Leaf Nitrogen Levels Research Articles

Waste stream utilisation for sustainable viticulture

Field trials were established at four vineyards in January 1999 to evaluate the effects of four mulch mixtures on different soil and plant parameters. Mulches were made from wine industry and other commercially available plant and animal wastes. Soil, grape petioles, grape leaves and grape juice were analysed over three seasons. The mulches applied released considerable quantities of nutrients, which were available for use by the grapevines. Generally, the type of mulch used had little impact on the parameters that were measured and the greatest differences occurred between non-mulched and mulch treatments. Soil pH showed an increase at three of the four sites after application of mulch. Soil phosphorus increased moderately at one site and substantially at the other three sites in the first year and soil potassium levels increased dramatically at all sites in the first year. After the application of mulches in 1999 the petiole nitrate levels increased dramatically at all sites, however there were no differences in the second year. In the third year petiole nitrate levels were again high indicating that the differences between years was probably largely attributable to differences in rainfall received among the three seasons. Petiole potassium levels also increased after the application of mulch, however the increase was nowhere near as large as the increase in soil potassium. The use of mulch increased leaf nitrogen and potassium levels but not phosphorus levels. The use of mulch did increase juice potassium, however there was greater seasonal and site variation than variation due to the effect of mulch.

RELATIONSHIP BETWEEN CANOPY REFLECTANCE AND PLANT WATER CONTENT IN RICE UNDER DIFFERENT SOIL WATER AND NITROGEN CONDITIONS

The ability to non-destructively monitor crop water status by remote sensing is of significant importance for optimizing of crop irrigation systems and precision farming. In order to develop quantitative models for monitoring rice water status by canopy reflectance spectra, an investigation was conducted to study the relationship between canopy reflectance characteristics and plant water status under different water and nitrogen levels with different pot and pool experiments. The results showed that the crop spectral reflectance decreased in the visible wavelength regions and short-wave infrared (SWIR) (1 400-1 700 nm) regions with increasing water supply, because absorption of visible light (450-700 nm) by leaf chlorophyll was aggravated whereas the spectral reflectance in the near infrared (NIR) (750-950 nm) wavelength regions increased. A high reflectance spectra flat roof formed which remained throughout the entire growth period. Under different water regimes, canopy reflectance showed similar patterns of change. Under the same water supply, the canopy spectral reflectance in the visible wavelength and SWIR regions was lower under high nitrogen supply than under low nitrogen supply rates but showed an opposite pattern in the NIR wavelength regions. Canopy reflectance in single bands is often subject to interference by biomass, background and so on, but the ratio of two bands can alleviate interference due to topography and enlarge the difference of spectral reflectance between vegetation types thus improving the precision of estimates by spectral reflectance. Consequently, in order to eliminate some of the interferences for distinguishing leaf and canopy structure and establish the best predictive model for assessing leaf water content, all regressions between ratio indices, normalized difference indices and leaf and plant water content were conducted. The results indicated that there was a linear relationship between the vegetation index ratio (R 810 /R 460 ) and canopy leaf water content and plant water content after jointing stage regardless of leaf nitrogen levels, with an RMSE of 0.93 and 1.50, respectively, for model testing. It is concluded that the vegetation index ratio of R 810 /R 460 can be used to monitor leaf water content and plant water content at different growth stages of rice.

Effects of bark mulch and npk fertilizer on yield, leaf nutrient status and soil mineral nitrogen during three years of strawberry production

The effects of bark mulch and NPK fertilizers on yield and leaf and soil nutrient status of ‘Korona’ strawberry plants (Fragaria×ananassa Duch.), were studied over a period of three years. A significant effect of mulching was found in the first harvest year, but additional fertilizer did not affect total yield. Bark mulch slightly decreased the level of leaf nitrogen, but increased the level of leaf phosphorus and potassium in all years. Bark had a significant, negative effect on soil nitrate and ammonium content in the two first seasons. Mulching increased the soil moisture content in all years.

