Structure of plankton communities in Ilchir, an alpine lake in eastern Siberia

 Lake Ilchir is an alpine lake located 1963 m above sea level in the mountain ranges of eastern Sayan, eastern Siberia. Observations are presented from October 1998 to September 1999 in order to provide the phytoplankton and zooplankton community structures. Sixty-six taxa of phytoplankton and 66 taxa of zooplankton were recorded. Of much interest was the finding of rare species, such as the dinoflagellate Gymnodinium coeruleum, the diatoms Pliocaenicus costatus and Cyclotella tripartita, and the calanoids Acanthodiaptomus tibetanus and Arcthodiaptomus (S.) paulseni. Received: August 24, 2001 / Accepted: April 13, 2002     

The breakdown of buried and surface-placed leaf litter in an upland stream

The breakdown of buried leaves (Eucalyptus viminalis) was investigated using surface-placed and buried leaf packs in a riffle of the Acheron River, Victoria. Leaf packs buried to a depth of 10 cm were rapidly colonized by invertebrates, with the total numbers of individuals and species exceeding those on surface leaf packs. A larger proportion of leaves in buried leaf packs was grazed in comparison with those on the surface, with the intensity of grazing also being higher for leaves in buried packs. Both surface and buried leaf packs broke down rapidly with no significant difference in weight loss with time. The high level of breakdown of buried E. viminalis leaf litter observed in this study suggests that the hyporheos of Australian headwater streams may significantly contribute to the decomposition of particulate organic matter.     

RFLP tagging of QTLs conditioning specific leaf weight and leaf size in soybean

 Selection for high specific leaf weight (SLW) in soybean [Glycine max (L) Merr.] may increase apparent photosynthetic rate per unit leaf area (AP), which in turn may improve seed yield. In general, the SLW and leaf size are negatively correlated in soybean. To maximize total photosynthetic performance, and perhaps the seed yield, of a soybean cultivar, it would be necessary to establish a large leaf area rapidly while maintaining a high SLW. The objective of the present study was to identify quantitative trait loci (QTLs) conditioning SLW and leaf size in soybean. One hundred and twenty F₄-derived lines from a ‘Young’×PI416937 population were evaluated using restriction fragment length polymorphism (RFLP) markers. The genetic map consisted of 155 loci on 33 linkage groups (LGs) covering 973 cM of map distance. The phenotypic data were collected from two different environments – a greenhouse at Athens, Ga. and a field site at Windblow, N.C. The SLW and leaf-size measurements were made on leaves from the 8th and 9th node of soybean plants at the V12 stage of development. Combined over environments, six putative independent RFLP markers were associated with SLW, and four of these loci were consistent across environments. Individually, the six markers each explained between 8 and 18% of the phenotypic variation among lines for SLW. The Young alleles contributed to a greater SLW at four of the six independent marker loci, and transgressive segregation occurred among the progeny for SLW. Three putative independent RFLP markers were associated with leaf size, each explaining between 6 to 11% of the phenotypic variation in the trait, and one of these markers was identified in both environments. There was no correlation between SLW and leaf size in this population. Similarly, none of the six QTLs conditioning SLW were linked to any of the three QTLs for leaf size. In this soybean population, it is possible to select for progeny lines with greater SLW than either parent perhaps without affecting the leaf size. It is feasible to pyramid all of the desirable alleles for greater SLW and large leaf size in a single genetic background. Received: 16 August 1997 / Accepted: 20 October 1997     

Early stages of root and leaf decomposition in Hawaiian forests: effects of nutrient availability

We examined the effects of soil nutrient availability and tissue chemistry on decomposition of both fine roots (<2 mm diameter) and leaves in three sites along a forest chronosequence in the Hawaiian Islands. These sites form a natural fertility gradient, with the youngest and oldest sites having lower nutrient availability than the intermediate-aged site. Nitrogen (N) limits aboveground net primary productivity (ANPP) in the youngest site, while phosphorus (P) limits ANPP in the oldest site. Both root and leaf litter decomposed most slowly in the 4.1-Myear-old site. We also investigated root decomposition in fertilized plots at the youngest and oldest sites; when roots were produced and decomposed in fertilized plots, root decomposition rates increased with N and P additions at the 4.1-Myear-old site. At the 300-year-old site, however, root decomposition rates did not respond to N or P additions. Roots decomposed faster than leaves at the more infertile sites, in part because of lower lignin-to-nitrogen ratios in roots than in leaf litter. Decomposing roots immobilized more nutrients than did decomposing leaves, and may serve an important role in retaining nutrients in these forests. Received: 30 November 1998 / Accepted: 12 August 1999     

