demonstrated in many herbaceous plant species, but information on woody plants is scarce. It has been suggested that accumulation of phenolic compounds plays a role in the development of cold hardiness in herbaceous plants but also that B deficiency decreases winter hardiness. Here we study the effects of B nutrition on phenolic compounds in Norway spruce (Picea abies L.) in the course of cold acclimation. Phenolic compounds were analysed in Norway spruce seedlings from three different B-fertilisation treatments in two harvests: non-acclimated and cold-acclimated seedlings. Norway spruce phenolic compounds consisted mainly of condensed tannins. During B deficiency, condensed tannins and monocoumaroyl–astragalin der. 1 increased in non-acclimated seedlings. The increase in tannins was 21%, which was nearly significant. However, the effect of B on phenolic compounds was almost absent in cold-acclimated seedlings. The condensed tannin concentration increased much more with time in the simulated autumn than due to B deficiency, and we conclude that the B effect was probably not large enough to be important for the hardening of the seedlings. The total phenolic concentrations more than doubled during the course of cold hardening suggesting that phenolics have a role in the winter hardiness in Norway spruce.     

Effects of nitrogen supply on photosynthetic and anatomical changes in current-year needles of <Emphasis Type="Italic">Pinus koraiensis</Emphasis> seedlings grown under two irradiances

We investigated the responses of photon-saturated photosynthesis rate (P _sat) and its simultaneous acclimation of anatomy and nitrogen use patterns of current needles of Korean pine (Pinus koraiensis) seedlings grown under factorial combinations of two nitrogen levels and irradiances. Although N supply resulted in a significant increase of N content in needles under both irradiances, the increase of P _sat tended to be suppressed only in shade (S). The significant increase of P _sat in full sunlight (O) was associated with the increase of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) and chlorophyll (Chl) contents. In contrast, small increase of Chl content and no increase of RuBPCO content were found in S (90 % cut of full irradiance), which would result in a small increase of P _sat. This result suggests that extra N is stocked in needles under shade for the growth in next season. With N supply, a significant decrease of specific leaf area (SLA) was detected only in O. This decrease of SLA was due to the increase of density of needle. Furthermore, the increase of needle density was not due to the increased number and size of mesophyll cells, but the increased density of each mesophyll cell. Therefore, although SLA changed in O, the change did not involve anatomical adaptation to use increased N effectively, at least observable by light microscopy. Hence, even though the SLA would change, N deposition will improve the photosynthetic capacity of Korean pine seedlings, not through the development of needle anatomy but through improvement of the allocation of N in both irradiances.     

Effects of temperature, irradiance and photoperiod on growth and pigment content in some freshwater red algae in culture

The responses of relative growth rate (% day‐1) and pigment content (chlorophyll a, phycocyanin and phycoerythrin) to temperature, irradiance and photoperiod were analyzed in culture in seven freshwater red algae: Audouinella hermannii (Roth) Duby, Audouinella pygmaea (Kützing) Weber‐van Bosse, Batrachospermum ambiguum Montagne, Batrachospermum delicatulum (Skuja) Necchi et Entwisle,‘Chantransia’ stages of B. delicatulum and Batrachospermum macrosporum Montagne and Compsopogon coeruleus (C. Agardh) Montagne. Experimental conditions included temperatures of 10, 15, 20 and 25°C and low and high irradiances (65 and 300 μmol photons m^?2 s^?1, respectively). Long and short day lengths (16:8 and 8:16 LD cycles) were also applied at the two irradiances. Growth effects of temperature and irradiance were evident in most algae tested, and there were significant interactions among treatments. Most freshwater red algae had the best growth under low irradiance, confirming the preference of freshwater red algae for low light regimens. In general there was highest growth rate in long days and low irradiance. Growth optima in relation to temperature were species‐specific and also varied between low and high irradiances for the same alga. The most significant differences in pigment content were related to temperature, whereas few significant differences could be attributed to variation in irradiance and photoperiod or interactions among the three parameters. The responses were species‐specific and also differed for pigments in distinct temperatures, irradiances and photoperiods in the same alga. Phycocyanin was generally more concentrated than phycoerythrin and phycobiliproteins were more concentrated than chlorophyll a. The highest total pigment contents were found in two species typical of shaded habitats: A. hermannii and C. coeruleus. The expected inverse relationship of pigment with irradiance was observed only in C. coeruleus. In general, the most favorable conditions for growth were not coincident with those with highest pigment contents.     