Corrigendum to: The relative limitation of photosynthesis by mesophyll conductance in co-occurring species in a temperate rainforest dominated by the conifer Dacrydium cupressinum

The capacity to conduct CO2 from the intercellar spaces in leaves to the site of fixation (mesophyll conductance, gm) may pose a significant limitation to photosynthesis. Dacrydium cupressinum Sol. ex Lamb. (rimu), a native conifer of New Zealand, and other members of the Podocarpaceae evolved during the Jurassic when the partial pressure of CO2 exceeded 200 Pa. This species has low rates of photosynthesis and high levels of leaf nitrogen, which have led to the hypothesis that low gm restricts photosynthesis. Mesophyll conductance was estimated from gas-exchange and fluorescence measurements for this and other co-occurring tree species [Prumnopitys ferruginea D.Don (miro), Weinmannia racemosa L.f. (kāmahi), Meterosideros umbellata Cav. (rata)]. Pinus radiata D. Don (radiata pine) and Phaseolus vulgaris L. (bean) were included to provide comparisons with a rapidly growing tree and herbaceous plant with relatively high photosynthetic rates. Mesophyll conductance was not statistically different among indigenous tree species but was lowest for D. cupressinum. This species also had the lowest ratio of mesophyll to stomatal conductance, gm / gst and was the only species where the decline in partial pressure of CO2 was greater from the intercellular air space to the site of fixation (16.3 Pa) than between the bulk air and the intercellular spaces (8.8 Pa), providing support for the hypotheses that low gm limits photosynthesis in this species. As a group, conifers had marginally lower gm and gm / gst ratio than angiosperms, but this difference was strongly influenced by the high values for Phaseolus vulgaris. That co-occurring members of the Podocarpaceae operated differently suggests that low gm may reflect a response to evolutionary pressures other than high atmospheric CO2 partial pressure.

Fatores naturais afetando a infestação de mosca-branca em mandioca

The objective of this study was to determine the effects of predators, parasitoids, leaf chemical composition and levels of leaf nitrogen and potassium, total rainfall, mean temperature, sunlight and relative humidity on the attack rate of the whitefly Aleurothrixus aepim (Goeldi) on the cassava plants Manihot esculenta Crantz. It was observed a negative correlation between nymphs of whitefly and mean temperature and nymphs and adults with total rainfall. There were observed relationships between Aelothripidae with eggs, nymphs and adults of whitefly; Encarsia sp., spider Araneidae and Syrphidae with adults of whitefly; and Hyaliodes vitreus with nymphs of whitefly. Ants of the genus Crematogaster were observed associated to nymphs of this whitefly. The peaks 25.503 and 47.763min. (retention time) correlated with whitefly adults. Even though different factors, such as ecological and physiological conditions of plants, besides parasitoids and predators, can affect population fluctuation of the whitefly; the most important one for this insect seems to be the plant phenology (leaf senescense).

The relative limitation of photosynthesis by mesophyll conductance in co-occurring species in a temperate rainforest dominated by the conifer Dacrydium cupressinum.

The capacity to conduct CO2 from the intercellar spaces in leaves to the site of fixation (mesophyll conductance, gm) may pose a significant limitation to photosynthesis. Dacrydium cupressinum Sol. ex Lamb. (rimu), a native conifer of New Zealand, and other members of the Podocarpaceae evolved during the Jurassic when the partial pressure of CO2 exceeded 200 Pa. This species has low rates of photosynthesis and high levels of leaf nitrogen, which have led to the hypothesis that low gm restricts photosynthesis. Mesophyll conductance was estimated from gas-exchange and fluorescence measurements for this and other co-occurring tree species [Prumnopitys ferruginea D.Don (miro), Weinmannia racemosa L.f. (kāmahi), Meterosideros umbellata Cav. (rata)]. Pinus radiata D. Don (radiata pine) and Phaseolus vulgaris L. (bean) were included to provide comparisons with a rapidly growing tree and herbaceous plant with relatively high photosynthetic rates. Mesophyll conductance was not statistically different among indigenous tree species but was lowest for D. cupressinum. This species also had the lowest ratio of mesophyll to stomatal conductance, gm / gst and was the only species where the decline in partial pressure of CO2 was greater from the intercellular air space to the site of fixation (16.3 Pa) than between the bulk air and the intercellular spaces (8.8 Pa), providing support for the hypotheses that low gm limits photosynthesis in this species. As a group, conifers had marginally lower gm and gm / gst ratio than angiosperms, but this difference was strongly influenced by the high values for Phaseolus vulgaris. That co-occurring members of the Podocarpaceae operated differently suggests that low gm may reflect a response to evolutionary pressures other than high atmospheric CO2 partial pressure.