Spectral changes with leaf aging in Amazon caatinga

 Significant gaps exist in the knowledge of tropical leaf spectra and the manner in which spectra change as leaves age in their natural environment. Leaf aging effects may be particularly important in tropical vegetation growing on nutrient poor soils, such as Amazon caatinga, a white sand community common in the Amazon Basin. Spectral changes observed in six caatinga dominants include decreased reflectance and transmittance and increased absorptance for epiphyll-coated older leaves. Near-infrared (NIR) changes were most significant. More detailed spectral and physical changes were studied in one dominant, Aldina heterophylla. Over 16 months, Aldina study plants produced one or two leaf flushes. During leaf expansion, leaf water content and Specific Leaf Area decreased rapidly. Over the first 6 months spectral changes occurred across the spectrum, resulting in decreased transmittance and increased absorptance in the visible and NIR and decreased visible and increased NIR reflectance. In contrast, significant spectral changes were restricted to the NIR over the last 9 months, which showed a 10% absorptance increase associated primarily with increasing epiphylls and necrosis. At the canopy scale, increased NIR absorptance provides a mechanism for producing seasonally varying forest albedo and changing NIR to red ratios, independent of changes in other canopy attributes. In the Amazon caatinga studied, all canopy dominants were subject to epiphyllic growth providing a mechanism for distinguishing these forest types spectrally from more diverse terra-firme forest or forest types with more rapid leaf turnover, such as second growth. These changes are observable using remote sensing and could be used to map caatinga and monitor interannual or seasonal variability in phenology. If these results can be extended to other communities with long-lived foliage, they may offer a means for mapping vegetation on the basis of leaf longevity. Received: 18 November 1996/Accepted: 24 December 1997     

Warming water and leaf litter quality but not plant origin drive decomposition and fungal diversity in an experiment

The fungi associated with leaf litter play a key role in decomposition and can be affected both by the warming water and the invasion of non-native species in riparian vegetation. Warming water and invasion of non-native riparian species on stream fungal communities have been studied mainly in temperate ecosystems. We tested the effects of warming water and non-native plant Psidium guajava on leaf litter decomposition, conidia density, species richness and beta diversity of tropical stream fungi. Thus, we carried out an experiment using the current mean temperature of streams from northwestern Paraná in South Brazil (22 °C) and two temperatures above the current mean temperature (26 °C and 29 °C). We also used the leaves of a non-native plant (P. guajava), and two native plants (one of similar nutritional quality, and the other of higher nutritional quality than the non-native species) occurring in Neotropical streams riparian vegetation. Warming water accelerated leaf litter decomposition and reduced conidia density and fungal richness in native and non-native plants. However, species composition and beta diversity were not affected by water temperature. Our study showed that warming affects the fungi of streams, the main microorganisms responsible for decomposition and that the nutritional quality of the leaves may be more important than the origin of riparian plant species. Despite this, further investigations should be conducted on the interaction of P. guajava with the flow of nutrients in these environments and how it can affect other ecosystem processes and the food chain. Efforts to study the effects of water warming and biological invasion on the attributes and distribution of fungi in streams are vital, making them a tool for the conservation of riparian ecosystems.     

AFLP and STS tagging of Lr19, a gene conferring resistance to leaf rust in wheat

Amplified fragment length polymorphism (AFLP) markers were used to enrich the map of the wheat chromosomal region containing the Thinopyrum-derived Lr19 leaf rust resistance gene. The region closest to Lr19 was targeted through the use of deletion and recombinant lines of the translocated segment. One of the AFLP bands thus identified was converted into a sequence-tagged-site (STS) marker. This assay generated a 130-bp PCR fragment in all Lr19-carrying lines tested, except for one deletion mutant, while non-carrier template failed to amplify any product. This sequence represents the first marker to map on the distal side of Lr19 on chromosome 7el₁. The conversion process of AFLP fragments to STS markers was technically difficult, mainly because of the presence of contaminating fragments. Various approaches were taken to reduce the frequency of false positives and to identify the correct clone. We were able to formulate a general verification strategy prior to clone sequencing. Various other factors causing problems with converting AFLP bands to an STS assays are also discussed. Received: 15 September 2000 / Accepted: 5 January 2001     