Long-term effects of boron and copper on phenolics and monoterpenes in Scots pine (Pinus sylvestris L.) needles

Backgroud and aims

Plant boron (B) status is known to affect plant secondary metabolites but most studies have been short termed and in controlled environments. Copper (Cu) effects on phenolics are better known at toxic than at low levels. Here, the chemistry of Scots pine (Pinus sylvestris L.) needles was studied 20 years after fertilisation with B and Cu in a long-term field experiment on a drained boreal peatland.

Methods

Phenolic compounds were analysed from three needle year classes using high performance liquid chromatography (HPLC) and condensed tannins with modified acid-butanol assay. Monoterpenes in the youngest needles were analysed by gas chromatography–mass spectrometry (GC–MS).

Results

Needle B concentrations were at deficient level in controls (5.7 μg g^?1), but at the optimum level (12 μg g^?1) still 20 years after fertilisation. Copper concentrations were low but not deficient (4.0 μg g^?1 in unfertilised, 4.8 μg g^?1 in fertilised). Needle ageing increased the concentrations of individual phenolics in most cases, but decreased the concentration of condensed tannins. The concentrations of several individual phenolics were reduced by B fertilisation compared to B-deficient control, significantly in the cases of (+)-catechin and a neolignan. The concentrations of eight compounds and the sum of small-molecule phenolics were higher in Cu fertilised trees. Condensed tannins and monoterpenes were not affected by the micronutrients.

Conclusions

Boron and copper additions affected mostly the same phenolic compounds, but B decreased while Cu increased their concentrations, Cu effects being clearer. The higher phenolic concentrations in B deficient trees were not likely large enough to explain leader dieback in B-deficient trees. The effects and interactions of these micronutrients need to be further studied in field conditions to establish firstly if the changes in phenolics are consistent among species, and secondly what mechanisms lead to the changes. Although small, the changes in phenolic concentrations may affect the interactions of the trees with their biotic and abiotic environment, when consistent over many years.     

Effects of irradiance on growth,photosynthesis, and water use efficiency of seedlings of the chaparral shrub,Ceanothus megacarpus

Summary The effects of irradiance during growth on biomass allocation, growth rates, leaf chlorophyll and protein contents, and on gas exchange responses to irradiance and CO₂ partial pressures of the evergreen, sclerophyllous, chaparral shrub, Ceanothus megacarpus were determined. Plants were grown at 4 irradiances for the growth experiments, 8, 17, 25, 41 nE cm^-2 sec^-1, and at 2 irradiances, 9 and 50 nE cm^-2 sec^-1, for the other comparisons.At higher irradiances root/shoot ratios were somewhat greater and specific leaf weights were much greater, while leaf area ratios were much lower and leaf weight ratios were slightly lower than at lower irradiances. Relative growth rates increased with increasing irradiance up to 25 nE cm^-2 sec^-1 and then leveled off, while unit leaf area rates increased steeply and unit leaf weight rates increased more gradually up to the highest growth irradiance.Leaves grown at 9 nE cm^-2 sec^-1 had less total chlorophyll per unit leaf area and more per unit leaf weight than those grown at 50 nE cm^-2 sec^-1. In a reverse of what is commonly found, low irradiance grown leaves had significantly higher chlorophyll a/b than high irradiance grown leaves. High irradiance grown leaves had much more total soluble protein per unit leaf area and per unit dry weight, and they had much higher soluble protein/chlorophyll than low irradiance grown leaves.High irradiance grown leaves had higher rates of respiration in very dim light, required higher irradiances for photosynthetic saturation and had higher irradiance saturated rates of photosynthesis than low irradiance grown leaves. CO₂ compensation irradiances for leaves of both treatments were very low, <5 nE cm^-2 sec^-1. Leaves grown under low and those grown under high irradiances reached 95% of their saturated photosynthetic rates at 65 and 85 nE cm^-2 sec^-1, respectively. Irradiance saturated rates of photosynthesis were high compared to other chaparral shrubs, 1.3 for low and 1.9 nmol CO₂ cm^-2 sec^-1 for high irradiance grown leaves. A very unusual finding was that leaf conductances to H₂O were significantly lower in the high irradiance grown leaves than in the low irradiance grown leaves. This, plus the differences in photosynthetic rates, resulted in higher water use efficiencies by the high irradiance grown leaves. High irradiance grown leaves had higher rates of photosynthesis at any particular intercellular CO₂ partial pressure and also responded more steeply to increasing CO₂ partial pressure than did low irradiance grown leaves. Leaves from both treatments showed reduced photosynthetic capability after being subjected to low CO₂ partial pressures (100 bars) under high irradiances. This treatment was more detrimental to leaves grown under low irradiances.The ecological implications of these findings are discussed in terms of chaparral shrub community structure. We suggest that light availability may be an important determinant of chaparral community structure through its effects on water use efficiencies rather than on net carbon gain.