Correlations between leaf constituent levels and the densities of herbivorous insect guilds in an Australian forest

Abstract Significant correlations were found between herbivorous insect densities and leaf constituent levels across 18 species of understorey shrub in an Australian forest. In general, insect densities were positively correlated with nitrogen and water and negatively correlated with fibre and its constituents (cellulose and lignin), but not all insect guilds were significantly correlated with all leaf constituents. When mature leaf traits were considered, total herbivore density among plant species was most strongly correlated with levels of nitrogen and water. However, when insects were divided into functional guilds, only densities of sucking insects were significantly correlated with mature leaf nitrogen and water, whereas chewing insect densities were significantly correlated with mature leaf fibre and lignin. Low leaf nitrogen levels were recorded for all plants surveyed (among the lowest reported for woody angiosperms), and many plant species also had high levels of leaf fibre. These features are characteristic of Australian forests and have been linked to the generally nutrient‐poor soils of this continent. Levels of new leaf nitrogen (% fresh weight) were generally less than or equal to levels of mature leaf nitrogen (% fresh weight). Hence the new leaf preference of several herbivore guilds could not be explained by higher levels of leaf nitrogen. However, significant negative correlations were found between chewer densities and levels of leaf fibre, cellulose and lignin for new and mature leaves, suggesting that higher levels of fibre, cellulose and lignin in mature leaves may be contributing more strongly to the new leaf preference of chewers than leaf nitrogen levels. Despite the significant correlations between leaf constituent levels and the densities of individual guilds, multivariate analyses found no significant relationship between leaf constituent levels and the taxonomic or guild composition of herbivorous insect assemblages.

Effects of leaf compounds, climate and natural enemies on the incidence of thrips in cassava

The objective of this study was to determine the effects of rainfall, temperature, sunlight and relative humidity, as well as predators and parasitoids, leaf chemical composition and levels of leaf nitrogen and potassium on the intensity of Scirtothrips manihoti (Thysanoptera: Thripidae) attack on cassava Manihot esculenta Crantz var. Cacau. The leaf compounds (E)-farnesene/trans-farnesol and D-friedoolean-14-en-3-one correlated significantly with the population of S. manihoti. Insect population decreased in the dry and cold season probably due to leaf senescence. Significative correlation was observed between Syrphidae with S. manihoti populations.

Light alters the allocation of nitrogen to cyanogenic glycosides in Eucalyptus cladocalyx.

The effect of light on the partitioning of resources between photosynthesis and chemical defence was studied in Eucalyptus cladocalyx F. Muell. This species allocates up to 15% of leaf nitrogen to the constitutive cyanogenic glycoside, prunasin, making it an ideal system for studying resource allocation. By controlling the level of leaf nitrogen we were able to test the hypothesis that light limitation would result in the effective reallocation of nitrogen from the defensive to the photosynthetic apparatus. Seedlings were grown in full light or shade and supplied with 1.5mM or 6mM nitrogen in a 2×2 factorial design. We found that shading effected a decrease in the concentration of the cyanogenic glycoside, prunasin, and little if any change in the concentration of carbon-based secondary metabolites (total phenolics and condensed tannins). There was also significantly less prunasin, relative to total leaf nitrogen, chlorophyll concentration and carbon assimilation rates, when grown plants were grown in shade, particularly when there was an ample supply of nitrogen. This pattern is likely to be the result of relative changes in the energetic and resource costs of photosynthesis and defensive compounds at different photon flux densities.