Leaf structure and anatomy as related to leaf mass per area variation in seedlings of a wide range of woody plant species and types

The structural causes of variation in leaf mass per area, and of variations in leaf structure accounted for by leaf habit and life form, were explored in a set of laboratory-grown seedlings of 52 European woody species. The leaf traits analysed included density, thickness, saturated mass/dry mass, and leaf nitrogen per mass and per area. Other traits described the anatomy of leaves, most of them relating to the lamina (proportions of palisade and spongy parenchymata, epidermis, air space and sclerified tissues, expressed as volume per leaf area, and per-cell transversal areas of epidermis and parenchymata), and another referring to the mid rib (transversal section of sclerified tissues). Across the whole set of species leaf mass per area was correlated with leaf density but not with thickness, and this was confirmed by taxonomic relatedness tests. Denser leaves corresponded with greater proportion of sclerified tissues in the lamina, smaller cells and lower water and N contents, but no relation was found with the proportion of air space in the lamina. Taxonomic relatedness analysis statistically supported the negative association of leaf density with saturated to dry leaf mass ratio. Thicker leaves also exhibited greater volume per leaf area and greater individual cell area in each of the tissues, particularly parenchyma. Mean leaf mass per area and leaf thickness were lower in deciduous than in evergreen species, but no significant differences in leaf density, proportion of sclerified tissues in the lamina or cell area were found between the two groups. Leaf mass per area was higher in trees and subshrubs than in shrubs and climbers-plus-scramblers, this rank being equal for leaf density and proportion of sclerified tissues in the lamina, and reversed for cell area. Given the standardised environment and ontogenetic phase of the seedlings, we conclude that variation in leaf structure and anatomy among species and species groups has a strong genetic basis, and is already expressed early in the development of woody plants. From an ecological viewpoint, we can interpret greater leaf mass per area across this species set as greater allocation to support and defence functions, as shown predominantly by species from resource-poor environments. Received: 16 August 1999 / Accepted: 29 March 2000     

Altitude trends in conifer leaf morphology and stable carbon isotope composition

The natural ratio of stable carbon isotopes (δ¹³C) was compared to leaf structural and chemical characteristics in evergreen conifers in the north-central Rockies, United States. We sought a general model that would explain variation in δ¹³C across altitudinal gradients. Because variation in δ¹³C is attributed to the shifts between supply and demand for carbon dioxide within the leaf, we measured structural and chemical variables related to supply and demand. We measured stomatal density, which is related to CO₂ supply to the chloroplasts, and leaf nitrogen content, which is related to CO₂ demand. Leaf mass per area was measured as an intermediate between supply and demand. Models were tested on four evergreen conifers: Pseudotsuga menziesii, Abies lasiocarpa, Picea engelmannii, and Pinus contorta, which were sampled across 1800 m of altitude. We found significant variation among species in the rate of δ¹³C increase with altitude, ranging from 0.91‰ km^–1 for A. lasiocarpa to 2.68‰ km^–1 for Pinus contorta. Leaf structure and chemistry also varied with altitude: stomatal density decreased, leaf mass per area increased, but leaf nitrogen content (per unit area) was constant. The regressions on altitude were particularly robust in Pinus contorta. Variables were derived to describe the balance between supply and demand; these variables were stomata per gram of nitrogen and stomata per gram of leaf mass. Both derived variables should be positively related to internal CO₂ supply and thus negatively related to δ¹³C. As expected, both derived variables were negatively correlated with δ¹³C. In fact, the regression on stomatal density per gram was the best fit in the study (r ²=0.72, P<0.0001); however, the relationships were species specific. The only general relationship observed was between δ¹³C and LMA: δ¹³C (‰)=–32.972+ 0.0173×LMA (r ²=0.45, P<0.0001). We conclude that species specificity of the isotopic shift indicates that evergreen conifers demonstrate varying degrees of functional plasticity across environmental gradients, while the observed convergence of δ¹³C with LMA suggests that internal resistance may be the key to understanding inter-specific isotopic variation across altitude. Received: 1 June 1999 / Accepted: 2 November 1999     

Identification and mapping of a new leaf stripe resistance gene in barley (Hordeum vulgare L.)

Pyrenophora graminea is the seed-borne pathogen causal agent of barley leaf stripe disease. Near-isogenic lines (NILs) carrying resistance of the cv ”Thibaut” against the highly virulent isolate Dg2 were obtained by introgressing the resistance into the genetic background of the susceptible cv ”Mirco”. The segregation of the resistance gene was followed in a F₂ population of 128 plants as well as on the F₃ lines derived from the F₂ plants; the segregation fitted the 1:2:1 ratio for a single gene. By using NILs, a RAPD marker associated with the resistance gene was identified; sequence-specific (STS) primers were designed on the basis of the amplicon sequence and a RILs mapping population with an AFLP-based map were used to position this molecular marker to barley chromosome 1 S (7HS). STS and CAPS markers were developed from RFLPs mapped to the telomeric region of barley chromosome 7HS and three polymorphic PCR-based markers were developed. The segregation of these markers was followed in the F₂ population and their map position with respect to the resistance gene was determined. Our results indicate that the Thibaut resistance gene, which we designated as Rdg2a, maps to the telomeric region of barley chromosome 7HS and is flanked by the markers OPQ-9₇₀₀ and MWG 2018 at distances of 3.1 and 2.5 cM respectively. The suitability of the PCR-based marker MWG2018 in selection- assisted barley breeding programs is discussed. Received: 22 June 2000 / Accepted: 16 October 2000     

Ontogenetic patterns of leaf CO2 exchange, morphology and chemistry in Betula pendula trees

In order to explore ontogenetic variation in leaf-level physiological traits of Betula pendula trees, we measured changes in mass- (A _mass) and area-based (A _area) net photosynthesis under light-saturated conditions, mass- (RS_mass) and area-based (RS_area) leaf respiration, relative growth rate, leaf mass per area (LMA), total nonstructural carbohydrates (TNC), and macro- and micronutrient concentrations. Expanding leaves maintained high rates of A _area, but due to high growth respiration rates, net CO₂ fixation occurred only at irradiances >200 μmol photons m^–2 s^–1. We found that full structural leaf development is not a necessary prerequisite for maintaining positive CO₂ balance in young birch leaves. Maximum rates of A _area were realized in late June and early July, whereas the highest values of A _mass occurred in May and steadily declined thereafter. The maintenance respiration rate averaged ≈8 nmol CO₂ g^–1 s^–1, whereas growth respiration varied between 0 and 65 nmol CO₂ g^–1 s^–1. After reaching its lowest point in mid-June, leaf respiration increased gradually until the end of the growing season. Mass and area-based dark respiration were significantly positively correlated with LMA at stages of leaf maturity, and senescence. Concentrations of P and K decreased during leaf development and stabilized or increased during maturity, and concentrations of immobile elements such as Ca, Mn and B increased throughout the growing season. Identification of interrelations between leaf development, CO₂ exchange, TNC and leaf nutrients allowed us to define factors related to ontogenetic variation in leaf-level physiological traits and can be helpful in establishing periods appropriate for sampling birch leaves for diagnostic purposes such as assessment of plant and site productivity or effects of biotic or abiotic factors. Received: 29 December 1998 / Accepted: 26 July 1999     

Genetic analysis of durable leaf rust resistance in winter wheat

Quantitative resistance that delays the epidemic development of leaf rust in wheat is an important source for durable resistance breeding. The Swiss winter wheat variety ’Forno’ shows a high level of quantitative resistance against leaf rust. This resistance has been effective for more than 10 years and can therefore be considered to be durable. In order to map quantitative trait loci (QTL) for durable leaf rust resistance we analysed 204 F₅ recombinant inbred lines (RILs) of the cross between the winter wheat ’Forno’ and the winter spelt ’Oberkulmer’ for their level of leaf rust resistance (LR) and leaf tip necrosis (LTN) in four different environments. Both traits showed a continuous distribution and were significantly correlated (r=−0.5). Across environments we detected 8 QTL for leaf rust resistance (6 inherited from ’Forno’) and 10 QTL for the quantitative expression of LTN (6 inherited from ’Forno’). Of the 6 QTL responsible for the durable leaf rust resistance of ’Forno’, 1 major QTL coincided with a thaumatin locus on 7BL explaining 35% of the phenotypic variance. Four QTL for LR coincided with QTL for LTN. At these loci the alleles of ’Forno’ increased the level of resistance as well as the extent of LTN, indicating pleiotropy. Received: 1 July 1999 / Accepted: 30 July 1999     