Nitrogen Controls on Climate Model Evapotranspiration

Most evapotranspiration over land occurs through vegetation. The fraction of net radiation balanced by evapotranspiration depends on stomatal controls. Stomates transpire water for the leaf to assimilate carbon, depending on the canopy carbon demand, and on root uptake, if it is limiting. Canopy carbon demand in turn depends on the balancing between visible photon-driven and enzyme-driven steps in the leaf carbon physiology. The enzymedriven component is here represented by a Rubisco-related nitrogen reservoir that interacts with plant‐soil nitrogen cycling and other components of a climate model. Previous canopy carbon models included in GCMs have assumed either fixed leaf nitrogen, that is, prescribed photosynthetic capacities, or an optimization between leaf nitrogen and light levels so that in either case stomatal conductance varied only with light levels and temperature. A nitrogen model is coupled to a previously derived but here modified carbon model and includes, besides the enzyme reservoir, additional plant stores for leaf structure and roots. It also includes organic and mineral reservoirs in the soil; the latter are generated, exchanged, and lost by biological fixation, deposition and fertilization, mineralization, nitrification, root uptake, denitrification, and leaching. The root nutrient uptake model is a novel and simple, but rigorous, treatment of soil transport and root physiological uptake. The other soil components are largely derived from previously published parameterizations and global budget constraints. The feasibility of applying the derived biogeochemical cycling model to climate model calculations of evapotranspiration is demonstrated through its incorporation in the Biosphere‐Atmosphere Transfer Scheme land model and a 17-yr Atmospheric Model Inter comparison Project II integration with the NCAR CCM3 GCM. The derived global budgets show land net primary production (NPP), fine root carbon, and various aspects of the nitrogen cycling are reasonably consistent with past studies. Time series for monthly statistics averaged over model grid points for the Amazon evergreen forest and lower Colorado basin demonstrate the coupled interannual variability of modeled precipitation, evapotranspiration, NPP, and canopy Rubisco enzymes.

Direct and Indirect Relationships Between Specific Leaf Area, Leaf Nitrogen and Leaf Gas Exchange. Effects of Irradiance and Nutrient Supply

We present a series of competing path models relating interspecific patterns between specific leaf area, leaf nitrogen content, net photosynthesis and stomatal conductance and test these against data from 22 species of herbaceous plants grown under controlled conditions with contrasting irradiance and nutrient supply rates. We then compare these results with two previous data sets, one based on field measures and one based on glasshouse measures, to determine the robustness of the results. Only one model was able to account for the patterns of direct and indirect effects between the four variables to all data sets. In this model specific leaf area is the forcing variable that directly affects both leaf nitrogen levels and net photosynthetic rates. Leaf nitrogen then directly affects net photosynthetic rates which in turn then affect stomatal conductance to water.

A Survey to Determine the Leaf Nitrogen Concentrations of 25 Landscape Tree Species

A survey was conducted to determine the concentrations of leaf nitrogen in 25 landscape tree species. Leaf samples were taken from mature, healthy trees in the landscape and analyzed for percent (total) nitrogen. Concentrations ranged from 1.0% (dry weight basis) for deodar cedar (Cedrus deodara) and Southern magnolia (Magnolia grandiflora) to 3.6% for white mulberry (Moms alba). The leaf nitrogen levels determined by the current study were compared to two other published surveys. From a practical standpoint, the list of tree species and their corresponding minimum leaf nitrogen values from visually healthy trees will allow arborists and landscape maintenance professionals to more effectively use leaf analysis for diagnosing nitrogen deficiency. The information can also be used for designing fertilizer programs, much as critical leaf nutrient level guides are currently used in the fruit and nut tree industries.