Phototolerance of lichens, mosses and higher plants in an alpine environment: analysis of photoreactions

 Adaptation to excessive light is one of the requirements of survival in an alpine environment particularly for poikilohydric organisms which in contrast to the leaves of higher plants tolerate full dehydration. Changes in modulated chlorophyll fluorescence and 820-nm absorption were investigated in the lichens Xanthoria elegans (Link) Th. Fr. and Rhizocarpon geographicum (L.) DC, in the moss Grimmia alpestris Limpr. and the higher plants Geum montanum L., Gentiana lutea L. and Pisum sativum L., all collected at altitudes higher than 2000 m above sea level. In the dehydrated state, chlorophyll fluorescence was very low in the lichens and the moss, but high in the higher plants. It increased on rehydration in the lichens and the moss, but decreased in the higher plants. Light-induced charge separation in photosystem II was indicated by pulse-induced fluorescence increases only in dried leaves, not in the dry moss and dry lichens. Strong illumination caused photodamage in the dried leaves, but not in the dry moss and dry lichens. Light-dependent increases in 820-nm absorption revealed formation of potential quenchers of chlorophyll fluorescence in all dehydrated plants, but energy transfer to quenchers decreased chlorophyll fluorescence only in the moss and the lichens, not in the higher plants. In hydrated systems, coupled cyclic electron transport is suggested to occur concurrently with linear electron transport under strong actinic illumination particularly in the lichens because far more electrons became available after actinic illumination for the reduction of photo-oxidized P700 than were available in the pool of electron carriers between photosystems II and I. In the moss Grimmia, but not in the lichens or in leaves, light-dependent quenching of chlorophyll fluorescence was extensive even under nitrogen, indicating anaerobic thylakoid acidification by persistent cyclic electron transport. In the absence of actinic illumination, acidification by ca. 8% CO₂ in air quenched the initial chlorophyll fluorescence yield F_o only in the hydrated moss and the lichens, not in leaves of the higher plants. Under the same conditions, 8% CO₂ reduced the maximal fluorescence yield F_m strongly in the poikilohydric organisms, but only weakly or not at all in leaves. The data indicate the existence of deactivation pathways which enable poikilohydric organisms to avoid photodamage not only in the hydrated but also in the dehydrated state. In the hydrated state, strong nonphotochemical quenching of chlorophyll fluorescence indicated highly sensitive responses to excess light which facilitated the harmless dissipation of absorbed excitation energy into heat. Protonation-dependent fluorescence quenching by cyclic electron transport, P700 oxidation and, possibly, excitation transfer between the photosystems were effectively combined to produce phototolerance. Received: 10 December 1999 / Accepted: 13 April 2000     

Identification and mode of action of quantitative trait loci affecting seedling height and leaf area in Eucalyptus nitens

 Regions of the genome influencing height and leaf area in seedlings of a three-generation outbred pedigree of Eucalyptus nitens have been identified. Three QTLs affecting height and two QTLs affecting leaf area were located using single-factor analysis of variance. The three QTLs affecting height each explained between 10.3 and 14.7% of the phenotypic variance, while the two QTLs for leaf area each explained between 9.8 and 11.6% of the phenotypic variation. Analysis of fully informative marker loci linked to the QTLs enabled the mode of action of the QTLs to be investigated. For three loci the QTL effect segregated from only one parent, while for two loci the QTL showed multiple alleles and the effect segregated from both parents in the pedigree. The two QTLs affecting leaf area were located in the same regions as two of the QTLs affecting height. Analysis of these regions with fully informative markers showed that both QTLs were linked to the same markers, but one had a similar size of effects and a similar mode of action for both height and leaf area, whilst the other showed a different mode of action for the two traits. These regions may contain two closely linked genes or may involve a single gene with a pleiotrophic effect on both height and leaf area. The QTL with the greatest effect showed multiple alleles and an intra-locus interaction that reduced the size of the effect. Assessment for two of the QTLs in a second related family did not show an effect associated with the marker loci; however, this was consistent with the mode of action of these QTLs and the pattern of inheritance in the second family. Received: 1 August 1996 / Accepted: 25 October 1996     

Simulating ozone detoxification in the leaf apoplast through the direct reaction with ascorbate