The role of leaf nitrogen content in determining turtlegrass (Thalassia testudinum) grazing by a generalized herbivore in the northeastern Gulf of Mexico.

In shallow marine environments the variability in grazing on seagrasses has been hypothesized to be controlled, in part, by the nutritive quality (i.e., nitrogen content) of their leaves. The few existing studies of the relationship between leaf nitrogen content and seagrass grazing have all found a positive relationship between leaf nitrogen content and preference by selective vertebrate grazers (i.e., the bucktooth parrotfish, green sea turtles, and dugongs). However, most marine herbivores (both vertebrate and invertebrate) are thought to be extreme generalists with broad diets of variable nutritive quality (e.g., detritus, living plants, and animals), suggesting the currently held view on the role leaf nutrient content in explaining the variability of seagrass grazing is an oversimplification.In this study, we evaluated how leaf nitrogen content influenced grazing on turtlegrass by a generalist invertebrate herbivore (the pink sea urchin Lytechinus variegatus) in the northeastern Gulf of Mexico. Using a short-term laboratory test and a longer-term field experiment, we tested the hypothesis that leaf nitrogen content controls sea-urchin grazing on seagrass leaves. We hypothesized that if poor nutritive value of seagrasses is responsible for reduced rates of feeding, then increasing leaf nitrogen concentrations should lead to increased rates of seagrass consumption by sea urchins.In the field experiment, we significantly enriched seagrass leaf nitrogen concentrations (some 10-20% depending on month) in experimental plots with a commercial fertilizer and we manipulated grazing intensity by enclosing adult sea urchins at densities that bracketed the range of average densities observed in the region (i.e., 0, 10 and 20 individuals/m(2)). Comparisons of changes in aboveground seagrass production and biomass showed no evidence that sea urchins grazed significantly more in treatments where leaf nitrogen was enriched. Because the statistical power of our test to detect such differences was low and aboveground seagrass production varied significantly among treatments, we also used a mass balance equation to estimate sea urchin consumption of nitrogen-enriched and unenriched leaves. This showed that sea urchins compensated for low nitrogen levels in our unenriched treatments by eating more leaves than in treatments where leaf nitrogen was elevated. Using a laboratory test, we also found that sea urchins ate less nitrogen-enriched seagrass than unenriched seagrass. In combination, these results show that, in contrast to findings reported for vertebrate herbivores, sea urchins feed at higher rates when offered seagrass leaves of lower leaf nitrogen content, and that low levels of leaf nitrogen are not always an effective defense against herbivores.

Leaf nitrogen and phosphorus levels in macadamias in response to canopy position and light exposure, their potential as leaf-based shading indicators, and implications for diagnostic leaf sampling protocols