 This paper presents a mathematical model which enables the semi-quantification of ozone (O₃) detoxification, based upon the direct reaction of the pollutant with ascorbate (ASC) located in the aqueous matrix associated with the cell wall (i.e. the apoplast). The model describes the uptake of ozone into the leaf and its direct reaction with ASC, taking into consideration the regeneration of dehydroascorbic acid in the cytosol, the rate of replenishment of cell wall ASC and the distribution of ASC between sub-cellular compartments – based upon the permeability of biomembranes to the neutral species, ascorbic acid and the pH of various sub-cellular compartments. The importance of various physico-chemical characteristics (e.g. stomatal conductance, mesophyll cell wall thickness and tortuosity, chloroplast volume, apoplast pH, ASC:O₃ reaction stoichiometry) in mediating the flux of ozone to the plasmalemma is analysed. Model simulations, supported by experimental observations, suggest that the ASC concentration in the leaf apoplast is high enough to scavenge a significant proportion of the O₃ taken up into the leaf interior, under environmentally relevant conditions. However, there is considerable variation between taxa in the potential degree of protection afforded by apoplastic ASC, emphasizing the need for an improved understanding of the reaction chemistry of O₃ in the cell wall. Received: 13 May 1999 / Accepted: 5 August 1999     

Inheritance of nuclear DNA content in leaf epidermal cells of Zea mays L.

 The nuclear DNA content (ploidy level) of maize leaf-epidermal cells was investigated by Feulgen cytophotometry in two lines, Illinois High Protein (IHP) and Illinois Low Protein (ILP), their reciprocal hybrids, and their F₂s. Epidermal cells have a 2C, 4C or 8C nuclear DNA content. The mean DNA content per nucleus in IHP was significantly higher than in ILP; the mean DNA content per nucleus in hybrids was intermediate between the parental lines, and the same DNA content was measured in reciprocal crosses. In F₂s the same mean DNA content as in F₁s was observed but with larger variability than in the F₁, possibly indicating genetic segregation. It is inferred that the ploidy level in the leaf epidermis is inherited, and incomplete dominance occurs in hybrids. The same behaviour in the different genotypes was observed for epidermal cell-surface area, except that an increase of mean surface area occurred in the F₁, probably due to heterotic effects. The difference in the accumulation of 4C and 8C nuclei in leaf epidermis parallels that reported between two genotypes for the endosperm tissue: to the greater chromosome endoreduplication found in the endosperm there were correspondingly higher frequencies of 4C and 8C nuclei in the leaf epidermis, indicating a higher general tendency to chromosome endoreduplication in IHP than in ILP. It is suggested that the accumulation of 4C nuclei (G₂-block) in the leaf epidermis may be regarded as the initial step of chromosome endoreduplication, the two phenomena being related to the control of the sequence DNA synthesis-mitosis, possibly involving the same genes in both endosperm and leaf. However, the inheritance of DNA content per nucleus in epidermal tissue seems to be different from that observed in endosperm tissue of the same genotypes, suggesting that differences may occur in the regulation of the activity of these genes. Received: 19 November 1996 / Accepted: 29 November 1996     

Light distribution and foliage structure in an oak canopy

 Leaf angle distribution and shoot bifurcation ratio were measured and related to photon flux density (PFD) distribution in an oak canopy. Leaf angle distribution deviated substantially from random and changed markedly throughout the canopy. The observed leaf angle distribution was described by an ellipsoidal function with the single parameter of the distribution, x, changing from 1.6 at the top of the canopy to 3.2 in the lowest branches. In vertically homogeneous canopies, the extinction coefficient for diffuse radiation is expected to decline with increasing leaf area index (LAI). However, in the canopy studied here, the leaf angle distribution changed with height such that the effective extinction coefficient remained constant. Both shoot bifurcation ratio and leaf number per shoot declined with decreasing PFD inside the canopy. Based on these observed relationships, a simple canopy growth model that assumes horizontal homogeneity of the canopy was constructed. Calculations showed that a steady state, when growth in the upper of the canopy is in equilibrium with decline of lower canopy, the total canopy LAI should equal to 4.3. This predicted value of equilibrium LAI is larger than that estimated from measurements of PFD transmission (LAI=3.3), but smaller than that directly determined by litter collection (LAI=6.2 in 1998). Possible reasons for these discrepancies are discussed. Received: 22 June 1998 / Accepted: 7 April 1999     