The relationships between leaf nutrient content, leaf age, and within-canopy light exposure were studied in 10–11-year-old Macadamia integrifolia cvv. 660, 781, and 344 at Alstonville (28˚59′S, 149˚E), New South Wales, during autumn and spring 1996. Quantum point sensors were placed at 16 positions in the canopy to give mean 24-hourly photosynthetic photon flux density (PFD) readings, which ranged from 13 to 540 mol/m2.sec. At each of these positions, the youngest terminal leaf (YTL), the youngest fully expanded leaf (FEL) from a current flush, and a 6–7-month-old hardened off leaf (HOL) were sampled. In 1997, at 12 sites in the Alstonville district, leaves of cv. 344 were sampled (FEL and HOL) at 5 equidistant positions from the bottom, a height of 1.2 m (position 1), to the top (position 5), on the N–NE side of trees in late spring. The sites varied in canopy density from 50% to 95% ground cover, and PFD from the bottom shaded position to the top exposed position in the canopy across all sites increased by a factor of 1.3 to 17.9. At Alstonville, leaf parameters [N%, P%, specific leaf weight (SLW), N amount per unit leaf area (N area), and P area] increased (P < 0.001) with increasing PFD. Using regression analyses, the maximum R2 was 0.59. Age affected (P < 0.05) leaf parameters: for N%, N area, and SLW, HOL > FEL = YTL; and for P% and P area, YTL = FEL > HOL. Cultivar did not affect (P > 0.05) N%, N area or SLW; for P% and P area, cv. 660 > 781 > 344 (P < 0.05). At the Alstonville district sites, leaf parameters increased with PFD (P < 0.05). At each tree sampling position there was a weak negative correlation (P < 0.05) between the leaf parameters and percentage ground cover across all sites, which declined with height (and PFD). Nitrogen area and P area gave the highest R values (–0.60 and –0.40 at low canopy positions), and neither was a suitable replacement for percentage ground cover as a leaf-based shading indicator. The slope of the regression line (regression coefficient) between a leaf parameter and tree height for each macadamia site was determined. The regression coefficient for N area gave the best correlation with percentage ground cover (R2 = 0.55, P < 0.01) and may be useful as a leaf-based shading indicator. At position 1, HOL N concentration ranged from 1.3% to 1.8% and P concentration from 0.06% to 0.11% across all sites. At each of the 5 tree positions, the N parameters were very poorly correlated with kernel yield, and for the HOL P parameters, there was a weak negative correlation (R = –0.521 to –0.673, P < 0.05) at tree positions 1 and 2 with kernel yield. Current recommendations to reduce macadamia leaf N concentrations because of detrimental effects of high leaf N on yield were not supported by the current study. Modification of the current diagnostic leaf sampling protocol is recommended to avoid the reduction in leaf N and P concentrations through shading and the cultivar effects on P concentration. We conclude that the current diagnostic leaf N and P standards cannot reliably diagnose the nutritional status of macadamia orchards.

Juvenile tree growth rates and species sorting on fine‐scale soil fertility gradients in a Chilean temperate rain forest

AbstractAimWe sought to clarify the role of juvenile tree growth rates in species sorting along fine‐scale fertility gradients in the coast range forests of southern Chile.LocationIn montane forests in the coast range, the conifer Fitzroya cupressoides occupies the poorest soils, whereas dominance shifts to the evergreen angiosperms Nothofagus nitida and/or Weinmannia trichosperma on moderately infertile sites. On the most fertile sites, N. nitida is usually the sole overstorey dominant.MethodsWe examined the effects of soil depth and nitrogen availability on height growth and leaf nitrogen levels of the three common overstorey dominants. Sapling height growth rates and foliage nitrogen concentration were measured in 20 large gaps (>0.1 ha), on sites of varied soil depth and potential N‐mineralization rates.ResultsHeight growth rates of Weinmannia and Nothofagus were strongly positively correlated with both soil depth and potential N‐mineralization. Height growth of Fitzroya was strongly correlated with soil depth, but not with N‐mineralization. Nothofagus and Weinmannia enjoyed large growth‐rate advantages over Fitzroya on the more fertile soils of the study area, and this advantage was reduced or nullified (but not reversed) on poor soils. This pattern was associated with species differences in nitrogen use: on fertile soils, Nothofagus and especially Weinmannia, achieved more height growth per unit of leaf N than Fitzroya, whereas differences were minimal on poor soils.Main conclusionsResults suggest that comparative height growth rates of juvenile trees, associated with nitrogen productivity differences, play a key role in determining eventual dominance on productive sites, but that traits other than growth (possibly related to nutrient retention) are more important on low fertility sites. Disturbance regimes appear to vary in relation to site fertility, and differential species responses to this superimposed disturbance gradient are also probably influential in determining overstorey composition.

Shading Effects on Susceptibility ofRosaspp. to Defoliation byPopillia japonica(Coleoptera: Scarabaeidae)

Abstract Published anecdotal reports suggest that Japanese beetles, Popillia japonica Newman, feed more heavily on host plants growing in full sun than on shaded plants. We studied the effects of shading on foliar characteristics of roses (Rosa variety floribunda ‘Class Act’) and determined preference and fecundity of beetles provided with sun- or shade-conditioned leaves. Defoliation by P. japonica also was compared between sun-grown and experimentally shaded roses in the field. Leaves from plants grown in full sun were smaller and thicker than ones from shaded plants, with slightly higher tannins. Leaf toughness and nitrogen levels were not affected by shading, but leaves from sun-grown plants had relatively higher sugar content. Beetles consistently consumed more foliage from sun-grown plants than from shade-grown plants in laboratory preference tests. However, beetles fed continuously for 2 wk on leaves from sun- or shade-grown plants had similar fecundity. In the field, beetles fed somewhat more heav...

Influence of variety on the within-plant distribution of cassava green spider mite (Acari: Tetranychidae), and leaf anatomical characteristics and chemical components in relation to varietal resistance

The within-plant distribution of the cassava green spider mite, Mononychellus tanajoa Bondar, and the anatomical characteristics and the chemical components relating to varietal resistance of cassava, were studied using 11 cassava genotypes with varying levels of resistance for two dry seasons and one wet season. The results show that M. tanajoa aggregates on the top leaves of cassava at low levels of resistance as compared with a more even within-plant distribution at higher levels of resistance. Thus, for accurate sampling of mite populations, it might be important to consider young and old leaves, not just the young leaves, in fields containing resistant and susceptible cassava genotypes. Correlations between the anatomical characteristics and mite population density and damage scores were not consistent across months, either within or over seasons. This suggests that leaf anatomical characteristics may not be important in the varietal resistance of cassava to M. tanajoa. During the dry season, mite population density was positively correlated with leaf nitrogen, potassium and phosphorus and negatively correlated with leaf calcium and fat. Only calcium was negatively associated with mite damage at the peak of the dry season (January 1993 and 1994). Breeding cassava genotypes with high levels of leaf calcium and fat, and low levels of leaf nitrogen, potassium and phosphorus, may improve the level of resistance to M. tanajoa.

PREHARVEST FACTORS AND POSTHARVEST QUALITY DECLINE OF APPLES

Two types of experiment were conducted to identify preharvest factors that might be correlated with fruit quality at harvest and rate of postharvest loss of quality. The research was planned as a first step towards predicting the loss of quality in terms of firmness, green ground colour, acid- and soluble solids concentration. The first, inventory experiment involved a large number of orchards of 'Cox's Orange Pippin', 'Elstar', 'Red Boskoop' and 'Jonagold', all on M9 rootstock. Samples for chemical fruit analysis were taken 3 weeks before harvest and at harvest. Fruit for quality measurements were collected at harvest and after storage and shelf life. In the second experiment, N, P, K, Ca and Mg were applied, each at 5 levels, in a new orchard planted with 'Elstar' on M.9 to create fruit with different concentrations of these nutrients in order to study the relationship with post-harvest quality development. Fruit firmness at harvest was negatively correlated with fruit nitrogen level in August and at harvest and (in 'Elstar') with leaf nitrogen level in June and July. Green ground colour was (at least in 'Elstar') correlated positively with leaf and fruit nitrogen level in June, July and August, but not in September. Acid concentration was highly correlated with fruit K and Mg levels and with fruit weight at harvest. In 'Elstar', total soluble solids content was correlated positively with leaf P level and % of dry matter. Following storage and shelf life, the level of fruit characteristics was generally best correlated with the level at harvest. To a smaller extent significant correlation was observed with nutrients that did not correlate significantly with the level at harvest (e.g. P and Mg with firmness). The correlation between acid concentration and fruit K and Mg concentration, already high at harvest, was even higher after storage. Multiple regression models explaining the loss of firmness during storage and shelf life had a better % of variance accounted for than those explaining the absolute level at any moment. These first results are discussed in physiological terms and with respect to their possible significance for cultural practice and for prediction of fruit quality.