Relationships between nuclear DNA content and seed and leaf size in soybean

 A correlation between genome size and agronomically important traits has been observed in many plant species. The goal of the present research was to determine the relationship between genome size, seed size, and leaf width and length in soybean [Glycine max (L.) Merr.] Twelve soybean strains, representing three distinct seed size groups, were analyzed. Flow cytometry was used to estimate their 2C nuclear DNA contents. Data on seed size and leaf size of the 12 strains were obtained from 1994 and 1995 field experiments. Variation of 2C nuclear DNA among the 12 soybean strains was 4.6%, ranging from 2.37 pg for a small-seed strain to 2.48 pg for a large-seed strain. Strain seed size was positively associated with leaf width (r=0.92) and leaf length (r=0.93). Genome size was highly correlated with seed size (r=0.97), leaf width (r=0.90) , and leaf length (r=0.93). The results of our study indicate that there is a significant correlation between genome size and leaf and seed size in soybean. It is possible that selection for greater seed size either leads to, or results from, greater genome size. If so, this relationship might be worth exploring at a more fundamental level. Received: 5 April 1997 / Accepted: 9 January 1998     

Specific leaf area and leaf nitrogen concentration in annual and perennial grass species growing in Mediterranean old-fields

 We evaluated the hypothesis that photosynthetic traits differ between leaves produced at the beginning (May) and the end (November–December) of the rainy season in the canopy of a seasonally dry forest in Panama. Leaves produced at the end of the wet season were predicted to have higher photosynthetic capacities and higher water-use efficiencies than leaves produced during the early rainy season. Such seasonal phenotypic differentiation may be adaptive, since leaves produced immediately preceding the dry season are likely to experience greater light availability during their lifetime due to reduced cloud cover during the dry season. We used a construction crane for access to the upper canopy and sampled 1- to 2-month-old leaves marked in monthly censuses for six common tree species with various ecological habits and leaf phenologies. Photosynthetic capacity was quantified as light- and CO₂-saturated oxygen evolution rates with a leaf-disk oxygen electrode in the laboratory (O_2max) and as light-saturated CO₂ assimilation rates of intact leaves under ambient CO₂ (A_max). In four species, pre-dry season leaves had significantly higher leaf mass per unit area. In these four species, O_2max and A_max per unit area and maximum stomatal conductances were significantly greater in pre-dry season leaves than in early wet season leaves. In two species, A_max for a given stomatal conductance was greater in pre-dry season leaves than in early wet season leaves, suggesting a higher photosynthetic water-use efficiency in the former. Photosynthetic capacity per unit mass was not significantly different between seasons of leaf production in any species. In both early wet season and pre-dry season leaves, mean photosynthetic capacity per unit mass was positively correlated with nitrogen content per unit mass both within and among species. Seasonal phenotypic differentiation observed in canopy tree species is achieved through changes in leaf mass per unit area and increased maximum stomatal conductance rather than by changes in nitrogen allocation patterns. Received: 7 March 1996 / Accepted: 1 August 1996     

Flow cytometric sorting of maize chromosome 9 from an oat-maize chromosome addition line

Large numbers of maize chromosome 9 can be collected with high purity by flow cytometric sorting of chromosomes isolated from a disomic maize chromosome addition line of oat. Metaphase chromosome suspensions were prepared from highly synchronized seedling root-tips of an oat-maize chromosome-9 addition line (OM9) and its parental oat and maize lines. Chromosomes were stained with propidium iodide for flow cytometric analysis and sorting. Flow-karyotypes of the oat-maize addition line showed an extra peak not present in the parental oat line. This peak is due to the presence of a maize chromosome-9 pair within the genome of OM9. Separation of maize chromosome 9 by flow cytometric sorting of a chromosome preparation from a normal maize line was not possible because of its size similarity (DNA content) to maize chromosomes 6, 7 and 8. However, it is possible to separate maize chromosome 9 from oat chromosomes and chromatids. An average of about 6×10³ chromosomes of maize chromosome 9 can be collected by flow-sorting from chromosomes isolated from 30 root tips (ten seedlings) of the oat-maize addition line. Purity of the maize chromosome 9, sorted from the oat-maize chromosome addition line, was estimated to be more than 90% based on genomic in situ hybridization analysis. Sorting of individual chromosomes provides valuable genomic tools for physical mapping, library construction, and gene isolation. Received: 28 February 2000 / Accepted: 14 July 2000