「加賀太」キュウリ（Ｃｕｃｕｍｉｓ ｓａｔｉｖｕｓ Ｌ．ｃｖ．Ｋａｇａｆｕｔｏｋｙｕｒｉ）の葉および果実における苦味発現と窒素代謝との関連

苦味のない高品質の'加賀太'キュウリの栽培体系を確立するために, 苦味の発現と窒素代謝との関係について検討した.1. 自根苗の無苦味系統株と苦味系統株の葉における全窒素含有率, 硝酸イオンとアミノ酸態窒素含有率の比較を行った.その結果, 苦味系統株の方が無苦味系統株より, 苦味果の発生率は高く, 茎長, 葉重, 根重は大きかったが, 葉色には差がなかった.葉中の全窒素含有率, アミノ酸態窒素含有率は, 苦味系統株の方が無苦味系統株より高かったが, 硝酸イオン含有率は低かった.2. 接ぎ木苗の苦味を有する上位葉あるいは果実と苦味を有しない下位葉あるいは果実とにおける全窒素含有率, 硝酸イオンとアミノ酸態窒素含有率の比較を行った.その結果, 葉の苦味は上位葉が下位葉より強く, 全窒素含有率, アミノ酸態窒素含有率は高く, 硝酸イオン含有率は低かった.また, 苦味果では無苦味果よりも, 全窒素含有率, 硝酸イオンとアミノ酸態窒素含有率のいずれも高かった.以上の結果, 苦味果の発生する株の葉, 苦味を有する葉および苦味果では, 苦味のないものに比べて, 窒素代謝が活発であり, それに伴ってククルビタシンCの生合成も促進されるために, 苦味が強く発現するものと考えられる.

Leaf structure (specific leaf area) modulates photosynthesis–nitrogen relations: evidence from within and across species and functional groups

1. Net photosynthetic capacity (Amax, defined as light‐saturated net photosynthesis under near optimal ambient environmental conditions) of mature leaves often depends on the level of leaf nitrogen (N), but an assortment of relationships between these variables has been observed in studies of diverse plant species. Variation in leaf structure has been identified as an important factor associated with differences between the area‐ and mass‐based expressions of the Amax–N relationship. In this paper we test the hypothesis that leaf structure, quantified using a measure of leaf area displayed per unit dry mass invested [specific leaf area (SLA)], is more than just a conversion factor, but itself can influence Amax–N relationships. We test this using several kinds of comparisons, based on field data for 107 species from sites representing six biomes and on literature data for 162 species from an equally diverse set of biomes. 2. Species and genera with thicker and/or denser leaves (lower SLA) consistently have flatter slopes of the Amax–N (mass‐based) relationship than those with higher SLA. These and all other contrasts usually applied as well using area‐based expressions, although such relationships were less consistent and weaker overall. A steeper slope indicates greater incremental change in Amax per unit variation in N. 3. Functional groups (e.g. needle‐leafed evergreen trees, broad‐leafed trees or shrubs, forbs) show the same patterns: groups with lower SLA have lower Amax–N slopes. Functional groups differ in mean leaf traits as well as in Amax–N relationships. Forbs have the highest SLA and mass‐based N and Amax, followed by deciduous species (whether needle‐leafed or broad‐leafed, shrub or tree), with lowest values in evergreen species (again regardless of leaf type or functional group). 4. Interspecific variation in mass‐based Amax is highly significantly related to the combination of leaf N and SLA (r2 = 0·86). At any value of leaf N, Amax increases with increasing SLA and at any value of SLA, Amax increases with increasing leaf N. Because this relationship, between Amax and the combination of N and SLA, is similar in two independent data sets, and as well, across broad taxonomic and geographic gradients, we hypothesize that it is universal in nature. Therefore, for broad interspecific contrasts among dicotyledons in any biome, we can reasonably well predict Amax based on the combination of SLA and leaf N. These findings have important implications for convergent evolution of leaf adaptation and great potential utility in models of global vegetation functioning.